J-Band Polarimetric Radar Measurements of Surfaces at High Angles of Incidence

This article reports on polarimetric radar backscatter responses of different types of surfaces at high angles of incidence (80 degrees-89 degrees) at J-band frequencies (221-231 GHz). This study is motivated by the desire to understand the radar phenomenology of target scenes for the next-generation automotive radars. Measured data were collected for paved and unpaved surfaces under different conditions (dry, wet, ice- and snow-covered). At these frequencies, dry road surfaces are electrically rough and sizes of the subsurface aggregates are comparable to the signal wavelength giving rise to significant surface and volume scattering. The measured backscattering coefficients of all surfaces exhibit over 30 dB dynamic range across all datasets and significant depolarization (between -12 and -4 dB). For paved surfaces, the dynamic range narrows to 16 dB and the depolarization ranges between -9 and -4 dB. The data represent the first reported observations of radar response of surfaces at high incident angles at J-band frequencies. They demonstrate the radar's potential for discriminating between different types of road surfaces needed for improved safety of driverless cars. Also, based on the measured data, a semi-empirical model for the backscattering coefficients of the paved surfaces at high incident angles is presented.