29 Sep 2022
29 Sep 2022
Status: this preprint is currently under review for the journal ESSD.

Refining the resolution of DUACS along track (level 3) altimeter Sea Level products

Marie-Isabelle Pujol1, Stéphanie Dupuy1, Oscar Vergara1, Antonio Sánchez-Román2, Yannice Faugère1, Pierre Prandi1, Mei-Ling Dabat1, Quentin Dagneaux1, Marine Lievin1, Emeline Cadier1, Gérald Dibarboure3, and Nicolas Picot3 Marie-Isabelle Pujol et al.
  • 1CLS, 11 rue Hermès, Parc Technologique du Canal, 31520 Ramonville St Agne, France
  • 2IMEDEA, C/Miquel Marquès, 21 – 07190 Esporles – Illes Balears, Spain
  • 3CNES, 18 avenue Edouard Belin, 31401 Toulouse Cedex 9, France

Abstract. This paper describes a high-resolution Level-3 (L3) altimeter Data Unification and Altimeter Combination System (DUACS) experimental regional product developed with support from the French space agency (CNES). Deduced from full rate (20 Hz to 40 Hz) Level-2 (L2) altimeter measurements, this product delivers Sea Level Anomalies (SLA) and other essential physical variables with a nearly 1-Km sampling over the North Atlantic 0cean. It allows us to resolve wavelengths from ~35 km to ~55 Km depending on the altimeter considered. This was made possible by recent advances in radar altimeter processing for both Synthetic aperture Radar (SAR) and Low-Resolution Mode (LRM) measurements, and improvements made to different stages of the DUACS processing chain. Firstly, the new adaptive and LR-RMC (Low Resolution with Range Migration Correction) processing techniques were considered for Jason and Sentinel-3 (S3A) respectively. They significantly reduce errors at short wavelengths and, for the adaptive processing, possible land contamination near the coast. Next, up-to-date geophysical and environmental corrections were selected for this production. This includes specific corrections intended to reduce the measurement noise on LRM measurement and thus enhance the observability at short wavelengths. Compared to the 1 Hz product, the observable wavelength reached with the experimental high-resolution product are reduced by up to one third, or up to half in the North-East Atlantic region. The residual noises were optimally filtered from full rate measurements taking into consideration the different observing capabilities of the altimeters processed. A specific data recovery strategy was applied, significantly optimizing the data availability both in the coastal and open ocean. This experimental L3 product is thus better resolved than the conventional 1 Hz product, especially near the coast where it is defined up to ~5 km against ~10 km for the 1 Hz version. The multi-mission cross-calibration processing was also optimized with an improved Long Wavelengths Error (LWE) correction leading to a better consistency between tracks with an 9–15 % reduction of SLA variance at cross-over. The experimental L3 product improves the overall consistency with tide gauge measurements with a reduction of the variance of the SLA differences by 5 and 17 % compared to the 1 Hz product from S3A and Jason-3 (J3) measurements respectively. Primarily intended for regional applications, this product can significantly contribute to improving high resolution numerical model outputs via data assimilation. It also opens new perspectives for a better understanding of regional sea surface dynamics, with an improved representation of the coastal currents and a refined spectral content that reveals the unbalanced signal.

Marie-Isabelle Pujol et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CEC1: 'Comment on essd-2022-292', Giuseppe M.R. Manzella, 25 Nov 2022

Marie-Isabelle Pujol et al.

Data sets

SSALTO/DUACS along-track Sea Level Anomalies at 5Hz Experimental products Pujol, M.-I., Dupuy, S., Vergara, O., Sánchez-Román, A., Faugère, Y., Prandi, P., Dabat, M.-L., Dagneaux, Q., Lievin, M., Cadier, E., Dibarboure, G., and Picot, N.

Marie-Isabelle Pujol et al.


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Short summary
An altimeter sea level along-track level-3 product with a 5 Hz (~1.2 km) sampling is proposed. It takes advantage of recent advances in radar altimeter processing, and improvements made to different stages of the processing chain. Compared to the conventional 1 Hz (~7 km) product, it significantly improves the observability of the short wavelength signal in open ocean and near coast areas (> 5 km). It also contributes to improving high resolution numerical model outputs via data assimilation.