First coastal validation results of an open-source low-cost GNSS Reflectometry sensor for sea level altimetry

Abstract:

Contemporary sea level rise renders tide gauging essential in support of adaptation and mitigation strategies and to minimize the economic and societal impacts of extreme events. Global Navigation Satellite System Reflectometry (GNSS-R) has been widely demonstrated for coastal sea level monitoring. One particular configuration of GNSS-R, called GNSS multipath reflectometry (GNSS-MR), is based on the combined reception of direct and reflected radio waves after transmission by GNSS satellites. The main observable in GNSS-MR is the signal-to-noise ratio (SNR), which records the constructive/destructive interference pattern arising from the superposition of the two coherent rays. Recently we reported the development of a complete hardware and software system for SNR-based GNSS-R. We made it freely available as opensource based on the low-cost commercial off-the-shelf components. We have deployed multiple working prototypes of the sensor in the field, where they have operated uninterruptedly 24/7 for more than a year, having resisted severe weather conditions. Initial validation occurred by a lake (30.0277° S, 51.2287° W) for 317 days by comparison to a co-located radar-type tide gauge. Statistics confirmed that the sensor can retrieve water level with very high correlation (0.989) and centimeter-level RMSE (2.9 cm). Here we report additionally on the first coastal validation results of our GNSS-R sensor. The experiment was setup in a port (28.232019° S, 48.651064° W) with several co-located tide gauges. Although the location is sheltered from breaking waves, wind-driven waves are much greater, compared to the initial lake experiment. The increased surface roughness affects the coherence of radio wave reflections, which may eventually hamper the interferometric superposition principle, essential in GNSS-MR. We will report on ongoing validation efforts to quantity how correlation and RMSE in sea level altimetry are degraded due to the above error sources.