Influence of Water Content and Temperature on the Dielectric and Radio-Emitting Properties of the Salt Crust of Puffy Solonchak

Abstract

The use of remote microwave methods for monitoring saline soils is limited by the poor knowledge of the dielectric and microwave emissivity characteristics of salt crusts forming on the surface of solonchaks. The results of multiple studies on the estimation of diurnal variations in the real and imaginary parts of the dielectric permittivity of a puffy solonchak are discussed. Samples of the salt crust of the solonchak were taken during the summer period in the Kulunda Steppe (Altai region) from a 2 × 2 m plot for 34 h with a periodicity of 1 h. Under laboratory conditions, their dielectric characteristics were measured, the water content and density were determined, and the chemical analysis of water extract was performed. Laboratory measurements of the dielectric parameters were carried out using bridge circuits at a frequency of 1.41 GHz with the temperature control in the range 265–320 K and the moisture control in the range 0–0.50 cm³/cm³. The dependence of the volumetric water content of the solonchak on the radiation coefficient was obtained. This dependence can be used to estimate the salinity of the soil from remote sensing data in the microwave range. The effect of temperature on the dielectric and emissivity characteristics of the solonchak was also studied. Dependences of the microwave emissivity on the temperature were assigned to intervals with different behaviors of the emissivity characteristics. For each interval, linear dependences of the solonchak emissivity on the temperature were established. Daily variations in the emissivity characteristics of the solonchak surface were also determined. It was shown that the microwave emissivity of the solonchak depends on the soil temperature, water content, and salinity. The studied regularities of microwave radiation from the solonchak can be used in the development of the methods for radiophysical monitoring of saline soils.