GNSS Interferometric Reflectometry (GNSS-IR) Tidal Monitoring in Limay, Bataan with Analysis of Antenna Orientation and GNSS Signal Variability

Abstract. This study aimed to establish a foundation for a GNSS-IR network for tidal measurements in the Philippines, focusing specifically on Limay Port, Bataan, over two weeks from July 15 to July 30, 2024. A field setup was conducted in Limay to optimize GNSS-IR performance using cost-effective UBX receivers and two antenna orientations: SIDE, oriented towards the water surface, and ZENI, oriented towards the sky. Classical GNSS-IR techniques were employed, which included Fresnel zone analysis and tidal wave height calculations. These measurements were then compared with traditional tide gauge data to evaluate accuracy and reliability. Th e SIDE antenna demonstrated superior accuracy with an RMSE of 4.18 cm, MAE of 3.44 cm, and a correlation coefficient of 0.997, compared to the ZENI antenna, which had an RMSE of 10.22 cm, MAE of 9.41 cm, and a correlation coefficient of 0.995. The GPS L1 frequency provided the most accurate measurements, especially with the antenna towards the water. The study confirmed that GNSS-IR can provide accurate tidal measurements when satellite frequencies are combined and outliers are filtered. Additionally, the GNSS-IR system was found to be significantly more cost-effective than traditional tide gauges. With a total cost of PHP 47,500, compared to PHP 500,000 for tide gauges, there was a substantial cost difference of PHP 452,500. This cost advantage underscores the viability of GNSS-IR for sea-level monitoring, particularly for projects with budget constraints. The findings suggest that GNSS-IR has the potential to enhance sea-level monitoring capabilities in the Philippines and other regions with similar requirements.