A Fully Software GNSS-R Receiver for Soil Monitoring

Global Navigation Satellite System reflectometry (GNSS-R) is an emerging technique used for the remote sensing of soil surfaces. In this work, a bistatic radar equation method was implemented for soil moisture remote sensing using GNSS-R. Both direct and reflected GPS signals were collected by a fully software receiver mounted onboard an aircraft. The reflected signal was processed with an open loop approach, obtaining delay-Doppler maps (DDMs) and the corresponding delay waveforms. Signal to noise ratio (SNR) time series were estimated from non-coherently integrated delay waveforms. To take into account variations in system parameters from nominal values, a calibration was performed in regard to signals reflected from a water lake. Finally, a retrieval process to estimate the permittivity of soil surfaces from the evaluated SNR was applied and the results showed good correlation with the status of field flooding.