Microwave remote sensing of soil moisture, progress, potential and problems

Over the past decade or so, tremendous progress has been made in both passive and active microwave remote sensing of soil moisture. Much of this progress can be attributed to improved instrumentation such as with the development of the Electronically Steered Thinned Array Radiometer (ESTAR) and the SIR-C/X SAR. However, equally important has been the demonstration of soil moisture´s importance to hydrologic processes through comprehensive field campaigns. During this period, there has been a parallel development of an awareness of the importance of soil moisture, particularly with climate modellers and scientists studying land surface-atmospheric interactions. Unfortunately, inspite of the technological advances and the scientific interests, we are apparently not any closer to being able to obtain routine soil moisture measurements from a space platform than we were ten years ago. This paper reviews the progress in both passive and active microwave soil moisture measurements, especially as demonstrated by the intensive field campaigns. The scientific interest in soil moisture is discussed-and an attempt is made to define the science and application measurement requirements. Finally, the problems associated with developing a soil moisture mission is addressed