Monitoring Continental Surface Waters by Satellite Altimetry

The monitoring of continental water stages is a requirement for meeting human needs and assessing ongoing climatic changes. However, regular gauging networks fail to provide the information needed for spatial coverage and timely delivery. Although the space missions discussed here were not primarily dedicated to hydrology, 18 years of satellite altimetry have furnished complementary data that can be used to create hydrological products, such as time series of stages, estimated discharges of rivers or volume change of lakes, river altitude profiles or leveling of in situ stations. Raw data still suffer uncertainties of one to several decimeters. These require specific reprocessing such as waveform retracking or geophysical correction editing; much work still remains to be done. Besides, measuring the flow velocity appears feasible owing to SAR interferometer techniques. Inundated surfaces, and the time variations of their extent, are currently almost routinely computed using satellite imagery. Thus, the compilation of the continuous efforts of the scientific community in these various investigative directions, such as recording from space the discharges of rivers or the change in water volume stored in lakes, can be foreseen in the near future.