RISAT-1. Radar Imaging Satellite

Modes
Coarse Resolution ScanSAR
Mode (CRS)
Medium Resolution ScanSAR
Mode (MRS)
Fine Resolution Stripmap
Mode-2 (FRS-2)
Fine Resolution Stripmap
Mode-1 (FRS-1)
SAR Payload
RISAT-1 will carry a C-band
Synthetic Aperture Radar (SAR) catering
to the needs of various applications
stated elsewhere. It is well known that
radar backscattering depends on sensor
parameters such as frequency,
polarisation, and incidence angle as well
as on the target parameters such as
dielectric constant, roughness and
geometry. The RISAT-1 SAR sensor will
be based on active phased array
antenna technology, which will provide
required electronic agility for achieving
multimode capability. This state-of-theart
technology is expected to survive
technological obsolescence for long
time to come and is upgradeable to
other frequency bands in succeeding
missions.
RISAT SAR will operate with basic
0 0
elevation beam-width of 2.9 to 1.6
over a total ground distance of 400 kms
starting from a stand-off distance of
200 kms. Elevation beamwidth will be
Resolution
made to vary with pointing angles in
order to achieve pointing independent
swath of 30 kms and near constant
optimum radar cross section
performance. Fast beam pointing and
beam width control in elevation
direction is achieved electronically
with the help of an active phased
array antenna.
The active phased array antenna is
the heart of SAR payload. Essentially,
active antenna consists of a printed
dual polarized radiating aperture; dual
channel Transmit-Receive (TR)
modules comprising TR-RF, TR control
and miniaturized EPCs; the control
unit; and a signal distribution and
calibration network. The RF and baseband
system consists of feeder Solid
State Power Amplifiers (SSPA);
frequency generator; receiver; digital
chirp generator; data acquisition unit
comprising of high speed digitiser,
BAQ and formatter; calibration switch
matrix; and payload controller.
2-4 look (depending upon pointing) 50 m
resolution over a swath of 240 km in either
single or dual polarisation imaging
1-2 looks (depending upon pointing) 25 m
resolution over a swath of 120 km in either
single or dual polarisation imaging
Single look 9-12 m resolution image over
30 km swath in quad polarisation
Single look 3-6 m resolution image over 30 km
swath in either single or dual polarization