Enhancement in interference pattern technique for altimetry and tide/wave measurements: Offshore 60-meter lighthouse case study

Ocean altimetric applications of GNSS-R have particularly been developed through the last decades. Interference Pattern Technique (IPT) based on the analysis of the Signal-to-Noise Ratio (SNR) of a classical GNSS antenna presents the main advantage of being applicable everywhere by using a single geodetic antenna and a classical GNSS receiver, transforming them to real wave/tide gauges. Such a technique has been already tested in various configurations of acquisition of surface-reflected GNSS signals with an accuracy of a few centimeters. Nevertheless, the traditional method for estimating the reflecting surface-antenna height is limited by an approximation: the vertical velocity of the reflecting surface must be negligible. This article presents a significant improvement of the IPT technique to solve this problem and broaden the scope of SNR-based tide monitoring. This method was validated in situ, with an antenna placed at 60 meters above the Atlantic Ocean surface which variations reach ±3 meters, and amplitude rate of the semi-diurnal tide up to 0.5 mm/s. Over the three months of SNR records for sea level determination, we found linear correlations of 0.94 by comparing with a traditional tide gauge. Our SNR-based time series was also compared to the TUGO tide theoretical model [1] and amplitudes and phases of the main astronomical periods (6-, 12- and 24-h) were perfectly well detected.