A Temperature-Dependent Dielectric Model for Thawed and Frozen Organic Soil at 1.4 GHz

Abstract

A single-frequency dielectric model for thawed and frozen Arctic organic-rich (80%–90% organic matter) soil was developed. The model is based on soil dielectric data that were measured over the ranges of volumetric moisture from 0.007 to ${0.573}\;\text{cm}^{{3}}/\text{cm}^{{3}}$ , dry soil density from 0.564 to $0.666\;\text{g/cm}^{3}$ , and temperature from 25 °C to $-\mathbf{30}^{\circ}\mathbf{C}$ (cooling run), at the frequency of 1.4 GHz. The refractive mixing model was applied to fit the measurements of the soil’s complex refractive index (CRI) as a function of soil moisture, with the values of temperature being fixed. Using the results of this fitting, the parameters of the refractive mixing model were derived as a function of temperature. These parameters involve the CRIs of soil solids as well as bound, transient, and free soil water components. The error of the dielectric model was evaluated by correlating the predicted complex relative permittivity (CRP) values of the soil samples with the measured ones. The coefficient of determination ( $\mathbf{R}^{\mathbf{2}}$ ) and the root-mean-square error (RMSE) were estimated to be $\mathbf{R}^{\mathbf{2}}= \mathbf{0.999}$ , $\mathbf{RMSE} = \mathbf{0.27}$ and $\mathbf{R}^{\mathbf{2}}= \mathbf{0.993}$ , $\mathbf{RMSE} = \mathbf{0.18}$ for the real and imaginary parts of the CRP, respectively. These values are in the order of the dielectric measurement error itself. The proposed dielectric model can be applied in active and passive remote-sensing techniques used in the areas with organic-rich soil covers, mainly for the SMOS, SMAP, and Aquarius missions.