Passive microwave observation of diurnal soil moisture at 1.4 and 2.65 GHz

Microwave radiometers operating at low frequencies are sensitive to surface soil moisture changes. Few studies have been conducted that have involved multifrequency observations at frequencies low enough to measure a significant soil depth and not be attenuated by the vegetation cover. Another previously ignored aspect of microwave observations at low frequencies has been the diurnal variations of the soil moisture and temperature and the impact of these on the brightness temperature. In this investigation, observations were made using a dual frequency radiometer (1.4 and 2.65 GHz) over bare soil, corn and grass for extended periods in 1994. Comparisons of emissivity and volumetric soil moisture at four depths for bare soils showed that there was a clear correspondence between the 2 cm soil moisture and the 2.65 GHz emissivity and between the 5 cm soil moisture and the 1.4 GHz emissivity, which confirms previous studies. Observations during drying and rainfall demonstrate that new and unique information for hydrologic and energy balance studies can be extracted from these data