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Coastal Waveform Retracking in the Slick-Rich Sulawesi Sea of Indonesia, Based on Variable Footprint Size with Homogeneous Sea Surface Roughness

1
School of Marine Science and Environment Engineering, Dalian Ocean University, Dalian 116023, China
2
Research Institute for Applied Mechanics, Kyushu University, Fukuoka 8168580, Japan
3
Dalian Marine Environmental Monitoring Station of Chinese State Oceanic Administration, Dalian 116015, China
*
Author to whom correspondence should be addressed.
Remote Sens. 2019, 11(11), 1274; https://doi.org/10.3390/rs11111274
Received: 29 March 2019 / Revised: 9 May 2019 / Accepted: 24 May 2019 / Published: 29 May 2019
(This article belongs to the Special Issue Advances in Satellite Altimetry and Its Application)
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Abstract

Waveforms of radar altimeters are often corrupted due to heterogeneous sea surface roughness within footprints, such as slicks. In past studies, subwaveform retrackers such as the adaptive leading edge subwaveform retracker (ALES) which use only a section of the waveform have been proposed. However, it is difficult to choose a reasonable estimation window from an individual waveform. In the present study, a post-processed subwaveform retracker is proposed which identifies the waveforms of surrounding along-track points. The size of the estimation window is variable and is determined to keep the sea surface roughness within the corresponding footprint homogeneous. The method was applied to seven years of 20 Hz Jason-2 altimeter data over the slick-rich Sulawesi Sea of Indonesia and compared with ALES and sensor geophysical data record (SGDR) products. The standard deviation of the sea surface dynamic heights was around 0.13 m, even without spatial smoothing or some geophysical corrections. This is only 75% and 25% of the ALES and SGDR results, respectively. Moreover, all retrievals of the range, SWH, and sigma0 include less outliers than the other products. These results indicate that the variable estimation windows determined in the present study can adapt well to the variation of sea surface roughness. View Full-Text
Keywords: radar altimeter; sea slick; subwaveform retracker; echogram; ALES; Sulawesi Sea of Indonesia radar altimeter; sea slick; subwaveform retracker; echogram; ALES; Sulawesi Sea of Indonesia
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Wang, X.; Ichikawa, K.; Wei, D. Coastal Waveform Retracking in the Slick-Rich Sulawesi Sea of Indonesia, Based on Variable Footprint Size with Homogeneous Sea Surface Roughness. Remote Sens. 2019, 11, 1274.

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