Seasonal Differences in Dielectric Properties of Dwarf Woody Tundra Vegetation in a Microwave Range

It is vital to study seasonal variations in dielectric properties of woody tundra vegetation for the development of algorithms for satellite data interpretation and for the accuracy improvement of microwave methods for remote tundra sensing. This paper presents the measurement results of dielectric characteristics of dwarf birch (Betula nana) and willow (Salicaceae) at a frequency of 1.41 GHz. Vegetation samples were taken in the Yamal-Nenets Autonomous Okrug in different seasons (April, August, and November). Dielectric properties were measured by means of a bridge-type setup in the temperature range from 263 to 293 K at different water content in plant samples. Seasonal differences in temperature dependences of the real and imaginary parts of complex permittivity (CP), the loss-angle tangent were established for the studied tree species. These variations were caused by the water amount change in plants, the formation of ice in plant cells, the difference in dielectric properties of dry wood, cell sap, and ice. For branches and leaves, empirical dependences of CP on volume moisture were established. CP is higher in branch wood than that of in leaves due to greater volume of free water in the intercellular space of branch wood. Significant seasonal differences in woody tundra CP are indicative of the need for consideration of such seasonal changes under tundra remote sensing.