Extraction of ocean tides in the Bohai Sea from GFO satellite altimeter via a modified tidal harmonic analysis algorithm

Exact tidal information is essential for multifarious human activities in the global ocean. Satellite altimeters especially Topex/Poseidon (T/P) and Jason series play fundamental roles in improving our understanding of global tides. Compared to T/P-Jason series, other satellite altimeters such as Geosat Follow-On (GFO) have been rarely used in tidal studies mainly due to their unfavorable aliasing features for tidal estimates. Classical harmonic analysis requires 12-year GFO records to fully resolve eight major tidal constituents while the longest GFO data is only 8-year. As a result, it is challenging for classical harmonic analysis to derive reliable tidal estimates from short GFO records. In this study, a modified tidal harmonic analysis algorithm based on the credo of smoothness (i.e. MHACS) is introduced to extract ocean tides from GFO records in the Bohai Sea. Via utilizing the inherent natural links between main constituents, MHACS breaks the constraint of the Rayleigh criterion and effectively solves tidal aliasing problems in GFO records. Practical experiments indicate that GFO-derived tidal constants via MHACS have high consistencies with the tidal theory and satellite-based EOT20 tidal model. Spatially-averaged vector difference between the EOT20 model and GFO results in the Bohai Sea is only 2.12 cm (eight major constituents averaged). Moreover, except for GFO, MHACS also has the potential to be applied to sun-synchronous satellites such as Envisat, Sentinel series, and Haiyang series.