Electromagnetic characterization of organic-rich soils at the microwave L-band with ground-penetrating radar, radiometry and laboratory measurements

Microwave remote sensing of the environment strongly relies on knowledge of the soil electrical properties. In this study, we characterized organic-rich soils using remote ground-penetrating radar (GPR) and radiometer as well as resonant cavity and waveguide reference methods. Organic-rich soil samples were collected from the HOBE (Hydrological Observatory) test site in the Skjern River Catchment (Denmark) and set up at the TERENO (Terrestrial Environmental Observatories) controlled test site in Selhausen (Germany). GPR and L-band radiometer measurements were performed above the soils during two months in order to cover a wide range of soil moisture conditions. GPR data were processed using full-wave inversion based on layered media Green´s functions and radiometer data were inverted using a two-stream radiative transfer model for estimating the soil electrical properties. Results were compared to reference measurements carried out at the IMS laboratory (Laboratoire de l´Intégration du Matériau au Système, France) using two different methods, i.e., the small perturbation method with resonant cavity and the waveguide method. Relatively large differences were observed between the different estimation methods for the real part of the relative dielectric permittivity, while reasonable agreement were obtained with respect to its imaginary part. This was attributed to a higher sensitivity of the real part of the relative dielectric permittivity with respect to soil samples heterogeneities. This study provided valuable insights into the electrical characterization of organic soils to improve space-borne remote sensing data products.