Dpto. Proyectos e Ingeniería Rural - Landa Ingeniaritza eta Proiektuak Saila

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Browsing Dpto. Proyectos e Ingeniería Rural - Landa Ingeniaritza eta Proiektuak Saila by Author "Baets, Bernard de"

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    PublicationOpen Access
    Effective roughness modelling as a tool for soil moisture retrieval from C-and L-band SAR
    (Copernicus Publications, 2011) Lievens, Hans; Verhoest, Niko E. C.; Keyser, E. de; Vernieuwe, Hilde; Matgen, P.; Álvarez-Mozos, Jesús; Baets, Bernard de; Proyectos e Ingeniería Rural; Landa Ingeniaritza eta Proiektuak
    Soil moisture retrieval from Synthetic Aperture Radar (SAR) using state-of-the-art backscatter models is not fully operational at present, mainly due to difficulties involved in the parameterisation of soil surface roughness. Recently, increasing interest has been drawn to the use of calibrated or effective roughness parameters, as they circumvent issues known to the parameterisation of field-measured roughness. This paper analyses effective roughness parameters derived from C- and L-band SAR observations over a large number of agricultural seedbed sites in Europe. It shows that parameters may largely differ between SAR acquisitions, as they are related to the observed backscatter coefficients and variations in the local incidence angle. Therefore, a statistical model is developed that allows for estimating effective roughness parameters from microwave backscatter observations. Subsequently, these parameters can be propagated through the Integral Equation Model (IEM) for soil moisture retrieval. It is shown that fairly accurate soil moisture results are obtained both at C-and L-band, with an RMSE ranging between 4 vol% and 6.5 vol%.
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    PublicationOpen Access
    Error in radar-derived soil moisture due to roughness parameterization: an analysis based on synthetical surface profiles
    (MDPI, 2009) Lievens, Hans; Vernieuwe, Hilde; Álvarez-Mozos, Jesús; Baets, Bernard de; Verhoest, Niko E. C.; Proyectos e Ingeniería Rural; Landa Ingeniaritza eta Proiektuak
    In the past decades, many studies on soil moisture retrieval from SAR demonstrated a poor correlation between the top layer soil moisture content and observed backscatter coefficients, which mainly has been attributed to difficulties involved in the parameterization of surface roughness. The present paper describes a theoretical study, performed on synthetical surface profiles, which investigates how errors on roughness parameters are introduced by standard measurement techniques, and how they will propagate through the commonly used Integral Equation Model (IEM) into a corresponding soil moisture retrieval error for some of the currently most used SAR configurations. Key aspects influencing the error on the roughness parameterization and consequently on soil moisture retrieval are: the length of the surface profile, the number of profile measurements, the horizontal and vertical accuracy of profile measurements and the removal of trends along profiles. Moreover, it is found that soil moisture retrieval with C-band configuration generally is less sensitive to inaccuracies in roughness parameterization than retrieval with L-band configuration.