Synthèses mensuelles de la durée d'enneigement dans les Alpes françaises

Pour le Conservatoire botanique national alpin j'ai généré les cartes de durée d'enneigement par mois (avril, mai, juin et juillet) pour 2016, 2017 et 2018 à partir de toutes les images Sentinel-2 et Landsat-8 disponibles chez Theia sur les Alpes (tuiles 31TGM 32TLS 31TGL 32TLR 31TGK 32TLQ). Normalement la méthode est conçue pour faire des synthèses annuelles donc j'étais curieux de voir le résultat au pas de temps mensuel.

Sentinel-2 sees caterpillars nibbling French forests


One of my colleagues from CESBIO and CNES, a specialist in automatic classification methods and creator of free software named after Monteverdi's opera, told me that during his last Sunday walk in the Bouconne forest, the trees were being devoured by caterpillars. By listening, you could even hear them nibbling on the leaves. Even if he doesn't have my exaggeration tendencies, I wanted to check with my favourite satellite, Sentinel-2.

The image below compares, in false colours (the more red the vegetation is, the more vigorous the vegetation), the images acquired on 5 July 2017 and 5 July 2019 (the same period was cloudy in 2018). The differences are impressive, the red colour fades and almost disappears in places.

False color comparison (vegetation appears red) of Sentinel-2 level 2A images (processed by Theia) acquired on July 5, 2017 and 2019 over Boucone Forest near Toulouse. Some forest areas appear darker in 2019, due to the appetite of gypsy moth caterpillar...

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Une attaque à la bombyx vue par Sentinel-2


Un de mes collègues du CESBIO et du CNES, spécialiste des méthodes de classification automatique et créateur de logiciels libres, m'a raconté que lors de sa dernière ballade dominicale dans la forêt de Bouconne, les arbres étaient en train d'être dévorés par des chenilles. En tendant l'oreille, on pouvait même les entendre grignoter les feuilles.  Même s'il n'a pas mes tendances à l’exagération,  j'ai voulu vérifier avec mon satellite préféré, Sentinel-2.

L'image ci dessous compare, en fausses couleurs (plus c'est rouge plus la végétation est vigoureuse), les images acquises le 5 juillet 2017 et le 5 juillet 2019 (la même période était nuageuse en 2018). Les différences sont impressionnantes, la couleur rouge s'atténue et disparaît presque par endroits, signe que les chenilles ont consommé une bonne partie des feuilles.


Comparaison en fausse couleur (la végétation apparaît en rouge) d'images Sentinel-2 de niveau 2A (traitées par Theia) acquises les 5 juillet 2017 et 2019 sur la forêt de Bouconne, près de Toulouse. Certaines zones forestières apparaissent plus sombres en 2019, du fait de l’appétit des larves de bombyx..

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[Theia] Un nouveau bulletin Theia est paru

Le Bulletin n°11 de Theia, préparé par Isabelle Biagiotti, vient de paraître !

Au sommaire

  • les nouvelles du réseau : l’ART Nouvelle-Calédonie, les produits Humidité du sol, la chaîne Maja, la traque des moustiques, l’occupation des sols de la Réunion…
  • des articles sur les missions satellitaire SWOT et Thrishna, la plateforme A2S, Mundi Web Service, le Cospar…
  • un focus sur le produit Neige
  • des échos de recherche sur l’assimilation des données à haute résolution spatiale sur les surfaces terrestres et le suivi de la biomasse
  • deux nouveaux portraits de chercheurs impliqués dans Theia

Lire le nouveau Bulletin

>>> Télécharger le .pdf en version impression
>>> Télécharger le .pdf en version allégée
>>> Lire le Bulletin sur Calaméo
>>> Retrouver les numéros précédents.

Call for experiment ideas for VENµS last phase

The VENµS satellite has two missions, a scientific mission that requires to have the satellite exactly at the same place every second day to make repetitive observations with constant view angles, and a technological payload (IHET, Israeli Hall Effect Thruster) to change the satellite's orbit (that's why there is a blue and a red circle in VENµS's logo). It may sound a bit odd to couple two such missions on a single spacecraft, but anyway we found ways to accommodate them.


The current plans for Venµs Mission (VM) are as follows :

  • VM1 : Venµs scientific mission is supposed to work until Mid 2020 at 720 km altitude, imaging 123 sites with a 2 days repeat cycle
  • VM2 : Venµs altitude is progressively decreased to 410 km using the IHET engine
  • VM3 : low altitude orbit keeping, compensating drag, while continuing to image as a secondary mission at 410 km (which is an orbit with a two days repeat cycle)


The interest of VM2 and VM3 is to show the capacity of the IHET to drastically change the orbit, and to compensate the atmospheric friction on the satellite at 410 km. At 410 km, the Venµs resolution will be close to 2,5m, but will require a rotation of the spacecraft for motion compensation. The viewing capacity of the satellite will therefore be reduced.


But the plans for VM2 and VM3 phases are principles which are going to be detailed and finalized this autumn during a Joint Steering Committee with France and Israel. It is therefore time to receive suggestions and ideas from the community of Venµs users.


We have already had our own ideas, such as :

  • keeping Venµs Satellite on the current orbit for a longer time to allow for a longer  scientific mission
  • select the one day repeat cycle orbit at 560 km altitude instead of two days orbit at 410 km
  • include observations from different viewing angles over a few sites to work on directional effects
  • ...


But the more of us, the more imagination. Please feel free to rack your own minds and to suggest your ideas. Do you remember this experiment that you dreamed to be able to do with a high resolution optical satellite, a few months ago, but were never able to implement ? Maybe VENµS can do it... or maybe not, the only way is to ask us.


Feel free to add a comment here, or to send us an email, before mid August.

Philippe Gamet, Gérard Dedieu, Olivier Hagolle


Observable zones during VM1 phase Observable zones during VM3 phase... if we do not change the current project

India water crisis: Sentinel-1 detects surface water, ForEarth app restitutes and shares water stresses

In the framework of an open call Science4society funded by ESA, researchers at CESBIO have implemented a surface water detection algorithm from radar data Sentinel-1 on a cloud computing system. An API developed by Geomatys and JeoBrowser, two IT companies in France, is used to send the resulting surface water masks to a smartphone App named ForEarth, which display the surface water fluctuation in time for Indian regions.

The beta version is available on PlayStore and displays statistics and water masks for the Hyderabad region, Telangana, India.

The Hyderabad area has been processed. rest of India will be processed soon

Select your area of Interest

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Major changes for Venµs data processing

We are about to implement a major change in the ground segment of VENµS. Until now, L1C and L2A products were produced in the Venµs Image Processing (VIP) center, and imported into THEIA catalog. Next week, this will be changed.


L1C products will still be produced by the VIP, but the L2A will be generated by MUSCATE center within Theia. Moreover, it will soon be possible to generate L3A products which are bi-weekly composites of cloud free surface reflectances. And the cherry on the cake, all these products will be delivered at 5m resolution, while the L2A products were only available at 10m resolution.


This change comes with some drawbacks for users : the formats will slightly change to keep homogeneity between all the products distributed by MUSCATE.

  • the metadata format is different, the keywords have changed.
  • the images are still provided with TIFF format, but there is now one file per band. For L2A only, The scaling factor has changed, it is now 10000, as for Sentinel-2.
  • the L2A resolution is now 5m !
  • the grid used corresponds to that of Sentinel-2, you only have to account for the upper left origin of each site to obtain the registration of the images. No reprojection and no resampling is necessary.


These changes will be first applied to the real time processing, but the whole archive will be reprocessed later on.


A description of the new formats is provided in the following references :


During a few days, both versions will coexist in Theia distribution server. The new products contain the "_XS_" string in their filenames, so they are easy to recognise.


MAJA and LIS selected for the next Pan European high resolution snow and ice monitoring service

The European Environment Agency (EEA) has selected a consortium led by Magellium to implement the next Pan European high resolution snow and ice monitoring of the Copernicus Land Monitoring Service.

EEA 34 countries and corresponding Sentinel-2 tiles

This future service aims to monitor three variables at 20 m resolution over the tiles displayed above:

  1. Fractional Snow Cover (FSC)
  2. Permanent Snow Line (PSL)
  3. River and Lake Ice (RLI)

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Le catalogue Theia/Muscate compte maintenant 200 000 produits Sentinel2 de niveau 2 et 3


Le centre de production THEIA MUSCATE a franchi une nouvelle étape dans la nuit du 26 au 27 juin 2019. Il y a maintenant 200 000 produits Sentinel-2 N2A et N3A dans notre catalogue. Il a fallu deux ans et demi pour passer le cap des 100 000 produits en août dernier , mais nous avons doublé ce nombre en moins d'un an. C'est la preuve que notre système de production est maintenant mature et robuste, même s'il demande encore beaucoup de travail de la part de l'équipe d'exploitation, que nous remercions beaucoup !


Mais comme vous pouvez le voir ci-dessous, si le nombre de produits Sentinel-2 est le plus élevé, et aussi le plus téléchargé, le nombre de types de produits que nous fournissons aux utilisateurs augmente régulièrement. Nous vous parlerons bientôt du produit " qualité de l'eau" qui vient d'apparaître à la fin de la liste.


200 000 Sentinel-2 L2A and L3A products in Theia catalog


THEIA MUSCATE production center passed a new milestone during the night of the 26th to 27th of June 2019. There are now 200 000 Sentinel-2 L2A and L3A products in our catalog generated with MAJA. It had taken two years and half to pass the 100000 products milestone last august, but it took less than a year to double that number. This is a proof that our production system is now mature and robust, even if it still requires a lot of work from the exploitation team, which we thank a lot for their hard work !


But as you can see below, if the  number of Sentinel-2 products is the highest, and also the most downloaded by far, the catalogue has grown a lot, and the number of products we provide to the users is steadily increasing. We will soon tell you about the water quality product that just appeared at the end of the list.