Improved Inland Water Level Estimates with Sentinel-6 Fully Focused SAR Processing: A Case Study in the Ebre River Basin
The observation of small to medium inland water targets with nadir radar altimeters is currently limited by the along-track resolution of UnFocused SAR (UFSAR) altimetry, which is approximately 300 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inli...
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MDPI AG
2025-02-01
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| author | Xavier Domingo Ferran Gibert Robert Molina Maria Jose Escorihuela |
| author_facet | Xavier Domingo Ferran Gibert Robert Molina Maria Jose Escorihuela |
| author_sort | Xavier Domingo |
| collection | DOAJ |
| description | The observation of small to medium inland water targets with nadir radar altimeters is currently limited by the along-track resolution of UnFocused SAR (UFSAR) altimetry, which is approximately 300 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi mathvariant="normal">m</mi></semantics></math></inline-formula> for Delay-Doppler processors. In this study, we analyze the benefits of the sub-meter along-track resolution provided by Fully Focused SAR (FFSAR) altimetry applied to Sentinel-6 Michael Freilich data over a collection of small to medium targets in the Ebre Basin, Spain. The obtained water level estimations over a 2-year period are compared to in situ data to evaluate the long-term accuracy of the algorithm. The proposed FFSAR altimetry methodology achieves an average MAD precision of roughly 4 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi mathvariant="normal">c</mi></semantics></math></inline-formula><inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi mathvariant="normal">m</mi></semantics></math></inline-formula>, and allows for a full operational implementation as it can be processed in a totally unsupervised manner. The precision improvement with respect to Delay-Doppler products over the same targets is essentially attributed to the FFSAR capabilities to better filter out waveforms contaminated by off-nadir scatterers. Moreover, we evaluate the application of extended water masks, which exploit nadir–altimeter measurements where water is at nadir or up to 250 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi mathvariant="normal">m</mi></semantics></math></inline-formula> across-track from nadir to increase the number of acquisitions while maintaining the same level of accuracy, increasing by an average of 48% the number of valid measurements per pass, while maintaining the same level of accuracy as nadir measurements over water. We thus demonstrate the potential of FFSAR altimetry to monitor the water level of small to medium inland water targets. |
| format | Article |
| id | doaj-art-c1d0e5aba0574dc9b505d08e7561b4d8 |
| institution | DOAJ |
| issn | 2072-4292 |
| language | English |
| publishDate | 2025-02-01 |
| publisher | MDPI AG |
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| series | Remote Sensing |
| spelling | doaj-art-c1d0e5aba0574dc9b505d08e7561b4d82025-08-20T02:48:03ZengMDPI AGRemote Sensing2072-42922025-02-0117353110.3390/rs17030531Improved Inland Water Level Estimates with Sentinel-6 Fully Focused SAR Processing: A Case Study in the Ebre River BasinXavier Domingo0Ferran Gibert1Robert Molina2Maria Jose Escorihuela3isardSAT SL, Dr Trueta 113, 1r, 08005 Barcelona, Catalonia, SpainisardSAT SL, Dr Trueta 113, 1r, 08005 Barcelona, Catalonia, SpainisardSAT SL, Dr Trueta 113, 1r, 08005 Barcelona, Catalonia, SpainisardSAT SL, Dr Trueta 113, 1r, 08005 Barcelona, Catalonia, SpainThe observation of small to medium inland water targets with nadir radar altimeters is currently limited by the along-track resolution of UnFocused SAR (UFSAR) altimetry, which is approximately 300 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi mathvariant="normal">m</mi></semantics></math></inline-formula> for Delay-Doppler processors. In this study, we analyze the benefits of the sub-meter along-track resolution provided by Fully Focused SAR (FFSAR) altimetry applied to Sentinel-6 Michael Freilich data over a collection of small to medium targets in the Ebre Basin, Spain. The obtained water level estimations over a 2-year period are compared to in situ data to evaluate the long-term accuracy of the algorithm. The proposed FFSAR altimetry methodology achieves an average MAD precision of roughly 4 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi mathvariant="normal">c</mi></semantics></math></inline-formula><inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi mathvariant="normal">m</mi></semantics></math></inline-formula>, and allows for a full operational implementation as it can be processed in a totally unsupervised manner. The precision improvement with respect to Delay-Doppler products over the same targets is essentially attributed to the FFSAR capabilities to better filter out waveforms contaminated by off-nadir scatterers. Moreover, we evaluate the application of extended water masks, which exploit nadir–altimeter measurements where water is at nadir or up to 250 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi mathvariant="normal">m</mi></semantics></math></inline-formula> across-track from nadir to increase the number of acquisitions while maintaining the same level of accuracy, increasing by an average of 48% the number of valid measurements per pass, while maintaining the same level of accuracy as nadir measurements over water. We thus demonstrate the potential of FFSAR altimetry to monitor the water level of small to medium inland water targets.https://www.mdpi.com/2072-4292/17/3/531radar altimetryFFSARUFSARwater levelinland waters |
| spellingShingle | Xavier Domingo Ferran Gibert Robert Molina Maria Jose Escorihuela Improved Inland Water Level Estimates with Sentinel-6 Fully Focused SAR Processing: A Case Study in the Ebre River Basin Remote Sensing radar altimetry FFSAR UFSAR water level inland waters |
| title | Improved Inland Water Level Estimates with Sentinel-6 Fully Focused SAR Processing: A Case Study in the Ebre River Basin |
| title_full | Improved Inland Water Level Estimates with Sentinel-6 Fully Focused SAR Processing: A Case Study in the Ebre River Basin |
| title_fullStr | Improved Inland Water Level Estimates with Sentinel-6 Fully Focused SAR Processing: A Case Study in the Ebre River Basin |
| title_full_unstemmed | Improved Inland Water Level Estimates with Sentinel-6 Fully Focused SAR Processing: A Case Study in the Ebre River Basin |
| title_short | Improved Inland Water Level Estimates with Sentinel-6 Fully Focused SAR Processing: A Case Study in the Ebre River Basin |
| title_sort | improved inland water level estimates with sentinel 6 fully focused sar processing a case study in the ebre river basin |
| topic | radar altimetry FFSAR UFSAR water level inland waters |
| url | https://www.mdpi.com/2072-4292/17/3/531 |
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