Analysis of polarimetric GNSS-R airborne data as a function of land use

In recent years, GNSS-R data have shown great potential in monitoring and characterizing the states of continental and ocean surfaces. Numerous studies have also demonstrated the potential of GNSS-R polarimetry, showing high precision for the estimation of surface properties such as vegetation, soil moisture, and flooded areas. Very generally, on continental surfaces, the most commonly used observable is reflectivity under the assumption of dominance of the coherent component over the incoherent component.

The objective of this study is to analyze GNSS-R data variations as a function of land cover using airborne measurements obtained with the GLObal Navigation Satellite System Reflectometry Instrument (GLORI), which is a polarimetric instrument. GNSS-R measurements were acquired at the agricultural Urgell site in Spain in July 2021. In situ measurements describing the soil and vegetation properties were then obtained simultaneously with flight measurements. For land use mapping, supervised classification is performed based on the Level-2A Sentinel-2 time series for the summer season of the 2021 cloud-free selected and ground-truth observations.

The behavior of the observable copolarization (right-right) reflectivity  and the cross-polarization (right-left) reflectivity as a function of land use is discussed.

The distribution of coherent and incoherent components in the reflected power is estimated for different types of land cover (maize, alfalfa and grass, apple and pear orchards, water and urban constructions and roads).

The dependence of our observations on moisture is analyzed by examining the evolution of a  (percentage of the incoherent component relative to the total scattering power) over the three flights, since the first flight was conducted in a very dry context, the second flight was conducted after precipitation, and the third flight was conducted after the beginning of the drying process.