DUACS DT2018: 25 years of reprocessed sea level altimetry products

Abstract

For more than 20 years, the multi-satellite Data Unification and Altimeter Combination System (DUACS) has been providing near-real-time (NRT) and delayedtime (DT) altimetry products. DUACS datasets range from along-track measurements to multi-mission sea level anomaly (SLA) and absolute dynamic topography (ADT) maps. The DUACS DT2018 ensemble of products is the most recent and major release. For this, 25 years of altimeter data have been reprocessed and are available through the Copernicus Marine Environment Monitoring Service (CMEMS) and the Copernicus Climate Change Service (C3S).Several changes were implemented in DT2018 processing in order to improve the product quality. New altimetry standards and geophysical corrections were used, data selection was refined and optimal interpolation (OI) parameters were reviewed for global and regional map generation. This paper describes the extensive assessment of DT2018 reprocessing. The error budget associated with DT2018 products at global and regional scales was defined and improvements on the previous version were quantified (DT2014;Pujol et al., 2016). DT2018 mesoscale errors were estimated using independent and in situ measurements. They have been reduced by nearly 3 % to 4 % for global and regional products compared to DT2014. This reduction is even greater in coastal areas (up to 10 %) where it is directly linked to the geophysical corrections applied to DT2018 processing. The conclusions are very similar concerning geostrophic currents, for which error was globally reduced by around 5 % and as much as 10 % in coastal areas.

Ship- and island-based atmospheric soundings from the 2020 EUREC<sup>4</sup>A field campaign

“…MeteoModem M10 radiosondes were chosen for availability and cost. In order to decide the period of intensive sampling using these sondes, we first identified on a daily basis the ocean mesoscale eddies and currents by applying the TOEddies detection algorithm (Laxenaire et al, 2018) to the Ssalto/Duacs Near Real Time (NRT) altimeter products (Absolute Dynamic Topography -ADT -and the associated surface geostrophic velocities; Ablain et al, 2017, Taburet et al, 2019. These data were successively analyzed together with the Near Real Time (NRT) SST produced by Collecte Localisation Satellites (CLS), the ship's ThermoSalinoGraph (TSG) 5 m-depth temperature measurements, and ARPEGE and ECMWF forecasts in order to decide in real time the launching strategy.…”

Integration of HF Radar Observations for an Enhanced Coastal Mean Dynamic Topography

“…For the computation of a time series of daily ADT maps (coastal MDT + SLA, referenced to 1993-2012), SLA maps from the regional European DT2018 product (Taburet et al, 2019) over 2009 to 2018 have been selected. Additional SLA maps from the Global DT2018 products (Taburet et al, 2019) have been used within the in situ data processing (section "Drifters and T/S Profiles").…”

“…For the year 2018, daily ADT maps over the Bay of Biscay are computed by adding the coastal MDT to the SLA (both referenced to 1993-2012) from the European DT2018 dataset (Taburet et al, 2019). To get closer to the total currents, the Ekman currents obtained using Rio et al (2014) are added to the ADT derived geostrophic currents.…”

“…To get rid of geoid errors, oceanographers work with Sea Level Anomalies (SLA), computed by removing a Mean Sea Surface above a reference ellipsoid (MSS) from the SSH and therefore, representing the time-dependent variability with respect to a "mean" circulation (e.g., Wunsch and Stammer, 1998). Global gridded SLA fields from several altimetric missions are being produced by data centers such as Copernicus SLTAC (e.g., Taburet et al, 2019), resolving wavelength scales ranging from ∼100 km at high latitudes to ∼800 km in the Equatorial band (Ballarotta et al, 2019). Global geostrophic currents can be derived from the sea level fields, and an approximation to the global currents can be obtained by also considering the wind contribution (Rio et al, 2014).…”

A Major Ecosystem Shift in Coastal East African Waters During the 1997/98 Super El Niño as Detected Using Remote Sensing Data

“…This gridded geostrophic velocity current field product uses all satellite missions and applies the β plane approximation to overcome the geostrophic limitation near the equator (see Pujol et al [44]). This altimetry product version is generated with a specific reprocessing which holds short spatial scale variations (along-track loess filter with a 40 km wavelength cutoff) and a high-resolution tidal correction (see Taburet et al [45]). It is noteworthy that this AVISO product contains long-wavelength error correction which removes correlated noise due to orbit errors or uncertainties in geophysical corrections.…”