Abstract
It is widely believed that altimetry-derived sea surface heights (SSHs) in coastal zones are seriously degraded due to land contamination in altimeter waveforms from non-marine surfaces or due to inhomogeneous sea state conditions. Spurious peaks superimposed in radar waveforms adversely impact waveform retracking and hence require tailored algorithms to mitigate this problem. Here, we present an improved method to decontaminate coastal waveforms based on the waveform modification concept. SSHs within 10 km offshore are calculated from Jason-2 data by a 20% threshold retracker using decontaminated waveforms (DW-TR) and compared with those using original waveforms and modified waveforms in four study regions. We then compare our results with retracked SSHs in the sensor geophysical data record (SGDR) and with the state-of-the-art PISTACH (Prototype Innovant de Système de Traitement pour les Applications Côtières et l’Hydrologie) and ALES (Adaptive Leading Edge Subwaveform) products. Our result indicates that the DW-TR is the most robust retracker in the 0–10 km coastal band and provides consistent accuracy up to 1 km away from the coastline. In the four test regions, the DW-TR retracker outperforms other retrackers, with the smallest averaged standard deviations at 15 cm and 20 cm, as compared against the EGM08 (Earth Gravitational Model 2008) geoid model and tide gauge data, respectively. For the SGDR products, only the ICE retracker provides competitive SSHs for coastal applications. Subwaveform retrackers such as ICE3, RED3 and ALES perform well beyond 8 km offshore, but seriously degrade in the 0–8 km strip along the coast.
Highlights
Satellite radar altimetry is a powerful technology for remotely sensing physical properties of global oceans
Nine retrackers were compared in this study, including three retrackers (ICE, OCEAN, MLE3) from sensor geophysical data record (SGDR), three retrackers (ICE3, OCE3, RED3) from PISTACH, and three retrackers (Ori-threshold retracker (TR), MW-TR, DW-TR) performed in this study
OCE3 only successfully retracked 54% waveforms, which is equivalent to the percentage of ocean waveforms classified in PISTACH
Summary
Satellite radar altimetry is a powerful technology for remotely sensing physical properties of global oceans. Altimeter waveforms show diversely complex shapes because of land in the footprint and complicated sea state conditions [5,6] In this case, erroneous range measurements might be delivered by on-board retrackers, which are designed for normal waveforms in the open ocean. Inaccurate media and geophysical corrections such as atmospheric delay corrections, tides, sea state bias (SSB), etc., are non-negligible factors for the poor quality of coastal SSHs [7,8,9]. These corrections are more complex near the coast and it is considerably more difficult to improve them
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