Hydrologie distribuée, teledetection et problèmes d'échelle

Hydrological modeling do not integrate easily the Earth observation data. If new improvements and facilities are awaited on behalf of the new sensors, the complexity of the natural systems slow down their coherent use in modeling. Scale issues, heart of this transfer between raster data and models, are key points of comprehension and correct use. We develop here some elements of comprehension of these problems : scale parameters, hierarchical theory, In distributed hydrological modeling, new issues are : segmentation of the catchment in homogeneous units, number of pieces, and interest ; then aggregation, desaggregation issues and finally the non-unicity in models parameterization. Remote sensing throught the internal description of catchments, can help to reduce this not-unicity. This induces questions about the elementary physical processes we have to schematize and induces also to define new ground observations protocols, spatialized, in order to collect numerous and well distributed measurements, even if they are less accurate than the traditional ones.