Satellite Remote Sensing and its Contribution to Monitoring Surface Hydrography from Space

This paper presents results from ongoing work to better understand the potential contribution of satellite remote sensing to monitoring the state of inland waterways, through detection of the time-varying characteristics of rivers, wetlands, and lakes/reservoirs. This presentation focuses on river discharge and summarizes ongoing work to merge satellite retrievals with the hydraulic properties and discharge (Q) of rivers. River Q can be characterized by time-varying stage, velocity, or widths which in principle can be secured from satellites. The overall goal is to produce high-resolution runoff fields, supporting a broad array of Earth systems applications, and derived ultimately over the entire global domain. To achieve this, relationships need to be developed linking riverbed geometry to corresponding rating curves (i.e. relating Q to flow depth, width, velocity). We developed synthetic rating functions based on theoretical considerations and idealized cross-sections. These relationships used >2000 USGS discharge gauging sites where observed rating curves were available. Optimized cross-sectional parameters are being analyzed for generalizable patterns, which can then be used for a priori prediction. Simple rules have been found governing the macro-scale behavior of rivers, and in particular, average conditions over suitably long river reaches. These relationships are being used to infer the satellite-observable variables as a function of Q. A 6' (longitude/latitude) resolution, spatially-distributed Q field was developed by co-registering USGS discharge gauging stations to a 6' simulated gridded network representing the entire conterminous United States. This Q field is being used in conjunction with the hydraulic relations to predict spatially and temporally-varying river widths, depth, and velocities, which in turn can be sampled using different simulated orbital and sensor configurations. Tests have been performed on the TOPEX/POSEIDON and ERS1 satellites as preliminary guidance for future spaceborne missions. A summary of how such an approach can be used to support the planning of the NASA post-2002 inland waters monitoring mission, HYDRA-SAT (HYDRological Applications SATellite), is offered.