Radiobrightness Dynamics of Freezing/Thawing Processes for Different Soils

Radiobrightness observations of the freeze/thaw cycle for several treeless soils, namely humus rich (6.6%) and humus poor (0.6%) clayey soils, and sandy soil, are reported at the frequencies of 2.7, 6.0 and 8.2 GHz. The observation site was located in the steppe area of West Siberia near the city of Omsk, and the measurements were performed during November 2005. The radiobrightness measurements allow for detecting and locating the layered structure arising and developing in the soil during the period from sunrise to early afternoon. Due to different hydrological and hydrophysical properties of the soils under study the observations exhibited specific radiobrightness patterns for each soil. With the use of these data the thickness and depth of the thawing frozen layer were derived through fitting the modeled radiobrightnesses to the measured ones. In such a fitting procedure, agreement between the observed and simulated radiobrightnesses appeared to be reached only due to taking into consideration the permittivity for the soil bound water, which remained unfrozen even at the temperatures below 0 C. The values of depth and thickness for the frozen layer were also directly measured to reveal a good agreement to those derived from the radiobrigntness measurements.