Abstract
The sensing depth of passive microwave remote sensing is a significant factor in quantitative frozen soil studies. In this paper, a microwave radiation response depth (MRRD) was proposed to describe the source of the main signals of passive microwave remote sensing. The main goal of this research was to develop a simple and accurate parameterized model for estimating the MRRD of frozen soil. A theoretical model was introduced first to describe the emission characteristics of a three-layer case, which incorporates multiple reflections at the two boundaries. Based on radiative transfer theory, the total emission of the three layers was calculated. A sensitivity analysis was then performed to demonstrate the effects of soil properties and frequency on the MRRD based on a simulation database comprising a wide range of soil characteristics and frequencies. Sensitivity analysis indicated that soil temperature, soil texture, and frequencies are three of the primary variables affecting MRRD, and a definite empirical relationship existed between the three parameters and the MRRD. Thus, a parameterized model for estimating MRRD was developed based on the sensitivity analysis results. A controlled field experiment using a truck-mounted multi-frequency microwave radiometer (TMMR) was designed and performed to validate the emission model of the soil freeze–thaw cycle and the parameterized model of MRRD developed in this work. The results indicated that the developed parameterized model offers a relatively accurate and simple way of estimating the MRRD. The total root mean square error (RMSE) between the calculated and measured MRRD of frozen loam soil was approximately 0.5 cm for the TMMR’s four frequencies.
Highlights
Permafrost and seasonally frozen soil, whose thermal and physical properties differ from unfrozen soil, are key components of the cryosphere
The controlled experiment data is used to investigate the effects of frequency and soil parameters on the microwave remote sensing response depth and validated a parameterized model of the microwave radiation response depth (MRRD) in frozen soil
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Summary
Permafrost and seasonally frozen soil, whose thermal and physical properties differ from unfrozen soil, are key components of the cryosphere. The regional energy and water balance are dramatically modified by the phase transition of soil water during the freeze–thaw process. The freezing–thawing of soil induced the release of decomposable organic carbon, and had a profound influence on the overall functioning of ecosystems [1]. The degradation of permafrost, which releases latent heat and carbon, has become a positive global warming feedback [2]. Previous experiments have shown that the carbon emission in soil profile varied spatially and temporally and was correlated with soil frozen depth [3]. It is necessary to determine the soil frozen depth for a given frozen area and explore the extent and distribution of frozen areas
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