[MUSCATE News] A very productive summer

=>

Updated on October 4th

 

This summer, while most of us were getting sunburnt near the coast, or getting sore legs after hiking in mountains, or having long naps after hectic nights, the lucky MUSCATE teams stayed at work, with a good and efficient air conditioning, convenient armchairs, fast computers and accessed to the best canteen in the world at CNES. So it's no surprise they progressed a lot in all aspects, but even if they benefited from perfect conditions, we should thank them a lot.

 

Improved production performances

Theia's L2A counter reached 100 000 images on August 12th

 

First of all, the colleagues solved the issue that delayed a lot MUSCATE production in late spring. It was a memory issue, with a heavy swap consumption that slowed then crashed the MUSCATE ground segment. Doubling the available memory on the catalogue server solved the issue.

As a result, since beginning of July, MUSCATE had only two interruptions of production, due to maintenance interventions on the CNES platform. As it may be seen below, the monthly average plot in orange shows that the production rate is at its best in two years.

 

Number of L2A produced each day by MUSCATE (after removing the products with more than 90% of clouds)

Continue reading

On-demand SENTINEL2 L2A processing with MAJA on PEPS

Update : added a script to submit and download MAJA jobs on PEPS

 

Getting a Sentinel-2 L2A product (with atmospheric correction and cloud detection) anywhere has never been so easy.  Until now, you had two options to access to Sentinel-2 L2A products obtained from the MAJA processor :

 

 

Starting from today, there is another possibility: an on-demand MAJA processing from the French Sentinel collaborative ground segment PEPS.  The possibility is a proof of concept, and if a lot of people use it at once, we do not know how the processing time will evolve. But the only way to know it is to try it, hoping the processing and download capacity is sufficient. Anyway, it you intend to process a whole country, we hope you are from Belgium, and not from Australia.

 

However, if your site is above 60°N or under 60°S, you are still unlucky, as MAJA needs SRTM DEM to work. We will try to implement the use of Arctic DEM one day.

 

PEPS/MAJA processing page (don't worry, english language is also available)

Continue reading

Spot the 1 000 000 differences

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.

 

Dozens of landslides after the 2018 Hokkaido earthquake

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.
 


 
Links:
- 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!

A seamless and cloudless Sentinel-2 image of France in July 2018

=>
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

Continue reading

Sentinel-2 captured a jökulhlaup in Afghanistan

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.

Belgium at 10 m resolution in July 2018

Using the new L3A product in Theia it is possible to make nice cloud-free mosaics from Sentinel-2 imagery. Here is an example for Belgium and the script to do it in your terminal.

 

Click here to view in full screen.
 


# download L3A images over Belgium
python theia_download.py -l 'Belgium' -d 2018-07-01 -f 2018-07-31 --level LEVEL3A -a config_theia.cfg
# unzip using GNU parallel
parallel unzip ::: SENTINEL2X_201807*zip
# make a mosaic of each band
# WARNING only works if all images have the same projection otherwise an extra step is required with gdalwarp
parallel gdalbuildvrt {}.vrt SENTINEL2X_201807*/*{}*.tif ::: B2 B3 B4
# stack the band mosaics
gdalbuildvrt -separate B432.vrt B4.vrt B3.vrt B2.vrt
# export as a RGB image at full resolution
gdal_translate -ot Byte -scale 0 2000 B432.vrt B432.tif
# Optionally clip the image using the polygon of the Belgium borders

gdalwarp -dstnodata 0 -q -cutline Belgium.kml -crop_to_cutline B432.tif B432_Belgium.tif
# make a tiled map to display in a browser
gdal2tiles.py -z 6-12 B432_Belgium.tif

 

NB) I used this command to generate the file Belgium.kml from the Eurostat Countries datasets:


ogr2ogr -f KML Belgium.kml -where "NAME_ENGL='Belgium'" CNTR_RG_01M_2016_4326.shp

Whitewhashing the Plastic Sea near Almería

Almería province in Spain is "one of the most recognisable spots on the planet from the lens of a passing satellite. The roofs of tens of thousands of closely packed plastic greenhouses form a blanket of mirrored light beaming into space." (The Guardian).

True color image Sentinel-2 on 22 Aug 2018

Greenhouses in Almería are typically made with transparent plastic to increase the air temperature near the crops. This enables to boost the yield and to harvest earlier than in open field. However, in summer, the temperature increases too much and must be reduced to maintain more suitable conditions for plant growth. Natural ventilation is generally not sufficient to evacuate the heat during sunny days. Therefore, the farmers cover the roofs of the greenhouses with white painting to reduce the incoming solar radiation (Baille et al. 2001). This operation is called blanqueo in Spanish.

Continue reading