Dielectric spectroscopic model for tussock and shrub tundra soils

Abstract

In this paper, the measured microwave dielectric data are presented for some soils collected in the tussock and shrub tundra area located on the North Slope, Alaska, near Toolik Lake, at N 68deg 38', W 149deg 35' with an elevation of 730 m. The measured samples represented the organic rich soil picked up from the middle and base of tussock, organic poor soil from the depth of 20 cm in the valley between tussocks, and organic rich soil from the depth of 20 cm in the shrub tundra site. The measurements were carried out in the range of frequencies from 0.5 to 16.0 GHz and temperatures from -30degC to +25degC. On the basis of that data, the spectroscopic model of complex dielectric constant was developed for the moist soils measured, using the methodology of the generalized refractive mixing dielectric model [1]. This model takes into account contributions from the organic/mineral contents of soil, soil ice, free liquid soil water, and bound soil water arising due to interaction of soil water molecules with the surface of organic/mineral and ice particles. The complex dielectric constants for all the types of soil water observed were shown to follow the Debye formulas, with a single relaxation frequency for every distinct type of soil water. The temperature dependences were obtained for the parameters of the generalized refractive mixing dielectric model, including the parameters of soil water Debye relaxation, that is, the low and high frequency limits of dielectric constant and relaxation time, as well as the ohmic conductivity relating to every component of the soil water. The previously unknown physical phenomenon of liquid soil water transformation into a transition type of bound water, instead of ice, was observed in the range of temperatures below -6degC, which appeared to arise in the organic rich soils studied. The results obtained can be considered as a substantial contribution to the soil dielectric database, to be employed in the physically based data processing algorithms for radar and radiometry remote sensing of the northern circumpolar region.