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Efficiency evaluation of waveform modification and decontamination methods in the enclosed basin of the Baltic Sea
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Saleh Mafi   , Saeed Farzaneh * , Mohammad Ali Sharifi , Ehsan Forootan |
| University of Tehran |
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Abstract: (969 Views) |
| One of the important challenges in the coastal altimetry is the contamination of the waveforms by non-oceanic effects. These effects, which have complex behavior, appear in different forms on the waveforms. Therefore, omitting or mitigating their effects is one of the important issues in preparing the precise time series of Sea Surface Height (SSH). So far, several statistical methods have been proposed by the altimetry experts, which can be classified into two categories: waveform modification and decontamination. The main difference between these two methods is related to detecting the erroneous gates of the waveforms in which the standard deviation of the residual waveform is used for modification, and the Root-Mean-Squared-Error (RMSE) of all of the residual waveforms of the echogram is used for decontamination. The residual waveform is obtained by subtracting a waveform from the reference waveform of the echogram. In this study, a comparison is made between the efficiency of each of these methods. Some novel ideas are also presented regarding the construction of the reference waveform and the methods for trimming the gates contaminated by non-ocean effects. The gate trimming is conducted by three methods, namely, weighted averaging of inverse distance, two-step weighted averaging, and the median of the adjacent powers around the erroneous gate. In the end, the trimmed waveforms are retracked by the spline retracker, and the time series of the SSH is compared with the tide-gauge data. This algorithm, which is evaluated on the three stations of Vinga, Onsala, and Halmstad on the coast of the Baltic Sea, on Jason-2 and Jason-3 data from passes 137, 68, and 213, provides a high-quality time series of the SSH 15 km away from the coastline. The comparisons between the SSH time series derived from the trimmed and raw waveforms reveal an improvement between 2.5 to 23.5% in unbiased RMSE and a maximum increase of 11% in the correlation coefficient. |
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| Keywords: waveform, waveform modification, waveform decontamination, Jason-2, Jason-3, retracking the waveform |
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Full-Text [PDF 1237 kb]
(240 Downloads)
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Type of Study: Research |
Subject:
Geodesy
Received: 2024/05/24 | Accepted: 2024/10/14 | ePublished ahead of print: 2024/10/29 | Published: 2024/10/29
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