nrsc risat1 handbook
TRANSCRIPT
pg. 1
CONTENTS 4.4.1 Brief description of data reception station 1. RISAT-1 Satellite Overview
4.5 Detailed functional reception of data reception station
2. Mission Overview 2.1 Mission
Specifications 4.6 Antenna and tracking pedestal
2.2 Mission elements 4.6.1 Antenna 3. RISAT Specifications 4.6.2 Pedestal
3.1 RISAT-1 Orbit 4.6.3 Drive chain 4.6.4 Azimuth housing 3.2 RISAT Subsystems with
heritage / new element 4.6.5 Elevation housing 3.3 Mechanical Systems
4.7 Technical specifications 3.3.1 Structure
3.3.2 Coordinate System & Panel Nomenclature
4.8 Dual Polarized S/X band feed & RF systems 3.3.3 Mechanisms 4.8.1 Dual Polarized
S/X band Feed 3.4 Thermal 3.5 BDH 4.8.2 Feed
Specifications 3.6 SSR 3.7 RF Systems 4.8.3 X-band DPC
(Divider, Phase, Shifter, Coupler)
3.7.1 TTC RF 3.7.2 X-Band RF 3.8 SPS 4.8.4 S-band DPC 3.9 Power Systems 4.8.5 X-band Up/Down
Converter 3.10 On Board Computer (OBC) 4.8.6 X-band down
Converter 3.11 AOCS 3.12 Actuators 4.8.7 X-band Up
Converter 4. Data Reception Systems 4.1 Introduction 4.8.8 S-band Down
Converter 4.2 Station requirements to track and receive RISAT-1 data
4.8.9 Integrated tracking system
4.3 IMGEOS configuration 4.9 IF and Base band Systems 4.4 Data reception station
specifications
pg. 2
8.4 Radiometric check 4.9.1 Programmable IF matrix 8.5 Band to band
registration (BBR) 4.9.2 IF Fiber optic link 9 Data Access and
Distribution 4.9.3 High data rate
demodulators 9.1 Services 4.10 Digital servo control
system 9.1.1 Polygon based query / ordering/ collects
4.11 Antenna drive unit 4.11.1 Antenna
control unit 9.1.2 Map sheet number based query
4.12 tracking network configuration
9.1.3 Location name based query
4.12.1 Station automation system 9.1.4 Point (Lat-Long )
based query 4.13 Station Control computer 9.1.5 Search for
images based on shape file
5 Level ‘ 0 Systems 5.1 Introduction
9.1.6 Search for images based on date of pass/ ordering
5.2 Station work flow manager
5.3 Data ingest system 5.4 Timing systems
9.2 Product status monitoring
5.4.1 IRIG-G time code translator
6 SAR payload for RISAT 9.3 Services for offline users 6.1 Modes of operation
10 Payload Programming 7 RISAT data products and formats 10.1 Introduction
10.1.1 Registered users
7.1 Raw signal products (Level-0)
10.1.2 Offline users
7.2 Ellipsoid Geocoded Products (Level-2)
10.1.3 Ground station users
7.3 Value added products 7.4 Image Quality
parameters 10.2 Payload Programming activity 8 Product quality control 10.2.1 Options for
placing the 8.1 Meta file verification 8.2 Format validation 8.3 Geometric check
pg. 3
programming request
10.2.2 Request
status 10.2.3 PPS-
System 11 Applications 11.1 Forestry
11.2 Crop 11.3 Agricultural 11.4 Flood
1. RISAT-1 SATELLITE OVERVIEW
RISAT mission is envisaged to fly a SAR
imaging payload for supplementing to
the needs of remote sensing data
users across the globe. With its
pg. 4
capabilities to operate in day, night and
all weather conditions, SAR is an
important sensor, which either in stand-
alone mode or as complementary to
electro-optical sensors, will cater to
diverse resources and environmental
monitoring applications even during
cloud cover times. The basic nature of
data, which is a function of a microwave
returned signal, will significantly
enhance the scope of satellite remote
sensing and develop newer applications.
RISAT will be launched by ISRO’s own
PSLV launch vehicle, as the launch
parameters are well within the
capabilities. The interface of the satellite
with the launch vehicle is through
circular merman band clamp (937VB
Version) to match with PSLV launcher
interface.
ii) To develop and operate a compatible
satellite to meet the mission
requirements operating in three axis
stabilized mode in 536.38 km circular
sun synchronous orbit.
iii) To establish ground segment to
receive and process SAR data.
iv) To develop related algorithms and
data products to serve in well
established application areas and also to
enhance the mission utility.
2.2Mission elements
To meet the defined mission objectives,
various components as required by the
mission including SAR payload, satellite,
orbit, satellite management in orbit and
data handling on ground have been
defined.
SAR mission will be operational in
nature. Mission specifications are
similar to contemporary international
missions. SAR payload has a multi-mode
capability for catering to
2. Mission
2.1Mission Objectives
The objectives of RISAT are, i)To
develop a multimode, agile SAR payload
operating in scanSAR, strip and spot
modes to provide images with coarse,
fine and high spatial resolutions
respectively.
• Continuous fine resolution strip mode
for initial reconnaissance, infrastructure
development applications, disaster
management etc. ,
pg. 5
A polar sun synchronous orbit at 536.38
kms altitude and inclination of 97.554
deg. with repetivity cycle of 377 orbits in
25 days with a descending node local
time of 6:00 AM +/- 5 min is chosen .
Main guiding parameter for choosing the
orbit for RISAT-1 is achieving a global
coverage in a systematic way for a
given swath. Other considerations such
as interferometric applications, the
presence of atomic oxygen and
atmospheric drag have also been kept in
view. Orbit parameters are planned to
be variable as per mission operation
requirements for various imaging
modes.
• Wide swath scanSAR mode for agriculture, forestry, flood mapping, geological applications etc.
• High resolution spotlight mode for
special applications The satellite is fabricated to have agility
for maximizing the imaging in high-
resolution mode, with Data
transmission in real time as well as in
storage mode. RISAT technology has
been chosen so that the continuity is
maintained in follow-on missions of
RISAT.
Mission Elements of RISAT-1 are
presented in Figure :1 , and these will
result in theDevelopment of user-
friendly data products and data archival. 3.2RISAT Subsystems with
heritage /new elements Fig.1 Mission Elements of RISAT-1
3RISAT Specifications
3.1RISAT-1 Orbit:
RISAT-1 has 13 new sub systems, and
hertitage and past experience exists for
remaining 10 subsystems. Power Sub
systems works on 70 V bus, generated
from CFRP based solar panels and 70
AH Ni-H battery. Miniaturized version of
TTC-RF sub systems and High data rate
modulator, Phase locked loop based
Xband system are used. Phase array
antenna is used for SAR data
transmission using Dual polarized wave
pg. 6
guide radiating elements. SPS sub
system is same as used in Carto-2
mission. INSAT type SPSS, two axes
DSS, IRS-P6 Star sensor with
improvement in update rate, package
density and satellite interface to MIL-
STD-1553B interface, Conventional
conical earth sensor are used. 50NMS &
0.3NM Torque wheels , IRU sub systems
as in Carto-2 and (8+1) 11 N Thrusters
are used as actuators. SAR payload is
based on TR module based architecture.
BDH and SSR are new type of sub
systems for RISAT-1.
3.3 Mechanical systems
Radar Imaging satellite (RISAT) is built
around a bus for ongoing IRS missions
in the weight class of 2000kg. RISAT
weight is 1850 kg out of which SAR
payload weight is around 950 kg.
3.3.1 Structure
The main structure of RISAT consists of
one single cylinder of 2.77 m height
(approx). The bottom side of the
cylinder has a truncated triangular
structure to hold the SAR antenna and
major bus service elements. At the
topside of the cylinder a cuboid
structure to accommodate the solar
arrays, majority of the sensors and
antennae is provided. The triangular
structure with SAR antenna is identified
as PAYLOAD module and the cuboid
structure with solar arrays is called as
SOLAR PANEL module. Sufficientgap is
available between the payload module
and the solar panel module so that
there is no interference between the
solar array and the SAR antenna in
launch configuration as well as on-orbit
configuration.
3.3.2 Coordinate System & Panel
Nomenclature
The center of gravity of the satellite is
taken as the origin of the co-ordinate
system considered for the satellite
attitude control and attitude
determination purposes. Refer the
following figure for axis definition of
RISAT mission.
pg. 7
Fig. 2 Roll, Yaw and Pitch Positive Yaw Axis From CG towards and
perpendicular to SAR antenna in
deployed configuration (towards center
of earth) Positive Pitch Axis From CG
towards the bottom deck of the
triangular structure supporting the SAR
Antenna. Positive Roll Axis Perpendicular
to +ve Yaw and +ve Pitch axis
completing the right handed system.
Roll axis is along the deployed SAR
Antenna.
3.3.3 Mechanisms
RISAT employs SAR deployment
mechanism andSolar array deployment
mechanism
3.4 Thermal
Thermal control will be provided using
space proven thermal control elements
such as OSR, MLI, paints, thermal
control tapes, quartz wool blanket, Sink
plates and heat pipes. Heaters will be
provided to maintain temperatures
during cold conditions. The orbit and
orientation of RISAT gives rise to the
following factors that decide the thermal
design approach of the Main Bus as well
as payload :No eclipse during winter and
equinox, Eclipse only during summer
(22 minutes maximum), Sun rays
incident on SAR radiator with small
incident angle resulting in high
temperature, More earthshine load on
Earth viewing panel due to reduced
altitude. Reduced albedo load due to
6AM/6PM equatorial crossing time
3.5 BDH The data handling system of RISAT is
configured in the form of two formatters
for each of RX1 (V) and RX2 (H)
receivers from the SAR payload. The
SAR data is transferred to BDH through
LVDS Serializer -Deserializer interface
where each data line is at the rate of
218.75 Mbps and clock signal of 31.25
MHz. The de-serialized output (SAR
Data) is written in memory as long as
the data window from SAR P/L is HIGH.
In the next data window, the SAR data
pg. 8
is read from the memory by the
formatter for formatting along with
necessary auxiliary data. Two memories
per receiver are used for the ping-pong
operation of memory write and memory
read simultaneously. The formatter
clock is 32 MHz or 10 MHz depending
upon the data rates of SAR P/L. All
clocks are derived from 160 MHz crystal
oscillators. Null flag concept is used for
optimum utilization of SSR. When the
data rate of SAR P/L and BDH overhead
together is greater than 640Mbps, real
time transmission is not possible and
data have to be recorded in SSR.
Recorded data can be played back later.
Differential Encoder is used to remove
four-phase ambiguity of QPSK. BDH has
functionalities like payload interface,
formatter, 1553 interface, differential
encoding clock generation, final parallel
to serial conversion and DC/DC.
Main Mode Description
a) Standby mode
b) Retention mode
c) Record mode
d) Playback mode
3.7 RF Systems
3.7.1TTC RF
The TT&C (RF) system for RISAT
consists of two chains of PLL coherent
SBand Transponder connected to a
common antenna system (Two
antennae system consisting of main and
null filling antenna). The basic
configuration is identical to the ones
employed in earlier IRS missions. The
TC demodulation scheme is PSK/PCM
with a date rate of 4KBPS.
Frequencies:
Receiver frequency : 2071.875 MHz
Transmitter frequency : 2250.00 MHz
3.7.2 X-Band RF
The X-Band RF is required to do the
following operations: 3.6 SSR
The RISAT SSR has a capacity of 300 G
bits , realized with six memory boards of
50 G bits capacity each . The memory
boards, by default are configured into
two partitions each of 150 G bits with
three memory boards per partition.
To accept the payload data from the
base band Data Handling system.
To modulate the above data on two X-
Band carriers and transmit the
same to ground after suitable
amplification and filtering.
pg. 9
In the proposed data transmission for
RISAT, half the data i.e. 320 MBPS will
be transmitted in right hand circular
polarisation (RHCP) and the remaining
320 MBPS in the left hand circular
polarisation (LHCP); two identical chains
operating at 8.2125 GHz are used to
transmit 640 MBPS of payload data. The
carrier generation section, QPSK
modulator section, filter units, selection
of Main and redundant chain units are
identical in all the chains as the
frequency of operation and modulation
schemes are identical. Both the chains
have end to end redundancy. The
spherical phased array antenna has
radiating elements distributed almost
uniformly on a hemispherical surface. It
generates a beam in the required
direction by switching ‘ON’ only those
elements, which can contribute
significantly towards the beam direction.
It is proposed to use the 64 element
array.
computing the state vector of the high-
dynamic platform.
3.9 Power Systems
Radar Imaging Satellite (RISAT) Power
System consists of Solar array with 6
panels of rigid Al honeycomb
sandwiched between CFRP face skin and
arranged in two wings with three panels
in each wing in +ve roll and -ve roll
axes, chemical Battery for power
storage and power electronics for power
conditioning and distribution. The power
system for RISAT is designed to (a)
meet the 6AM/6PM orbit illumination
conditions; (b) to cater to large power
requirement of HRSAR (High Resolution
Synthetic Aperture Radar) payload; and
(c) solar eclipse conditions during
summer solstice. The power system
configuration is arrived to meet all the
requirements and consists of a fully
regulated 70V Bus, regulated by Solar
array regulator during sunlit. Battery
Discharge Regulator (BDR) supports
power to the bus when the load demand
exceeds the array generation during
payload operation and eclipse conditions
by regulating the bus to 70V and
protected against over voltage, under
voltage, over current and is single point
3.8 SPS
Satellite Positioning System (SPS) for
RISAT comprises of 10-channel C/A
code GPS receiver at L1 (1575.42 MHz)
frequency. SPS is designed for
pg. 10
failure proof. To provide the required
voltage to the subsystems which cannot
adopt to 70V bus within RISAT time
frame, there is a provision for auxiliary
bus of 42V which is fully protected and
distributed through two hubs as ABUS1
and ABUS2 each with separate high
current fuses. Further distribution to
individual users is from fuse boxes
placed at convenient locations. To
power the core power and uplink even
under Battery Emergency conditions
during eclipse two uninterrupted Buses
are formed by Or-ing Battery and Main
Bus. U-Bus1 and U-Bus2 will power Main
&Redt Domestic & OBC DC/DCs and are
distributed through separate fuses.
SADA is incorporated to compensation
for the reduction in power during space
craft +-36 deg rotations and eclipses.
The energy storage system for RISAT
employs a single NiH2 battery of 70AH
capacity, consisting of 42 cells. The
protection mechanism exists for battery
during over discharge conditions similar
to other spacecrafts. Power Electronics
elements ensure, regulation of solar
array power to regulate the bus,
performs battery managements and
distributes power to the various users.
Power Electronics subsystem also
consists of Domestic Regulator,
individual cell monitoring, Four-cell
logic, Battery charge controller, OBC
and GC Interfaces.
3.10 On Board Computer(OBC)
In order to minimize power, weight, and
volume, the spacecraft functions like
command, housekeeping (Telemetry),
Attitude and Orbit Control, Thermal
Management, Sensor data processing
etc., have been integrated into a single
package called On board computer
(OBC) which also implements the MIL
STD 1553B protocol for interfacing with
other subsystems of the spacecraft..
The use of MIL-STD-1553B interfaces
between OBC and other subsystems
greatly decreases the volume and mass
of
cabling and the associated connectors.
The OBC system is realizing the
following spacecraft functions:
• Sensor electronics
• Command Processing
• Telemetry and House-keeping
• Attitude and Orbit Control (AOCS)
Besides, the OBC interfaces with Power,
TM-TTC (RF) for command and
telemetry, Sensors, Heaters, Thrusters
pg. 11
4 Actuators and Reaction Wheels through special
logics. A functionally redundant OBC is
also present. Either of the OBCs can be
selected for operation. It also
implements the 1553 protocol for
interfacing with other subsystems of the
spacecraft for
5 Eight Numbers of Canted 11 N
thrusters (Mono propellant drazine
system operating in blow down
mode) with two axis canting from
+Pitch axis for Acquisition and OM
operation. One Center 11 N
thruster for OM operation, four
Nos of Reaction Wheels of
Capacity (0.3 Nm Torque and 50.0
NMS @ 4410 RPM) mounted in
tetrahedral configuration about –
Pitch axis. Maximum Operating
Speed is upto ±4500 RPM.
Reaction wheels are used for
Normal Mode and for OM Rotation.
- 2 Magnetic Torquers of 60.0 A-
m2 Capacity mounted along Roll
and Pitch axis for Momentum
Dumping.
data transfer - Star Sensor, SPS, WDE,
DTG, DH, SSR and PAA.
11 AOCS
RISAT AOCS modules are derived from
Carto-2B with modifications
required for RISAT mission and are
implemented in OBC.
AOCS Specifications during Imaging are
stated as follows :
Pointing : ± 0.05 ° (3σ)
Drift Rate : ± 3.0 e-04 °/s (3σ)
The attitude orbit control system for
RISAT is configured with thefollowing
sensors:
4π Sun sensor
2 Nos. Magnetometer
2 Nos. IRU (Inertial Reference Unit)
Digital sun sensor 1 No., Solar panel
sun sensor 2 sets (4 Nos.)
3 Nos., RW 4 nos.and SADA, Star
Sensor 2 Nos., Earth sensor 2 Nos.,
pg. 12
Basic system configuration of a high resolution Synthetic Aperture Radar (SAR) on an IRS
Mission Requirements
1.1 Mission Requirements Basic system configuration of a high resolution Synthetic Aperture Radar (SAR) on an IRS platform is outlined in this chapter. Primarily, the SAR system configuration is designed to meet the following basic objectives: ♦ It should meet applications
conforming to national requirements. ♦ It should be multimode one to meet
different resolution and swath requirements.
♦ It should be agile for minimizing revisit time and maximizing operational flexibility.
♦ Technology used should be state of the art, survive obsolescence and adaptable for other different frequency bands in future missions.
As the first development of spaceborne SAR in ISRO, the SAR will be developed for single frequency because of technical complexity and the need for developing the sensor in shortest possible time frame. From application considerations, the SAR will be designed in C-band with single/dual/quad polarization capability. For this purpose, active antenna technology with the capability of electronic beam steering, meeting all the above requirements of multi mode operation, agility and state of the art features, has been identified. Implementation of High Resolution SAR development is planned in two stages: ♦ Development of prototype model
SAR with scaled version of active antenna using commercial components. The basic aim is to
develop and demonstrate expertise at reduced cost.
♦ Subsequent delivery of flight model spaceborne SAR within a further time frame of 2 years.
1.2 Frequency and Polarization Selection
The selection of operational frequency and polarization are driven by the applications demanding a wide range of resolution / swath / polarization combinations. From resolution considerations, resolution cell should be sufficiently large in comparison with the wavelength (about 10 times the wavelength). Hence, typically 3 m is the highest resolution in L-band, 1.5 to 2 m in S-band, 1 m in C/X-bands and 10-20 cm in Ku/Ka band. Higher resolutions (1m or better) are feasible for C-band frequencies and higher because of bandwidth allocation considerations. Total bandwidth allocation for radar applications is 80 MHz for L-band, 210 MHz for C-band, 350 MHz for X-band and 500 MHz for X-band. Hence, for ground mapping and coastal applications, like oil slick & ships detection, etc. C- and X-band are preferred. For civilian applications like agriculture, soil moisture, forestry, flood mapping and ocean related studies both C- and L-band with cross polarization are preferred. Ocean related studies are served best by VV-polarization and land related
pg. 13
studies are aided by HH-polarization. Provision of both co- and cross- polar data aids significantly in discrimination of features. Co-polar return is mainly affected by surface or canopy scattering. Cross-polar return is mainly governed by volume scattering which depends on penetration through canopy/surface. So, higher the frequency poorer will be the return in cross-polarization. Hence, polarimetry is best suited in lower frequency bands like P, L and C. Polarimetry is not usually applicable for X and higher frequency bands. These considerations have led to the choice of C-band frequency operation with single/dual/quad polarization capability to exploit the maximum gamut of applications.
1.3 Modes of Operation The RISAT High Resolution SAR will be operating in C-band at a frequency of 5.35 GHz. The spacecraft altitude has been fixed at 608.958 km from the 13-day repetivity considerations. The SAR system has been designed to provide constant swath for all elevation pointing and almost near constant minimum radar cross section performance. The proposed SAR will operate in the following basic modes, the details of which are given in Table-2.1. (Operational philosophy of the modes is briefly outlined here for better comprehensibility of the discussion that follows. Key issues pertaining to these modes are discussed later in this chapter under separate section.) • Fine Resolution Stripmap Mode-1
(FRS-1) with 3 m resolution. This mode is based on Stripmap imaging,
which is the conventional mode of SAR. In this, the orientation of the antenna beam is fixed with respect to flight path so that a strip of constant swath (here, 30 km) is illuminated along the flight direction. The stripmap SAR image dimension is limited only in the across track and not in the along track dimension (limited only by on-board recorder capacity).
• Coarse Resolution ScanSAR Mode (CRS) with 240 km swath. The ScanSAR mode allows for a multifold increase of the range swath dimension. This is achieved by periodically stepping the antenna beam to the neighboring subswaths (in the range direction). In this case, the radar is continuously ON, but only a portion of the full synthetic antenna length is available for each target in a subswath. This causes a degradation of the achievable azimuth resolution with respect to the strip map case. In other words, the range swath dimension increases at the expense of azimuth resolution. In the CRS-mode of RISAT, there will 12 beams to cover each sub-swath of 20 km (either side of the intermediate sub-swaths will have an overlap of 10 km from the preceding and succeeding sub-swaths, thereby reducing the effective sub-swath width from 30 km to 20 km). Therefore, total swath in CRS mode would be 240 km.
• Medium Resolution ScanSAR Mode (MRS) with 120 km swath. This is a 6-beam scanSAR mode, similar to the CRS mode.
• Fine Resolution Stripmap Mode-2 (FRS-2) with quad polarization
pg. 14
capability. Philosophically, this mode is a hybrid stripmap&scanSAR. It is stripmap in the sense that the beam orientation is kept fixed with respect to the flight path and a strip of constant swath width is covered. Also, in a way it is similar to scanSAR, because for part of the aperture time the beam polarisation is switched from V-transmit to H-transmit, and vice-versa. Hence, this mode would be used for polarimetry, as we can have all the four combinations of polarisation, viz, VV, VH, HH& HV.
• High Resolution Spotlight Mode (HRS) with 1 m resolution. In the spotlight mode, the antenna beam is oriented continuously to illuminate a particular spot on the ground. This way, the target aperture time is increased which results in improved azimuth resolution (compared to that in the stripmap case). The improved resolution is obtained at the cost of azimuth coverage. The latter is partly improved by making use of sliding spotlight mode (hybrid spotlight-stripmap mode). This imaging would be done over a spot size of 10 km x 10 km. An experimental mode to extend the azimuth coverage upto 100 km is also planned in this.
These modes have been illustrated in Fig.2.1.
1.4 RISAT Imaging Geometry In order to provide greater flexibility in the selection of the look angles for different applications and to increase the effective repeatability, a region on the ground may be accessed by different look angles ranging from 9° to
47° corresponding to off-nadir distances of 100 km and 700 km, respectively. Hence, a repeatability period of 13 days may be reduced to 2 days. This look angle variation is effected by electronic switching of the antenna beam in the elevation direction. This electronic switching of the beams is also necessary for ScanSAR modes of operation (MRS/ CRS). As shown in Fig.-2.1, SAR will operate with basic elevation beam width of 2.48o -1.67o, over a total ground distance of 600 km, starting from an off nadir distance of 100 km and upto 700km. Radiometric performance is guaranteed for the swaths covered from off-nadir distance of 200 km to 600 km (qualified region) and for the regions lying between 100 km to 200 km and 600 km to 700 km, the performance is not guaranteed (unqualified). Figure –2.1 shows the basic system geometry of the proposed SAR for operation of all the above-mentioned modes. The variation of the look angle and incidence angle for various off-nadir distances is illustrated in Fig 2.2.
pg. 15
200km 400km
608.958 km
200
490
2.480-1.670
EL.BEAM
100
700km
100km 540
100 km (UNQUALIFIED)
400 km (QUALIFIED)
200 KM
608.958 km
100 km (UNQUALIFIED)
FRS-1/FRS-2 Mode
MRS Mode
CRS Mode
HRS Mode
Fig.-2.1 Basic System Geometry and Operating Modes of High Resolution SAR
pg. 16
Table-2.1
Major Mission Parameters for Spaceborne High Resolution SAR
Altitude 608.958Km Orbit Sun synchronous (6 AM / 6 PM equatorial crossing) Frequency 5.35 GHz Polarisation Single / Dual / Quad-polarization Swath coverage Either side of the flight track
Selectable within 100 – 700 km off-nadir distance (100-200 km & 600-700 km regions are unqualified,
the rest is qualified) Qualified (200-600 km)
18° - 43° Look angle coverage
Total 9° – 47° (100-700 km) Qualified (200-600 km)
20° – 49° Incidence angle coverage
Total 10° – 54° (100-700 km)
Antenna Microstrip Active antenna, 6m x 2m Peak Gain 44.5dB Total no. of beams 63 on each side of the flight track (total 126) On board storage SSR with 240 Gbits No. of TR Modules 288 Transmitted power per TRM
10 W
Antenna peak power 2.88 kW AverageDC Input Power 3.86 kW Range Compression On Ground Pulse width 20 μs Imaging Modes HRS FRS-1 FRS-2 MRS CRS Applicable Polarization combinations
Single & Dual
Single & Dual
Quad Single & Dual
Single & Dual
Swath/Spot (km)
Defined 10 (Az) x 10(Rng)
30 30 120 240
pg. 17
Imaging Modes HRS FRS-1 FRS-2 MRS CRS Experimental
100 (Az) x
--- --- --- ---
10(Rng) Resolution 1m x
0.7m 3m x 2m
9m x 4m
21-23m x 8m
41-55m x 8m (Az x slant range)
Minimum sigma naught (dB)
-16.3 -17 -18 -18 -18
(Qualified Region) Chirp bandwidth (MHz) 225 75 37.5 18.75 18.75 Sampling frequency (MHz) 250 83.3 41.67 20.83 20.83
96-163 55-181 55-181 55-181 55-181 Data window (μs) PRF 3500± 3000± 3000± 3000± 3000±
200 Hz 200 Hz 200 Hz 200 Hz 200 Hz Qualified (200-600)Km
27040-37120
7424-14366
3840-7168
2048-3584
2048-3584
No. of Complex Samples
Total 23960-40720
4864-15104
2560-7680
1280-3840
1280-3840 (100-
700)Km Data Compression 3-bit BAQ Onboard BAQ (6/5/4/3/2 bits)
Considering 3-BAQ (for
100km azimuth)
6-BAQ 6-BAQ 6-BAQ 6-BAQ Data Rate (in Mbps)
Single pol 507-739 176-556 ---- 44-142 44-142 Dual pol 1014-
1478 352-1112
---- 88-284 88-284
Quad pol ---- ---- 176-556 ---- ---- Considering 3-BAQ
(for 100km
azimuth)
6-BAQ 6-BAQ 6-BAQ 6-BAQ Data Coverage/ Storage
Single pol 4 spots 2950 km
---- 11500 km
11500 km
Dual pol 2 spots 1475 km
---- 5750 km
5750 km
Quad pol ---- ---- 2950 km
---- ----
Azimuth Ambiguity -21 dB -22 dB (over qualified region) Range Ambiguity -20 dB -20 dB (over qualified region) Radiometric Resolution 3 dB (single look)
pg. 18
Imaging Modes HRS FRS-1 FRS-2 MRS CRS Accuracy (over orbit)
2 dB (Goal) Performance (over qualified region)
Accuracy TBD (over Lifetime)
pg. 19
In the non-imaging mode antenna will be looking downwards towards the nadir. By having an option of roll-tilting the satellite by ±34°, SAR can be made to see either side of the track (one at a time), thereby improving the revisit time by a factor of two. The pointing is chosen such that between two successive beam positions, swath overlap of 10 km is always ensured. This overlap is important for achieving MRS/CRS mode. Fast electronic beam pointing and beamwidth control is achieved by electronic elevation beam control in the active antenna. 61 beam-pointing positions have been identified to enable sufficient agility in imaging anywhere over 600 km region (qualified and unqualified) with best possible performance. Each beam is centered at off-nadir intervals of 10 km. Two additional beams with no pointing (0° w.r.t. antenna orientation angle i.e.
±34°) are defined for two halves of
antenna, 6m x 1m each. Therefore, there are 63 beam positions defined for imaging on each of the sides of the sub-satellite track. As a result, a total of 126 beams would be used for imaging on either sides of the track.
1.5 Antenna configuration –in brief and Elevation beamwidth considerations
Area of the SAR antenna is dictated by the frequency band of operation, and is of the order of 12 m2 for C-band operation. Hence, RISAT active antenna is configured with 6m (azimuth) x 2m (elevation/range) dimensions, with 288 pairs (V & H) of TR-modules. The RISAT antenna consists of three panels each of 2m×2m size, as shown in Fig.2.3, to facilitate stowing during launch and later, deployment in the space. The longer dimension of the antenna is aligned with azimuth direction and the width in the elevation/range direction. Each panel consists of 4 tiles of size 1m×1m, each consisting of 24×24 radiating elements. In the azimuth direction (antenna length) 24 elements are grouped together to be fed by a single TR-module pair (V/H polarization), hence we have 6 TR-module pairs in the antenna length direction. Each radiating element in the width direction is fed by a different TR-module pair, hence there are 48 (=24 x 2m) TR-module pairs in the antenna width. The total number of TR-module pairs is therefore 288 (=6m x 48). The inter-element spacing has been kept 0.7λ, where λ stands for wavelength which is 5.6 cm. If the spacing between the radiators is more than this, grating
Fig. 2.2 Variation of Angles with Off Nadir
pg. 20
lobes will occur in the antenna patterns. At the junction of two tiles, the inter-element spacing is 1.4λ, therefore, one blank row of radiating elements may be assumed which is at a distance of 0.7λ from the nearest radiating elements from the adjacent tiles. In short, 49 rows of TR-modules may be assumed in the antenna width (for system analysis purposes), with the centre row as a hypothetical blank (inactive) one to attribute to the inter-tile spacing. Elevation beamwidth will be made to vary with pointing angles in order to
achieve pointing-independent swath of 30 km and constant minimum radar cross section performance. If the antenna beamwidth is kept constant, there will be varying footprint size in the range direction, due to change in slant ranges. At near off-nadir distances, the beam footprint will be smaller than the desired 30 km. Hence, in order to maintain the constant footprint of 30 km, the beamwidth is increased by switching off the TR-modules and in effect reducing the electrical width of the antenna (at near off-nadir distances). The
Fig.2.3 Distributed Antenna For h Resolution SAR Hig
Group of 24 patches fed by single TR
module in azimuth direction
Azimuth
6 m
2 m
Panel-1 Panel-2 Panel-3
Elevation 1 m
1 m
1 Tile of 24 x 24 radiating elements
2 m
2 m
pg. 21
1.6 Selection of PRF for different Beam
positions TR-modules are switched off in the width direction, equally from outer edges of the adjacent two tiles, as shown in Fig.2.4. Hence, elevation beamwidth is varied from 2.48° to 1.67° corresponding to off-nadir distances from 100 km to 700 km, respectively, as shown in Fig.2.5. The corresponding number of active TR-module rows in the elevation direction is illustrated in Fig-2.6.
The Doppler bandwidth corresponding to antenna length of 6m and spacecraft velocity of 7.5 km/s will be 2500 Hz.
Azimuth
Elevation
6m Illuminated region of the antenna
2m
Fig.2.4: Change of Antenna electrical width to cater to variable elevation beamwidth
F ig.2.6: Variation of No. of Active TR-modules inthe width direction
Fig.-2.5 Elevation Beam-width with Beam Pointing
pg. 22
Hence, the PRF should be greater than about 1.1 times the Doppler bandwidth, i.e. 2750 Hz. Changes in slant range corresponding to off-nadir distance change from 100 km to 700 km, lead to different echo start times and variable data windows. To accommodate the same, variable PRF is necessary. Therefore all the modes, except HRS, have PRF between 2800 – 3200 Hz. Maximum PRF is limited by the minimum data window that has to be accommodated. In the case of HRS mode, Doppler centroid estimation (for different sub-apertures) requires additional 500 Hz (over the Doppler bandwidth of 2500 Hz), therefore PRF would lie between 3000 – 3700 Hz. This large range of PRF is required to satisfy the slant range change during pitch tilting of the satellite for azimuth coverage of 100 km, for each of the off-nadir distances.
Fig-2.7 presents nomenclature related to the timing window parameters. As the slant range varies from 616 km to 928 km for off-nadir positions of 100 km to 700 km respectively, the echo return times change from 4.1 ms to 6.2 ms. Typical PRI (Pulse Repetition Intervals)
for the PRFs under consideration is about 0.3 ms. Therefore, echo corresponding to a transmitted pulse is received after certain number of pulses. The number of such pulses varies from 12 to 19 for off-nadir distances starting from 100 km to 700 km, respectively. Near margin and far margin as defined in Fig-2.7 should be more than 20μs to allow for pulse rise & fall times and sub-system switching (like, switching off the transmitter and switching on of the receiver(s), data acquisition enabling, etc.). PRF is optimized for nearly equal near & far margins within the given PRF ranges. The PRF is commandable from the ground through Payload Controller. The command is given in terms of 12-bit count corresponding to a clock frequency of 3.90625 MHz. Hence, the PRI should be an integer multiple of the
clock interval corresponding to 3.90265 MHz. Similarly, data window start time and number of data samples to be acquired are also commandable by ground commands of 12-bit and 16-bit counts, respectively. Hence, these parameters should also be integer
Start Window
Data window
No. of Pulses after which echo occurs
Pulse Width
Near Margin Far Margin
Fig.2.7: Representation of Timing Window Parameters
pg. 23
multiples of the above-mentioned clock interval. In addition to the above requirements, the number of data samples within a data window should be a multiple of BAQ (Block Adaptive Quantization, to be described later) block size of 128.
Figures 2.8 – 2.11 present the PRF and timing window parameters for FRS-1, FRS-2, MRS & CRS modes. Best and worst case sigma naught values have been tabulated for MRS & CRS modes in Tables-2.2 & 2.3 alongwith the corresponding off-nadir values at which they occur. Fig.2.31 & 2.32 show comparison graphs for the best and worst sigma naught values for MRS & CRS mode, respectively.
Based on the above considerations, two sets of optimum PRFs have been generated for all the beam positions: 1) For all the modes, except HRS, considering a swath of 30 km 2) For HRS mode, considering a swath of 10 km.
Table-2.2
Best and Worst Sigma Naught values for
Fig: 2.8 Variation of optimum PRF with off-nadir distance
Fig: 2.9 Variation of the number of pulses after which echo is received (for (for FRS-
FRS 1 FRS 2 MRS CRS d )
Fig.2.10 Variation of data window with off-nadir distance (for FRS-
1,FRS-2,MRS,CRS modes)
Fig.2.11 Variation of timing window parameters with off-nadir distance (for FRS-1,FRS-2,MRS,CRS modes)
RISAT-1 : Orbit
The following orbit is selected
: 377
: 536.38
nation : 97.554
to-path distance : 106.3 km
RISAT-1 into 476 km
altitud
km and inclination is corrected to 97.59
with th
keeping in view, minimum number of
days for systematic coverage in MRS
and CRS mode.
Repeat cycle
orbits in 25 days
Altitude
pg. 24
km
Incli
deg
Path-
Mean Local Time : 6 AM at
descending node
PSLV placed
e with the inclination 97.63 deg.
Orbit was raised to 536.4 km from 476
deg with a series of maneuvers. When
the spacecraft was launched, the Mean
Local Time of the orbit was 5:51 AM and
it is going to reach 6 AM around
October 2013, as there is a bias of 0.04
deg with respect to nominal inclination.
In the above orbit, ideally it takes
25 days for systematic global coverage
e same set of beams (i.e. with
same incidence angle) but, being in the
same orbit, it is possible to have global
coverage in CRS mode, every 13 days
with the same set of beams. The path
pattern for the above orbit is provided in
the diagram below.
Paths 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Days 1 14 2 15 3 16 4 17 5 18 6 19 7 20
Path pattern for the new orbit( Repeat cycle : 377 orbits in 25 days, h = 536.38 km, i = 97.544 deg )
pg. 25
Paths 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Days 1 14 2 15 3 16 4 17 5 18 6 19 7 20
Path pattern for the new orbit( Repeat cycle : 377 orbits in 25 days, h = 536.38 km, i = 97.544 deg )
Fig.1
223 km
Path 1 Path 3Path 2
Day 1 Day 2
11 km
Day 14
106 km
212 km
115 km
Fig.2
T
he above diagram in fig.2 shows that
the images in CRS mode on two
consecutive days have overlap and with
a set of consecutive 13 days, it is
possible to have global coverage. Path -
1 is fixed at 330.3 longitude, to avoid
pg. 26
high elevation passes over Shadnagar.
The ground track is maintained within ±
3 km with respect to the nominal
pattern. The maximum revisit time for a
given region of interest is 2.5 to 3 days
for latitudes between 20 and 40 deg.
Fig.
Fig.7
pg. 27
Fig-6 shows the eclipse variation over a
year. It is seen that the orbit is free
from eclipse for almost 9 months in a
year and the maximum duration is 22
minutes on 21st Jun. The latitude
below which eclipse occurs on the
calendar days is shown in fig.7.
RISAT-1 : Referencing Scheme The Referencing scheme implemented
for RISAT-1 is a generalized one due to
the following factors.
SAR operates in four different
payload modes
The swath for different payload
modes can be placed anywhere
within the range between 107
km and 659 km away from nadir.
Imaging is done in both
ascending and descending passes
Roll bias of +36 degand – 36
deg are given to view on either
side of the track.
SAR is always operated in off-
nadir mode
Hence the payload trace never
coincides with the ground trace
of the orbit from which it is
operated.
The payload trace does not
follow any one ground trace, but
it crosses over many ground
traces.
With positive and negative roll
bias, the payload trace reaches
latitudes beyond ground trace
latitudes
Referencing scheme requirements
• As SAR operates in ascending as
well as descending pass, rows
over full orbit have to be
addressed
• Referencing scheme should
address scenes for different
payload modes.
• Scenes with both positive and
negative roll bias reaching
latitudes beyond the ground trace
latitude, have to be addressed.
Scheme
Nodal points are defined along
meridians and parallels
pg. 28
The longitude range of 360 deg is
divided into 8640 points at the interval
of 2.5 arc minutes.
The latitude range of +90 deg to –90
deg is divided into 4320 points at
interval of 2.5 arc minutes.
This means that every 1deg x 1deg
grid is partitioned into 24 x 24 nodal
points. Figure – 3.3.2 shows as an
example, how 1 deg X 1deg grid with
latitude 0 deg and longitude 100 deg as
the left bottom corner, is partitioned
into nodal points.
Nodal points are addressed by four
integers i, j, m, n
i and j are the latitude and longitude
of the left-bottom corner of the 1 deg x
1deg grid to which the nodal point
belongs.
The latitude is biased by 90 deg so that
it is addressed as positive number. i
ranges from 0 to 180. 0 is –90 deg
latitude. 180 is +90 deg latitude. j
ranges from 0 to 360. and m, n range
from 1 to 24.
Partitioning of 1 deg X 1 deg grid
90,100,1,1 (lat 0.0 lng 100.0)
90,100,1,24 (lat 0.0 lng 100.9583)
91,101,1,1 (lat 1.0 lng 101.0)
91,100,1,1 (lat 1.0 lng 100.0)
90,100,24,1 (lat 0.9583 ln 100.0)
90,100,24,24 (lat 0.9583 lng 100.9583)
g
pg. 29
X
Descending scene
Ascending sceneScene centre
c2c1
c4c3 c1
c4c3
c2
The size of CRS, MRS , FRS and HRS
scenes vary as per their swath and for
CRS and MRS mode, the total scene
with the combination of selected beams
is addressed.
• Scene framing is done in the
following manner. From the start
time, a fixed duration is
considered for each scene with
sufficient along track overlap
between consecutive scenes.
The duration for scene in each
payload mode is specified by
payload team. So, there are no
fixed latitudes for scene centres
and this avoids partial scenes in
the beginning.
• The center latitude (φ) and
longitude (λ) of the actual scenes
are identified with respect to
nearest nodal point addressed
by i, j, m, n.
pg. 30
i = int(φ) + 90
j = int(λ)
m = int((φ- int(φ)) *24) +1
n = int((λ- int(λ)) *24) +1
For example,
φ = 1.750 deg and λ = 30.499 deg
i = int(1.750) + 90 = 91
j = int(30.499) = 30
m = (int(0.750*24)) + 1 = 19
n = (int(0.499*24)) + 1 = 12
• Also the pass type Ascending /
Descending has to be attached.
Imaging paths
As the orbit follows the repeat
cycle (377 orbits in 25 days), the
concept of path still holds good and
these are the nadir ground traces from
which imaging is done. As imaging is
done in both ascending and descending
part of the orbit, the descending ground
trace is extended on both sides (to the
previous ascending node from north
pole and next ascending node from
south pole) to get one path. Hence
there will be a break in the path number
at ascending node.
pg. 31
pg. 32
4.DATA RECEPTION SYSTEM
INTRODUCTION
RISAT-1 (Radar Imaging Satellite)
satellite transmits SAR (Synthetic
Aperture Radar) payload data
through X-Band carrier using dual
polarization. The data is transmitted
through one or two RF chains
depending on mode of payload
operation. The data stream of each
chain is at 320 Mbps data rate and
modulated using QPSK modulation
scheme. The bandwidth available
for data reception in X-Band is being
375 MHz, the two streams with a
total data rate of 640 Mbps are
transmitted to ground through RHC
and LHC polarized signals at X-Band
carrier frequency of 8212.5 MHz
using the frequency re-use
technique.
A new ground station has been
designed and established under the
project to cater for RISAT-1 data
pg. 33
reception.. The ground station consists of a high efficient 7.5 m
diameter antenna system with dual
shaped reflectors in Cassegrain
configuration. A new dual polarized
feed has been designed, fabricated
and integrated with antenna system
. The station provides G/T of 32
dB/deg K. The new dual polarized
feed has been designed, fabricated
and evaluated at CATF for primary
radiation patterns and at BEL Test
range for secondary antenna
patterns
All the RF and IF subsystems of the
receive station will handle higher
bandwidth of 320 MHz. Design
implementation of individual
subsystems of ground station and the
specifications of each unit are so
drawn out that they will cater for the
required over all ground station link
margin.
Integrated Multi mission Ground
segment for Earth Observation
Satellites (IMGEOS) is being
established at NRSC Shadnagar with
an objective to have a highly reliable
and an easily adaptable system to
cater for future mission requirements
in order to achieve reduced
turnaround time for the data
product generation and
dissemination. In IMGEOS scenario,
four terminals with dual polarized S/X
band feed and identical receive chain
configuration are being established.
Two of the four terminals are currently
completed and made operational.
Data Reception Station
Configuration
4.1Station requirements to track and receive RISAT-1data
• Dual circularly polarized
X/S-Band composite Feed
• Reception of high data rate
(320 Mbps) modulated signals
• Additional LHCP chain for
X-Band Auto Track
• Synthesized Up/Down
Converter with additional
channels
• X-Band Auto Track either
through RHCP or LHCP carrier
pg. 34
All the subsystems are designed
with provision for remote
monitoring and control capability
through Ethernet interface. Thus
all the subsystems are in a
common network configuration
,controlled and monitored through
a central station control computer.
• Auto diversityto facilitate
tracking on either of
threetracking Channels
IF Fiber optic link for
transfer of high data rate
modulatedIF spectrums.
High data rate
Demodulators at 320 Mbps (I+Q)
data rate
The Data and Tracking IF signals
from each of the four Primary
antenna systems are driven from
Concrete pedestal to Centralized
control room through Fiber Optic
links. The IF Outputs from the
Fiber optic receivers in Control
room are fed to the common
Programmable IF matrix ,which
routes these IF signals to the
respective second down converter
subsystems. The output of the
Second down converter is fed to
the Multi-mission programmable
Demodulators . The Data and clock
signals from each of the
demodulators are hard patched to
Data ingest systems.
High Data Rate RF
Simulator for simulation of RISAT-
1 RF signals
4.2IMGEOS configuration
The configuration of centralized
control room in IMGEOS
architecture is designed to meet the
automation requirements of the
data reception systems. In each of
the four primary antenna
systems, some of the Digital
Servo control and RF subsystems
are located in the concrete
pedestal , all the IF/base band
subsystems and Antenna control
computer are located in centralized
control room .
The data ingest systems are co-
located with respective
Demodulators. There will be five
dual channel data demodulators
pg. 35
with dedicated Data ingest
systems in order to cater to
simultaneous dual carrier data
reception requirements of the four
Antenna systems, one of them being
a common redundant system .
4.3Data Reception Stationspecifications Dual shapedmain reflector :7.5 meter dia, parabolic dish Sub-reflector : 0.8 meter dia, Hyperbolic dish Frequency Range
X-Band : 8.000 to 8.500 GHz S-Band : 2.2 to 2.3 GHz
Feed : X/S band composite, Cassegrain Single Channel MonopulsePolarization X-Band : Simultaneous RHCP & LHCP S-Band : RHCP Cross pol. Isolation :20 dB
Antenna gainX-Band: 54dBi
S-Band: 40 dBi G/T X-band : 32 dB/ºK @ 5º EL S-Band : 16 dB/ºK @ 5º EL
Half power beam width X-Band : 0.27º S-Band : 1.1º
Type of mount :
Elevation over Azimuth
Fig. 3 IMGEOS Configuration of Data Reception Station
Maximum Velocity : AZ- 20º/sec , EL- 10º/sec
Maximum accélération :
AZ- 10º/sec² , EL- 2º/sec²
Data rates : 320 Mbps (I+Q) in each chain
Tracking : S/ X (R) /X (L) AutoTrack
Program Track as back-up
Threshold Eb/No :13.3 dB for 1X10-
6BER
4.3.1Brief description of Data Reception Station
pg. 36
The station consists of a dual
shaped antenna system with a
7.5 m dia parabolic reflector.
The dual shaped antenna along
with feed in
Cassegrainconfiguration provides
G/T of 32 dB/º K. The composite
S/X feed is dual circularly
polarized in both S & X
bands.with the capability to
receive LHC and RHC polarized
signals simultaneously.
The antenna and feed system is
mounted over an EL over AZ
drive pedestal. The feed and
front-end system realizes single
channel monopulse tracking. The
X-Band data is received through
RHCP and LHCP
simultaneouslyusing frequency
re-use technique.
The X Band data and tracking error
signals from RHCP & LHCP chains in
identical configuration are amplified
in LNA and down converted toa first
Intermediate frequency in the range
of 2.2 to 2.9 GHz IF. The S-band
Telemetry Data and Tracking signals
are down converted to 70 MHz IF.
The down converted X and S band
tracking IF signals are fed to a
three channel Integrated Tracking
system (ITS), located at antenna
pedestal. The ITS demodulates the
tracking IF signal and extracts AZ
and EL DC error information from the
tracking video. The DC errors are
fed to Digital Servo System to
control the antenna movement for
satellite tracking in Auto Track mode.
The Digital Servo System
comprises of Antenna Control
Computer, Drive Power Amplifiers
Drive motors and Optical shaft
Encoders to operate the Antenna in
different modes of operation viz,
Rate mode, PTS mode, command
angle mode and Auto mode . The
System has provision for remote
control and configuration through
Ethernet interface
The Drive system consists of Power
Amplifiers, Brush less DC motors, Gear
boxes (Dual drive mode) and Slew-rings
pg. 37
in each El. and Az, axis. Each axis is
driven by two motors in counter torque
mode to avoid backlash. Absolute
optical shaft encoders are used for
measuring the angular position of the
antenna. All safety interlocks are
provided in the drive system.
The IF outputs from first data down
converter (2 carriers) and S band
data IF are driven to the control
room through a multi-core optical
fiber cable. The S band Data IF is
driven to SPS receiver in control
room for further processing of SPS
Data.
The twodata IF signals received
in control room are fed through
programmable IF Matrix to the
second down converter and then to
High data rate digital demodulator.
The data and clock signals from
demodulators aredriven through
LVDS interface to Data Ingest
System for further processing and
product generation. The total data
acquisition system for all the
Antenna Systems are automated
through Station Control Computer.
4.4Detailed Functional Reception of
Data Reception station
The data reception station comprises
of the following major systems. The
functional block diagram of data
reception station is given in fig 2.
• Antenna &Tracking Pedestal
• Dual Polarized Feed& RF systems
• Digital Servo & Automation
system
• IF &Base-Band system
• Data Ingest System
The detailed functional
description and specifications of
each of the subsystems is given
in the following sections.
pg. 38
Fig.4 Data Reception Station
block age and sub reflector spill
over, which significantly affect the
gain of the antenna. The main
reflector consists of a machined,
reinforced circular hub, which
supports 16 radial trusses and
other interconnecting braces.
The 16 trusses support 16 solid
surface reflector panels. Aviation
warning lights and lightening
arrestor are mounted on the
reflector. Sub reflector is
4.5 Antenna &Tracking Pedestal
4.5.1 Antenna
The reflector is a 7.5-meter
diameter Parabolic Antenna with a
focal length to diameter ratio (F/D)
of 0.41. The focal length of the
reflector is 3.07 meters. The sub
reflector diameter has been
selected as an optimum value in
the trade-off between reflector
pg. 39
4.5.3Drive chain hyperboloid supported by four
aluminum quadri-pods. Antenna
mounting frame attaches the
reflector to a pair of Yoke arms
with Counter weight arms.
The drive chain is a dual drive
system in both Azimuth and
Elevation axes, using brush less
DC motors to enhance the
reliability and performance. The
drive system is configured with
precision anti backlash gear
system and torque bias
arrangement to provide better
tracking and pointing accuracies.
All the four drive motors are
identical with integral
tachometer, resolver and brakes.
The brushless DC servo motors
are coupled to the output axis by
means of a high efficiency gear
reducer and torque coupling.
4.5.2 Pedestal
The pedestal system is an
Elevation over Azimuth mount
type. The Elevation housing
contains the necessary drive
system for antenna movement
about an Elevation axis between -
2° (below the horizon) to zenith
and Azimuth housing containing
the drives to achieve ± 360°
rotation about the Azimuth axis.
The Azimuth housing (Fig.)
consists of a fabricated
stiffened cylindrical steel drum
supported on a concrete
pedestal. The Azimuth drive
mechanism is housed inside it.
The Pedestal assembly consists
of drive components, gear
boxes, optical encoders, Electrical
limit switch assembly and Stow
lock motors.
A cable wrap system will be
provided in the pedestal housing
to protect the cable elements
from damage due to uncontrolled
cable twist loops, during the
antenna movement.
4.5.4Azimuth housing
The Azimuth Slew ring bearing is
supported at the top of the Azimuth
housing which is properly machined
pg. 40
to match the Slew ring bearing
surface and attached to it using high
strength bolts. The Azimuth housing
is connected to Elevation housing
using high tension bolts fitted to
inner ring of Azimuth Slew ring
bearing.
4.5.5Elevation housing
The Elevation housing (Fig. 4) is
a structure fabricated out of
steel plates. It houses the
elevation drive mechanism. The
bottom of the Elevation housing is
machined to suit the fixed part of
the Azimuth Slew ring bearings
and is fitted to it by high tensile
steel bolts. An access is provided
in the Elevation housing for routing
cables through the hatch. The Yoke
arms are attached through Slew ring
bearings to Elevation housing. The
Physical structure of the antenna
with details of complete mechanical
components of the pedestal
assembly is shown in fig.3.
Fig.5 5m Dia. Antenna System
pg. 41
4.7Technical Specifications: Pointing Error : 0.08° peak Operating Temperature : 0° C
to 55° C Antenna Type : Parabolic
reflector Wind Speed Diameter Main Reflector :
7.5 meter shaped parabolic solid
dish
(a) Operational wind speed
: 60 Kmph
(b) Occasional gusting : 80
Kmph Sub-reflector : 0.736 meter
Hyperbolic dish ( c)Drive to stow : 100 Kmph F/D : 0.41 (d) Survival wind speed in Zenith
: 200 Kmph Focal length : 3.077 meters
FeedConfiguration :Cassegrain Natural resonant Frequency :
4 Hz S Band : 8 Helices
X-band :4 Conical dielectric
elements Weight : 1.4 Tons
4.8Dual Polarized S/X Band Feed &RF Systems
Overall RMS
(a) Main Dish : 0.5 mm
RMS
4.8.1Dual Polarized S/X Band Feed (b) Sub-reflector : 0.05
mm
The feed is of multi-element Single
channel mono pulse tracking type,
capable of receiving dual circularly
polarized S & X-band signals. The
feed comprises of an array of 4
conical radiating elements designed
for simultaneous reception of
RHCP&LHCP X-band signals and an
array of 8 helical elements, 4
elements for reception of RHCP & 4
elements for LHCP signals in S-
Sky coverage
(a) Elevation : 2°to182°(Mech),-
0°to 180° (Electrical)
(b) Azimuth :±360°Velocity
(a) Elevation Axis : 10° / sec.
(b) Azimuth Axis : 20° / sec.
Angular Acceleration
(a) Elevation Axis
: 2° /sec2
(b) Azimuth Axis : 10° /sec2
pg. 42
band. The feed array inmono pulse
configuration receives offset
beams corresponding to Azimuth
and Elevation axes in both Right
Hand Circular and Left Hand
Circular Polarizations .
The septum polarizer receives the
signals from feed elements of X
Band and provides linear polarized
signals corresponding to RHC and
LHC signals. The linearly polarized
signals are in turn fed to a wave
guide mono pulse comparator to
generate sum and difference
signals. The feed elements are
assembled on a cylindrical shroud
and covered with a radome casing
which gives environmental
protection. The shaped antenna
system together with the RF front-
end system realizes a G/T of better
than 32 dB /deg. K at 5 deg.
Elevation in X Band.
The antenna has highly directive
pattern with half-power beam
widths of 0.27 ° in X-band and 1.1°
in S-band. The feed elements are
arranged to produce two beams
which are offset in AZ plane, and
two beams offset in EL plane .The
feed assembly also contains
waveguide Mono Pulse Comparator
(MPC)and Mono Scan Converter
(MSC) for RHCP and LHCP chains
in X-band and micro stripline
MonoPulse Comparator and Mono
Scan Converter (MSC) for S-band.
The Mono Pulse Comparator
compares each pair of beams to
produce the tracking error signals,
when the antenna RF axis is exactly
on Boresightaxis , each beam has
equal amplitude and their
comparison results in zero signals in
difference port. The sum channel is
formed in the MPC by adding all
four beams together. The AZ and
EL error signals coming out of
the MPC are given to MSC,
which carries out time division
multiplexing such that the
Azimuth and elevation tracking
error signals are combined in to
pg. 43
a single channel tracking signal ,
with reference to the Azimuth-
Elevation Scan pulses and 0°, 180°
phase scan pulses which are
driven from Integrated Tracking
System to the feed. In case of X-
band, these pulses are routed
through driver card in RF junction
box. Fig.4shows the functional
block diagram of dual polarized
feed.
.
Fig.6 Block diagram of dual
polarized feed
The received signals in X-Band are
passed through 30 dB test loop
coupler and amplified in low noise
amplifiers. The loop coupler is used
to introduce the test signal in the RF
chain to evaluate the system
performance in Local loop simulation
mode. The amplified outputs are fed
to 2 way in-phase power divider.
One output of power divider is taken
out as Sum/Data signal and applied
to X-band down converter to
generate Data IF. The other output
of power divider is combined with
the Single channel tracking error
signal to generate the Amplitude
modulated tracking Signal, which is
then down converted to generate
tracking IF.
pg. 44
The input X-band sum signal is
divided by a power divider to
provide two outputs.
4.8.2Feed specifications
Type : Cassegrain feed One output is used for data and the
other output is given to a 6 dB
coupler, where amplified error signal
is coupled for generation of tracking
error signal. The X- band
directional coupler is a 6 dB
strip line type with SMA coaxial
connectors. It has minimum insertion
loss and good directivity.
Frequency Range X-Band : 8.000 to 8.5 GHz S-Band : 2.2 to 2.3 GHz Polarization X-Band: RHC & LHC S-Band: RHC & LHC Half power beamwidth X-Band: 0.27º Before getting coupled with sum
signal, the difference signal at the
input is passed through a digital
phase shifter in order to compensate
for phase mismatch between sum
channel and difference channel. The
phase shift is digitally controlled
using 6 bit TTL signals, driven
from Integrated Tracking System.
The step size of minimum phase shift
is about 5.6° . These 6 bits can be
optimized and programmed to
facilitate tracking through any
carrier frequency over X-Band
frequency range.The phase match
can be adjusted periodically if
required through local or remote
control.
S-Band: 1.1º
Side lobe level : 14 dB Null depth : Better than 25 dB Axial Ratio : 2.0 dB max
4.8.3X-Band DPC (Divider, Phase
Shifter, Coupler) The X-band sum and error signal
amplifier outputs of both RHC and
LHC signals are fed to the input
ports of DPC. The unit has two
independent channels to provide
tracking and data signals of RHC
and LHC chains.
pg. 45
The DPC subsystem comprising 2
way power divider, digital phase
shifter and a 6 dB directional coupler
is wall mounted in pedestal room.
4.8.4 S-Band DPC
The S-Band DPC has a single
channel to process RHC signals. and
the rest of the configuration and
function are the same as that of X-
band DPC.The S band Data signal is
driven to the control room for further
processing of SPS data after down
conversion to 70 MHZ.
4.8.5 X- Band Up/Down Down Converter
The up/down conversion of X-Band
signals is based on dual conversion
technique.The received X-Band
signal in the frequency range 8000-
8500 MHZ is converted into first
IF signal in the range 2345-2845
MHzduring first conversion, by
mixing with a fixed local oscillator
signal at 5655MHz.
In the second conversion, the first IF
signal beats with a local oscillator
signal derived from frequency
synthesizer. The frequency of built-in
synthesizer is programmable over
the range 1560-2185 MHz in order
to derive the desired Intermediate
Frequency of 720 MHz and
facilitate multi mission data
reception. The frequency
synthesizer is controlled and
monitored through TCP/IP remote
interface.
4.8.6 X-Band Down Converter
The data and tracking down
converters, each consists of two
identical channels to support LHCP
& RHCP chains for the first
conversion. The data and tracking
down converters are housed in
separate boxes and they are
located at antenna pedestal.
The second down converter for
tracking is located at pedestal.
The second IF output of tracking at
720 MHz is fed to Integrated
tracking system for extraction of AZ
and EL DC error signals and
drive the digital servo system. The
second data down converter unit is
pg. 46
co-located with demodulators in
control room.
4.8.7X-Band Up Converter
Up-converter is used to convert
desired IF signal at 720MHz to a
suitable first Intermediate frequency
in the range 2345-2845 MHZ in
first conversion unit and
subsequently converted to
desired X-Band signal frequency in
the range of 8000-8500 MHz in the
second conversion unit of up-
converter.
The first up-conversion unit is
located in the control room and
the outputs of up-converter are
compatible to both bore sight
system and local loop simulation.
The second up-converter unit for
Local Loop is located at
pedestal and that of Boresight
system is located at Boresight
room .The selection for routing of
the up-converter output between
bore sight and local loop is
carried out through remote
interface.
4.8.8 S-Band Down converter
The S-Band Down converter is
based on single conversion. The
down converter consists of two
identical channels to support data
and tracking. The received S-Band
data and tracking IF signals in the
range of 2.2 to 2.3 GH z are down
converted to a 70 MHZ IF. The L.O
signal for down conversion is
derived using a programmable
frequency synthesizer module.
4.8.9Integrated Tracking System
The S tracking IF at 70 MHz and X
band (R&L) tracking IF signals at
720 MHzfrom corresponding down
converters are fed to Integrated
Tracking system (ITS). The ITS
demodulates AM tracking video from
IF signals. ITS works in non-
coherent mode and the AM video
detection is achieved by simple
envelope/peak detection method.
ITS has built-in Automatic gain
pg. 47
control modules to provide constant
amplitude signal and DC errors for
varying input signal leevls. The AGC
bias signal is also provided as an
output signal for facilitating auto
diversity reception and auto
acquisition.
Two Spectrum analyzers are required
for real time monitoring of the X
band data and S band tracking IF
signals and for carrying out regular
maintenance of the receive chain.
ITS has auto diversity reception to
select any one of the two (In case of
both S & X –band inputs) input
signals being present, based on their
signal strength (AGC). ITS uses
separate error demodulator modules
in both Elevation and Azimuth axes
to extract dc error. ITS unit also
consists of a Scan code generator
module which generates two sets of
Scan pulses. One set of Pulses called
AZ-EL scan pulses are of 1 KHz
frequency and the other set called
Phase scan pulses are of 500 Hz
frequency. These pulses are
simultaneously applied to the
Monoscan converter module in the
Single channel monopulse feed and
used in the tracking demodulator
circuits in both Elevation and
Azimuth channels for synchronizing
the process of Error generation and
demodulation.
The Azimuth and Elevation DC
output errors are applied to the
Servo system for driving the antenna
towards the target position and to
nullify the tracking errors. ITS has
provision for adjustment of various
parameters of the tracking chain like
Phase shifter adjustments, DC offset
error gradient and Acquire /Loss
threshold.
4.9IF and Base Band Systems
4.9.1Programmable IF Matrix
The Programmable 4X4 (RHCP )
4X4 (LHCP) IF Matrix facilitates
automated inter connectivity of IF
signals(Output of first down-
converter) from different Antenna
Terminals to the input of the Second
pg. 48
down-converter followed by the
Demodulator. The main function of
the IF matrix is to facilitate total
automation of the data reception
chain including the IF signal path
routing. IF Matrix also eliminates
the problems associated with
manual patch panel like, loose
contact problems, mechanical
wear and tear of the patch chords,
operator errors etc., thereby
improving the reliability of the
system ,while increasing the
flexibility and reducing the
complexity.
4.9.2IF Fiber Optic Link The first IF signal in the range of
2345-2845 MHz from the output
of 1st down converter is driven
to control room through Fiber
Optic link. The Fiber optic
linkcomprises of fiber optic
transmitters and receivers. The
transmitters are placed at the
Pedestal end and the output of
transmitter is driventhrough a
Single mode multi core fiber
optic cable. The Fiber optic
receivers are placed at the
controlroom to receive the
signals. The two downlink data IF
signals corresponding to RHCP
and LHCP, two uplink data IF
signals and S-Band data IF
signals are driven through F.O
link from pedestal to control
room.
4.9.3High Data Rate Demodulators
The down converted IF signals of
data channels passed through
band pass filters. The pass band
of band pass filters is 320 MHz
with minimum group delay and
good rejection characteristics.
The filtered signal levels are
amplified in IF amplifiers so that
the boosted levels are within the
dynamic range of demodulators.
The multi mission High Data
Rate Receivershave the
capability to receive and
demodulate QPSK signals of
RISAT, which are modulated at a
very high data rate of 320 Mbps.
The demodulator and bit
pg. 49
synchronizer are supported in a
single unit. The unit receives
QPSK modulated signals at 720
MHz IF and provides
synchronized data and clock
signals as outputs. The LVDS I
and Q output data and clock
signals arefed to Direct Ingest
System (DIS) for further
processing of data. The
Demodulator unit has the feature
of supporting any data rate
continuously variable from 1 to
320 Mbps.
• Monitoring & Control of
through TCP/IP
• Automated/unmanned
tracking operations
• FO link for remote operation
of ACSS
• Built in Test & calibration
software for comprehensive
maintenance
Specifications: Tracking Velocity :
20 deg/sec in AZ, 10deg/sec in EL
Tracking Acceleration : 10 deg/sec² in AZ, 2 deg/sec² in EL
4.10 Digital Servo Control System
Servo pointing accuracy : < 0.03 deg
Position display Resolution : 0.001 deg The Servo Control System has all
the salient features of modern
digital control system available in
any of the latest ground stations,
using the state of the art
technology. The main features of
the system are
Position Transducer :19 bit or higher, single turn
Absolute rotary shaft optical encoders
Position loop bandwidth : Tunable from 0.1 to 2.0 Hz
Rate loop bandwidth : Tunable 1.0 to 10.0 Hz
Operating modes : Standby, Slew, Manual, Program, • DSP based Antenna Control
Unit Designate,X-Auto,S-Auto,Sun/Star, Auto sequence mode • Software based digital
control loops Type of motor/drive :
• Zenith pass handler
pg. 50
Brushless AC servo motor with Resolver feedb
ack and built
in brake/PWM drive 4. Tracking & Control
software Drive configuration : Two motor Counter-torque Secant correction : Azimuth axis through software
4.11Antenna Drive Unit System Control Options :
Local/Remote
The ADU houses the DC servo
drive unit that includes 4 Pulse
Width Modulated (PWM) servo
amplifiers to drive the azimuth
and elevation Brushless DC servo
motors. Two motors are used for
each axis.
The Servo Control System has the
following sub systems. The
complement of above equipments
shall provide a wide variety of
operating modes for the antenna.
The block diagram of servo control
system is shown in fig 4. The drive unit operates as a
current / torque loop with torque
bias set by the ACU to minimize
backlash and maximize pointing
and tracking accuracy. The
torque bias parameters are
configurable in the ACU to
optimize performance.
1. Antenna control unit (ACU)
2. Antenna drive unit (ADU)
3. Tracking Network
configuration
pg. 51
ADU contains drive amplifiers and
logic for azimuth and elevation
axes control, power on sequence
and safety interlocks. The ADU
also provides power and interface
points for the discrete I/O
antenna points. The ADU includes
all the required power supplies
for drive amplifiers, drive
electronics, switches, stow pins,
alarms and motor brakes. These
status points are controlled and
monitored by the ACU. The
additional protections built into
the drive systems are bus
under/over voltage protection,
short circuit protection, Over
Temperature (Heat sink)., Over
current trip, Electronic fusing,
Resolver connection fault (open
circuit).
4.11.1Antenna Control Unit
The Antenna Control Unit (ACU),
along with the Antenna Drive
Unit, is responsible for closing the
position loop, reading the
position sensors, commanding
the Antenna azimuth/elevation
Drives. The ACU contains the
hardware and firmware to close
each axis position loop with the
position feedback from the on
axis position transducers (optical
rotary shaft encoders). The
sources of the position
commands shall, apart from
internally generated, include
tracking receiver generated error
signal. The generated position
error is frequency compensated
and converted to rate commands.
For the full motion control, the
rate command is compared with
the motor rate feedback. The
error is then used to control drive
amplifiers that effectively apply
armature supply to the brush less
DC servomotors. The ACU
provides all manual and
automatic target acquisition and
antenna positioning functions.
The ACU communicates with the
drive system and Ethernet
through TCP/IP protocol. ACU
issues drive enable commands as
well as to read the various status
parameters from Drive system
through this interface.
pg. 52
The Antenna Control servo
system shall have extensive
operational modes to meet the
antenna requirements for orbiting
satellites. The system shall have
two operating control
environments. One is “Local mode
(operator control)” from Remote
Fig.7 Block Diagram of servo
control system
4.12Tracking Network Configuration
antenna control computer (ACC)
at Control room or Antenna
Control Unit (ACU) at Antenna
pedestal room and another is
“Remote mode” via Station
Control Computer (SCC) system
from Earth station control room.
The operating modes supported
by ACU are Standby, Ready,
Manual Position, Slew Rate,
Command angle , Auto track (X-
band & S band) and Program
Track.
The primary operational interface for the
Antenna control servo system is the
Remote Antenna Control Computer
(RAC), which provides remote control of
the
E
E
AZ Axis
EL Axis
Drive
Delta Tau UMAC Motion
Controller
EL absolute encoder & limit signals
AZ absolute encoder, cable wrap & limit
GPS Timing Signal
S-band Signal
Generato
Other I/O
Signals
Integrated
Tracking
ACU Computer
Down Converter
Drive
Drive
Drive
Etherne
Ethernet Switch
RS-232 RS-232 Etherne
Analo
RAC
Fig 5: Block Diagram of servo control system
pg. 53
Antenna control unit (ACU) from
the Control room. The Remote
antenna Computer (RAC)
communicates with the Antenna
Control Unit (ACU) over
dedicated Fiber optic link.
The ACU communicates with the
drive systems of both azimuth
and elevation axis through
Ethernet. ACU issues drive enable
commands to the drive system as
well as monitor the status of the
drive system through this
network. The other important sub
systems like Integrated Tracking
System, Multi channel tracking
down Converter etc. are
connected on the same network.
The typical network configuration
is shown below.
pg. 54
Tracking Down
Converter
Integrated Tracking System
Antenna Drive System
Antenna Control Unit
Antenna Pedestal Switch
FO Link
DRS LAN Switch
Fig.8 Tracking Network Configuration
4.12.1Station Automation System
The purpose of the station automation
system is to operate
the ground station in a fully
automated environment aiming
towards unmanned operations.
The main functions of the Station
automation are carried out by
Station Control Computer in
coordination with Antenna
Control Computer.
pg. 55
Fig.9 Station Automation
System Configuration
NRSCground
station has four antenna systems
and five data receive chains and
its configuration is shown in
Figrue-6. The Antenna Systems
are located in the
Antenna Pedestal room and its
purpose is to track satellite in
auto or program track mode.
These antenna systems are
controlled from the Data
Acquisition Control Room (DACR)
by Remote Antenna Control
Computer (RAC) through Servo
Fiber optic (SFO) link.
The 2 GHz Data output from the
antenna system is driven by
another Fiber Optic link DFO to
bring to the DACR. These
outputs from all four antenna
systems are routed through IF
Matrix to connect it to different
Data Receive Chains. Each Data
Receive chain has two streams to
support IRS-P5, Resourcesat-2
etc. Both the streams are
configured to same in case of
Single stream missions like
Carotsat-2/2A, Oceansat-2 etc.
pg. 56
4.13Station Control Computer
Station Control Computer carries out the
automation of IF matrix and Data
receive chain and its configuration
diagram shown in Figure-7. Each data
receive chain has one down converter
and one demodulator. These systems
are connected on Two 24 Port Ethernet
Switches.
Fig.10 Devices connectivity of Station Control Computer
The software is developed with the
following features to carry out the above
functions
• It facilitates highly
configurable environment
which is adaptable to addition,
deletion or change in
configuration parameters in
various configuration file.
• All the independent modules
are made to run on different
threads. This helps in running
other modules smoothly when
a particular module faces
some problem.
pg. 57
• Two TCP/IP application level
protocols are developed for
message passing between
SCC and various ACC systems.
One for SCC server to ACC
client and the other for ACC
server to SCC client.
pg. 58
5.LEVEL’0 SYSTEMS • Data Ingest and Quick Look
Display System 5.1Introduction • Ancillary Data Processing System
• SPS PB Data Archival System RISAT-1 is the first Microwave Indian
Remote Sensing Satellite. It carries an
Active Microwave payload SAR
(Synthetic Aperture Radar) operating in
C-Band, enabling data collection in
Day/Night and all weather conditions.
The Ground Segment comprises the
Data Reception, Processing &
dissemination facilities. The following
sections describe the various sub-
systems of the Level-0 Systems for
RISAT-1.
• Data Serializer System
• Timing System.
Level-0 Systems will be realized in
IMGEOS Configuration. Each of the
FOUR antenna and Data Receive Chains
have a dedicated Data Ingest System
(Shown in Figure 8) for real-time data
ingest onto RAID and subsequent
transfer to SAN for ADP Processing.
Based on clash scenario Two antenna &
data receive chains will be assigned for
RISAT-1 as Main & redundant chains. Level ‘0’ Systems
• Station Work Flow Manager for
Event Scheduling and Monitoring
pg. 59
IF MATRIX
AS - 1 AS - 2 AS - 3 AS - 4
DEMODULATOR 1 DEMODULATOR 2 DEMODULATOR 3 DEMODULATOR 4
Data Ingest System 1 Data Ingest System 2 Data Ingest System 3 Data Ingest System 4
Fig.11 Data Chain Configuration
5.2 Station Work Flow Manager
Station Workflow Manager provides
centralized event monitor and control
functions for Station operations with
appropriate interfaces with UOPS for
pass schedules, state vectors, and
Urgent/Emergency requests. On receipt
of Pass Schedules for a Day, SWFM
generates Work Orders for Station
Control Computer System for
assignment of Antenna Systems &
Receive Chains. It also generates WO
for the respective Data Ingest Systems.
On receipt of successful data ingest
message post pass from DI, Work
Orders are issued by SWFM for the ADP
Processing Nodes. Event Monitor &
Controller displays Process status and
provides control for Process initiation,
restart & abort.
pg. 60
Pass Schedules / UrgentRequests / SVs
Data Exchange GatewayU O P S
Station Work Flow Manager
Data IngestSystems ADP Systems
W O Files
RAW Data ADIFFRED
Fig.12 Station Work Flow Interfaces
5.3Data Ingest System The Data Ingest systems consist of PC
servers with RAID for real-time data
ingest. 2 Nos of PCI Front End Hardware
(FEH) Cards which are connected to the
Demodulators with LVDS interface.
IRIG-G Time is fed to the Time Code
Translator which translates the serial
time and provides parallel BCD Time to
FEH for time stamping the Raw Data.
TCT provides RS-232 I/F for system
time synchronization.Data Ingest
System gets work orders from SWFM,
schedules the supported passes,
acquires real-time data, provides a real-
time display of important parameters
like Sync Status, FS Errors, GRT & Line
Count Jumps, etc. After the completion
of LOS, RAW data acquired in RAID is
transferred over FC network to SAN
along with the quality report.
Appropriate Event Message indicating
the status of data acquisition is sent to
SWFM for further initiation of ADP
Processes.
pg. 61
RAIDLEVEL-0 SAN
Data Ingest Server
4 Gbps FC Link
SWFM
DI Work OrdersStatus Messages
FEH card 1
FEH 2
PCI (64 BIT, 66 MHZ)
PCI (64 BIT, 66 MHZ)
Stream1
Stream2
FEH 1
PCI (64 BIT, 66 MHZ)
PCI (64 BIT, 66 MHZ)
Parallel BCD time I/F
Stream2
DEMODULATOR
LVDS/ECL
LVDS/ECL
TCT
IRIG - G Fig.13Data Ingest System Configuration
5.4Timing Systems The NTP server port on the Unit is
used for accurate system Time
synchronization. Serial IRIG-G
time code from XLI unit is fed to
the Serial Time Distribution Unit,
which buffers and provides the
Serial Time to the Time Code
Translators on Data Ingest
Systems.
Station Timing Systems consist of
XLI Time and Frequency Unit (NTP
Server), Serial Time Distribution
Unit and Time Code Translator
Units.
The XLI Time & Frequency System
has 12-channel GPS Receiver, GPS
synchronized Time Code
Generator, high precision rubidium
oscillator for clocking the TCG.
pg. 62
GPS Antenna
Serial Time Distribution Unit
IRIG-G
TCT 1 TCT 4TCT 2 TCT 3
NTP Time Unit
N/W SwitchNTP Time
Fig.14 Timing System Block Diagram
5.4.1IRIG-G Time Code Translator
Serial Interface provides the ASCII
time for System time
synchronization and scheduling of
events. The Set-time and Read-
time Utilities are provided for off-
line configuration of the system
and validation of the interface
respectively. Displays DAYS:
HOURS: MINUTES and SECONDS
on the front panel.
IRIG-G TCT has been developed
in-house for meeting the GRT time
stamping requirements of RISAT-
1. The TCT accepts IRIG-G Serial
Time Code and translates it into
Parallel BCD format up to 10
Microseconds to Front End
Hardware (through 68 Pin SCSI
connector) for Time stamping the
RAW data being ingested. The
pg. 63
AGC Logic DECODER
SCAN LOGICMINOR FRAME SECTION
MAJOR FRAME SECTION
BCD TO 7 SEGMENTDECODER / DRIVERS
68 PIN SCSI Connector /50 PIN Centronics Connector
IRIG -GMODULATED SIGNAL
IRIG ADC CODE
Dec
oded
Par
alle
l BC
D C
ode
Parallel BCD Data
1 PPS Clock
Frame Sync
Load Pulses
7-SEGMENT DISPLAY
Fig.15Time Code Translator
pg. 64
6.SAR Payload for RISAT
Radar backscattering depends
upon the sensor parameters such
as frequency, polarisation and
incidence angle as well as on
target parameters such as
dielectric constant, roughness and
geometry. In RISAT, SAR sensor is
selected in C-band (5.35 GHz)
with both co- and cross-
polarization, which will meet most
of the resource applications and
also enable achieving high
resolution capability. The SAR
sensor is based on active phased
array antenna technology, which
will provide requiredelectronic
agility for achieving multimode
capability.
6.1Modes of Operation
The RISAT High Resolution SAR
will be operating in C-band at a
frequency of 5.35 GHz. The
spacecraft altitude has been fixed
at 536kmfrom the 25-day
repetivity considerations. The SAR
system has beendesigned to
provide constant swath for all
elevation pointing and almost
near constant minimum radar
cross section performance. The
proposedSAR will operate in the
following basic modes: Figure-
15&Table-1
Fine Resolution Stripmap
Mode-1 (FRS-1): This mode is
basedon Stripmap imaging, which
is the conventional mode of SAR.
In this,the orientation of the
antenna beam is fixed with
respect to flight pathso that a strip
of constant swath (here, 30 km) is
illuminated along theflight
direction. The intended resolution
is 3m for FRS-1 mode.
Coarse Resolution ScanSAR
Mode (CRS): The ScanSAR mode
allows for a multifold increase of
the range swath dimension. This
isachieved by periodically stepping
the antenna beam to the
neighboringsubswaths (in the
range direction). In the CRS-mode
of RISAT, therewill 12 beams
(either side of the intermediate
sub-swaths will have anoverlap of
pg. 65
High Resolution Spotlight
Mode (HRS): In the spotlight
mode,
7km from the preceding and
succeeding sub-swaths). This
results, total swath in CRS mode
would be 220 km. the resolution the antenna beam is oriented
continuously to illuminate a
particularspot on the ground. This
way, the target aperture time is
increasedwhich results in
improved azimuth resolution
(compared to that in thestripmap
case) which will be 1m for this
mode. The improved resolution
offered in this mode will be 50 m.
Medium Resolution ScanSAR
Mode (MRS): This is a 6-beam
scanSAR mode, similar to the CRS
mode, providing a resolution of 25
m over a swath of 115 km.
Fine Resolution Stripmap
Mode-2 (FRS-2): This mode has
quadpolarization capability.
Philosophically, this mode is a
hybrid strip mapand scanSAR. It is
stripmap in the sense that the
beam orientation iskept fixed with
respect to the flight path and a
strip of constant swathwidth is
covered. Also, in a way it is similar
to scanSAR, because forpart of
the aperture time the beam
polarisation is switched from
Vtransmitto H-transmit, and vice-
versa. Hence, this mode would be
is obtained at the cost of azimuth
coverage. The latter is
partlyimproved by making use of
sliding spotlightmode (hybrid
spotlightstripmapmode). This
imaging would be done over a
spot size of 10 kmx 10 km.
Circular Polarimetric Modes
(C-HRS, C-FRS-1, C-FRS-2,
CMRS,C-CRS): All the modes
mentioned above can be operated
inhybrid-circular polarization. This
is achieved by transmitting H & V
used for polarimetry, as we can
have all the four combinations of
polarized signals simultaneously
but with a relative phase-shift of
90°.Hence, the transmit signal is
in circular polarization and the
receivesignal is in linear (dual-pol)
polarisation, viz, VV, VH, HH &
HV.
pg. 66
– this makes it a hybrid-
circularpolarization operation. To
keep the average power-
requirements sameas the original
specifications, the pulse-width is
reduced to half.
FIGURE-15 Basic modes of SAR
Fig.16 Non Imagable area
Except FRS-2 mode, which is
inherently quad pol mode, all
othermodes can be operated
either in single polarization modes
(HH, VV,HV, VH), dual polarization
modes (HH+HV / VH+VV) or
Circularpolarization modes.
Also it shouldbe remembered that
as it is a side looking active sensor
around 107 Km either side of the
Sub satellite Track comes under
Non Imagable area for that orbit
under consideration.( Figure 14)
Fig.17 Basic Mode of SAR
Antenna Pedestal Room
pg. 67
Table.2 Payload Modes
DRS Systems
7.RISAT DATA PRODUCTS & FORMATS
pg. 68
Radar Imaging Satellite (RISAT-1) will acquire data in C band with following modes:
Geo-Tagged Products (Level-1) :The image is geo-tagged using orbit and attitude data from the satellite. This allows latitude and longitude information to be calculated for each line in the image. The earth geometry is assumed to be the standard ellipsoid. Each image line contains auxiliary information which includes the latitude and longitude of the first, mid and last pixels of the line. The raw radar signal data is processed to provide SAR image data pixels. The image pixel data is represented by a series of CEOS processed data records, each record containing one complete line of pixels lying in the range dimension of the image. The product can be obtained as slant range data (16 bit I and 16 bit Q) or ground range data (16 bit) amplitude data. Additionally, an auxiliary file containing a dense grid of geo-locations is associated along with the data file.
• Fine Resolution Strip map Mode-1 (FRS-1): It provides 2 m slant resolution image over 25 km swath in either single or dual polarisations
• Fine Resolution Strip map Mode-2 (FRS-2): It provides 4 m slant resolution image over 25 km swath in quad polarisation.
• Medium Resolution ScanSAR Mode (MRS): It provides 8 m slant resolution image over swath of 115 km in either single or dual polarisation
• Coarse Resolution ScanSAR Mode (CRS): It provides 8 m slant resolution image over swath of 223 km in either single or dual polarisation.
• High Resolution Spotlight Mode (HRS): It generates better than 1 m resolution image fora spot of 10 km (Azimuth) and 10 km (ground range swath) for either single or dual polarisation.
7.2Ellipsoid Geocoded Products (level-2) : This product contains geometrically corrected data. There exists provision for UTM (default) and Polyconic map projections. For systematic processing UTM projection will be provided. The pixel spacing in the product will depend on mode, no. of looks and look angle. For a given mode and a range of look angle, no. of range and azimuth looks will be worked out in such a way that pixel spacing in both range and azimuth direction remain uniform. The options for product format are CEOS and GEOTIFF.
The various levels of products defined for RISAT-1 are as follows: 7.1 Raw Signal Products (Level-0):This product contains raw or unprocessed radar echo data in complex in-phase and quadrature signal (I and Q) format. The only processing performed on the data is the stripping of the downlink frame format, BAQ decoded (optional) and re-assembly of the data into contiguous radar range lines. Each range line of data is represented by one Signal Data Record in the RAW CEOS product. Auxiliary data required for processing is also made available along with echo data.
7.3Value added products: Beside the above mentioned standard data products, additional products such as precision geocoded and terrain
pg. 69
geocoded will be available for FRS-1 & 2 and MRS mode data with user supplied GCPs’ information and available Digital Elevation Map information. Also for FRS-2 mode Polsar products will be available after proper validation.
(ii) Level-1 : Geo-Tagged Products (iii) Level-2 : Ellipsoidal Geocoded products Value added Products: �Precision Geocoded
7.4Image Quality Parameters: RISAT-1 products will nominally provided in CEOS format. This format will contain various products quality parameters like range resolution, ground resolution, azimuth resolution, peak side lobe ratio, integrated side lobe ratio, radiometric resolution, geometric error, resampling option, Datum used, relative phase error etc depending on the level of product. Also format will have information on processing related parameters such as no. of range and azimuth looks, azimuth bandwidth, range and azimuth weighting, Doppler centroid etc.
�Terrain Geocoded �Pol-SAR Products Fig.18 Strip map Imaging: FRS-1
The derivation of product code and the product code list are provided in Table-2& Table-3 Fig.19ScanSAR Imaging: MRS Definition of RISAT Data Products LEVELS (i) Level-0 :Raw signal products
TABLE.3 DPWFM RISAT-1 DATA PRODUCT CODES Code is 9 chars: PTMREELFM
SL.NO Description Typical
Values Meaning
1. Product Type ST Standard
Control Room
pg. 70
PT
2. Map Projection M
0 P U
No Projection Polyconic UTM
6. Format C CEOS F T GeoTIFF
7. Media V DVD
3. Resampling R
0 C
No Resampling Cubic Convolution
M D DISK
4. Enhancement EE
00 No Enhancements
5. Correction Level L
0 Raw G** K N
Georeferenced (Terrain Corrected) ** Single Look Complex Slant range Multi Look Ground range
Note Please note that geo-referenced products are corrected for terrain heights.
TABLE.4 DPWFM PRODUCT
CODE LIST FOR RISAT-1 User Products 1) Level – 0 Raw Products
2) Level-1 Geotagged Products Single Look Complex (SLC) Products
Multi Look Ground Range Products
Product type Map Proj Resampling Enhancement Proc. Level Format Media
ST 0 0 0 0 C V/D
Product type Map Proj Resampling Enhancement P
ST 0 0 00 K
Product type Map Proj Resampling Enhancement P
ST 0 C 00 N
pg. 71
3) Level-2 Terrain Corrected Products
8.Product Quality Control
Product Quality Control is responsible for checking the quality of all satellite data products that reach users. All RISAT-1 data products will be thoroughly verified and are subjected for stringent quality checks at PQC. Data products that conform to quality standards and specifications will be delivered to users. QC criteria for digital data products: All digital products will be verified as per thefollowing Checksheetthat comprises of different checks for products clearance. The main components of the checksheet are �Meta file verification �Format validation �Geometric check �Radiometric check through Visual inspection method �Band to Band Registration ( formultidate registered & merged products ) 8.1Meta file verification: A meta file is a .txt file that contains information about Satellite,Product and User. QC ensures the generation of a correct product from this file by crossverifyingthe information of user product with Data Products Work Flow Manager ( DPWFM ). QC verifies user specified parameters like Satellite, Mode ,Frequency, Incidence angle, date of pass, scene centre and corner coordinates , Projection, datum ,resampling and product code etc.
Product type Map Proj Resampling Enhancement Proc. Level Medium Media /Format /Size
ST U/P C 00 G C/T V /D
pg. 72
8.2Format validation: RISAT-1 data products are supplied in CEOS and Geotiff formats. Data products are validated for correctness of format in auto mode at PQC through indeginous software. 8.3Geometric check :All digital products are checked for correctness of datum,mapprojection,resampling, resolution, scene centre, area coverage ( in terms of Lat./Long.) etc and should meet the user requirements ( in terms of corner co-ordinates and scene centre Lat./Long. ) and Location accuracy (as per mission ). 8.4Radiometric check :Radiomeric quality of data products is thoroughly verified for all products. . Different types of radiometric anomalies can be observed in data due to the complex nature of SAR data acquisition and processing. All RISAT-1 data products are subjected for data qualification through Visual quality assessment method. All digital products are displayed and viewed in full resolution mode with an option to zoom and roam in the image.Cent percent visual check is carried out to ensure good radiometric quality product. 8.5Band to Band Registration ( BBR ): BBR is a parameter that is to be verified for colour composite products . This is not an applicable parameter for RISAT-1 images since they are in black & white .But a colour composite product can be generated by registering different dates of SAR images or through merge process with optical data ( multi date registered product, merged etc). For such type of products , Band to band
registration check will be carried out byPQC .
pg. 73
Products that meet QC standards will be delivered to users. Non conformal
products will undergo regeneration and re-certification.
pg. 74
Flow chart of Digital products process Chain
RAC Computer
Pg 58
9DATA ACCESS AND DISTRIBUTION
Introduction
Data products will be announced to the users after the initial phase validations by mission. User will be able to request for the data products either directly or through the User Order Processing System (UOPS). UOPS is an integrated web based application enables the user to register, browse and select the satellite images either from archives or plan for future collections, perform account related transactions, place orders and monitor the order status. Users, after browsing the images using the various queries and selecting the scenes, can place an order for the same using the ordering tools. Facility to obtain the status of user accounts and the orders placed is also available
online. Registered users can also change their details like address and their login password and send general queries through e-mail. ( Figure-15)
Upon connecting to the NRSC User order processing system site, the user is presented with a page with various links which enable the user to navigate through the application. If the user is new, he has to register himself for the ordering service to be enabled. While registering, the user has to agree to the terms and conditions displayed. A registration form is displayed in which he has to provide details like name, user identification (uid), password, user category, mailing address etc.,. Users
Pg 59
have to remember their uid and password for future logins.
If the user is a registered user, he can sign in with his uid and password and enable the services.
UOPS opening page
Fig.20 Block diagram of User Order Processing System
Pg 59
First page presented to the user. 9.1Services
Pre-requisites The services provided through UOPS are Browsing , ordering & future collections. If the user wants to just browse the data available in the archives browse should be clicked. If he wants to order the data he needs to click the order button then it will help him to browse as well as place order. If future collections are required then click on the collect button. Browsing / ordering services is a pre-requisite information provided to the users for converting the required area of interest into scenes and checking the data availability for the required area of interest. Before placing an order for data, the users need to browse through the data, to check for cloud and quality of the data. To meet this requirement, NRSC generates sub-sampled and compressed browse images along with
necessary ancillary information. This facility is made available to users through Internet. Compressed JPEG images are generated only for the Optical data sets for RISAT-1 no images are generated only the meta information is populated. This enables the user to verify coverage. The Browse facility has been integrated with data ordering and payload programming systems. Data can be browsed online and suitable scenes can be selected and converted into and data request by registered users who have an account with NDC. The different means of searching the image catalogue / ordering are : Either Map based search can be performed , which allows free draw on the world map or the options are AOI ,
Path and Date options. Under AOI based following options are provided.
• Shape file.
• Polygon Any one of these means can be selected as per the user convenience. • Mapsheet • Location
• Point Browsing / ordering services
9.1.1 Polygon based query/ordering/collects This option is useful to browse/order the images for a given geographical area. Users can input their area of interest either in terms of latitude/longitude in degrees, minutes, seconds or degrees decimal format of top left and bottom right corners or draw the area on a map with the help of mouse. On submitting the query, a form requesting the user to
enter the period of interest is displayed. On submitting, a list of scenes covering the user’s area of interest during the desired period shown to the right of the screen. On selecting the scenes and clicking on the layout option the scenes are plotted on the map. This enables the user to verify his area of coverage and also the number of scenes required. If the order button is clicked then the scenes selected can be ordered.
Pg 59
Pg 59
Polygon based search
Pg 59
The next screen presents the valid products based on the sensor , and allows various combinations of projections datum & resampling. The mode of dispatch also needs to be mentioned. If courier is opted then the products will be sent by courier if FTP is opted then the products will be uploaded on the web site for the users to download.
Once the cost estimate is shown Save PI Append PI and Generate Order are presented to the user. The user can Save the PI or Append into a already existing PI or directly generate order.
On clicking the estimate button it shows the cost estimate of the products.
Once the generate order button is clicked the complete PI is presented to the user along with accounts handled/allotted to the user. Then the user needs to select the account
through which the data cost has to be debited. Once the account number is selected. The Shipping address needs to be filled and confirm button to be clicked
.
Pg 59
After the confirmation a pop-up window will be shown on the screen showing the Order No. This order number needs to be quoted for all future correspondences. After generation of products the status will be updated automatically. For the products through FTP mode , a mail will be sent to the user with the ip address and user name password. User can download the data using this.
Map sheet based products are one of the most popular products. So provision to query by map sheet number has been provided to facilitate easy querying by the user. In this case, apart from satellite, sensor, user has to select the map sheet number, either in open series map or as per the old SOI mapsheet numbers along with the period of interest. On submitting the query, a list of scenes covering the map sheet, during the desired period, are displayed. The user can then select the scenes and click layout option. This will plot the scenes on the map.
9.1.2 Map sheet number based Query
Pg 59
9.1.3 Location name based query In case the user does not know anything other than the name of the location, he can use this query to browse the images covering the place during the desired period. The inputs to be provided by the user are satellite, sensor and the name of the place. Option
is available to use the data base of locations with “prefix” or “suffix” matching. The user is presented with the details of the scene covering his place and on what dates it was covered. The user can then, view the meta along with the plot on the map.
Location name based search
9.1.4. Point (Lat-Long) based query This query takes latitude and longitude of a single point and it maps to a square
based on the extent chosen. This query is useful if particular area around a point is to be viewed. User has to select the satellite, sensor, enter latitude and longitude of the point in degrees minutes seconds or degrees decimal
format and choose the extent of region desired. The extent of the region varies w.r.t. the sensor. On submitting, a list of scenes covering the extent with the
point as center, during the desired period, along with a graphical plot, is displayed. The user can then, view the meta along with the plot on the map.
Pg 59
Point based search
9.1.5 Search for images based on shape file This query is useful for viewing the images dates when the input is in the form of a shape file generated in arcview format with geographic co-ordinates. The maximum number of points required in constructing the shape file should not exceed 10,000
.Users have to choose the satellite and sensor and submit along with the shape file in WGS 1984 Geographic /UTM projection format only. On submitting, a list of scenes covering the shape file are displayed. Provision for viewing the selected scenes plotted on the shape file is also provided. The users can then view the images and select.
Shape file based search 9.1.6Search for images based on date of pass /ordering When the date field is not entered at all, an alert message asking the date is displayed. However, a calendar is also provided along the date field for easy
operation. Based on the satellite relevant paths or orbits and sensor/modes are presented to the user. Users have to choose the satellite, sensor and the date of pass in dd-mm-
Pg 59
yyyyformat . If a wrong value entered, an alert is displayed asking the correct
These scenes can then be ordered in the way explained in previous options.
This query is useful if the user wants to browse the images for a specific date. Date based search 9.2 ProductStatusMonitoring
Users can view the status of the request placed through the above options. This option gives the status as , dispatched , under production or alternate action .After viewing the status of the products, in case if any of the product
Order Processing and monitoring on Intranet by NDC
fails due to technical reasons, it can be re-generated by submitting a different date using the utility - Alternate date provided under pending actions.
9.3 Services for Offline Users: An off-line user is one who has one or more account numbers with NDC but has been placing orders for data by filling a paper order form. Order processing facility on Intranet enables NDC to monitor, distribute, process and dispatch the generated products to the customers placed offline.
10. Payload Programming
Pg 58
10.1 INTRODUCTION RISAT is the first of the type with Synthetic Aperture Radar payload. Radar backscatter depends upon the sensor parameters such as frequency, polarization and incidence angle as well as on target parameters such as dielectric constant, roughness and geometry. The SAR on RISAT will operate in C band with both horizontal and vertical polarization. The SAR sensor is based on active phase array antenna technology and it provides electronic agility for achieving multimode imaging capability. So the imaging can be done both in ascending and descending passes of a day. The payload basically consists of an antenna 6mx2m in size consisting of 12X2 = 24 tile each tile having 24 X 24 radiating elements. The antenna is capable of generating 126 beams on either side of roll (i.e., +34 / -34). The payload is designed to operate in five different operation modes varying in swath and resolution. The swath and resolution are dictated by the usage of any set of beams out of 126 beams. (63 on each side) covering a very large of look angles. The beam width of the beams are so adjusted o provide a constant swath on ground irrespective of look angle.
Table.6 Mode wise Polarization
Table 1 & Table 2 gives the details of the modes an polarisations that are operable. Table.5 Imaging Modes
RISAT is a programable satellite. The data will be collected based on the
user specifications and as users need to give the look angle, period mode etc. Details of the inputs are discussed in the further sessions.Apart from data from arriving at the data collection needs NDC is also responsible in generating the final schedule files which is used by ISTRAC to further command the satellite. ISTRAC uploads the state vectors and other related files through the online facility which are further used for preparing the schedules. Total flow of action is described in the flow chart.
Flowchart of the programming activities
Various types of users are Handled by NDC as described below. 6.1 TYPES OF USERS: For programming 10.1.1 Registered Users: They are the registered users who can place programming requests for data acquisition. The users can place their programming request online through Internet . Once the inputs for collects are fed an online along with the product details ,proposal is displayed to the user. The proposal shows the dates on which the request can be serviced. Once the confirm button is clicked the dates are blocked for the user. After the data collection the status will be updated as serviced in the request status. Further the data
will be processed and dispatched to the user.
10.1.2 Offline Usres: The usres who do not have online accounts for placing request or still follow the conventional methods send us the request through fax or email. UOPS – INTRANET ( used by NDC scientists) has a provision for placing request offline. The proposals are sent to the usres and confirmation is saught for the user before planning. 10.1.3 Ground Station Users: Ground station users are the registered users who will acquire data in real time over their respective ground stations. These users are:
Nodal Ground station: They are responsible for the requests received from the ground stations handled by them. Ex. Space Imaging, Scanex. Individual Ground stations: These stations take care of the requests planned over their respective ground stations. Ex; TRN, DIP, DDN etc. Virtual Ground Stations: These are stations, which act as ground stations and they are governed by visibility circles. The data is collected by SSR and dumped at Svalbard or Shadnagar. 10.2 PAYLOAD PROGRAMMIGN ACTIVITY Payload programming activity involves programming the satellite acquisitions - based on the user requirements, International ground station requirements and for archival buildup. As RISAT provides different beam modes and the incidence angle or "beam positions”, this flexibility makes the
planning and ordering of RISAT data slightly more complex than that for other systems such as Resources at –I; This activity is split across three different systems located at NRSA and SCC. The UOPS is the front-end module, which accepts requests from users and International Ground stations online, through a web application. This system validates and transfers the requests to Swath planner. The Swath Planner is a tool, which calculates the predicted RISAT's orbit. It allows to generate, view, edit and analyse swath plans in order to identify the most suitable acquisition plan. Then a technical proposal is displayed to the user along with the graphical representation. After receiving the confirmation from user, PPS at NDC generates the schedules based on NDC selected options and sends it to SCC. At SCC the command sequence is generated for up-linking the satellite. The flow is described in the following flow chart.
10.2.1 Options for placing the programming request
5. High resolution spot light mode
Specify a range of beam positions an/or incidence angles
The different means of placing request for programming are Either Map based (free draw on the map) can be done or the options are AOI , Path and Date options. Under AOI based following options are provided.
Based on the modes acceptable beam positions will automatically be decided while planning. • Polygon CRS Mode – 12 Beams • Mapsheet MRS Mode – 6 beams • Location FRS Mode – • Point Or • Shape file. Minimum and Maximum Incidence angle should will be taken as input.
Location name – is treated as point request with specific radius around the point.
Or User application will be taken as input
Mapsheet:Can input Open series or the old SOI mapsheet numbers.
Period of Interest Inputs required form the user: Start Date
Specify pass direction End Date Polarization: Dual /circular 1. Ascending mode Priority: 2. Descending mode Urgent 3. Ascending and descending
mode Normal Emergency
Specify the imaging mode User can choose one of the priority options.
1. Coarse resolution mode
Normal: These requests can be placed 15 days in advance. These requests will not be charged for programming.
2. Medium resolution mode 3. Fine resolution striping
mode 4. Fine resolution strip map
mode Urgent: The requests, which are placed within T-2 days of
acquisition are treated as urgent. These will be included in the daily acquisition plan. These requests will be charged extra for acquisition. Ground stations send their stations request for a period of one week. The urgent request can be placed up to T-2 day
Confirmed: The requests which are confirmed for acquisition at SCC-PPS Serviced: The requests which are acquired on the specified day Cancelled: The requests which are cancelled by SCC due to various reasons
Closed: The requests which are successfully acquired (good quality,), will be updated as closed
Emergency: The user requests are of highest priorty followed by the archival build up. However in case of Natural calamities and man madeemergencies , all other requests take a lower priority. Requests placed in such cases with have high priority.
Repost: The requests for which the acquisition is not successful (bad quality) can be posted for another date. The status of such requests will be shown as Reposted. We need to have three such alternate dates for reposting. Only normal and urgent requests can have the reposting facility. Emergency requests for natural calamities will have only one acquisition.
10.2.2 REQUEST STATUS A request can have various statuses between posted and closed. The user will be able to view his request status online by keying in the request number. Various statuses are:
10.2.3 PPS - System
The Payload Programming system at NDC is designed as a multi mission Payload Programming system.
Posted: After the requests are finalized at SWATH PLANNER/UOPS they are posted at NDC-PPS. These requests show the status as posted.
It takes inputs from UOPS and allows for scheduling. Scheduled: The requests which
are accepted by NDC-PPS and sent to SCC-PPS
11.Applications
SAR is often used because of its all-weather, day or night capability, it also finds application because it renders a different view of a “target” with synthetic aperture radar being at a much lower electromagnetic frequency.Observations of the Earth using the SAR (Synthetic Aperture Radar) have a wide range of practical applications, such as: 11.1Forestry
BACKGROUND National Programmes as well as several corporates are investing
hugely on afforestation / plantation projects under Forestry / NREGS as well as social responsibility projects. In order to sustain them in long term, it is very important to monitor the progress of these planting efforts. Delineation of plantations in the forested area with optical RS data has several constraints. Use of high resolution SAR data has been very useful in the delineation of different type of plantations such as teak and associated species in deciduous forest areas.
INDIVIDUAL TREE CROWN DETECTION AND
FOREST OPENINGS
IDENTIFICATION OF Forest edges are generally marked by
remnant trees and clearances.
Individual trees are considered as key resources to sustainable livelihoods; contribute to above and below ground carbon stock and play a key role in the regulation of nutrient cycling. Forest clearances need to be
monitored for maintaining ecosystem quality. Hence, an all-weather observation tool is essential in tropical forest context. It can be realized with C-band high resolution remote sensing for this purpose. Fig.21 (A) RISAT-2- x-band VV data (B) FCC of variance (R),mean(G),Second moment (B) generated from GLCM matrix
Fig.22 (A)RISAT-2 X-band data (B) Cartosat-1 data showing individual tree crowns(C) FCC of IRS-P6 LISS-IV data and (D) RISAT-2 X-band data showing forest openings
11.2 Crop
One of major applications of SAR data is in the field of agriculture due to non-availability of cloud free optical data during the monsoon season and presently,
High resolution Spot mode Strip mode
Water
Scru
b la
nd
Urb
an
Water
Scru
b la
nd
Urb
an
Water
Scru
b la
nd
Urban
Water
Scru
b la
nd
Urban
Mango-new, Subabul, Trees, UnplowedPlowed fields, Mango-old,
SAR data is useful for delineating field boundaries, analysis of inter-field
variability and discrimination crops.
Fig.23Various Crop Fields
11.3 AGRICULTURE High resolution SAR data has potential application in the field of agriculture especially for generating field level information.
Fig.24 various agricultural
fields 11.4 Floods
Identification of flood inundated areas and estimation of flood damages are very crucial and difficult tasks to achieve during/after a flood wave. Flood mapping is one of the successful applications of SAR data in providing a synoptic view of the flood affected area due to its ability to penetrate through clouds. SAR data also helps in monitoring the flood situation at regular intervals of time.
ICRISAT Office
ICRISAT Office
R IS AT ‐2
DL R ‐E S AR C
DL R ‐E S AR X
DL R ‐E S AR L
Mango Urban WaterSubabul Trees Plowed land
To reduce the impact of flood disaster on human life and property, various flood control measures are implemented to protect the vulnerable areas. The major thrust was given for structural measures such as construction of embankments and spurs. Monitoring of these flood control structures are planned by flood control departments to identify the vulnerable river reaches after the flood recedes. High resolution SAR data helps in monitoring the vulnerability of these structures and plan for future flood control structures.
Pg 58