Local tide and geoid corrections significantly improve coastal retracked Jason sea surface heights in the Philippines
2022
Flores, P.C.M. | Reyes, R.B. | Amedo-Repollo, C.L. | Rediang, A. | Alfante, R.M. | Bauzon, Ma.D.A. | Pasaje, N. | Bringas, D.
Retracking algorithms increase the accuracy of coastal sea surface height (SSH) measurements. However, it is still important to validate these retracking estimates with tide gauge (SSH sub tg) observations. Authors downloaded the freely available Jason altimeter SSH processed using the XTRACK-ALES algorithm, then detided the SSH using different tide models. The first model is the default tidal correction based on Finite Element Solution 2014 (SSH sub fes), and the second model is the T_Tide harmonic analysis of the nearest tide gauge (SSH sub altimeter). SSH sub fes showed a very poor correlation ( 0.31) and very high root mean square error (RMSE, 29 cm). In contrast, SSH sub altimeter generally showed a very high correlation ( 0.91) and low RMSE ( 17.4 cm). A further quality check based on the average and standard deviation of the difference between the SSH readings (SSH sub fes SSH sub tg and SSH sub altimeter SSH sub tg) also showed the superior performance of SSH sub altimeter,which scored 9.3 and 16.5 cm, respectively; compared to SSH sub fes, which scored 9.3 cm and 27 cm for the same parameters. The poor performance from the SSH sub fes likely comes from the complex bathymetry and coastal geomorphology of the country, which is not accounted for in the FES. The Philippines generally has a narrow shelf, and the FES tide corrections may be related to deep-water tides rather than the shallow-water tides observed from tide gauges. Despite the high correlation and agreement between the SSH sub altimeter and SSH sub tg, the rate of sea level rise from the SSH sub altimeter in some sites is more than twice the rate from SSH sub tg, which indicates the possible influence of the vertical land movement.
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