SOIL-WATER INFILTRATION OBSERVATION WITH MICROWAVE RADIOMETERS

Experiments were conducted using truck-based microwave radiometers ope rating at 1.41- (L-band) and 2.65-GHz (S-band) horizontal polarization to observe small plots during and following sprinkler irrigation. The se experiments were conducted on a sandy loam soil in 1994 and a silt loam in 1995. Sandy loam soils typically have higher infiltration capa bilities than clays, and in our studies, we were not able to exceed th is with the irrigation system. The observed brightness temperature (T- B) quickly reached a nominally constant value during irrigation, When the irrigation was stopped, the T-B began to increase as drainage took place. Contributing depth-related differences were observed for L- an d S-band as expected, The irrigation rates in 1995 with the silt loam soil exceeded the saturated conductivity of the soil. During irrigatio n, the T-B values exhibited a phenomenon that had not been previously observed and identified and is associated with coherent interference. The L- and S-band exhibited similar patterns but were not identical du e to contributing depth. These results suggested the existence of a sh arp dielectric boundary (wet over dry soil) that was increasing in dep th with time. The temporal description of the wetting front boundary w as used with a coherent radiative transfer model to predict T-B for L- and S-band.