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

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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

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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.

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

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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

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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.

 

 

Sentinel-2 captures new data centers in Iceland

In a remote sensing study published in Nature, the authors claimed that they used "101 CPU-core years of computation (..) within the Google data centres". This made me wonder what could be the carbon footprint of such a study?. I estimated that it should be 65 tonnes of carbon dioxide, but a Google engineer replied:

Google purchases enough renewable energy to offset 100% of its energy use for its offices and data centers.

In just a few years, the company has made an impressive move to renewables, true to its famous motto "don't be evil". Google is the largest corporate purchaser of renewable energy on the planet. However, it's better to save energy than to buy renewable energy, as explained by Forbes:

It is true that Google is buying all its electricity from renewable sources, but it is unlikely that all the electricity it is using comes from renewable sources. This is because solar and wind, Google’s choices for renewable sources, are both variable, while Google’s electricity demand is not. In other words, there are times and locations when Google must use electricity that comes from traditional sources, while simultaneously the electricity generated from the renewable projects funded via Google’s PPAs is curtailed and lost.

To save energy (and cost), large tech companies are moving data centers in Nordic countries like Iceland to take advantage of the "free air cooling". Moreover in Iceland the electricity production relies primarily on hydropower and geothermal heat.

Sentinel-2 images of data centers in Reykjanesskagi, Iceland


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Detecting geolocation errors in glacier outlines with Sentinel-2 snow cover duration maps

Two years ago I posted an animation of the snow cover area evolution near Zermatt, Switzerland from Sentinel-2 L2A data processed by LIS.

From this time series of snow maps I generated a snow cover duration map and
added the glacier outlines from the Randolph Glacier Inventory 5.0.

Colors: Snow cover duration between 01 Sep 2016 to 31 Aug 2017 (in days). Black line: Glacier outline from RGI.



I was satisfied by the overall good agreement between the areas with a high snow cover duration and the glacier outlines. However by looking more closely at the small isolated glacier in the eastern part I noticed a mismatch between both datasets..
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THEIA's Sentinel-2 L2A processing on Sahel is progressing

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As we had announced in November, the MUSCATE production centre in Theia is gradually adding areas in the Sahel, which are shown in the image below. The data are processed from December 2016 onwards, which means that we have a large amount of data to process. So we started with the most westerly tiles, in Senegal on the UTM28 zone, then progressed from one zone to another towards the East.


Theia Sentinel-2 processing area on the Sahel

 

In red, the tiles available from Dec 2016 to NRT, in blue , the remaining tiles to be added.

In recent days, Theia has completed the processing of tiles in the UTM29 area, which mainly covers northern Guinea and western Mali, but also partially covers southern Mauritania and Sierra Leone and north-western Côte d'Ivoire. The treatment of the UTM 30 zone, which covers Burkina Faso and Mali, is also well advanced. The east of this area is finished, and the west is progressing well, as shown in the animation below. The UTM31 zone has also been brought into production. Feel free to take a look from time to time at the map of areas covered by MUSCATE. The blue tiles turn red as soon as we switch to run-of-river processing.

 

The data can be downloaded from here:

https://theia.cnes.fr

 

Animation in the region of the city of Mopti, Mali, with about one image per month in 2017. The displayed time series extends between two rainy seasons and covers the dry season. Many fire scars are visible during the dry season. Some shadows appear, which actually correspond to the shadows of cirrus clouds corrected by MAJA. Shadows and cirrus are marked in the products.