Sensing soil moisture and vegetation using GNSS-R polarimetric measurement

GNSS-Reflectometry is an efficient tool for remote sensing and plays a key role in several applications. The estimation of soil moisture and vegetation in the land field is attracting widespread interest in hydrology, climatology and carbon cycles. In order to investigate the scattering polarization properties from different types of surface environments, an airborne measurement was performed, equipped with a new 4-channel prototype for collecting the direct, reflected left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP) signals. Both the reflected LHCP and RHCP signals were acquired at the same time by a dual polarization antenna. A data averaging procedure was used to reduce the incoherent part of the received power and two reflected signals were normalized by direct signals obtained from each front-end (FE). Then three polarimetric observables were used to analyze vegetation biomass and soil moisture fluctuations. It was concluded that the polarimetric ratio (PR) is sensitive to soil moisture content (SMC) and considerably independent of roughness and vegetation biomass. The trunk component is confirmed to be the most important factor affecting the amplitude of scattering polarizations. Furthermore, the measurement results showed that the PR variation between different elevation angles was affected by roughness and biomass. The PR variation in forests with big biomass shows the least amount of changes when compared to other geographical environments. The results show another possibility of further geophysical parameter evaluations employing polarimetric applications in GNSS-R.