As every month, Peter Kettig from CNES processed the Sentinel-2 L3A composites of France from the Month before. The data can be downloaded from Theia's distribution server at CNES.
If you are not afraid to spend too much time while you have urgent things to do, you may have a look to the mosaic of Sentinel-2 monthly syntheses for each month since July over France. Each monthly synthesis is accessible using the following links :
Or you may also use the nive viewer below (merci à Michel Lepage !) to compare with the previous months and see how France starts to become slightly greener, at least in the North, while the mountains are getting brown after the first cold days, and corn is drying in the South West.
It is also the opportunity to observe our first neat swath edge effect in four months, near Cambrai, North of France. The Western part of the artefact is browner than the Eastern part. Because of the cloud cover, the average date used in the eastern part is several days before the average date of the western part. The only way to reduce the effect is to increase the revisit time of Sentinels, with the future generations, to allows us to reduce the synthesis window length which is currently 45 days.
See it full screen
The monthly syntheses are produced using the WASP processor, which is described here.
By comparing the various syntheses, you will see the evolution of the landscape, generally a little greener in October, but this representation will also help you spot the composite artefacts. These are not very numerous, but you will see them :
- on some web browsers (firefox V58), geometrical differences appear even at a low resolution. Other browsers and versions do not have this defect. It is really not due to Sentinel-2 or Theia products
- above water and snow (we must work on this defect)
- where clouds have covered a place during the whole month of July or August. These pixels are flagged as invalid in the products (but not on the mosaic).
- where clouds or shadows were not properly detected by MAJA
- at the edges of Sentinel-2 swath (but the effect is really faint)
- some tile edges in July, due to the fact that Level 3A products were not all generated for the 15th of July, but for dates between the 8th and the 26th. This has been corrected for August and September.