Airborne Coherent GNSS Reflectometry and Zenith Total Delay Estimation over Coastal Waters

High-precision GNSS (global navigation satellite e system) measurements can be used for remote sensing and nowadays play a significant role in atmospheric sounding (station data, radio occultation observations) sea surface altimetry based on reflectometry. A limiting factor of high-precision reflectometry is the loss coherent phase information due to sea-state-induced roughness. This work studies airborne observations recorded over coastal waters examine sea-state influence Doppler distribution residual retrieval. From observations, possibility zenith total delay inversion also investigated, considering hydrostatic mapping from Vienna function an exponential vertical decay depending height receiver changes. The experiment consists multiple flights performed along coast between cities Calais Boulogne-sur-Mer, France, July 2019. Reflected signals acquired right-handed circular polarization are processed through model-aided software passed retracking module obtain phase-corrected signal. Results grazing angle (elevation < 15°) show high sensitivity spread with respect state correlations 0.75 0.88 wave wind speed, respectively. An empirical threshold 0.5 Hz established reflections supported by obtained. Phase coherence occurs 15% observations; however, estimated best event corresponds 2.44 m, which differs typical (2.3 m) 5%.