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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Wildfires in California spotted by Sentinel-2A

Wildfires were raging in California this summer. Let's see if we can spot some of them in Sentinel-2A images with the new Sentinel-Playground by Sinergise.

 

The combination of the SWIR and NIR bands of Sentinel-2 or Landsat enables to produce accurate maps of burnt areas. The SWIR band is sensitive to the water content in the soil and vegetation, while the NIR band is sensitive to the vegetation health (photosynthetic activity).

 

In addition, the radiance measured by a spaceborne sensor in the SWIR wavelengths increases if the surface is very hot (as taught us Prof. Planck in Hawaïï).

 

As a result, a simple color composite of bands SWIR/NIR/Red gives a stunning view of burnt areas and can highlight ongoing fire areas if the smoke is not too opaque.

 

In Coalinga, the Mineral Fire burnt nearly 3000 ha close to the city of Coalinga.

Mineral wildfire near Coalinga, Californa USA. Time series of Sentinel-2A images (RGB color composite of bands SWIR/NIR/Red = 12/8A/4)

 

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Sentinel-2 et Landsat-8 font équipe pour suivre la coulée de lave du volcan Kilauea

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Le volcan Kilauea à Hawaï est un des plus actifs au monde. Cela fait déjà plus de trente ans qu'il est entré en éruption, mais il a fait les gros titres récemment car ses coulées ont atteint l'océan Pacifique, agrandissant le territoire hawaïen de deux hectares d'un coup ! Voilà une technique efficace pour lutter contre la hausse du niveau de la mer...

Photo aérienne de la coulée de lave 61G au point d'entrée dans l'océan Pacifique le 19 août 2016. Crédit: U.S. Geological Survey Department of the Interior/USGS U.S. Geological Survey.

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Sentinel-2A and Landsat-8 team up to track Kilauea Volcano's lava flow

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Kilauea Volcano in the largest active volcano in Hawaii and one of the most active on Earth. It has been erupting for over 30 years now but hit the headlines recently because a large lava flow traveled up to the ocean, adding 2 brand new hectares to the Hawaiian Islands.

Aerial view of the 61G lava flow ocean entry on August 19, 2016. Credit: U.S. Geological Survey Department of the Interior/USGS U.S. Geological Survey.

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Sentinel-2A (and Landsat-8) capture a giant ice avalanche in Tibet

After reading my previous post about the Rutog ice avalanche, my distinguished colleagues Antoine R. and Olivier H. challenged me to look for a pre-event image to better highlight the avalanche area. The closest clear-sky image that I could find is a Landsat-8 image that was acquired on June 24 (23 days before the slide).

 

Sequence of two Landsat-8 and Sentinel-2A images. Both images are level 1 product displayed as natural color composites. Click to enlarge.

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Sentinel-2A captures a giant ice avalanche in Tibet

The Nature News website reported yesterday on a massive ice avalanche that happened in Rutog, Tibet, on 17 July 2016. This ice avalanche killed 9 people and may be one the largest ever observed. The ice and rock mixture spread over 6 km from the collapse point up to the Aru Co lake shoreline.

Sentinel-2A image of the Rutog ice avalanche acquired on 21-Jul-2016 (4 days after the event). Click on the image to see at full resolution (1 pixel = 10m).

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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