Improved Filtering of ICESat-2 Lidar Data for Nearshore Bathymetry Estimation Using Sentinel-2 Imagery

The accurate estimation of nearshore bathymetry is necessary for multiple aspects of coastal research and practices. The traditional shipborne single-beam/multi-beam echo sounders and Airborne Lidar bathymetry (ALB) have a high cost, are inefficient, and have sparse coverage. The Satellite-derived b...

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Autores principales:	Congshuang Xie, Peng Chen, Delu Pan, Chunyi Zhong, Zhenhua Zhang
Formato:	article
Lenguaje:	EN
Publicado:	MDPI AG 2021
Materias:	bathymetry Lidar Sentinel-2 ICESat-2 DBSCAN outlier removal Science Q
Acceso en línea:	https://doaj.org/article/03976cb0ccdc458991b9e54dbe2bfb61
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spelling	oai:doaj.org-article:03976cb0ccdc458991b9e54dbe2bfb612021-11-11T18:53:30ZImproved Filtering of ICESat-2 Lidar Data for Nearshore Bathymetry Estimation Using Sentinel-2 Imagery10.3390/rs132143032072-4292https://doaj.org/article/03976cb0ccdc458991b9e54dbe2bfb612021-10-01T00:00:00Zhttps://www.mdpi.com/2072-4292/13/21/4303https://doaj.org/toc/2072-4292The accurate estimation of nearshore bathymetry is necessary for multiple aspects of coastal research and practices. The traditional shipborne single-beam/multi-beam echo sounders and Airborne Lidar bathymetry (ALB) have a high cost, are inefficient, and have sparse coverage. The Satellite-derived bathymetry (SDB) method has been proven to be a promising tool in obtaining bathymetric data in shallow water. However, current empirical SDB methods for multispectral imagery data usually rely on in situ depths as control points, severely limiting their spatial application. This study proposed a satellite-derived bathymetry method without requiring a priori in situ data by merging active and passive remote sensing (SDB-AP). It realizes rapid bathymetric mapping with only satellite remotely sensed data, which greatly extends the spatial coverage and temporal scale. First, seafloor photons were detected from the ICESat-2 raw photons based on an improved adaptive Density-Based Spatial Clustering of Applications with Noise (DBSCAN) algorithm, which could calculate the optimal detection parameters for seafloor photons by adaptive iteration. Then, the bathymetry of the detected seafloor photons was corrected because of the refraction that occurs at the air–water interface. Afterward, the outlier photons were removed by an outlier-removal algorithm to improve the retrieval accuracy. Subsequently, the high spatial resolution (0.7 m) ICESat-2 derived bathymetry data were gridded to match the Sentinel-2 data with a lower spatial resolution (10 m). All of the ICESate-2 gridded data were randomly separated into two parts: 80% were employed to train the empirical bathymetric model, and the remaining 20% were used to quantify the inversion accuracy. Finally, after merging the ICESat-2 data and Sentinel-2 multispectral images, the bathymetric maps over St. Thomas of the United States Virgin Islands, Acklins Island in the Bahamas, and Huaguang Reef in the South China Sea were produced. The ICESat-2-derived results were compared against in situ data over the St. Thomas area. The results showed that the estimated bathymetry reached excellent inversion accuracy and the corresponding RMSE was 0.68 m. In addition, the RMSEs between the SDB-AP estimated depths and the ICESat-2 bathymetry results of St. Thomas, Acklins Island, and Huaguang Reef were 0.96 m, 0.91 m, and 0.94 m, respectively. Overall, the above results indicate that the SDB-AP method is effective and feasible for different shallow water regions. It has great potential for large-scale and long-term nearshore bathymetry in the future.Congshuang XiePeng ChenDelu PanChunyi ZhongZhenhua ZhangMDPI AGarticlebathymetryLidarSentinel-2ICESat-2DBSCANoutlier removalScienceQENRemote Sensing, Vol 13, Iss 4303, p 4303 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	bathymetry Lidar Sentinel-2 ICESat-2 DBSCAN outlier removal Science Q
spellingShingle	bathymetry Lidar Sentinel-2 ICESat-2 DBSCAN outlier removal Science Q Congshuang Xie Peng Chen Delu Pan Chunyi Zhong Zhenhua Zhang Improved Filtering of ICESat-2 Lidar Data for Nearshore Bathymetry Estimation Using Sentinel-2 Imagery
description	The accurate estimation of nearshore bathymetry is necessary for multiple aspects of coastal research and practices. The traditional shipborne single-beam/multi-beam echo sounders and Airborne Lidar bathymetry (ALB) have a high cost, are inefficient, and have sparse coverage. The Satellite-derived bathymetry (SDB) method has been proven to be a promising tool in obtaining bathymetric data in shallow water. However, current empirical SDB methods for multispectral imagery data usually rely on in situ depths as control points, severely limiting their spatial application. This study proposed a satellite-derived bathymetry method without requiring a priori in situ data by merging active and passive remote sensing (SDB-AP). It realizes rapid bathymetric mapping with only satellite remotely sensed data, which greatly extends the spatial coverage and temporal scale. First, seafloor photons were detected from the ICESat-2 raw photons based on an improved adaptive Density-Based Spatial Clustering of Applications with Noise (DBSCAN) algorithm, which could calculate the optimal detection parameters for seafloor photons by adaptive iteration. Then, the bathymetry of the detected seafloor photons was corrected because of the refraction that occurs at the air–water interface. Afterward, the outlier photons were removed by an outlier-removal algorithm to improve the retrieval accuracy. Subsequently, the high spatial resolution (0.7 m) ICESat-2 derived bathymetry data were gridded to match the Sentinel-2 data with a lower spatial resolution (10 m). All of the ICESate-2 gridded data were randomly separated into two parts: 80% were employed to train the empirical bathymetric model, and the remaining 20% were used to quantify the inversion accuracy. Finally, after merging the ICESat-2 data and Sentinel-2 multispectral images, the bathymetric maps over St. Thomas of the United States Virgin Islands, Acklins Island in the Bahamas, and Huaguang Reef in the South China Sea were produced. The ICESat-2-derived results were compared against in situ data over the St. Thomas area. The results showed that the estimated bathymetry reached excellent inversion accuracy and the corresponding RMSE was 0.68 m. In addition, the RMSEs between the SDB-AP estimated depths and the ICESat-2 bathymetry results of St. Thomas, Acklins Island, and Huaguang Reef were 0.96 m, 0.91 m, and 0.94 m, respectively. Overall, the above results indicate that the SDB-AP method is effective and feasible for different shallow water regions. It has great potential for large-scale and long-term nearshore bathymetry in the future.
format	article
author	Congshuang Xie Peng Chen Delu Pan Chunyi Zhong Zhenhua Zhang
author_facet	Congshuang Xie Peng Chen Delu Pan Chunyi Zhong Zhenhua Zhang
author_sort	Congshuang Xie
title	Improved Filtering of ICESat-2 Lidar Data for Nearshore Bathymetry Estimation Using Sentinel-2 Imagery
title_short	Improved Filtering of ICESat-2 Lidar Data for Nearshore Bathymetry Estimation Using Sentinel-2 Imagery
title_full	Improved Filtering of ICESat-2 Lidar Data for Nearshore Bathymetry Estimation Using Sentinel-2 Imagery
title_fullStr	Improved Filtering of ICESat-2 Lidar Data for Nearshore Bathymetry Estimation Using Sentinel-2 Imagery
title_full_unstemmed	Improved Filtering of ICESat-2 Lidar Data for Nearshore Bathymetry Estimation Using Sentinel-2 Imagery
title_sort	improved filtering of icesat-2 lidar data for nearshore bathymetry estimation using sentinel-2 imagery
publisher	MDPI AG
publishDate	2021
url	https://doaj.org/article/03976cb0ccdc458991b9e54dbe2bfb61
work_keys_str_mv	AT congshuangxie improvedfilteringoficesat2lidardatafornearshorebathymetryestimationusingsentinel2imagery AT pengchen improvedfilteringoficesat2lidardatafornearshorebathymetryestimationusingsentinel2imagery AT delupan improvedfilteringoficesat2lidardatafornearshorebathymetryestimationusingsentinel2imagery AT chunyizhong improvedfilteringoficesat2lidardatafornearshorebathymetryestimationusingsentinel2imagery AT zhenhuazhang improvedfilteringoficesat2lidardatafornearshorebathymetryestimationusingsentinel2imagery
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Improved Filtering of ICESat-2 Lidar Data for Nearshore Bathymetry Estimation Using Sentinel-2 Imagery

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