Evaluating GNSS-Interferometric Reflectometry (GNSS-IR) for Sea Level Monitoring along the Tanzanian Coast: A Comparative Study with Tide Gauge Data

Traditional tide gauges provide essential records of sea level change but remain spatially limited, particularly along the Tanzanian coast, which has only two operational stations. This study evaluates Global Navigation Satellite System–Interferometric Reflectometry (GNSS-IR) as a complementary technique for sea level monitoring in Tanzania. A GNSS station was installed at the Dar Es Salaam port and co-located with operational pressure and radar tide gauges for 257 days.Signal-to-noise ratio (SNR) data were processed using the GNSS-REFL software to retrieve sea level variations from L1 and L2C signals. Over 5,000 reflector height estimates were obtained. The Comparison between the pressure and radar sensors themselves showed poor agreement (r = 0.208), indicating inherent inconsistencies in the validation data. Comparisons between GNSS-IR and the tide gauges also showed weak correlations, ranging from r = -0.043 to 0.08 for L1 and L2C signals. These discrepancies are likely due to site-specific issues like datum inconsistencies, obstructions, and a limited reflection zone from port activityThe results demonstrate GNSS-IR potential as a valuable supplementary tool in data sparse regions, although the weak agreement with the traditional gauges was unexpected. Performance can be enhanced through improved antenna placement, ensured reflection zone visibility, and longer observation periods.