RN-45 : Remote sensing application to sedimentation studies

Abstract

Monitoring of sediment load in water bodies is an integrated part of any water resources management programme. After the advent of satellite age, remote sensing technique with its unique synoptic and repetitive coverages could admirably supplement the conventional ground based data collection endeavour.

Remote sensing techniques to study sediments and turbid water are essentially based on complex energy water interaction physics. More the physics is understood, better is the result of remote sensing methods subjected to available spatial, spectral, radiometric and temporal resolutions which are being improved with each satellite mission.

Investigators by and large are able to found out a positive correlation between suspended solids and reflectance values recorded by sensors in the satellite in visible and near infrared wavelength of the spectrum. Water surface is excellent reflector in microwave band of the spectrum which results in a uniform black tone image and as such microwave band is unsuitable for deciphering any information of water quality. Also identification of potential erosive land use zones helps in estimating sedimentation. Besides providing valuable information about the turbid water, remote sensing methods offer effective assistance in properly designing and minimising the numbers of ground sampling points. Besides factors of spatial, spectral, radiometric and temporal resolutions, atmospheric correction is one of the main difficulty in using remote sensing methods for sedimentation studies.

Presently the status of sedimentation studies by remote sensing is experimental and to be used as supplemental data base. Though the remote signal from turbid water is more reflective than clear water, but the signal represent only the near surface conditions. Also the problems of calibration of the signal with respect to sediment size and concentration are often formidable.

Improved satellite missions like French satellite 'SPOT' and Indian Remote Sensing Satellite (to be launched) take care of these difficulties to the extent technology permits. All such future satellites will exhibit some improvement over the present satellites in terms of orbit and sensors in order to meet operational data requirement. It is expected that the status will improve appreciably in near future and the remotely sensed water quality data will serve as a good data base for both surveillance and modelling of water quality.