Use of Remote Sensing Data from Airborne and Spaceborne Active Microwave Sensors Towards Hydrological Modeling

In this paper, the current state of remote sensing applications is reviewed, including sensors, platforms and remote sensing systems for hydrological studies, as well as applications of remotely sensed data in studies of precipitation, snow and ice, evapotranspiration, soil moisture, surface water and runoff, and catchment characteristics.More attention is paid to active microwave remote sensing of soil moisture. After reviewing some representative electromagnetic backscattering models, a case study on the sensitivity of ERS-1/SAR data for soil moisture retrieval from bare soil fields is presented. Using the Integral Equation Model, it is shown that it is difficult to obtain accurate soil moisture estimates for smooth bare soil fields using single frequency, single polarization measurements. Further, it is also shown that the sensitivity of radar measurements to surface roughness quickly reduces as roughness approaches values observed in common agricultural fields. This indicates that retrieval of soil moisture for normal bare agricultural fields is feasible given that the roughness parameters are known a priori and with sufficient accuracy.A recent remote sensing experiment in hydrology, EMAC’94/95, is also outlined and some results obtained using data acquired from this experiment are presented. Based on ESAR multifrequency data sets, a methodology was proposed to retrieve surface soil moisture using “calibrated soil roughness” characteristics. This method provides an alternative to overcome the difficulties encountered in in-situ measurement of surface roughness parameters for input into theoretical backscattering models and hence provides opportunities for operational application of remotely sensed soil moisture in hydrological modeling.