Microwave remote sensing using space borne sensors

Microwaves are part of radio spectrum the frequency bands in the range of 3 GHz to 30 GHz are characterized as microwave. This part of spectrum has unique capabilities for microwave remote sensing. The microwaves can be used for remote sensing of objects in day as well as in night. They have all weather capability because microwaves can penetrate clouds. The soil moisture can be determined using microwave sensors. The microwaves can penetrate vegetation as well as soil and so they can give information about the objects which are under vegetation and under ground. The microwaves can penetrate dry snow and so one can detect buried objects under snow. There are two types of microwave sensors which can be used for microwave remote sensing. They are (i) passive sensors and (ii) active sensors. The Radiometers are passive sensors where as the scatterometer, altimeter, real aperture radar and synthetic aperture radar are part of active sensors. The microwave remote sensing using these sensors (both passive and active) can be done from different platforms. The platforms which can be used are ground based (on towers) platforms, Airborne platforms and Space borne platforms. The first microwave passive sensors were put on Nimbus satellites. These sensors were radiometers for study of oceans, atmosphere and land. The first synthetic aperture Radar system operating in L-band was placed in SEASAT in year 1978. Later at different times various passive and active sensors were put by American Agency NASA, Russian Space Agency, Indian Space Agency (ISRO), European Space Agency ESA, and Japanese Space Agency NASDA. The passive sensors were having courser resolution where as resolution of the active sensors was finer than that of passive sensors. The latest passive sensors which are being used for different applications are SSMI radiometers and AMSRE providing data at different microwave frequencies. The space borne active sensors are RADARSAT-2 of Canada and Oceansat-2 of India. In future the active microwave sensors will be put in spaceborne RISAT satellite in India and cosmoSkymed of USSR All these space borne sensors will provide very useful data for operational applications. The applications of these sensors are in agriculture, soil moisture estimation, flood mapping, geology/ geomorphology forestry, snow cover and glaciers, oceanography, Topography, Terrain and oil spill detection. The sensors have to be calibrated and all these applications have to be validated. From the data obtained from sensors the data products have to be generated. In this talk the evolution of the space borne sensors will be presented and the operational, quasi operational applications will be discussed.