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IRS (Indian Remote Sensing Satellite)

Following the successful demonstration flights of Bhaskara 1 and Bhaskara 2 launched in 1979 and 1981, respectively, India began development of an indigenous IRS (Indian Remote Sensing Satellite) program to support the national economy in the areas of "agriculture water resources, forestry and ecology, geology, water sheds, marine fisheries and coastal management". The Indian Remote Sensing satellites are the main-stay of National Natural Resources Management system (NNRMS), for which Department of Space (DOS) is the nodal agency, providing operational remote sensing data services. Data from the IRS satellites is received and disseminated by several countries all over the world. With the advent of high resolution satellites new applications in the areas of urban sprawl, infrastructure planning and other large scale applications for mapping have been initiated.

Remote sensing applications in the country, under the umbrella of NNRMS, now cover diverse fields such as crop acreage and yield estimation, drought warning and assessment, flood control and damage assessment, land use/land cover information, agro-climatic planning, wasteland management, water resources management, under-ground water exploration, prediction of snow-melt run-off, management of water- sheds and command areas, fisheries development, under development, mineral prospecting forest resources survey, Active involvement of the user ministries/ departments has ensured in an effective harnessing of the potential of space-based remote sensing. An important application of IRS data is in the Integrated Mission for Sustainable Development (IMSD) initiated in 1992. IMSD, under which 174 districts have been identified, aims at generating locale-specific action plans for sustainable development.

The first two IRS spacecraft, IRS-1A (March' 1988) and IRS-1B (August, 1991) were launched by Russian Vostok boosters from the Baikonur Cosmodrome. IRS-1A failed in 1992, while IRS-1B continued to operate through 1999. From their 22-day repeating orbits of 905 km mean altitude and 99 degrees inclination, the two identical IRS spacecraft hosted a trio of Linear Imaging Self-Scanning (LISS) remote sensing COD instruments working in four spectral bands: 0.45-0.52 µm 0.52-0.59 µm, 0.62-0.68 µm, and 0.77-0.86 µm. The 38.5-kg LISS-I images a swath of 148 km with a resolution of 72.5 m while the 80.5-kg LISS-IIA and LISS-IIB exhibit a narrower field-of-view (74-km swath) but are aligned to provide a composite 145-km swath with a 3-km overlap and a resolution of 36.25 m.

Each IRS spacecraft is 975 kg at launch with a design life of 2.5-3 years. The 3-axis stabilized spacecraft is essentially rectangular (1.1m by 1.5 m by 1.6 m) with two narrow solar arrays producing less than 1 kW electrical power. The Spacecraft Control Center at Bangalore oversees ail spacecraft operations, but the principal data reception station for the remote sensing payload is located at Shadnagar. Spacecraft data transmissions are effected via X-band and S-band antennas at the base of spacecraft.

IRS-1A and IRS-1B were to be joined in 1993 with IRS-1E, the modified IRS-1A engineering model' which had been equipped with the LISS-I and a German Monocular Electro-Optical Stereo Scanner. The spacecraft was lost, however, when its PSLV launch vehicle failed to reach Earth orbit. Thirteen months later, in October, 1994, the PSLV functioned correctly, allowing IRS-P2 to assume an 820-km, sun-synchronous orbit. This spacecraft continued in operations until September 1997. With an 870-kg mass (slightly less than IRS-1A and IRS-1B), IRS-P2 carried the LISS-II system with a ground resolution of 32 m across-track and 37m along-track. The total swath width is 131 km, and the CCD array is tuned to four spectral bands between 0.45 and 0.86 am. The spacecraft's solar arrays provide up to 500 W and are linked to conventional nickel cadmium storage batteries (References 565-570).

As of late 1999 five IRS satellites were operating, and more were scheduled for launch by the year 2000. IRS-1C, successfully launched on December 28, 1995 on board a Molniya rocket of Russia, was the last Russian launch of the program (Molniya rather than Vostok, while IRS-1D was orbited by India's PSLV. IRS-P3 was launched by PSLV in 1996 with a German modular electro-optical scanner and an Indian visible-lR scanner.

The Indian Space Research Organization (ISRO) and its commercial marketing arm, ANTRIX Corp. Ltd., successfully launched the IRS-1D Earth imaging satellite on 29 September 1997 from Sriharikota, India. The satellite is an identical twin to the IRS-1C, launched in December 1995. The dual use of these satellites provides 5.8-meter resolution images to customers twice as often as was possible with just the IRS-1C.

IRS-1C and IRS-ID introduced a heavier (1,350 kg), more capable Earth observation platform. The spacecraft bus will be similar to those of IRS-1A and IRS-IB, but a slightly larger solar array generates more than 800 W. Both IRS-1C and 1D produce 5.8-meter panchromatic (0.50.75 µm - black and white) imagery, which is resampled to five-meter pixel detail. This resolution, which as of early 1998 was the best of any civilian remote sensing satellites in the world, is superior to the 8-meter resolution initially reported for the panchromatic imager. These satellites are also equipped with two-band Wide Field Sensors (WiFS) that cover a 774-square-kilometer (481-square-mile) area in a single image, as well as LISS-3 4-band (0.52-0.59, 0.62-0.68, 0.77-0.86, and 1.55-1.70 µm) multispectral sensors that provide 23.5-meter resolution multispectral coverage. The 23.5-meter resolution imagery is resampled to produce 20-meter pixel detail. The spacecraft also carry a 2-channel (0.62-0.68 and 0.77-0.86 µm) wide-field sensor (190 m resolution) (References 568-569, 571-575).

The IRS C,D Pan sensor sacrifices swath width for its higher resolution. However, it can be pointed off the orbit path which allows 2 to 4 day revisits to specific sites. IRS-1C and IRC-1D data can be received and procured from EOSAT (USA) or in India at the NRSA, Hyderabad.

Upcoming launches include IRS-P5 in 1998, IRS-2A in 2000, and IRS-2B in 2004, all with the new LISS-4 sensor suite.

IRS-P4 (OCEANSAT-1) will have payloads, specifically tailored for the measurements of physical and biological oceanography parameters. An Ocean Color Monitor (OCM) with eight spectral bands, Multi-frequency Scanning Microwave Radiometer (MSMR) operating in four frequencies will provide valuable Ocean-Surface related observation capability. The OCEANSAT-1 was slated for launch by PSLV in early 1998.

IRS-P5 (CARTOSAT-1) has an improved sensor system that provides 2.5 m resolution with fore-aft stereo capability. This mission caters to the needs of cartographers and terrain modelling applications. The satellite will provide cadastral level information up to 1:5000 scale and will be useful for making 2-5 m contour maps.

IRS-P6 (RESOURCESAT-1) will be a state-of-art satellite mainly for agriculture applications and will have a 3-band multispectral LISS-IV camera with a spatial resolution better than 6 m and a swath of around 25 km with across track steerability for selected area monitoring. An improved version of LISS-III with four bands (red, green, near IR and SWIR), all at 23 m resolution and 140 km swath will provide the essential continuity to LISS-III. These sensors will provide data which will be useful for vegetation related applications and will allow multiple crop discrimination and species level discrimination. Together with an advanced Wide Field Sensor (WiFS) with 80 m resolution and 1400 km swath, the payloads will greatly aid crop/vegetation and integrated land and water resources related applications. The IRS-P6 is slated for launch by PSLV by end of 2000.

The IRS-2 series (OCEANSAT-2/CLIMATSAT-1/ATMOS-1) will be an integrated mission that will cater to global observations of climate, ocean and atmosphere. Microwave instruments to cater for oceanographic applications will be mainly a Ku band Altimeter, Ku band Scatterometer, Microwave Radiometer and Thermal Infrared Radiometer for observing oceanographic parameters like winds, sea surface temperature, waves, bathometry and internal waves. Instruments for atmospheric chemistry applications include spectrometers, sounders and radiometers for studying the atmospheric constituents, pollution and for monitoring ozone and greenhouse effect. Instruments to observe climate and meteorological parameters will include microwave sounders, radiometers and rain radars.

IRS-3, beyond 2002, will have all weather capabilities with multi-frequency and multi polarisation microwave payloads and other passive instruments.

REFERENCES

564. Annual Report 1988-89, Department of Space, Government of India, 1989.

565. PTI News Agency, 16 October 1994.

566. All-India Radio, 15 October 1994.

567. "IRS-P2 Remote Sensing Craft Declared Operational", Space News, 21 November- 4 December 1994, p. 17.

568. K.P. Corbley, "EOSAT-India Partnership Broadens International Remote Sensing Market", Earth Space Review, Vol. 3, No. 4, 1994, pp. 20-26.

569. D.F. Robertson, "India Strikes Out for Commercial Golds, Space, March-April 1995, pp. 3-5.

570. V. Raghuvanshi, "Germany to Supply Part for India's IRS-P2", Space News, 8-14 February 1993, p. 20.

571. A. Lawler, "India's IRS-1C Satellite To Offer Sharper Images", Space News, 25-31 May 1992, p. 11.

572. "India Building Follow-On Remote Sensing Spacecraft", Space Fax Daily, 23 November 1992, p. 1.

573. V. Raghuvanshi, "India Prepares Second Generation IRS Spacecraft for 1995 Launch", Space News, 1-7 August 1994, p.18.

574. W. Ferster, "India Readies Sharper IRS-1C for Molniya Launch", Space News, 9-15 January 1995, p. 3.

575. W. Ferster, "India's Data Policy Stalls Remote-Sensing Ambitions", Space News, 20-26 February 1995, p. 3.



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