Satellites expand data gathering

THE MONSOON in India is affected by such natural factors as sea surface temperature, Himalayan snow cover, atmospheric thermal changes and data on all of these is gathered by satellites, including the indigenous INSAT, which is stationed about 36,000 km above the equator and IRS-1A and IRS-1B, whose orbits are much nearer.

According to remote sensing data, about 260 mha of India's 328.7 mha are drought-prone, and 100-150 of the country's 459 districts are drought-affected each year. Satellite data also enables speedy assessment of flood damage. For instance, flood maps of the Brahmaputra basin in Assam, interpreted from IRS-1A imagery in 1988, distinguished the river clearly from inundated areas and from areas from where flood-waters had receded. Satellite data maps as well as crop damage information were made available to district authorities within one week of the flooding.

Remote sensing was used by the National Drinking Water Mission to map on a scale of 1:250,000 the country's groundwater potential, with priority given to the mapping of India's 112 drought-prone districts. Based on the satellite data, authorities drilled about 50,000 borewells, scoring a success rate of upto 95 per cent, as against 45 per cent through conventional methods. Clearly, remote-sensing technology has made the search for water not only more scientific but also less expensive.

Even urban areas can benefit from remote sensing. Urban sprawl, for example, in all the major Indian cities has been identified using data from France's System Pour l'Observation de la Terre (SPOT-1) satellites. Remote sensing also helped Bangalore Development Authority to align at a cost of less than Rs 5 lakh the cities proposed Ring Road. The cost of such a survey using conventional methods would have been Rs 2.5 crore.

Although the Indian coastline is more than 8,000 km long, the annual fish catch is less than two million tonnes, which is about one-fifth Japan's fish catch. Recently, Indian "authorities began using remote sensing technology to identify profitable fishing grounds. This was done by measuring sea surface temperature to delineate thermal gradients, fronts, eddies and upwellings. This technique was tried out successfully in 1989 off the Gujarat coast.