IEEE Geoscience and Remote Sensing Magazine - December 2014 - 48

table 1. broad cateGorY oF iSro'S electro
optical SenSorS.
Spectral
SenSor
bandS
complement (nm)

Spatial
Swath
reSolution width
(m)
(km)

IRS-1A/1B

LISS-1, and
LISS-2 A/B
(3 sensors)

0.45-0.52
0.52-0.59
0.62-0.68
0.77-0.86

72.5 m
LISS-I
36 m
LISS-II

148
74 # 2
(swath of
148 km)

IRS-1C/1D

LISS-3

0.52-0.59
0.62-0.68
0.77-0.86
1.55-1.70

23.5
23.5
23.5
70

142
142
142
148

PAN

0.50-0.75

5.8

70

WiFS

0.62-0.68
0.77-0.86

188

804

LISS-4

0.52-0.59
0.62-0.68
0.77-0.86

5.8
5.8
5.8

70

LISS-3

0.52-0.59
0.62-0.68
0.77-0.86
1.55-1.70

23.5
23.5
23.5
23.5

140

0.52-0.59
0.62-0.68
0.77-0.86
1.55-1.70

70
70
70
70

740

Carto Sat-1 PAN-F
PAN-A

0.50-0.75
0.50-0.75

2.5
2.5

30
30

Carto Sat-2 PAN camera

0.50-0.85

11

9.6

Satellite

Resource
Sat-1

AWiFS

Figure 2. Cartosat-1 camera and Cartosat-1 image of Ankara
draped over Carto-DEM (Courtesy: GAF/EUROMAP).

multi-linear gain to enhance radiometric accuracy (12 bit)
at low illuminations for AWiFS.
Stereo image acquisition was one of the important
application-specific requirements. Stereo images were
initially generated using IRS-1C/D, in multi pass mode,
by side-view imaging. The Cartosat-1 satellite was specifically designed with two cameras acquiring data of the
ground target with 2.5 m resolution and a 30 km swath,
in the panchromatic band. The two cameras provided 26°
fore and 5° aft views simultaneously in the same orbit.
Cartosat-1 data have been used to generate a specific high
resolution DEM product called "Carto-DEM." A CartoDEM example is shown in Fig. 2 along with an image
from one of the two cameras.
The challenge of designing and developing high resolution (<1 m) sensors was successfully met with the TES
(Technology Experiment Satellite) and Cartosat-2 series. In
order to improve signal-to-noise ratio in high resolution, a
step-and-stare approach was adopted in both TES and Cartosat-2 to improve integration time. A typical example of a
high resolution Cartosat-2 image over a part of Bangalore
is shown in Fig. 3.
B. SAR ImAgeR In mIcRowAve BAndS
The RISAT (Radar Imaging Satellite) class of satellites from
ISRO is dedicated to imaging in microwave bands. RISAT-2,
the first of the series, is an X-band SAR satellite, designed
48

with an unfurlable reflector antenna of 3 m diameter. The
miniaturized satellite (300 kg) and payload (100 kg) gives
the observing system very high agility. For quick revisit in
imaging, RISAT-2 was placed in an inclined orbit of 41° at
an altitude of 550 km.
The C-band RISAT-1 satellite, second in the series,
is designed with a versatile imaging capability, and
was placed in a polar dawn-dusk orbit at an altitude of
536 km. RISAT-1 carries a multimode, multi-polarisation
SAR, operating at 5.35 GHz. The SAR system is based on
active array technology, with a 6 m # 2 m dual polarized
antenna aperture, providing electronic antenna steering
capability in elevation only [3] [4] [5]. The basic imaging
modes of RISAT-1 are:
◗ Coarse Resolution ScanSAR Mode (CRS): 50 m resolution, 223 km swath

Figure 3. Cartosat-2 image of part of Bangalore, India.
ieee Geoscience and remote sensing magazine

december 2014
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