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Retracking contaminated Waveforms of Sentinel-3A Satellite Altimetry Observations in Coastal Areas by an Algorithm Based on Logistic Function (Case Study: Northeastern Coastals of Estonia)
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Arash Amini *   , Behzad Voosoghi , Masoud Fatemi , Parisa Agar , Mahmoud Pirooznia |
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Abstract: (586 Views) |
The use of satellite altimetry to monitor sea surface height (SSH) in coastal regions requires using retracking methods to correct the range of altimeter. This issue is caused by the difference between the ideal ocean waveform and the coastal confused waveform affected by some factors such as shallow depth, the presence of non-aquatic effects, and the large footprint of the altimeter. In this regard, in this study, the retracking method based on the logistic function has been proposed due to the geometric and parametric agreement of this function with the satellite altimetry waveforms.This function has two analytical approaches (equivalent to a mathematical retracker) based on the mathematical fitting of the function to the first meaningful sub_waveform of the waveform and a numerical approach (equivalent to an experimental retracker) based on selecting the optimal retracker gate, for that the function has the highest correlation with first meaningful sub_waveform of the waveform. Besides the proposed method, retracking approaches of full waveform, mean waveform, and waveform with the highest correlation based on threshold retracking method, the tracker and retrackers available in the level-2 data are also implemented. In order to check the effectiveness of the proposed method, the monitoring of SSH in the northeastern coast of Estonia using the Sentinel-3A mission, pass number of 72, with SAR mode from the cycle of 4 to 45, equivalent to the period of 05/08/2016 to 05/20/2019 is done. The SSH time series obtained from the retracking approaches are compared with the in situ tide gauge data using root mean square error (RMSE) as a statistical parameter. The results of the RMSE value for retracking approaches of the full waveform is 13 cm, the mean waveform is 30 cm, the waveform with the highest correlation is 21 cm by the optimal threshold in threshold retracking, optimal level-2 data is 18 cm, the analytical approach of the logistic function is 11 cm, and numerical approach of the logistic function is 8 cm. The results show that the numerical approach of the logistic function has optimal efficiency by comparing it with the analytical approach of this function. Moreover, this approach has superiority over other retracking methods checked in this research. Therefore, the logistic function can be recognized as an effective retracker method in both mathematical and experimental aspects and it can be used in the SSH monitoring of coastal areas.
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| Keywords: Satellite altimetry, coastal areas, synthetic aperture radar (SAR), waveform retracking, logistic function |
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Type of Study: Research |
Subject:
Geodesy
Received: 2023/02/2 | Accepted: 2023/07/11 | ePublished ahead of print: 2024/08/6
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