L-Band Reflectivity of a Furrowed Soil Surface

Abstract

Abstract-In a combined experimental and model study, we investigated the thermal L-band signatures of a sandy soil with periodic topography (furrows) with dimensions close to the observation wavelength of 21 cm. Measurements were carried out with a radiometer mounted on a tower and aimed at a soil box with an artificially prepared furrowed soil surface. Corresponding reflectivities were derived from brightness temperature measurements performed under dry and moist conditions, with the furrow direction either along or perpendicular to the plane of incidence. Results showed that the furrows had a pronounced effect on the reflectivity, depending on the polarization of the observed radiance, the direction of the furrows, and the soil moisture. A physical reflectivity model for dielectric periodic surfaces was used to explain the soil reflectivities measured for the different furrow directions and soil-water contents. Using this model improved the agreement between the measured and modeled reflectivities considerably compared to the Fresnel reflectivities. The observed dependence of soil reflectivity on furrow orientation and soil moisture could be reproduced by the reflectivity model. The quantitative agreement with the observed reflectivities was further improved by using a simple empirical approach to consider the small-scale heterogeneity of the top soil layer.Index Terms-Electromagnetic scattering by periodic structures, electromagnetic scattering by rough surfaces, microwave radiometry, permittivity.

Additional Reference Height Error Analysis for Baseline Calibration Based on a Distributed Target DEM in TwinSAR-L

“…Obviously, the dielectric values (both the real part and imaginary part) of the rocks are relatively large, so the SAR signal is difficult to penetrate; the dielectric values of the uniform sand region are relatively small, and the SAR signal is easy to penetrate. The average value of the real part and imaginary part of the uniform sand covered area marked by red rectangle is 2.675 and 0.052, respectively, which is consistent with the existing studies [29,40]. The calculated dielectric constant is then used to invert the penetration depth, i.e., ∆h errPen of L band, which is shown in Figure 8.…”

“…In this paper, based on the first and third methods, combined with the backscattering coefficient information of the actual SAR data, the soil surface roughness and moisture content of the study area are inverted firstly, then the dielectric constants are inverted by using the relationship between the dielectric constant and the soil moisture content established in the literature [40], and finally the penetration depth of the study area is calculated.…”

“…After obtaining the soil moisture content, based on the empirical model established by Volksch [40], as shown by Equation (11), we can invert the dielectric constant pixel-by-pixel, then take the dielectric constant into Ulaby's model, the additional reference height error ∆ errPen can be inverted. For distributed target, the backscattering coefficient can be simply defined as the radar-cross section (RCS) per unit area [41,46].…”

Soil Hydraulic Parameters of Bare Soil Plots with Different Soil Structure Inversely Derived from L‐Band Brightness Temperatures

“…This is due to the row structure of the surface (Fig. 2), which leads to interferences and different roughness correction factors for horizontal and vertical polarization (Wang et al, 1980; Promes et al, 1988; Volksch et al, 2011). From these observations, we conclude that the obtained roughness parameters and hydraulic properties would not change when measurements at vertical polarization were included in the inverse optimization.…”

A Three‐Dimensional Structure and Process Model for Integrated Hydro‐Geo‐Pedologic Analysis of a Constructed Hydrological Catchment

“…When included in the three‐dimensional structure model, these changes of the catchment during the initial period formed the basis for a stepwise adaption of the three‐dimensional distribution of hydraulic properties and boundaries. The surface topography and sediment composition could be used for a physical reflectivity model developed for estimating water contents of heterogeneous soil surfaces with a radiometer mounted on a tower and utilizing thermal L‐band signatures calibrated for soil water content measurements (Völksch et al, 2011).…”