N. GOPAL RAJ
Orbiting the earth, the satellite has a panoramic view and can continually take pictures of the ground below.
Satellite images are used these days for many purposes, including to update maps, plan city and town development, estimate crop production, track changes in land use patterns, and study the impact of natural disasters.On January 10, India's Polar Satellite Launch Vehicle (PSLV) put into orbit a powerful earth-viewing satellite as well as the country's first effort at a unmanned space capsule that could safely return to earth. An orbiting satellite has a panoramic view of the earth as it travels a few hundred kilometres above the ground. From its vantage point in space, the satellite can continually take pictures of the ground below. The technology was first developed for spy satellites so that the U.S. and what was then the Union of Soviet Socialist Republics could keep watch on each other. With the launch of the Landsat-1 satellite by the U.S. in 1972, the technology became available in the civilian domain as well.Satellite images are used these days for many purposes, including to update maps, plan city and town development, estimate crop production, track changes in land use patterns, and study the impact of natural disasters.
More technologyOver the years, the resolution provided by cameras on the earth-viewing satellites has steadily improved. Better resolution means that smaller objects can be seen on the images. India's first experimental earth-viewing satellite, the Bhaskara-I that was launched in 1979, carried a TV camera and only something fairly large, like the Chilka Lake in Orissa, could be readily identified in the images it sent back. Cartosat-1, which the Indian Space Research Organisation built and launched in 2004, takes black-and-white images with a resolution of less than 2.5 metres. With that sort of resolution, it is possible to make out the shape of building. The Cartosat-2 launched by the PSLV on January 10 will provide images with a resolution of about 80 cm. With such images, it is easy to see structures on the roof of buildings and distinguish a car from a bus.The U.S. QuickBird satellite offers an even better resolution of 60 cm and DigitalGlobe, the company that owns the satellite, is planning to send up WorldView-I later this year, which will provide images with 45 cm resolution.Re-entry is one of the technologies that India needs if it wants to establish an independent capability to send humans into space. But manned missions are hugely complex and the challenges in developing such capability are considerable. It is not for nothing that a recent study carried by the Indian Space Research Organisation suggested that Rs. 10,000 crores and eight years would be needed to undertake a manned mission.For scientific experimentsThe PSLV also launched a capsule to carry out scientific experiments in near-weightless conditions. After 12 days of circling the globe, on radio command from ground control, small rockets on the Space Capsule Recovery Experiment (SRE-I) were fired to slow it down and it re-entered the Earth's atmosphere. Special tiles protected the capsule from the fiery heat created by its high-speed passage through the air. Later, the capsule was further slowed by parachutes and it splashed into the Bay of Bengal.