Xe-Namnoy lake dam failure

[This post was written by Simon Gascoin and Sylvain Ferrant]
 

The Lao News Agency reported that the Xe-Pian Xe-Namnoy dam collapsed on Monday causing catastrophic flash floods. "The disaster has claimed several human lives [and] left hundreds of people missing," the agency reported. Construction of the Xe-Pian Xe-Namnoy dam began in 2013. Commercial operations were expected to begin in 2018. The animation below shows the water filling using a time series of Sentinel-1 images (IW orthorectifed VV only descending orbits).
 
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Speed-up downloads from PEPS S2 mirror site with peps_download.py

The French Sentinel mirror site, PEPS, has a very clever data management facility. All the products are stored on tapes, with a capacity of several PB, and there is some sort of cache made of disks. The products accessed recently are on disks, while the other products stay on tapes. The storage costs and also power consumption are therefore largely optimized.

 

The drawback is that before accessing a file on tape, some time is needed to get the tape, and read the file on tapes. This can take something like 2 to 10 minutes. My little tool, peps_download.py was designed when most of the products were on disks, and it was quite slow to download products on tapes. As I am not a patient person, I have tried to speed it up, and it works well, thanks to good advise from CNES peps  colleagues (Christophe Taillan and Erwann Poupart).

 

The previous version was working like that :

Make catalog request

For all product in the request result :

- while product is not downloaded

 - try to download the product

 - if still on tape, wait for 2 minutes

As a result, for each product on tape, it was necessary to wait for 2 to 10 minutes.

 
Now, it works like that

Make catalog request

For all products on tape in the request result

- ask to read it on disks

While (still some products to download):

- Redo catalog request

- Download products on disk

- If some products are not on disk yet

 - wait for 2 minutes

 
On my computer, it used to take more that 12 hours to download 2 years of Sentinel-2 data for a given tile. It has now been reduced to less that 3 hours (but my computer is on CNES network). I hope you will have similar results !

From Multitemp blog to Nature Geoscience

You probably remember Simon Gascoin's story about the Aru glacier avalanches, which started from Simon's observations of the twin avalanches using the Sentinels. It was one of the big buzz pages of the blog in 2016. The first images were published here, then spread out in many scientific websites and the social networks.

 

The same mountain valley in Tibet is shown before and after part of a glacier sheared off on 17 July 2016. Credit: NASA/Joshua Stevens/USGS/ESA

It seems that the story finally made its way to Nature Geoscience, after a large work from many scientists lead by Andreas Kaab.  Congratulations to all the team !

 

So, dear CESBIO colleagues, or remote sensing time series users, it is time to submit your work to this blog as a first step to future publications in Nature ;) !

 

 

Soil moisture maps at a high resolution over Occitania region

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Translated from Theia website.

The Theia forges just released a new product based on Sentinel-1 and 2 data. Le "High resolution soil moisture" Scientific Expertise Center, driven by Nicolas Baghdadi, from Tetis lab in Montpellier and Mehrez Zribi from CESBIO, distributes Soil Moisture maps from the French Occitania region at 20 m resolution, produced every sixth day from September 2016 to May 2017.

Soil Moisture maps for 2 Sentinel-1 images from the 19th and 26th of January 2017, over a part of Occitania région. On the 19th of January, the soil is dry with a moisture between 5 and 15 vol.%. After some precipitations, on the 26th of January 2017, moisture increases between 25 and 35 vol.%.

Des cartes d’humidité du sol à haute résolution en Occitanie

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Article rédigé à partir des articles du site Theia.

Les forges de Theia viennent de mettre à disposition un nouveau produit basé sur les données Sentinel 1 et 2. Le CES “Humidité du sol à très haute résolution spatiale”, animé par Nicolas Baghdadi, du laboratoire Tetis à Montpellier et Mehrez Zribi du CESBIO, propose des cartes d’humidité du sol sur la région Occitanie à l’échelle sub-parcellaire élaborées tous les 6 jours de septembre 2016 à mai 2017.

Cartes d’humidité des sols pour deux images Sentinel-1 du 19 et du 26 janvier 2017 sur une petite zone de la région Occitanie. La carte du 19 janvier 2017 montre que le sol est sec avec des valeurs d’humidité entre 5 et 15 vol.%. La carte du 26 janvier 2017, après des précipitations, montre des humidités entre 25 et 35 vol.%.

Deux gros glaçons quittent l'Antarctique

L'Antarctique sort à peine de sa torpeur hivernale que déjà deux évènements majeurs viennent de se produire sous l’œil de Sentinel-1.
 
Le 12 juillet dernier, une crevasse géante à fendu la barrière de glace Larsen C [1], mais il a fallu attendre que la banquise desserre son étau en septembre pour que l'iceberg A68 commence à dériver. Ce glaçon couvre une superficie de 5800 km² (les deux tiers de la Corse).
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Flooded areas in Houston by Sentinel-1

Hurricane Harvey hit Texas on August 25. The first Sentinel-1 image of Houston since landfall was acquired on Aug 29 at 00:26 UTC. I'm writing this post at 21:09 UTC. As reported by the local news website chron.com "The most severe flooding is around the Highway 90 and Eastgate areas". This is also what we can see on the image comparison below: dark areas are flooded areas:

Click on this link to see in full screen. Or check by yourself in the EO Browser.

Below is a zoom between Dayton and Highway 90 (full screen):

Images are orthorectified VV backscatter in dB (-20 dB is black, 0 dB is white). The backscatter intensity received by Sentinel-1 drops over flooded soil because the emitted electromagnetic waves bounces off the water surface and thus do not return to the antenna (as explained in this post).

Les Sentinels témoins de la déforestation en Amazonie

Le Monde.fr a publié un reportage frappant "Au Brésil, avec les policiers qui luttent contre la déforestation de l’Amazonie". Le journaliste et photographe Bruno Kelly a suivi les agents de l’institut pour l’environnement et les ressources naturelles renouvelables (Ibama) dans les environs d'Apui, une petite localité isolée au sud de l'état d'Amazonas. Il écrit que "le chef de la police reconnaît que contrôler avec 1 300 agents une zone de la taille de l’Europe occidentale est une tâche pour le moins difficile".
 
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Watching ice shelves break up with Sentinel-1

The animation below shows the evolution of Thwaites glacier eastern ice shelf in West Antarctica, from July 2016 to May 2017. I made it with 45 quicklooks of Sentinel-1 radar images processed by the Alaska Satellite Facility and available via the vertex data portal. All images were acquired in interferometric wide swath mode (polarization HH, only ascending passes, path: 65, frame: 914) and projected to ground range.
 

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New version of PEPS (French Sentinel mirror site)

As you probably know, PEPS is the French Collaborative ground segment for Copernicus Sentinel program. And, first of all, it is a mirror site that distributes all the Sentinel data in near real time. These last weeks, real time was not available for Sentinel-2, as the data format and structure of Sentinel-2 products had deeply changed, and the software needed adaptation. PEPS team created a new collection, named "Sentinel-2 Single Tiles", coded "S2ST" to separate the old format from the new one. Now that the new version has been installed and validated, the PEPS mirror site is once again up to date.

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