ABSTRACT
Soil moisture is a fundamental link between global water and carbon cycles and has major applications in predicting natural hazards such as droughts and žoods (National Research Council, 2007). From precipitation data, soil wetness can be estimated by hydrological land-surface models. In the United States, preliminary precipitation data are based on measurements gathered from many active stations nationwide each month, and it takes 3-4 months to assemble –nal, quality-controlled data. In the western United States, some climate divisions may have no stations reporting in a particular month or may lack –rst-or second-order stations, and
9.1 Introduction .................................................................................................. 197 9.2 Microwave Remote Sensing Science ............................................................ 198
9.2.1 Passive Remote Sensing .................................................................... 199 9.2.2 Active Remote Sensing .....................................................................200 9.2.3 Passive and Active Blending .............................................................202
