RADAR REMOTE-SENSING OF THE SOURCE AREAS FROM THE COET-DAN CATCHMENT

As interest shifts to the development of models for predicting runoff quality, identification of the source areas for runoff becomes increas ingly important. Active microwave remote sensing has a unique potentia l for surveying source areas at the catchment scale. Thresholding of t he back-scattering coefficient was initially proposed but proved unsat isfactory when applied to the ERS-1 SAR multitemporal images acquired during winter 1992 over the Coet-Dan catchment, concomitantly with gro und observations. Difference images may, instead, allow the wettest pa rt of the catchment to be identified provided that the two images enco mpass a marked hydrological event. A saturation plot could not however be obtained for each date; the use of a pair of images may be further limited by the residual speckle (although carefully filtered using th e multitemporal information) and a slight inaccuracy in the SAR image calibration. It is therefore argued that considering the whole tempora l back-scatter profile would be, at present, a safer approach to the r emote sensing of saturated areas. The back-scatter temporal standard d eviation appears, in this light, as a possible good indicator of the l ocal saturation likelihood during the period of study: it is based on the fact that saturation develops on parts of the catchment that are w etter than the others through lateral recharge. possible applications within the TOPMODEL framework are discussed. (C) 1998 John Wiley & Son s, Ltd.