Development of wideband crosshole and surface GPR for soil characterization: FDTD modeling and experiments

Original wide band antennas dedicated to the imaging of the subsurface by crosshole or surface radar for civil engineering application have been developed. The challenge in the developments is twofold: in the case of crosshole radar, the design of a narrow antenna less than 61 cm wide working in the frequency band [0.5;1.5] GHz, and in the case of a surface radar the design of a compact antenna less than 55 cm long working in the frequency range [0.3;1] GHz. FDTD simulations have allowed to propose optimized antenna geometries and to model both types of transmission links in the presence of a layered soil representing a moisture gradient. A first measurement campaign performed in the frequency domain in a clay sand embankment has allowed to validate the theoretical developments associated with the crosshole radar and to extract the dielectric parameters (permittivity and attenuation coefficient) as a function of the depth. The experimental validation of the surface radar will further be made and the performances of both types of radars will be compared.