Remote sensing has held a great deal of promise for hydrology, mainly because of the potential to observe areas and entire river basins rather than merely points. In addition, as the remote sensing science has developed we have learned of the potential to make entirely new measurements of hydrologic variables not generally possible with traditional techniques.
In spite of this promise, applied or engineering hydrology has been slow to embrace remote sensing as a useful source of data, presumably because existing techniques and data have been satisfactory for limited applications. Most of the advances in using remote sensing for hydrology have come from new areas of hydrologic analysis; areas where existing methods were unsatisfactory or limiting and areas where sufficient data were sparse or nonexistent. These areas include General Circulation Model (GCM) land parameterizations, advances in snow hydrology and the measurement of soil moisture.
In this review, the various applications of remote sensing to hydrology are treated as they are used to measure the different hydrologic variables or processes related to the water and energy cycle; that is precipitation, snow, evaporation, etc. Each of these hydrologic variables or processes are discussed individually with the emphasis on how remote sensing is being used, and not on the technology as far as sensor details and specific instruments are concerned.