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Analysis of Retrackers’ Performances and Water Level Retrieval over the Ebro River Basin Using Sentinel-3

1
isardSAT, Parc Tecnològic Barcelona Activa, Carrer de Marie Curie 8, 08042 Barcelona, Catalonia, Spain
2
CESBIO (CNRS/CNES/UPS/IRD), 31401 CEDEX 9 Toulouse, France
3
Observatori de l’Ebre (OE), Ramon Llull University, 43520 Roquetes, Spain
*
Author to whom correspondence should be addressed.
Remote Sens. 2019, 11(6), 718; https://doi.org/10.3390/rs11060718
Received: 29 January 2019 / Revised: 11 March 2019 / Accepted: 21 March 2019 / Published: 25 March 2019
(This article belongs to the Special Issue Advances in Satellite Altimetry and Its Application)
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Abstract

Satellite altimeters have been used to monitor river and reservoir water levels, from which water storage estimates can be derived. Inland water altimetry can, therefore, play an important role in continental water resource management. Traditionally, satellite altimeters were designed to monitor homogeneous surfaces such as oceans or ice sheets, resulting in poor performance over small inland water bodies due to the contribution from land contamination in the returned waveforms. The advent of synthetic aperture radar (SAR) altimetry (with its improved along-track spatial resolution) has enabled the measurement of inland water levels with a better accuracy and an increased spatial resolution. This study aimed to retrieve water levels from Level-1B Sentinel-3 data with focus on the minimization of the land contamination over small- to middle-sized water bodies (130 m to 4.5 km), where continuous clean waveforms rarely exist. Three specialized algorithms or retrackers, together with a new waveform portion selection method, were evaluated to minimize land contamination in the waveforms and to select the nadir return associated with the water body being overflown. The waveform portion selection method, with consideration of the Digital Elevation Model (DEM), was used to fit the multipeak waveforms that arise when overflying the continental water bodies, exploiting a subwaveform-based approach to pick up the one corresponding to the nadir. The performances of the proposed waveform portion selection method with three retrackers, namely, the threshold retracker, Offset Center of Gravity (OCOG) retracker and two-step SAR physical-based retracker, were compared. No significant difference was found in the results of the three retrackers. However, waveform portion selection using DEM information great improved the results. Time series of water levels were retrieved for water bodies in the Ebro River basin (Spain). The results show good agreement with in situ measurements from the Ebro Reservoir (approximately 1.8 km wide) and Ribarroja Reservoir (approximately 400 m wide), with unbiased root-mean-square errors (RMSEs) down to 0.28 m and 0.16 m, respectively, depending on the retracker. View Full-Text
Keywords: altimetry; retracking; Sentinel-3; synthetic aperture radar (SAR) altimetry; retracking; Sentinel-3; synthetic aperture radar (SAR)
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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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MDPI and ACS Style

Gao, Q.; Makhoul, E.; Escorihuela, M.J.; Zribi, M.; Quintana Seguí, P.; García, P.; Roca, M. Analysis of Retrackers’ Performances and Water Level Retrieval over the Ebro River Basin Using Sentinel-3. Remote Sens. 2019, 11, 718.

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