Direct Comparison of Sea Surface Velocity Estimated From Sentinel-1 and TanDEM-X SAR Data
This article presents the first direct comparison of the sea surface radial velocity (RVL) derived from the two satellite SAR systems Sentinel-1 and TanDEM-X, operating at different frequencies and imaging modes. The RVL is derived from the Doppler centroid (Dc) provided in the Sentinel-1 OCN produc...
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ftdoajarticles:oai:doaj.org/article:33fb3eb5e53c489c95944927ddf94054 2023-05-15T16:52:31+02:00 Direct Comparison of Sea Surface Velocity Estimated From Sentinel-1 and TanDEM-X SAR Data Anis Elyouncha Leif E. B. Eriksson Harald Johnsen 2022-01-01T00:00:00Z https://doi.org/10.1109/JSTARS.2022.3158190 https://doaj.org/article/33fb3eb5e53c489c95944927ddf94054 EN eng IEEE https://ieeexplore.ieee.org/document/9732190/ https://doaj.org/toc/2151-1535 2151-1535 doi:10.1109/JSTARS.2022.3158190 https://doaj.org/article/33fb3eb5e53c489c95944927ddf94054 IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, Vol 15, Pp 2425-2436 (2022) Along-track interferometry (ATI) ocean surface currents SAR Doppler centroid (Dc) Sentinel-1 TanDEM-X Ocean engineering TC1501-1800 Geophysics. Cosmic physics QC801-809 article 2022 ftdoajarticles https://doi.org/10.1109/JSTARS.2022.3158190 2022-12-31T13:44:36Z This article presents the first direct comparison of the sea surface radial velocity (RVL) derived from the two satellite SAR systems Sentinel-1 and TanDEM-X, operating at different frequencies and imaging modes. The RVL is derived from the Doppler centroid (Dc) provided in the Sentinel-1 OCN product and from the along-track interferometric phase of the TanDEM-X. The comparison is carried out using unique opportunistic acquisitions, collocated in space and time, over three different sites located in the Iceland Sea, the Pentland Firth, and the Kattegat Sea. First, it is observed that the RVL derived from both satellites is biased, thus calibration is applied using the land as a reference. The comparison shows that the correlation and the mean bias between the two datasets depend on the differences in acquisition time, incidence angle, and azimuth angle, and on wind and surface velocities. It is found that, given a time difference of $\lesssim$ 20 min, the spatial correlation coefficient is relatively high (between 0.70 and 0.93), which indicates that the two SAR systems observe similar sea surface current fields. The spatial correlation degrades primarily due to increasing time difference and decreasing velocity magnitudes. It is also found that the mean RVL bias increases primarily with the radial wind speed, which suggests that the bias is mainly due to the wave-induced Doppler shift. This article shows that under certain conditions, i.e., similar acquisition geometry and short time delay, a good agreement between the two independently derived RVL is achieved, both in the spatial variation and absolute mean value. This encourages a synergistic use of the sea surface velocity estimated from different C- and X-band SAR systems. Article in Journal/Newspaper Iceland Directory of Open Access Journals: DOAJ Articles Kattegat ENVELOPE(9.692,9.692,63.563,63.563) The Sentinel ENVELOPE(73.317,73.317,-52.983,-52.983) IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 15 2425 2436 |
institution |
Open Polar |
collection |
Directory of Open Access Journals: DOAJ Articles |
op_collection_id |
ftdoajarticles |
language |
English |
topic |
Along-track interferometry (ATI) ocean surface currents SAR Doppler centroid (Dc) Sentinel-1 TanDEM-X Ocean engineering TC1501-1800 Geophysics. Cosmic physics QC801-809 |
spellingShingle |
Along-track interferometry (ATI) ocean surface currents SAR Doppler centroid (Dc) Sentinel-1 TanDEM-X Ocean engineering TC1501-1800 Geophysics. Cosmic physics QC801-809 Anis Elyouncha Leif E. B. Eriksson Harald Johnsen Direct Comparison of Sea Surface Velocity Estimated From Sentinel-1 and TanDEM-X SAR Data |
topic_facet |
Along-track interferometry (ATI) ocean surface currents SAR Doppler centroid (Dc) Sentinel-1 TanDEM-X Ocean engineering TC1501-1800 Geophysics. Cosmic physics QC801-809 |
description |
This article presents the first direct comparison of the sea surface radial velocity (RVL) derived from the two satellite SAR systems Sentinel-1 and TanDEM-X, operating at different frequencies and imaging modes. The RVL is derived from the Doppler centroid (Dc) provided in the Sentinel-1 OCN product and from the along-track interferometric phase of the TanDEM-X. The comparison is carried out using unique opportunistic acquisitions, collocated in space and time, over three different sites located in the Iceland Sea, the Pentland Firth, and the Kattegat Sea. First, it is observed that the RVL derived from both satellites is biased, thus calibration is applied using the land as a reference. The comparison shows that the correlation and the mean bias between the two datasets depend on the differences in acquisition time, incidence angle, and azimuth angle, and on wind and surface velocities. It is found that, given a time difference of $\lesssim$ 20 min, the spatial correlation coefficient is relatively high (between 0.70 and 0.93), which indicates that the two SAR systems observe similar sea surface current fields. The spatial correlation degrades primarily due to increasing time difference and decreasing velocity magnitudes. It is also found that the mean RVL bias increases primarily with the radial wind speed, which suggests that the bias is mainly due to the wave-induced Doppler shift. This article shows that under certain conditions, i.e., similar acquisition geometry and short time delay, a good agreement between the two independently derived RVL is achieved, both in the spatial variation and absolute mean value. This encourages a synergistic use of the sea surface velocity estimated from different C- and X-band SAR systems. |
format |
Article in Journal/Newspaper |
author |
Anis Elyouncha Leif E. B. Eriksson Harald Johnsen |
author_facet |
Anis Elyouncha Leif E. B. Eriksson Harald Johnsen |
author_sort |
Anis Elyouncha |
title |
Direct Comparison of Sea Surface Velocity Estimated From Sentinel-1 and TanDEM-X SAR Data |
title_short |
Direct Comparison of Sea Surface Velocity Estimated From Sentinel-1 and TanDEM-X SAR Data |
title_full |
Direct Comparison of Sea Surface Velocity Estimated From Sentinel-1 and TanDEM-X SAR Data |
title_fullStr |
Direct Comparison of Sea Surface Velocity Estimated From Sentinel-1 and TanDEM-X SAR Data |
title_full_unstemmed |
Direct Comparison of Sea Surface Velocity Estimated From Sentinel-1 and TanDEM-X SAR Data |
title_sort |
direct comparison of sea surface velocity estimated from sentinel-1 and tandem-x sar data |
publisher |
IEEE |
publishDate |
2022 |
url |
https://doi.org/10.1109/JSTARS.2022.3158190 https://doaj.org/article/33fb3eb5e53c489c95944927ddf94054 |
long_lat |
ENVELOPE(9.692,9.692,63.563,63.563) ENVELOPE(73.317,73.317,-52.983,-52.983) |
geographic |
Kattegat The Sentinel |
geographic_facet |
Kattegat The Sentinel |
genre |
Iceland |
genre_facet |
Iceland |
op_source |
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, Vol 15, Pp 2425-2436 (2022) |
op_relation |
https://ieeexplore.ieee.org/document/9732190/ https://doaj.org/toc/2151-1535 2151-1535 doi:10.1109/JSTARS.2022.3158190 https://doaj.org/article/33fb3eb5e53c489c95944927ddf94054 |
op_doi |
https://doi.org/10.1109/JSTARS.2022.3158190 |
container_title |
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing |
container_volume |
15 |
container_start_page |
2425 |
op_container_end_page |
2436 |
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1766042845194485760 |