Sea Level estimations based on GNSS-IR with two antennas

Sea level estimations have an important influence on climate research, marine transportation, production and life of coastal people and so on. Global Navigation Satellite System Interferometry Reflectometry (GNSS-IR) has been verified as a promising alternative of remote sensing technique for coastal sea level monitoring. Signal-to-noise ratio (SNR) data received by one off-shelf antenna and a classic GNSS geodetic receiver, which contain the multipath information of the station environment, were usually used for sea level retrieval. However, due to its use of only observations at low satellite elevation angles, this GNSS-IR technique is limited by its low sampling rate, for which only one sea level retrieval can be obtained for each independent satellite ascending or descending arc. In this study, we proposed to use an improved GNSS-IR setup with two antennae to improve the sampling rate by realizing sea level estimation from both high- and low- elevation angle observation. Compared to the traditional GNSS station with one upward right-hand circular polarized (RHCP) antenna and one geodetic receiver, this new setup added one downward left-hand circular polarized (LHCP) antenna and one combiner.  Observations of the two antennae combined by the combiner were input to the geodetic receiver to output RINEX files. SNR data from the RINEX files were then used to estimate sea level. One-month coastal experiment using the new setup was performed from January 4, 2023, to February 5, 2023, in Weihai, China. By comparing with co-located tide gauge data, sea level estimations with RMSE of 7 cm and correlation coefficient of 0.99 were obtained from the experimental data obtained by using the proposed setup. Moreover, the results showed that, by using the proposed GNSS-IR setup, the sampling rate of sea level estimations was improved about 3 times comparing to the results of conventional setup with one antenna. Because of the cheap price of LHCP antenna and combiner, the proposed GNSS-MR setup can improve its sampling rate of retrievals while maintaining its low-cost advantage. This new setup could be applied to other GNSS-IR sites and is therefore beneficial for global sea level monitoring.