IEEE Geoscience and Remote Sensing Magazine - December 2014 - 51

e. saraL (saTeLLiTe for argos anD aLTiKa)
SARAL is another collaborative altimetry technology mission of ISRO and CNES, where CNES provided a Ka-band
altimeter (AltiKa) and ISRO provided the IMS-2 (Indian
Mini Satellite) bus. In addition to AltiKa, CNES provided DORIS, LRA (Laser Reflector Array), and Argos-3
DCS (Data Collection System). The overall objectives of
SARAL are to realize precise, repetitive global measurements of sea surface height, significant wave heights and
wind speed.
AltiKa is the prime payload of the SARAL mission, and
is the first space-borne altimeter operating at Ka-band
(35.75 GHz, 500 MHz bandwidth). The payload is accompanied by a two-channel radiometer operating at 23.8
and 37 GHz for providing requisite path delay corrections
to AltiKa measurements. Typical global products from
SARAL are shown in Fig. 9.
IV. GEO BASED METEOROLOGY PAYLOAD
ISRO has developed a number of VHRRs (Very High
Resolution Radiometers) as meteorology payloads on
GEO platforms. VHRRs for INSAT 2A/2B/2E/3A are sharing platforms with communication payloads. In contrast,
Kalpana-1 and INSAT 3D are dedicated mainly for VHRR
payloads. From Kalpana-1 onward, meteorology payloads
are separated from communication payloads, mainly to free
the operation and performance from constraints imposed
december 2014

ieee Geoscience and remote sensing magazine

Latitude (°)

O2SCT-20131011-21453-21454-L04-HVW Winds (m/s)
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FIGuRE 7. OSCAT measured wind circulation of Philin cyclone on

Oct 11, 2013.

18.7 H
23.8 V
36.5 H
89 H
157 H

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D. MeghaTropiques
In order to boost climate research with high repetivity data
over the globe, the Megha-Tropiques satellite was launched
as Indo-French collaboration between ISRO and CNES. The
satellite was placed in an inclined orbit with 20° inclination, for 6 hourly observations of complete tropical regions
covering 30°N to 30°S. It has three payloads:
a) MADRAS (Microwave Analysis And Detection Of Rain
And Atmospheric Structures) - An imaging microwave
radiometer operating at 18.7,23.8, 36.5, 89 to 157 GHz
(5 frequencies and 9 channels)
b) SAPHIR (Sounder for Atmospheric Profiling of Humidity in the Inter-tropics by Radiometry) - a mm wave
sounder operating at 6 channels around 183 GHz
c) SCARAB (Scanner for Radiation Budget) - a broadband
radiation measurement instrument in shortwave (0.2-
4 nm) and long wave (0.2-100 nm) along with visible
(0.55-0.65 nm) and IR (10.5-12.5 nm) channels
MADRAS was configured as a total power radiometer with a 65 cm diameter antenna that provides resolution from 40 km to 6 km over its frequency bands.
It provided measurements over a swath of 1700 km at
incidence angles of 53.5°. Approximately one year and
four months after launch, the MADRAS payload ceased
operation due to slip-ring related problems. However,
in its short life span, MADRAS provided very valuable
research data (Fig. 8). The other two payloads are functioning normally.

FIGuRE 8. Sample MADRAS products in different frequency bands.

by the presence of high power communication payloads
on the same platform. Further, they allow effective use of
scarce GEO slots.
All VHRRs up to Kalpana-1 have a ground resolution of 2
km in the visible, and 8 km in the IR. They provide temporal
sampling from 20 minutes to 1 hour of one third of Earth's
disk centered over India. The sensors are configured as a
whiskbroom along with an electro-mechanical scanner for
Earth disc scanning. They have a provision of calibration and
background removal using signals from cold sky viewing.
VHRR payloads in INSAT-3A and INSAT-2E were
upgraded with a SWIR channel (1-km resolution) for cloud
and snow delineation and other remote sensing applications such as forest fire detection. VHRRs in INSAT 2E, 3A
and Kalpana-1, in addition, have water vapor channels to
derive information on water vapor and wind movement.
INSAT 2E/3A has CCD cameras for fast observation in a
specific region with 1 km resolution.
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Table of Contents for the Digital Edition of IEEE Geoscience and Remote Sensing Magazine - December 2014