The observation of the earth from space is usually termed as remote sensing and satellites used for the purpose are known as Remote Sensing Satellites (IRS).
These satellites are usually deployed in Sun synchronous polar orbit at a height of 800- 1000 km.
It is also called a polar orbit because it passes over both the polar regions of the earth in a north-south direction. It is called Sunsynchro because the orbit also keeps step with the Sun that is passes over a specific location on the sunlight side of the earth.
India has the largest constellation of Remote Sensing Satellites, which are providing services both at the national and global levels. From the Indian Remote Sensing Satellites, data is available in a variety of spatial resolutions starting from 360 meters and highest resolution being 2.5 meters.
Besides, the state-of the art cameras of IRS spacecraft take the pictures of the earth in several spectral bands. In future, ISRO intended to launch IRS spacecraft with better spatial resolution and capable of imaging day and night. The satellites of IRS system which are in service today are IRS- IC, IRS-P6, Ocean sat-I, Resource sat-I and recently launched Risat-2 and Oceansat-2 etc.
Imagery sent by IRS spacecraft is being put to variety of uses in India with agricultural crop acreage and field estimation. Besides, these its imagery is being used for ground and surface water harvesting, monitoring of reservoirs and irrigation command areas to optimize water use. Forest survey and management, wasteland identification and recovery are other allied uses. IRS imagery is also used for mineral prospecting and forecasting of potential fishing zones.
With regard to applications in planning and management, IRS data is being used for under planning, flood prone area identification and the mitigation measures. The coastal zones map for entire country has been prepared and information being provided to Department of Ocean Development and State governments.
These maps give information on the status of wetlands, estuaries as well as identifying prospective sites for aquaculture. Satellite remote sensing data has been used to assess the impact of mining, Super-thermal stations, industries and urbanization on environment.