ABSTRACT
Soil moisture variability, both in space and time, plays a key role in global water and energy cycles. Soil moisture is a key control on evaporation and transpiration at the land–atmosphere boundary; thus, real-time monitoring of soil moisture dynamics is very useful not only for understanding land surface–atmosphere interactions but also for water and climate studies. Satellite remote sensing instruments used for soil moisture estimations include the multispectral scanner, thermal infrared scanner, thematic mapper, synthetic aperture radar (SAR), and microwave radiometers. Active microwave sensors are based on the technique of Radio Detection and Ranging (RaDaR). This type of method consists of a transmitter that emits the radiation toward the earth’s surface and an antenna that measures the returning backscattered radiation. The strength of the backscattered signal, measured to discriminate between dry and wet soils and the time delay between the transmitted and reflected signals, determines the distance to the surface.
