Remote sensing of soil moisture at various spatial scales

Soil moisture content partitions rainfall into infiltration and runoff, and determines radiative sensible and latent heat. The microwave portion of the electromagnetic spectrum causes a large contrast between water and dry soil, offering the greatest potential for monitoring soil moisture and therefore has dominated in the remote sensing of soil moisture. Long microwave wavelengths/low frequencies, (1-5 GHz), are especially beneficial because there is very large contrast between dry and wet soils, little absorption by the atmosphere, and low scattering by vegetation canopy, resulting in analysis over large areas with little or no contamination of the signal. Scaling of remotely sensed soil moisture is a very pertinent issue. We have point measurements at field scales, measurements from aircraft-based instruments and finally satellite-based sensors. In this paper, we will establish the various processes that provide a link to this scaling relationship, viz., the theory of radiative transfer, effect of heterogeneities and the sensitivity of brightness temperature to various land surface parameters. Sensitivity has been studied with respect to L- and S-bands