Remote Sensing of Complex Permittivity and Penetration Depth of Soils Using P-Band SAR Polarimetry

Abstract

A P-band SAR moisture estimation method is introduced for complex soil permittivity and penetration depth estimation using fully polarimetric P-band SAR signals. This method combines eigen- and model-based decomposition techniques for separation of the total backscattering signal into three scattering components (soil, dihedral, and volume). The incorporation of a soil scattering model allows for the first time the estimation of complex soil permittivity and permittivity-based penetration depth. The proposed method needs no prior assumptions on land cover characteristics and is applicable to a variety of vegetation types. The technique is demonstrated for airborne P-band SAR measurements acquired during the AirMOSS campaign (2012–2015). The estimated complex permittivity agrees well with climate and soil conditions at different monitoring sites. Based on frequency and permittivity, P-band penetration depths vary from 5 cm to 35 cm. This value range is in accordance with previous studies in the literature. Comparison of the results is challenging due to the sparsity of vertical soil in situ sampling. It was found that the disagreement between in situ measurements and SAR-based estimates originates from the discrepancy between the in situ measuring depth of the top-soil layer (0–5 cm) and the median penetration depth of the P-band waves (24.5–27 cm).

Remotely Sensed Soil Moisture Can Capture Dynamics Relevant to Plant Water Uptake

“…Measurements of these microwaves are used to estimate satellite soil moisture. Nearly identical emission length scales are found when using other common emission and dielectric models (Fluhrer et al, 2022;Lv et al, 2018).…”

“…This result holds for a wide range of clay fraction values (Figure 1 shows case of 20% clay fraction), with soil texture only minimally impacting emission depth (Shen et al., 2021). Furthermore, emission depth magnitudes from several different emission and dielectric models tend to agree with that of Equation (Fluhrer et al., 2022; Lv et al., 2018; Njoku & Entekhabi, 1996).…”

Estimating Soil Moisture Profiles by Combining P-Band SAR with Hydrological Modeling

“…The approach begins with decomposing polarimetric Pband SAR observations from the AirMOSS campaign [7] into the individual scattering mechanisms (soil, dihedral, vegetation) by applying the revised hybrid decomposition method from [5]. In this way, the influence of vegetation-only or double-bounce scattering is eliminated from the total SAR signal and only the soil scattering component, represented by the data-based polarimetric scattering angle 𝛼 𝑠 𝑆𝐴𝑅 , is considered for soil moisture profile estimation.…”

“…Microwave remote sensing proved to be a useful tool for estimating soil moisture at large spatio-temporal scales. Up to now, most soil moisture retrieval methods are able to estimate moisture from microwave observations near the soil surface (L-band) [4] or at the subsurface (P-band) [5]. These methods provide a single moisture value for the vertical integral from the soil surface until the penetration depth of the respective microwaves.…”

P-Band UAV-SAR 4D Imaging: A Multi-Master Differential SAR Tomography Approach

“…Due to the rapid deployment and high flexibility [20,21], the unmanned-aerial-vehicle (UAV)-based D-TomoSAR technique offers a new way for 4D urban mapping. In addition, benefiting from the advantage in penetration ability and temporal coherence maintaining [22,23], the P-band SAR is used in the vertical structure extraction of the forests [24,25], biomass mapping [26,27], moisture estimation of the soils [28], ground deformation surveying [29], etc. Therefore, it is worth exploring the application of UAV-based P-band D-TomoSAR.…”