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".
 
Continue reading

Watching ice shelfs 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.
 

Continue reading

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.

Continue reading

Chambord flooding: An update to "Mapping flooded areas using Sentinel-1 in Google Earth Engine" from Simon

Short after working with Simon on the script for the  article about the mapping of flooded areas, I wanted to be sure that our short script was realistic. I had some time to loose at the airport, so, after finding a wifi connection, I looked for pictures of the flooded areas of the north of France. I found some impressive pictures of the damages like the hippodrome of Mesnil Le Roy and surrounding places, but the most stunning one was surely this aerial view of Chambord.

Francis the 1st was the king of France during the first part of the XVI century. After winning the battle of Marignano, he decided to build a castle to its own glory. The castle is actually located 5 km south of the Loire river in between the cities of Blois and Orleans. The small Cosson river also crosses the park as can been seen on the aerial view. The Cosson overflowed at the end of May 2016 causing damages to the castle estimated in between 0.5 and 1 million euros.

After doing some slight adjustment to the original script, I exported the result from Earth Engine as a Geotiff file and encapsultated it into a KMZ file to load into Google Earth. Some people had already prepared a 3D model of the castle, so it was quite easy to create this  3D view.

Well, I'm really sorry for King Francis, but it seems our first guess of mapping flooded areas was not bad at all.

Mapping the Glacier Bay landslide using Sentinel-1 and Sentinel-2

Dave Petley wrote a nice article in the AGU's Landslide blog about a massive landslide in Glacier Bay, Alaska. This huge avalanche of debris was spotted by a local pilot Paul Swanstrom on June 28. When Paul was above it, "dust was still flying". Later, based on earthquake records in Alaska, the experts figured out that it probably happened at 8:21 am on the same day.

Photo of the the Glacier Bay landslide in Alaska by Paul Swanstrom - MountainFlyingService (click on the image to see the Facebook photo album)

 

Continue reading

Mapping flooded areas using Sentinel-1 in Google Earth Engine

Exceptional rainfall in May caused heavy flooding in the Paris region. Newspapers and TVs reported that the Seine flood forced the Louvre staff to move away from rising waters the art pieces that were stored in their cellar. But they did not tell you that about 50 km east of the Louvre museum, the flood of the Grand Morin river in Coulommiers also inundated the cellar of my parents-in-law. I'm really concerned about this cellar because I care about my parents-in-law of course, and also because I have let some of my bottles of wine in their cellar. Continue reading

Réfléchissez deux fois avant d'utiliser Google Earth Engine

=> L'une des tendances que l'on pouvait observer au Living Planet Symposium 2016, est l'utilisation croissante de Google Earth Engine. Pour ceux qui ne connaissent pas encore, Google met à disposition des utilisateurs de données de télédétection une plate-forme avec grosse puissance de calcul, bibliothèques et l'accès aux  données ouvertes, dont celles de LANDSAT et des Sentinel,  gratuitement tant qu'on ne dépasse pas certaines limites de stockage de données.  Google en retire une connaissance  des besoins des utilisateurs et des traitements et applications qu'ils développent, et améliore son image de marque (du "green washing")

Problèmes

Je vais répéter ici ce qu'à dit Jordi au Living Planet Symposium et ce qu'il a également expliqué dans son blog : l'utilisation de cette plate-forme est risquée et dangereuse.

Si vous travaillez sur GEE, sachez que :

  • vous n'avez pas les données
  • vous n'avez pas les machines
  • vous n'avez pas les codes

Les travaux que vous développeriez sur cette plate-forme ne pourraient donc pas être répétés ailleurs. Non seulement vous fourniriez donc un tas d'informations à Google, mais en plus, vous ne pouvez plus quitter GEE sans devoir reprendre vos travaux à zéro.

Mauvais scénarios

Voici quelques scénarios tout à fait plausibles mais non moins désagréables :

- google retire le service (c'est arrivé souvent à de nombreux services proposés par google): celà aurait à peu près le même effet qu'un incendie dans votre laboratoire (pendant l'absence du personnel). Plus de données, plus de machines, plus de codes qui tournent, on repart à zéro. Les clauses d'utilisation permettent tout à fait à Google d'arrêter leur service unilatéralement :

7.4 Termination for Convenience. Customer may stop using the Services at any time with or without notice. Customer may terminate this Agreement for its convenience at any time on prior written notice and upon termination, must cease use of the applicable Services. Google may terminate this Agreement for its convenience at any time without liability to Customer.

- google rend le service payant ou le vend à un autre industriel (c'est déjà arrivé aussi): vous devez donc payer cher pour continuer à l'utiliser, ou tout redévelopper chez vous.

- google modifie ses bibliothèques : vos chaînes ne donnent plus les mêmes résultats et vous devez en refaire toute la validation.

Alternatives ?

Ceci dit, le succès de la plate-forme montre qu'elle correspond à un besoin. C'est vrai qu'il est parfois plus long de télécharger la donnée que de la traiter et qu'un traitement à proximité des données permettrait de gagner beaucoup de temps. Mais il nous faudrait des plate-formes basées sur l'utilisation de logiciels open source, que l'on pourrait aussi faire tourner sur ses propres machines. Il est vrai qu'à part GEE, nous sommes plutôt démunis en Europe, à ma connaissance, malgré l'existence de nombreux démonstrateurs publics et moins ambitieux(PEPS, TEP, MEP), ou semi privés, mais largement financés par le public (Helix Nebula, SparkInData...). Pour ma part, je ne vois qu'un organisme public, ou une fédération d'organismes publics qui permettraient de monter une plate-forme libre du niveau de celle de Google, mais cette opinion, que certains qualifieront de passéiste et rétrograde, et qui manque certainement d'imagination, n'engage que moi.

Ceci dit, il y a les exemples pas tout à fait passéistes et rétrogrades du datacube australien, ou de la plate-forme NEX de la NASA.

Mon inventaire des plate-formes disponibles présente probablement des lacunes, n'hésitez pas à nous les signaler en laissant des commentaires..

 

Some news about Sentinel-2 from Living Planet Symposium

 

If I haven't posted for more than a week, it is because I have been participating to the Living Planet Symposium 2016 in Prague. With the preparation, travel, and participation to this crazy symposium. I say crazy because it is packed with about 3000 people, of which I know only about 300. When you want to go from a room to another, it takes as much as 20 minutes as you meet at least 3 or 4 of your colleagues and have a chat. But I do not need to tell you, as very likely, you were there too !

One of the 6 to 8 rooms, packed with people at the same time

 

The good news is that I have had access to a lot of information. I will start by some news about Sentinel-2 of course. Some of these news are not good.

  • The launch of Sentinel-2B has been postponed by to 2017, probably between March and June, due to a delay with the Rockot launcher. This is very annoying as accounting with the time needed for the commissioning phase, it means we will only rely on a 10 days repetitivity during modt of 2017.
  • The availability of Sentinel-2 ortho-rectified data with ground control points has also been postponed to the end of 2016, while initially it was planned in June. ESA says it is due to the fact that the global reference images (GRI) are not ready yet worldwide. We thus will have to cope with registration errors of about 1 pixel within the same orbit and 2 pixels when comparing data from 2 orbits. ESA had announced last year that they would introduce the reference data per continents starting by Europe, but it seems they changed their minds. Still I was told that the GRI for Europe and Australia are available or will be very soon, so why not starting a prodution of ortho-rectified data on those continents ?
  • ESA is also going to change and shorten the very long names of their products and start to distribute data tile wise. Of course, this is good news as the choices made before were not convenient, and it is better correcting it now, as the data backlog is short, but it means everyone will have to change his software. This might delay several productions downstream ESA ground segment.
  • ESA has published a new version of Sen2cor, which is said to seriously enhance the scene classification which was really bad in the previous version, especially for its cloud and cloud shadows mask. I will test it of course, as soon as I find some time.

 

This image background image is a monthly synthesis of Sentinel-2 images of august 2016, covering the whole Czech Republic. It was processed by MACCS to level 2A  and then to level 3A by the synthesis method we developed at CESBIO and implemented within Sen2Agri package. The overlayed landcover map itself was generated by GISAT in the Czech Republic based mainly on Sentinel-1 data, as Sentinel-2 data last summer were still quite scarce. This poster was shown on the 10x10m advert on the congress centre, alternating with a nice bikini (sorry, I only have the Sentinel image !)

 

I have been very positively surprised by how our user community has started using the time series, instead of using images only. It is clear we have entered a new chapter of remote sensing history on the application side, with much more robust results. The case studies based on one image have completely disappeared on the presentations, even if they are still present on the posters. Sentinel-1 examples were impressive and joint uses of both Sentinels 1 & 2 are rising. As the recently launched Sentinel-3A seems to be working well, it is clear ESA has set up a great system Europe can be proud of. And on top of that, ESA really know how to organise a symposium !