Tidal harmonics retrieval using GNSS-R dual-frequency complex observations

• Published in: Journal of geodesy Vol. 97; no. 10
• Main Authors: Rajabi, Mahmoud, Hoseini, Mostafa, Nahavandchi, Hossein, Asgarimehr, Milad, Semmling, Maximilian, Ramatschi, Markus, Goli, Mehdi, Wickert, Jens
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.10.2023; Springer Nature B.V
• Subjects: Earth and Environmental Science; Earth Sciences; Geodetics; Geophysics/Geodesy; Green energy; Navigation; Navigation satellites; Navigation systems; Navigational satellites; Offshore engineering; Original Article; Satellites; Sea level; Sea surface; Tidal analysis; Tide gauges; Global Navigation Satellite Systems Reflectometry (GNSS-R); GNSS; Coastal waters remote sensing; Least-squares harmonic estimation (LS-HE); Tidal analysis; GPS; Altimetry
• ISSN: 0949-7714; 1432-1394
• DOI: 10.1007/s00190-023-01782-6

Tidal analysis and methods for estimation and prediction of ocean tidal constitutes are essential in a large area of scientific disciplines, for example, navigation, onshore and offshore engineering, and production of green energy. Ground-based Global Navigation Satellite System-Reflectometry (GNSS-R) has been proposed as an alternative method for measuring sea surface height. We use 6 years of GNSS-R observations at In-phase and Quadrature levels from July 2015 to May 2021 obtained from a dedicated receiver and sea-looking left hand circular polarization antenna for estimating sea level (SL). In the first step, the multivariate least-square harmonic estimation (LS-HE) method is applied for SL estimation. Then, final SL time series are generated by combining estimated SL from all satellites at L1 and L2 frequencies in the averaging step. The 6-year root-mean-square error between GNSS-R L12 sea surface heights and a collocated tide gauge (TG) is 5.8 cm with a correlation of 0.948 for a high temporal resolution of 5 min with 15 min averaging window. Afterward, using the univariate LS-HE, we detect tidal harmonics with periods between 30 min to 1 year. The detection results highlight a good match between GNSS-R and TG. Higher harmonics, i.e., the periods shorter than 3 h, show stronger signatures in GNSS-R data. Finally, we estimate the amplitude and phase of standard tidal harmonics from the two datasets. The results show an overall good agreement between the datasets with a few exceptions.