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



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



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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Snow and Fire in the Dragon mountains

NASA's blog "Image of the Day" recently featured two beautiful MODIS images of the snow cover in Lesotho. In late July Lesotho experienced its heaviest snowfall in two decades. The snow is not uncommon in Lesotho given that over 80% of the country lies above 1800 m (wikipedia). However the frequency of such snow events has been reducing over the past decades due to the ongoing climate change. As a result the shepherds are less accustomed to the snow conditions so that "a severe storm like the one in July 2016 has greater potential to kill sheep and shepherds" [1]. Continue reading

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)


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Série temporelle de chats


La télédétection satellite optique est un outil formidable pour suivre l'étendue du manteau neigeux en montagne... sauf quand il y a des nuages ! La télédétection radar du manteau neigeux (indifférente aux nuages) n'est pas encore opérationnelle en zone de montagne, notamment en raison du fait que le signal rétro-diffusé par le manteau neigeux varie très fortement avec son contenu en eau liquide. Sur le plancher des vaches, en revanche, de nombreuses personnes observent le manteau neigeux, même sous un ciel couvert. Certains sont même assez gentils pour prendre des photos, les télécharger sur un site web de partage, et les mettre à disposition sous licence publique. Une bonne partie des photos est géolocalisée, soit parce que l'appareil photo est équipé d'une puce GPS, soit parce que le photographe a lui-même ajouté les coordonnées de la prise de vue lors de la publication de son album.
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