Electromagnetic characterization of organic-rich soils at the microwave L-band with ground-penetrating radar, radiometry and laboratory measurements
Résumé
Organic-rich soils were collected from the HOBE (Hydrological Observatory) test site in the Skjern River Catchment (Denmark). The soil structure was then reconstructed at the TERENO (Terrestrial Environmental Observatories) test site Selhausen (Germany) in a controlled field laboratory for ground-based microwave remote sensing in order to characterize electromagnetic properties of the different soil layers and the vegetation. GPR and L-band radiometer measurements were performed above the soils during two months in order to realize a large range of moisture conditions. GPR data were modeled using full-wave layered medium Green's functions while radiometer data were simulated using a two-stream radiative transfer model. Complex dielectric permittivities were retrieved from GPR and radiometer data by inverting the associated models. The remote estimations of the dielectric permittivity were compared to laboratory measurements carried out at the IMS laboratory (Laboratoire de l'Intégration du Matériau au Système, France) using two different methods, the small perturbation methods with resonant cavity and the wave-guide method. The results show rather large discrepancies between the field measurements of the real part of the dielectric permittivity and the laboratory measurements. For the imaginary part of the dielectric permittivity, laboratory measurements are well reproduced by the field radiometer measurements, with a reasonable assumption made for the soil surface roughness. This study provides valuable insights into the characterization of organic soils, which can be used to improve the performance of the space-borne remote sensing data products of such soils.