RN-39 : Remote sensing applications for flood inundation studies

Abstract

Mankind is beset with flood problems from the very ancient time. Fury of flood leaves its crippling effect on the economy. Flood inundation is one of the basic data need to understand, combat and to take ameliorative and preventive measures with respect to flood. There are established ground based survey methods for delineation of flooded area. But these are time consuming as well as often hazardous to undertake. At times all efforts are needed to be concentrated on flood relief work and inundation rapping work starts a bit later. So, the hydrologists and water resources planner quite often felt handicapped due to lack of proper and accurate data concerning flood.

Remote Sensing methods especially after the advent of satellite era have opened new vista in acquiring flood inundation data because of synoptic repetitive coverage of the satellite. These admirably suit to monitor and study the dynamic nature of flood over space and time. Reflected infrared (0. 7 to 10 micron) energy of the electromagnetic spectrum is readily absorbed by water. This unique characteristics of water is mostly been used. Presently, a fairly accurate overview of regional flooding and its impact could be mapped and studied from the Landsat and meteorological satellite images. Thermal infrared spectrum is also convenient to use as water has the highest specific heat. It means that by sensing emitted thermal energy, it is possible to identify water or moisture as cool areas.

But research work in search of other sensor system has indicated the potential of microwave band in flood mapping especially because of its all weather capability. Cloud cover at present obscure the utility of data from the present day satellites. Microwave system of sensor found to be more suitable for Indian conditions of weather and for small holdings than in the countries which are in mid latitudes.

Though the use of microwave band is much sought for by the user Community, it is worthwhile to mention that microwave reflections or emissions from earth materials bear no direct relationship to their counterparts in the visible and thermal portions of the spectrum. Water surface is excellent reflector of microwaves, resulting in a uniform black tone image which precludes measuring any physical, chemical or biological characterististies of water. At present use of microwave has been tried on experimental basis from airborne surveys. It has been recommended that flood studies capability could be enhanced considerably if a future satellite carries microwave sensors along with multispectral sensors. Development of technology in this regard is on.