MERCATOR OCEAN JOURNA: 
SEPTEMBER 2021 
The NRT gridded Level-4 SWH product benefited from 
Juality improvements of Level-3 datasets and from the 
dense coverage of altimeter observations. This product 
provides easy-to-use gridded observational SWH data and 
two types of wave height fields are available. First, daily 
SWH statistics (mean, maximum and standard deviation) 
merging altimeter observations over a 24-hour time 
window onto 2°x2° grid cells. Then, an estimate of the 
instantaneous SWH field at 12UTC each day. A weighted 
average of nearby observations is computed, based on the 
temporal distance between the time of the map and 
observations. Empty cells are filled using spatlal 
interpolation. This estimate was improved by adapting the 
selection time window to the local wave climatology. 
With a 7-satellite constellation, the daily instantaneous 
SWH field filled the gaps left with along-track coverage and 
shows a reasonable agreement with the in-situ buoy 
network, with a RMSD of about 15 cm and a correlation 
coefficient above 0.92. 
<= 
Wavelength 
200 m 
400 m 
600 m 
significant wave height 
) m 
A IT) 
igure 2: Pacific: SAR-derived swell conditions (size of dots indicates the wavelength, colour the wave height and tail the upcoming 
Jirection): Atlantic: Altimetrv-derived alona-track (lines) and gridded (contours) significant wave height