1126742b-a5da-4fe2-b687-e64d585e138c CERSAT Exploitation fpaf@ifremer.fr editor 2025-01-15T09:04:06.730589Z ISO 19115-3:2018 - Remote Sensing http://www.opengis.net/def/crs/EPSG/0/4326 SASSA Global Along-Track 1 Hz Denoised Sea Level Anomalies from Altimeter 2021-10-19 creation 1.0 Satellite altimeters routinely supply sea surface height (SSH) measurements which are key observations to monitor ocean dynamics. However, below a wavelength of about 70 km, along-track altimeter measurements are often characterized by a dramatic drop in the signal-to-noise ratio, making it very challenging to fully exploit available altimeter observations to precisely analyze small mesoscale variations in SSH. Although various approaches have been proposed and applied to identify and filter noise from measurements, no distinctive methodology emerged to be systematically applied in operational products. To best cope with this unresolved issue, the Copernicus Marine Environment Monitoring Service (CMEMS) actually provides simple band-pass filtered data to mitigate noise contamination in the along-track SSH signals and more innovative and adapted noise filtering methods are thus left to users seeking to unveil small-scale altimeter signals. Here demonstrated, a fully data-driven approach is developed and applied to provide robust estimates of noise-free Sea Level Anomaly (SLA) signals. The method combines Empirical Mode Decomposition (EMD), to help analyze non-stationary and non-linear processes, and an adaptive noise filtering technique inspired by Discrete Wavelet Transform (DWT) decompositions. It is now found to best resolve the distribution of the sea surface height variability in the mesoscale 30-120 km wavelength band. A practical uncertainty variable is attached to the denoised SLA estimates that accounts for errors related to the local signal to noise ratio, but also for uncertainties in the denoising process, which assumes that SLA variability results in part from a stochastic process. Here, measurements from the Jason-3, Sentinel-3 A and SARAL/AltiKa altimeters are processed and analyzed, and their energy spectral and seasonal distributions characterized in the small mesoscale domain. Anticipating data from the upcoming Surface Water and Ocean Topography (SWOT) mission, these denoised SLA measurements for three reference altimeter missions already yield valuable opportunities to assess global small mesoscale kinetic energy distributions. This dataset was developed within the Ocean Surface Topography Science Team (OSTST) activities. A grant was awarded to the SASSA (Satellite Altimeter Short-scale Signals Analysis) project by the TOSCA board in the framework of the CNES/EUMETSAT call CNES-DSP/OT 12-2118. Altimeter data were provided by the Copernicus Marine Environment Monitoring Service (CMEMS) and by the Sea State Climate Change Initiative (CCI) project. Yves Quilfen Ifremer / LOPS yquilfen@ifremer.fr author CERSAT Help Desk cersat@ifremer.fr pointOfContact Ifremer / CERSAT cersat@ifremer.fr publisher Jean-François Piollé Ifremer / LOPS 02 98 22 46 91 Jean.Francois.Piolle@ifremer.fr author https://sextant.ifremer.fr/geonetwork/srv/api/records/1126742b-a5da-4fe2-b687-e64d585e138c/attachments/sassa.png Oceanographic geographical features GEMET - INSPIRE themes, version 1.0 2018-01-01 publication 2018-07-27T14:39:48 publication geonetwork.thesaurus.external.theme.httpinspireeceuropaeutheme-theme Sea Surface Topography Cersat - Parameter 2024-07-26 publication 2024-07-26 publication geonetwork.thesaurus.local.theme.cersat_parameter SASSA Cersat - Project 2024-07-26 publication 2024-07-26 publication geonetwork.thesaurus.local.theme.cersat_project Historical Cersat - Latency 2024-07-26 publication 2024-07-26 publication geonetwork.thesaurus.local.theme.cersat_latency /Sea Surface Topography/Sea Surface Height Cersat - GCMD parameter 2024-01-04 publication 2024-01-04 publication geonetwork.thesaurus.external.theme.GCMDparameter CDS-CERSAT Centre de données ODATIS 2024-10-16 publication 2024-10-16 publication geonetwork.thesaurus.local.theme.odatis_centre_donnees Variables ODATIS 2023-10-13 publication 2023-10-13 publication geonetwork.thesaurus.local.theme.odatis_variables /Observational data/satellite Type de jeux de donnée ODATIS 2024-10-15 publication 2024-10-15 publication geonetwork.thesaurus.local.theme.type_jeux_donnee Sea surface height ODATIS aggregation parameters and Essential Variable names 2023-11-27 publication 2023-11-27 publication geonetwork.thesaurus.external.theme.NVS.OD1 Update Issue validityBegins validityExpires None Free and Open Ifremer / CERSAT. 2021. SASSA Global Along-Track 1 Hz Denoised Sea Level Anomalies from Altimeter dataset (v1.0). Ver. 1.0. Ifremer, Plouzane, France. Dataset accessed [YYYY-MM-DD]. DOI:10.12770/1126742b-a5da-4fe2-b687-e64d585e138c grid 1 oceans -180.00 180.00 -90.00 90.00 Global 2013-03-14 2020-05-31 pass L3 ftp://ftp.ifremer.fr/ifremer/cersat/data/ocean-topography/sassa WWW:FTP FTP CERSAT FTP ftp://ftp.ifremer.fr/ifremer/cersat/data/ocean-topography/sassa/documentation/ESSD_quilfen_2021.pdf WWW:LINK Processing and validation Towards improved analysis of short mesoscale sea level signals from satellite altimetry, Yves Quilfen et al., essd-2021-352 https://www.seanoe.org/data/00753/86455/data/91782.m WWW:LINK Processing and validation Quilfen Yves (2021). EMD-based function (matlab) to denoise measurements of satellite altimeter along-track sea level and significant wave height. SEANOE. https://doi.org/10.17882/86455 https://doi.org/10.12770/1126742b-a5da-4fe2-b687-e64d585e138c DOI Digital Object Identifier (DOI) V1.0