Derivation of a dryness index from NOAA-AVHRR data for use in large-scale hydrological modelling.

Modelling of soil moisture for large river basins relies on the spatial resolution of the input data. Therefore, in areas where spatial information. on hydrological variables is sparse, remotely sensed information can be of great importance. The surface temperature/vegetation index (Ts/NDVI) space, based on NOAA-AVHRR data covering the Senegal River basin, has been analysed in this study. The approach evaluates the shape of the Ts/NDVI-space for each available image acquisition, which makes this simple approach robust to atmospheric attenuation of the signal and to changes in, for instance, atmospheric forcings or net radiation that may determine the shape of the Ts/NDVI space. It has been shown that global parameters for estimation of a dryness index in the river basin can be used for various surface cover types, and that the approach can be applied for sparsely vegetated areas as well as for more dense vegetation covers.