Abstract's details
New processing capabilities in the SPP chain for improving the Sentinel-3 and Sentinel-6 altimetric parameter estimates
CoAuthors
Event: 2023 Ocean Surface Topography Science Team Meeting
Session: Instrument Processing: Measurement and Retracking
Presentation type: Type Poster
Contribution: PDF file
Abstract:
In the frame of the exploitation of the Sentinel-6 Michael Freilich (S6-MF) altimetry mission, CNES has contracted CLS for the development of the Sentinel-6 Processing Prototype (S6PP) [3]. S6PP is a multi-chain (LRM, UF-SAR, FF-SAR, Pulse-Pair, Transponder) processor in which the novel algorithms developed in the CNES/CLS R&D activities are implemented and validated in support to the different thematic applications and in view of promoting them for a possible implementation in operational ground segment. The chain also features the capability to process Sentinel-3A/B (S3A/B) data using the same algorithms as those used for S6-MF to ease their performance assessment. This prototype is renamed SPP (Sentinel Processing Prototype) to account for the new multi-mission processing specificity.
We present here the main updates that we have made on the SPP, with the objective to refine the accuracy of the Ku band measurements:
• We added the option of retracking the two-dimensional stacks [1] in UF-SAR, in order to estimate the azimuth smearing caused by the vertical velocity of the water. This recent development makes it possible to correct the bias in sea wave height (SWH) observed in HR modes, as well as to estimate the standard deviation of the swell vertical velocity on open ocean [2]. This quantity is related to the mean zero-upcrossing period and brings new information on the spectrum of the waves. We applied this processing to a cycle of UF-SAR Sentinel-6 data and compared the results to the LR mode and to the ERA5 model.
• On the other hand, we implemented the Fast-Adaptive retracker [4], an optimal, unbiased and computationally efficient algorithm to analyze LR mode data. It combines the advantages of the Adaptive algorithm [5] with the speed of the MLE4 retracker, which is currently implemented in the ground segments for conventional altimetry. The Fast-Adaptive retracker uses a weighted least square method instead of the ordinary least squares approach adopted in MLE4.
The SPP prototype allowed us to perform studies on new altimeter processing configurations and to evaluate their relevance in view of potential implementation in operational ground segment, in particular:
• The impact of varying the posting rate, i.e. the spacing between successive multi-looks, on the accuracy of different geophysical measurements, to answer questions about the optimal sampling to be used (considering speckle noise analysis and the impact of long ocean waves on S6-MF SAR altimeter data).
• The analysis of the numerical retracking algorithm [3] to process S6-MF C-band data and its performance evaluation compared to the conventional MLE3 solution.
References:
[1] Buchhaupt, C., Fenoglio, L., Becker, M., & Kusche, J. (2021). Impact of vertical water particle motions on focused SAR altimetry. Advances in Space Research, 68(2), 853-874.
[2] Buchhaupt, C., Egido, A., Smith, W. H., & Fenoglio, L. (2023). Conditional sea surface statistics and their impact on geophysical sea surface parameters retrieved from SAR altimetry signals. Advances in Space Research, 71(5), 2332-2347.
[3] Dinardo, S. et al. (2023). Sentinel-6 MF Poseidon-4 Radar Altimeter: Main Scientific Results from S6PP LRM and UF-SAR Chains in the First Year of the Mission. Advances in Space Research.
[4] Mangilli, A. et al. (2022). Fast-Adaptive: a new, optimal, unbiased and computationally efficient retracking solution for the analysis of conventional altimetry data. Oral presentation, OSTST.
[5] Tourain, C. et al. (2021). Benefits of the adaptive algorithm for retracking altimeter nadir echoes: Results from simulations and CFOSAT/SWIM observations. IEEE Transactions on Geoscience and Remote Sensing, 59(12), 9927-9940.
We present here the main updates that we have made on the SPP, with the objective to refine the accuracy of the Ku band measurements:
• We added the option of retracking the two-dimensional stacks [1] in UF-SAR, in order to estimate the azimuth smearing caused by the vertical velocity of the water. This recent development makes it possible to correct the bias in sea wave height (SWH) observed in HR modes, as well as to estimate the standard deviation of the swell vertical velocity on open ocean [2]. This quantity is related to the mean zero-upcrossing period and brings new information on the spectrum of the waves. We applied this processing to a cycle of UF-SAR Sentinel-6 data and compared the results to the LR mode and to the ERA5 model.
• On the other hand, we implemented the Fast-Adaptive retracker [4], an optimal, unbiased and computationally efficient algorithm to analyze LR mode data. It combines the advantages of the Adaptive algorithm [5] with the speed of the MLE4 retracker, which is currently implemented in the ground segments for conventional altimetry. The Fast-Adaptive retracker uses a weighted least square method instead of the ordinary least squares approach adopted in MLE4.
The SPP prototype allowed us to perform studies on new altimeter processing configurations and to evaluate their relevance in view of potential implementation in operational ground segment, in particular:
• The impact of varying the posting rate, i.e. the spacing between successive multi-looks, on the accuracy of different geophysical measurements, to answer questions about the optimal sampling to be used (considering speckle noise analysis and the impact of long ocean waves on S6-MF SAR altimeter data).
• The analysis of the numerical retracking algorithm [3] to process S6-MF C-band data and its performance evaluation compared to the conventional MLE3 solution.
References:
[1] Buchhaupt, C., Fenoglio, L., Becker, M., & Kusche, J. (2021). Impact of vertical water particle motions on focused SAR altimetry. Advances in Space Research, 68(2), 853-874.
[2] Buchhaupt, C., Egido, A., Smith, W. H., & Fenoglio, L. (2023). Conditional sea surface statistics and their impact on geophysical sea surface parameters retrieved from SAR altimetry signals. Advances in Space Research, 71(5), 2332-2347.
[3] Dinardo, S. et al. (2023). Sentinel-6 MF Poseidon-4 Radar Altimeter: Main Scientific Results from S6PP LRM and UF-SAR Chains in the First Year of the Mission. Advances in Space Research.
[4] Mangilli, A. et al. (2022). Fast-Adaptive: a new, optimal, unbiased and computationally efficient retracking solution for the analysis of conventional altimetry data. Oral presentation, OSTST.
[5] Tourain, C. et al. (2021). Benefits of the adaptive algorithm for retracking altimeter nadir echoes: Results from simulations and CFOSAT/SWIM observations. IEEE Transactions on Geoscience and Remote Sensing, 59(12), 9927-9940.