Abstract's details

A new CryoSat-2 regional product for ocean applications: the Cryo-TEMPO Coastal Ocean Thematic Data Product

Francesco Nencioli (CLS, France)

CoAuthors

Salvatore Dinardo (CLS, France); Thomas Zilio (CLS, France); Daguze Jean-Alexis (CLS, France); Antonio Sanchez-Roman (IMEDEA, Spain); Ananda Pascual (IMEDEA, Spain); Sylvie Labroue (CLS, France); Jerome Bouffard (ESA, Italy)

Event: 2022 Ocean Surface Topography Science Team Meeting

Session: Coastal Altimetry

Presentation type: Type Oral

Although the primary focus of CryoSat-2 is the cryosphere, the mission has provided over a decade of key altimetry observations across a diverse range of scientific domains (e.g. Bathymetry, Polar Oceanography, Coastal Ocean and Inland Waters). Due to its Interferometric Synthetic Aperture Radar (SARIn) altimeter, CryoSat-2 was a precursor of the development of Delay Doppler processing (the so called “SAR mode”) for ocean applications. Compared to traditional nadir altimeters, SARIn SAR mode observations are characterized by a much smaller footprint, and hence higher along-track resolution (~300-400 m instead of ~5-7 km), as well as reduced noise level. Over the oceans, these characteristics enable major advancements especially in coastal regions: the higher resolution allows a more detailed representation of the smaller structures (<100 km), while the smaller footprint improves data coverage and precision closer to the coast. Despite these advantages, CryoSat-2 ocean observations remain somehow underutilized in the oceanography community.

The overarching aim of the Cryo-TEMPO project is to develop agile, robust and state-of-the-art CryoSat-2 Products, which are dedicated to specific Thematic Areas, and which are accessible to a broad range of scientific and service users. The coastal ocean is one of the five thematic areas included in the project. The first goal of the Cryo-TEMPO Coastal Ocean Thematic Data Product (TDP) is to maximize the potential of CryoSat-2 observations over the ocean by implementing an ocean-specific processing chain based on the best performing methods and algorithms for coastal applications (and currently not implemented for the production of the official CryoSat-2 ocean products). These methods include, among others: the SAMOSA+ retracker, high-frequency adjustment (HFA) correction, iterative data editing, dedicated sea state bias (SSB) correction and regional mean dynamic topography (MDT). A second goal of Cryo-TEMPO is to expand the user base of its products beyond the traditional altimetry experts by providing an easy-to-use dataset. Thus, the Cryo-TEMPO Coastal Ocean TDP contains only few parameters (i.e. SLA, filtered SLA, flags) compared to traditional level 2 products. Furthermore, each variable is distributed with an associated transparent and traceable uncertainty.

The Cryo-TEMPO Coastal Ocean TDP is currently based on SAR and low resolution mode (LRM) CryoSat-2 observations over the Mediterranean region (-6.4 E to 36.5 E longitude; 30 N to 46 N latitude). Input data to generate the dataset are the official CryoSat-2 GOP baseline-C level1-b products. The Coastal Ocean TDP spans from the beginning of the mission (April 2010) to present, with new CryoSat-2 observations processed and added to the database on a monthly basis. The first version of the product (as well as monthly visualisations of the main variables) is currently available at the Cryo-TEMPO web portal (http://www.cpom.ucl.ac.uk/cryotempo/index.php?theme=coastaloceans). The data will be distributed and freely accessible via the ESA Cryosat science server (https://earth.esa.int/eogateway/missions/cryosat/data). Each year, the methods and algorithms used in the processing chain will be updated and optimized following altimetry expert and user feedbacks and the full Cryo-TEMPO Coastal Ocean TDP reprocessed.

The current version of the product has been compared to the official GOP baseline-C products. Our results show that the Cryo-TEMPO Coastal Ocean TDP is characterized by lower variance (especially in the LRM regions of the domain), indicating improved accuracy of the product. The largest impacts in the product are from the SSB and HFA corrections as well as from the iterative editing. Our analysis included also comparisons with in-situ observations. These include tide gauges sea-level records from the western part of the Mediterranean basin and surface velocities from the SOCIB HF-radar located in the Balearic Sea. Comparison between the Coastal Ocean TDS and tide gauges SLA indicates a good consistency between the two. Correlations are in line with those previously reported for Sentinel-3A and Jason-3 (although with larger root mean square error). Comparison between satellite-based across-track geostrophic currents and those from HF radar also shows good consistency. Furthermore, the errors between the two are smaller than previously reported in the same region from an analogous comparison using Saral-Altika altimeter observations, instead.
 

Oral presentation show times:

Room Start Date End Date
Sala Pasinetti Wed, Nov 02 2022,11:00 Wed, Nov 02 2022,11:15
Francesco Nencioli
CLS
France
fnencioli@groupcls.com