Didi Abuli (დიდი აბული) vu par Sentinel2-A

Le Didi Abuli domine la chaîne de montagne du petit Caucase en Géorgie. Ce secteur très peu fréquenté situé à proximité de la frontière Arménienne offre un terrain de jeu exceptionnel pour le ski de randonnée. Ainsi sur les traces des copains de la Timuzapata,  avec 2 collègues du Cesbio et 1 de l'ONERA, nous sommes allés arpenter les pentes de ce volcan endormi qui culmine à près de 3300m mais aussi découvrir l'hospitalité des habitants de cette région qui mérite vraiment de s'y attarder.
 
Oui mais quel rapport avec Sentinel2?

Trace de l'ascension du Didi Abuli-Sentinel-2A-2017-06-03

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Theia releases Sentinel-2A L2A data over Morocco

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After France, Belgium, North of Spain, Tunisia, a transect from Burkina Faso to Mali and some tiles in Ethiopia, Theia just released the production of one year of Sentinel-2A data at Level 2A above a large region of Morocco, from Ouarzazate to Casablanca. Level 2A products provide surface reflectances corrected from atmospheric effects, with a high quality cloud mask.

 

The L2A data are, as always, available from https://theia.cnes.fr. Please refer to the help page to find the data format description. To download the data without a click, you may use our python download tool (after having registered on Theia's site).

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La neige du Haut-Atlas marocain vue par Sentinel-2 et MODIS

Il était une fois, un jeune thésard qui se promenait dans les montagnes enneigées du Haut-Atlas avec un groupe d’amis. Pendant que ces derniers s’amusaient à prendre des selfies avec la neige il pensait à un autre type de selfies ! Il pensait aux photos de la Terre prises par les satellites : ces images refléteront-elles la beauté de cet endroit ? Leur résolution spatiale permettra-t elle de reproduire les subtilités de l’enneigement dans ce massif escarpé ?

 

Photo du Haut Atlas marocain prise à Oukaimeden. L’enneigement varie fortement selon la pente et l’orientation du terrain.

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Global sea ice area : a scary plot

When I say "a scary plot", I don't mean a Chinese plot aimed at confusing some naive North Americans, it just mean a figure (an American one, by the way, made with data from the National Snow and Ice Data Center) that provides the total sea ice area over the globe. And this figure is scary :

The red curve corresponds to last year's sea ice area.

Let's hope it is partly due to the el-niño phenomenon we had last year, and that next years will come closer to the average curves. However, as a cold wave is about to reach western Europe, let's record it for later !

White Christmas in Aleppo

This is a Sentinel-2A image of Aleppo on Dec 22, showing some snow through the clouds. I do not know if this sunny interval lasted a long time, and I wonder if the inhabitants of Aleppo had wished snow for Christmas. I walked through the streets of Aleppo in July 2003 at the end of my bachelor's internship which was held mainly in Damascus and Palmyra. Aleppo is the most fascinating city that I have visited in Syria. I remember the alignments of soap, cloth and hardware stores that narrowed even more the narrow alleys of the old city. I remember the Persian carpets hanging from the balustrades of the ancient caravanserais. I remember countless smiles exchanged with people whose language I did not speak, in the souk, in the mosques, where tourists like me were welcome. I remember the kids playing soccer in front of the walls of the citadel. I wonder if kids played snowballs on December 22, 2016 in Aleppo. I'm sad and I'm a little ashamed too.

Aleppo (Sentinel-2A image of 22-Dec-2016)

Patagonian skies are not cloudy anymore

"The most usual weather in these latitudes is a fresh wind between north west and south west with a cloudy overcast sky" - Phillip Parker King, Sailing Directions for the Coasts of Eastern and Western Patagonia (1832).

 

Patagonia is a beautiful place to visit but campers know that the weather is extremely variable and the sky is often cloudy. This can be a problem for glaciologists, too, since they rely on optical satellite imagery to study glacier area changes over the last decades (mainly Landsat). Clear-sky optical images can also be used to determine glacier velocity, albedo, front variations, etc.
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Monitoring the snow cover in ski resorts using Sentinel-2

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We are preparing the distribution of maps of the snow cover extent made from the Sentinel-2 data for Theia. If the method used to detect the snow is based on well-proven concepts, spatial and temporal resolution of the snow maps will however quite unprecedented. Until now, maps of the snow cover extent were usually produced from MODIS observations at 500 m resolution, which is adapted to hydro-climatic studies to rather regional scales. Landsat data were actually little exploited by snow scientists because of their low repeatability. The deployment of Sentinel-2 mission (global coverage at 20 m resolution every 5 days) opens new perspectives for monitoring snow cover.
 
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Suivi de l'enneigement des stations de ski avec Sentinel-2

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Dans le cadre du pôle thématique Theia nous préparons la distribution de cartes d'enneigement établies à partir des images Sentinel-2. Si la méthode utilisée pour la détection du manteau neigeux se base sur des concepts bien éprouvés, la résolution spatio-temporelle des cartes d'enneigement sera en revanche tout à fait inédite. Jusqu'ici les cartes d'enneigement était généralement produites à partir des observations MODIS à 500 m de résolution ce qui permet de faire des études hydro-climatiques à des échelles plutôt régionales. Les données Landsat étaient finalement assez peu exploitées par les nivologues en raison de leur faible répétitivité. Le déploiement de la mission Sentinel-2 (couverture globale à 20 m de résolution tous les 5 jours) ouvre de nouvelles perspectives pour le suivi de l'enneigement.
 
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