MERCATOR OCEAN JOURNA: 
SEPTEMBER 2021 
great circles is included. Also, a Level-4 gridded product 
was added to the catalog to provide SWH maps based on 7 
altimetry missions merged together. Finally, the relevance 
of the along-track SWH for data assimilation was 
strengthened by adding a collocated wind speed derived 
from altimeter measurements. 
The spatial and temporal coverage of measurements Is 
critical for users and one of the main assignments to the 
WAVE-TAC is to integrate new missions as soon as they 
have passed the Calibration/Validation phase. The 
constellation was consolidated with up to 9 missions 
zurrently available in Near-Real-Time (NRT): Jason-3, 
Sentinel-3A, SARAL/AltiKa, CryoSat-2, Sentinel-1A & 1B, 
sentinel-3B, CFOSAT and HaiYang-2B. The new exploratory 
French-Chinese mission CFOSAT, with the Surface Wave 
Investigation and Monitoring (SWIM) instrument onboard, 
is dedicated to the observation of surface waves. Nadir 
measurements were integrated in 2020 in the Level 3 SWH 
product, and the expected added-value of CFOSAT mission 
will soon be highlighted with the provision of Level-3 
partitioned wave spectra by the end of 2021. 
Finally, the WAVE-TAC also has had a role to investigate and 
to communicate on product quality. Continuous efforts 
have been made to implement new methods of validation 
and to facilitate the uptake of Copernicus Marine Service 
wave products by both internal and external users. 
1. MAIN ACHIEVEMENTS 2017-2021 
1.1 Consolidation of the constellation 
The production and dissemination of the first Copernicus 
Marine Service altimeter wave products started mid-2017 
within the SL-TAC using observations derived from Jason-3 
and Sentinel-3A altimeter missions. Since 2018, and the 
creation of the WAVE-TAC, the constellation has been 
constantly growing. First, in 2018, two secondary drifting 
missions SARAL/AltiKa and Cryosat-2 were added to the 
system. Then, the Copernicus Sentinel-3B mission, 
interleaved with Sentinel-3A, was integrated in 2019, 
optimizing the spatial sampling of measurements. Finally, 
CFOSAT nadir and HaiYang-2B were added to the system in 
2020. As shown on Figure 1, the consolidation of the 
altimetry constellation resulted in a significant increase of 
the spatial and temporal density of observations since 2017. 
In 2018, SAR missions Sentinel-1A and 1B were integrated 
in Copernicus Marine Service wave products for the first 
time to provide Level-3 SAR-derived ocean wave spectra, 
referred to as Level-3 SPC pnroduct 
Today, the wave service is processing measurements on 
the-fly, derived from a constellation of up to 9 satellites. 
This operational system requires numerous adjustments 
to adapt to the upstream product evolutions and potentia! 
incidents. Constant monitoring and adaptation are essentia. 
to guarantee consistent and qualified products deliverec 
on time for data assimilation and other NRT applications. 
1.2 Altimeter wave products 
Altimetry measurements are processed in two types of 
products: Level-3 along-track SWH and multi-mission 
Level-4 gridded SWH. 
Level-3 SWH product consists in along-track SWF 
measurements, derived from 7 altimetry missions. 
Measured values are edited using threshold and flags 
criteria to remove erroneous values. Measurements are 
then cross-calibrated onto the reference mission Jason-3 
to ensure consistent and bias-free values across al 
missions. This cross-calibration depends on SWH values 
and is computed by comparing values at crossovers for at 
least a year (when possible). This product benefited from 
several scientific evolutions since the beginning of the 
Wave service. 
First, the editing was reinforced by adding a criterion based 
an a maximum SWH root mean square dispersion as a 
function of SWH to eliminate potential erroneous data, as 
axplained in Queffeulou (2016). 
Then, another evolution reduced the noise of measurements 
by applying a filter based on Empirical Mode Decomposition 
'EMD). EMD consists in decomposing the signal into so- 
zalled intrinsic mode functions. These functions are 
zomputed with an iterative process on the input signal 
they are therefore signal-dependent). This is particularly 
well suited for signals that present noise distribution 
variability, such as SWH. The implementation of this new 
denoising method followed the work of Kopsinis anc 
McLaughlin (2009) and the specific tuning for SWH signa: 
proposed by Quilfen and Chapron (2019). 
“he comparison of Level-3 SWH with in-situ measurements 
shows a satisfying match, with a root mean square 
difference (RMSD) ranging from 4 to 10 cm, depending on 
the mission and a correlation coefficient above 0.98. 
Finally, wind speed derived from altimeter measurements 
was added as a new field in the Level-3 SWH datasets. This 
avolution addressed a specific user need to get wind speed 
collocated to wave height values. It led to a better assimilation 
in wave models and a better understanding of sources of 
errors, whether they depend on the foreing or on the wave 
model. As for SWH, wind speed measurements are editec 
and cross-calibrated onto the reference mission Jason-3.