Trees have a profound impact on human life that makes their year-round monitoring with dielectric characteristics (DCs) of wood water as controlled parameters of great importance. This article deals with studying some behavior features of DCs of different-type wood water in various phenophases under varying moisture, temperature, and concentrations of dissolved substances. It presents the measurement results of DCs (1.41 GHz) of freshly cut branches of birch sampled from the same tree in different phenophases of 2018–2020. DCs carry the information on the phase composition of water present in plant tissue, volume fractions of bound and free water, concentrations, and types of dissolved substances. For various phenophases, the dependences of refractive ( ${n}$ ) and absorption ( $\kappa $ ) indices on volume fraction of water in wood ( ${W}$ ) for whole branches are approximated by piecewise broken lines with one ( ${W} _{{{1}}}$ ) or two ( ${W} _{{{1}}}$ and ${W} _{{{2}}}$ ) break points. We identify three categories of wood water with different DCs and estimate the dielectric properties of bound and free water in wood tissue in different phenophases using the refractive model. The established seasonal dependences ( ${n}$ , $\kappa $ ) ( ${W}$ , ${T}$ ) and the developed dielectric model make it possible to calculate DCs of wood water.

Specific emissivity features of swamps and wetlands in Western Siberia were studied for changing seasonal conditions with the use of daily data from satellite microwave sounding. The research technique involved the analysis of the brightness temperatures of the underlying surface at the test sites. Variations in the seasonal dynamics of the brightness temperatures were mainly caused by different rates of seasonal freezing of the upper waterlogged layer of the underlying surface and the dielectric characteristics of the water-containing natural media (water body, soil, and vegetation). We analyzed the long-term trends in the seasonal and annual dynamics of the brightness temperatures of the underlying surface and estimated the hydrological changes in the Arctic and Subarctic. The findings open new possibilities for using satellite data in the microwave range to study natural seasonal dynamic processes and to predict hazardous hydrological phenomena.

The presence of water-dissoluble salts in soils leads to a wide variation in soil microwave radiation that makes precise determination of water-physical characteristics of soil using satellite data hardly possible. To assess the effect of soil salinization, the emissivity of salt-affected soils in the Kulunda plain located in the south of Western Siberia was studied. Steppe site and an inland salt marsh (ISM) formed at the bottom of depressions of dried-up salt lakes were the main objects of the research. Both sites are situated in the same natural-climatic conditions and have similar relief. The spatial distribution of the underlying surface brightness temperature was obtained from L1C product of Soil Moisture and Ocean Salinity (SMOS) mission. The diurnal temperature variations of ISM were measured in the course of a daily ground-based experiment to determine the temperature gradients. During the laboratory experiment, we defined the dielectric properties of soil and calculated its emissivity. The comprehensive studies are evidence of great diurnal variation in ISM microwave radiation. The joint use of satellite and laboratory data allows us to specify the contribution of salt-affected soils into total microwave radiation of the underlying surface. The brightness temperature obtained from SMOS and the one calculated from the laboratory dependencies of ISM emissivity on temperature and moisture are in fairly well correlation.

Dielectric properties of saline soil (SS) and Salicornia perennans Willd (SPW) were measured at a frequency of 1.41 GHz using a bridge-type laboratory setup and different volume fractions of water in the samples. Experimental dependences of the refractive index and absorption factor on a volume fraction of water were approximated by piecewise-broken lines with break two points corresponding to maximum volume fractions of bound water in the samples. In the SS and SPW, we identified three categories of water with different dielectric properties. Using the empirical dependences refractive index, absorption factor on a volume fraction of water and the refraction model, dielectric parameters of bound and free water from the samples were calculated. Based on the experimental data and model representations, the possibility of using the unified approach to the description of dielectric properties of SS and SPW was discussed. To describe the dependences of the refractive index and absorption factor of SS and SPW volume fraction of water, the refraction model is used.