After France monthly synthesis generated from Sentinel-2 data in July 2018, the monthly syntheses have become ... monthly. The new composite products for France from August 2018 are now available from Theia, using the WASP processor.
As a few days ago, we did a visualization of the mosaic at 20m resolution. You just need to click to on the links below to see them
But of course, we are interested in comparing the two. A very nice visualization was set-up by Michel Le Page, who also found the post title (Merci Michel !). Beware, do not go further if you have something urgent to do.
See it full screen
By comparing the two, you will see the evolution of the landscape, generally much dryer, with a lot of fields cropped, 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.
An earthquake with magnitude 6.7 occurred on 06 Sep 2018 in Hokkaido, Japan, killing at least 17 people and leaving nearly 3 million households in Hokkaido without electricity.
The quake came two days after typhoon Jebi, "the strongest storm of 25 years".
Below is an image comparison near Atsuma dam lake in the south of Hokkaido, before and after the earthquake, showing multiple landslides in the forest areas. Both images were acquired by Sentinel-2 and are shown as false color composites of bands 11-8-2. Click here to view a larger version.
The heavy rainfalls brought by typhoon Jebi probably explain why the earthquake triggered so many landslides. I would like to count the landslides in this area, but the Sep 15 image is not yet available in my favorite image processing engine. I will check later.
- in the AGU landslide blog
- Google published a crisis map but it seems that the imagery is not publicly available
Thanks to Laurent Longuevergne for letting me know about this!
Update (September 13th) : Both incidents are solved and production is resumed
Two incidents happened on MUSCATE production center.
- the authentication on the distribution server is not working any more, and as a result, it is not possible to download products.
- CNES HPC center has been stopped yesterday, due to a breakdown on the disk storage facility, stopping the production. We will have to catch-up a backlog when the production resumes.
The technical teams are working on the issues and we hope the production and distribution will resume before the end of the week. We apologize for any inconvenience.
UPDATE: resolution improved to 20m !
I had to tinker a couple of days with Theia's Sentinel-2 monthly syntheses, in order to produce the mosaic below. For that, I used:
- monthly syntheses of Sentinel-2 L3A products delivered by Theia in July 2018; this products are made from Level2A products, corrected from atmospheric effects, and provided with a good cloud mask, thanks to MAJA processor. Such L3A products will be delivered every month.
- a script developed by Simon Gascoin
- good advice from Simon and Michel Le Page
- and Gdal, (Thanks Gdal !)
This mosaic best resolution is 20m. It is already requiring 8 GB. We could have provided it at 10m resolution, but it would have required 32 GB and several dozens of hours of computation.
See it full screen
UPDATE: résolution améliorée à 20m !
Voilà, après quelques jours de bidouille, j'ai réussi à produire la mosaïque de la France à partir:
- des synthèses mensuelles de produits Sentinel-2 de Niveau 3A fournis par Theia en juillet 2018; Ces produits sont réalisés à partir de données de niveau 2A, corrigé des effets atmosphériques, et avec une bonne détection des nuages, grâce à la chaîne MAJA. Ces données seront produites tous les mois
- du script mis au point par Simon Gascoin
- des conseils avisés de Simon et de Michel Le Page
- et de Gdal, (Merci Gdal !)
La mosaïque vous est présentée à 20m de résolution, elle occupe déjà 8GO. Il aurait été possible de la produire à 10m, mais il aurait fallu 32 GO et quelques dizaines d'heures de plus.
Voir en plein écran
In the Landslide blog Dave Petley has analyzed Planet images of the Pashgor debris flow in Afghanistan (here and here). Here I used two Sentinel-2 images (before and after the event) to show the path of the debris flow from the high mountain area to the Panjshir Valley. Sentinel-2 images have a lower spatial resolution than Planet images but they have a larger swath and the near-infrared channel is useful to highlight the water-rich surfaces (dark blue) and the vegetation (red). Also, Sentinel-2 images are free to use for everyone.
According to the experts this event can be called a jökulhlaup since it was due to the abrupt collapse of a supraglacial lake, i.e. a lake formed on the surface of a glacier, in this case a debris-covered glacier. The debris flow (a mix of water and debris) has traveled 13 km from the source to the deposit area where it has dammed the Panjshir river.