Le 13 octobre on apprenait que le glacier des 2 Alpes n'ouvrira exceptionnellement pas à la Toussaint. Une décision prise en raison de précipitations insuffisantes et des températures élevées cet automne. J'ai fait tourner la chaîne Let-it-snow pour jeter un coup d’œil aux conditions d'enneigement. Hier Theia a mis à disposition l'image Sentinel-2A acquise mardi 17 octobre par temps clair. Voici le résultat :
Carte de l'enneigement le 17/10/2017 dans le domaine de ski d'été des Deux Alpes (en bleu cyan superposée sur le fond de carte OpenStreetMap)
You must have seen, in the press or social networks, images like these ones, showing yellow skies ( Loup de Bretagne said "Blade Runner skies"). Such a coloured sky was seen in the west of France, then later in England, and further East in the next days.
The Copernicus Atmosphere Monitoring Service, which keeps track of aerosols has also monitored these aerosols and tracked their provenance : is due to the combined presence of dust, ash from forest fires in Spain and Portugal, and humidity brought by the Ophelia cyclone. The IASI sensor on-board METOP satellites has also monitored the gases absorption due those wildfires.
So our question is: how such an event is handled by atmospheric correction software ?
Post préparé par Marine Bouchet pour le blog Kalideos Alpes (version originale)
Les séries temporelles d'images optiques des satellites Sentinel-2 permettent un suivi de la surface enneigée à une résolution spatiale de 20 m tous les 5 jours (en l’absence de nuages). Le CNES et le CESBIO développent, depuis 2015, une chaîne Let It Snow (LIS) pour extraire de façon robuste les masques de neige associés, distribués sur la plateforme Theia.
Update : MUSCATE is back on track for the real time production, thanks to PEPS return to nominal production, and a better stability of our platform.
Some of you will have probably noticed that Theia production of Sentinel-2 L2A data is quite slow these days, and is not producing all the data it should in real time. The reason is we started to implement a correction to solve the performance issues we had. This correction was tested and qualified during several days, in operational conditions, but when put in production, turned out to be unstable, due to occasional slowness in CNES cluster which did not happen when the correction was in tests. Moreover, our source of Sentinel2 data, PEPS, was experiencing some difficulties, providing a much reduced number of images.
We are waiting for a correction of the correction (the cause has been found and corrected but needs to be tested), The new version should be installed in less than 2.3 days, as Dilbert (dilbert.com) says. And all the team is very sorry for the delays and the inconvenience it is causing.
Villarrica volcano is one of the most active volcanoes in the Chilean Andes. A colleague of mine (Esteban Alonso) told me that last week he went ski touring up there and when he reached the summit he could see the bubbling lava in the bottom of the crater, and could even feel its heat...
Our MUSCATE ground segment just passed a new milestone, with 40 000 L2A products processed with MAJA ! Last week was a bit difficult, with a new repetition of the Friday Night Bug (on Saturday morning this time), followed by a "NFS" issue on CNES computing center that blocked production during two days. We are sorry for those of you waiting for the data in near real time. The production has resumed last Friday. These days, our production includes the near real time production and the processing of data acquired in 2016 over Spain, Italy, Switzerland and Netherlands. Some parts are already available, Burgos in Spain for instance, the others should come soon.
The version 2.4 of MUSCATE is nearly ready, but a final bug, noticed during the qualification tests remains to be corrected. As soon as it is installed and checked, this version will bring several improvements :
I just came back from Valencia, where I attended the fifth edition of the Recent Advances in Quantitative Remote Sensing Symposium. It is one of my favourites, thanks to an amazing team of organizers led by Jose Sobrino. It is a unique symposium, because it has only one session where you can even see opticians listen to radarists, or passive microwaves experts share ideas with active microwave experts ! Every three years, it is a way to gather quickly a good sense of the advances in each domain of remote sensing, over lands mainly. Next RAQRS will happen in 2020 in Valencia, and no doubt I'll be there, and not only for the delicious coffee breaks or for the giant paella.
Of course, my talk, available here or visible below, was about Sentinel-2 L2A products, including cloud detection and atmospheric correction. This time, I focused on product validation and provided a lot of validation results obtained by our little team at CNES and CESBIO, with special thanks to Camille Desjardins (CNES) and Bastien Rouquié (CESBIO) and Magdalena Main-Knorn (DLR). I also provided a comparison of MAJA and Sen2cor for various criteria that all show the benefits of using multi-temporal information, as done in MAJA. Despite all that, and although these results were perfectly known by ESA, ESA decided to stick with Sen2cor in their production, supposed to be global next year. The slides explain how this decision was made.
Anyway, as you probably know, you can access MAJA products from Theia, or you may also download MAJA's executable (if you have a powerful linux computer).
Following Simon's publication on Saint Barthelemy island after Hurricane Irma, one of our twitter friends, @Pierre_Markuse, posted a comparison of the South Western part of Haiti, before and after Mathew huricane ravaged it last year, on the 4th of October 2016. As you can see, the whole lands turn brown just after the hurricane. I am really not an expert, so I just can imagine it is caused by the wind cutting branches and trunks and by water run-off taking the lower vegetation away. I read that 40% or the forest and 20% of the shrub has been erased. Moreover, the wind and water must have left mud and dust on the remaining leaves, contributing to the brown color.
However, what is amazing is that by end of November, vegetation comes back ! My guess is that mud and dust disappear, shrubs and trees start to grow new leaves and the low vegetation grows back But experts are welcome to explain how it happens exactly, there is a comment section !
I have an additional special own interest in displaying this information : it is a hard test for how our multi-temporal methods included in MAJA to detect clouds, shadows and aerosols can manage such a case. Continue reading