Waveform Classification and Retracking of Jason-2 and Jason-3 in Halmahera Sea

Abstract

The accuracy of sea surface heights (SSHs) estimation from satellite altimeters is strongly influenced by the microwave reflected signals (or waveforms). Waveforms in open oceans generally have ideal shapes following the Brown (1977) model. However, in coastal and shallow waters, the signals are disturbed by lands, thus resulting in complicated waveforms (non-Brown). Non-Brown waveforms produce inaccurate SSH estimations; therefore, specialized protocols such as waveform classification and retracking are crucial when attempting to produce accurate estimations. In this study, waveforms of Jason-2 and Jason-3 satellite altimeters in the Halmahera were classified and retracked using several algorithms, such as Offset Centre of Gravity (OCOG), Ice, Threshold, and Improved Threshold. The results showed that waveforms in the Halmahera Sea had ten generic classes with dominant class of the Browns. The validation results showed that all retrackers (except OCOG) had the value of correlations exceeding 0.75, and Root Mean Square Error (RMSE) smaller than 25 cm at a distance of 5-20 km from the land. The Threshold 10% was the most common retracker that appeared with the highest improvement percentage (IMP), meanwhile the Ice retracker consistently produced the best correlation (0.86) and the lowest RMSE (16cm). The retracking results showed that waveform retracking generally can improve SSH estimation accuracy from ocean (standard) retracker.

Recent progress on sea-level rise over the marginal seas in Southeast Asia

“…A high-resolution data product such as the Adaptive Leading Edge Sub-waveform (ALES) for Jason series, Coastal and Hydrology Altimetry product (PISTACH) for Jason-2, and Prototype for Expertise on AltiKa for Coastal, Hydrology and Ice (PEACHI) for SARAL/AltiKa, and Coastal Altimetry Waveform Retracking Expert System (CAWRES) (Idris and Deng, 2012;Idris, 2020;Idris et al, 2017;Idris and Deng, 2013) altimeter are among the optimized datasets for coastal ocean applications. Through comprehensive assessments of regional Southeast Asia, several studies conclude that the optimal retracked SSHs are derived from the Ice retracker where it gave the highest correlation and the lowest root mean square error (RMSE) when compared to tide gauge data (Sinurata et al, 2021;Idris, 2020;Abdullah et al, 2016).…”

Waveform Decontamination for Improving Satellite Radar Altimeter Data Over Nearshore Area: Upgraded Algorithm and Validation

“…The closer to shore, the more complex the waveform is (Chaudhary et al, 2015;Idris et al, 2017, Bignalet-Cazalet et al, 2020Sinurata et al, 2021). The traditional retrackers for processing the ocean waveform, neither model-based nor empirical, sometimes fail to retrack the waveform or misestimate parameters in coastal regions due to the severe noise in the coastal waveform.…”