MERCATOR OCEAN JOURNA: 
SEPTEMBER 2021 
1.2 Product quality improvement 
and extension the portfolio 
Different evolutions were also implemented with to 
improve the product quality and propose new products and 
variables that better fit users’ needs. 
The SL-TAC upgraded regularly the 30-year timeseries 
through whole reprocessing. They allow to benefit from: up- 
to-date altimeter standards and corrections available in 
upstream L2P product; and improvements done in the 
processing of along-track (L3) and gridded (L4) products over 
global ocean or regional seas. All improvements were also 
simultaneously implemented in the NRT processing chain: 
in 2014, the DT-2014 series were delivered and NRT 
chain upgraded following the DT-2014 standards. 
Implemented evolutions enabled significant 
‚mprovements with a better restitution of the signal 
at wavelengths < 250 km (nearly 10% reduction of the 
variance of the differences between SLA gridded field 
and independent along-track data in high variability 
areas compared to the previous DT-2010 version; Table 
1). The spatial coverage in high latitude areas was also 
improved. This version was also characterized by the 
use of the new 20-year altimeter reference period. 
It Improved interannual signals with more relevant 
intensities and spatial signature (Pujol et al, 2016). 
in 2018, various evolutions at each step of the 
processing were also implemented and defined the 
DT-2018 standards. They improved significantly the 
mesoscale signal in the sub-tropical band and in 
high variability areas (reduction of the variance of 
differences between geostrophic current derived from 
altimetry and independent drifter measurements by 
nearly 5% compared to the previous DT-2014 version). 
Zoastal areas were also improved, with a better 
omparis®5 A EL 
SS 
Open Ocean / Low variability 
Open Ocean / High variability 
Coastal (dist < 200 km) 
consistency of the altimeter gridded product, thanks 
to independent tide gauge and along-track altimeter 
measurement (about -10% variance reduction 
compared to the previous DT-2014 version; Table 1) 
(Taburet et al, 2019). 
-in 2021, a new version of the product is under 
development, with DT-2021 standards. As for the 
previous versions, it will include numerous changes 
at different stages of the processing (upstream 
standards, data selection, cross-calibration, mapping). 
These evolutions are expected to significantly reduce 
the signal error at long-wavelengths for the along- 
track product and at mesoscale for the griddec 
product (expected 17% reduction of the variance 
of differences between SLA gridded field and 
independent along-track data in high variability areas 
compared to the previous DT-2018 version; Table 1). 
In order to better fit users’ needs and applications, new 
products and variables were introduced in the SL-TAC 
zatalogue: 
- different key geophysical corrections were provided 
in the along-track products. They enabled users to 
change the physical content of the sea level altimeter 
field according to their application. First implemented 
in the regional Mediterranean Sea product, this 
change was generalized to all along-track products 
in 2019. In late 2021, a new geophysical correction, 
dedicated to the internal gravity wave signal, will also 
be introduced, 
„the absolute dynamic topography (ADT) and 
geostrophic currents derived from the altimeter 
measurement were introduced as new variables in 
gridded products in 2017. They have facilitated and 
diversified possible applications of this product, 
The MDT field, necessary for ADT computation, was 
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Table 1: Reduction of the budget error between 2 reprocessing versions. Statistics issued from comparison between gridded SLA product and 
ındependent along-track measurement. Results presented for DT-2021 are preliminary and should be consolidated during the final DT-2021 
validation phase.