Great news, we can announce that the operational production of the Theia snow collection has started well. It means that maps of the snow cover area are now constantly added to the Theia portal. These maps are automatically generated from Sentinel-2 observations and have a spatial resolution of 20 m. The Snow collection will progressively cover most mountain regions in west Europe, but also the Atlas in Morocco, eastern Canada... The Snow collection can be freely downloaded from http://theia.cnes.fr by any registered user.
Today's front page of the Theia website featured this nice example in Sierra de Ancares (western end of the Cantabrian Mountains, Spain). In the southeast, snow was also detected on the Montes Aquilanos, including the small ski resort El Morredero. The image was captured yesterday! It illustrates well the value of multispectral imagery to discriminate the snow cover from the clouds. There is a cloud which looks alike snow but it is actually a valley fog confined by local topography.
Theia Sentinel-2 level 2A and snow product in the region de los Ancares, Spain. Image captured by Sentinel-2A on 30 Jan 2018.
Update January 31st, 10h00 : Distribution was just restarted, a few hundreds of images will be added today, and meanwhile, data are processed in Near Real Time.
This January was a nightmare for MUSCATE. Following database issues to send data to the distribution server, our production system was stopped during the Christmas break and unstable the weeks after.
After understanding the issues, the MUSCATE team stopped the automatic sending of products, resumed the production, and started to update the production server manually. We were nearly back on track last Thursday, when the distribution server refuse to accept any new product. The explanation was found, a directory in the High Performance Storage System (a robot that handles tapes and disks) had 65535 files and could not accept a new one. We need a little reorganisation of the folder structure to overcome that, and meanwhile, the distribution is stalled again.
Still, more than 60 000 L2A products are now available, and we have started distributing the snow cover products, in NRTWD ("Near real time with delay"). We hope to be soon really in NRT.
You probably remember Simon Gascoin's story about the Aru glacier avalanches, which started from Simon's observations of the twin avalanches using the Sentinels. It was one of the big buzz pages of the blog in 2016. The first images were published here, then spread out in many scientific websites and the social networks.
The same mountain valley in Tibet is shown before and after part of a glacier sheared off on 17 July 2016. Credit: NASA/Joshua Stevens/USGS/ESA
It seems that the story finally made its way to Nature Geoscience, after a large work from many scientists lead by Andreas Kaab. Congratulations to all the team !
So, dear CESBIO colleagues, or remote sensing time series users, it is time to submit your work to this blog as a first step to future publications in Nature !
Sentinel-2 a acquis cette belle image de la campagne autour de Notre-Dame-des-Landes le 17 janvier 2018, le jour même où le Premier ministre annonçait que le projet d'aéroport du Grand Ouest était abandonné. Pour fêter l'occasion le ciel breton s'était éclairci !
Image Sentinel-2 de Notre-Dame-des-Landes. La zone d'aménagement différé (ZAD) est délimitée en rouge (polygone téléchargeable sur data.gouv.fr).
Sorry for those of you waiting for our real time products, MUSCATE production is stalled these days. The teams are working hard to put it back in production.
Update: it seems that the issues happened when sending products to the distribution server. A data base request became infinitely long, and the system waited for it. While a solution is being tested, the production just resumed at full speed, but the distribution is still stalled and should be started again on Monday.
Désolé pour ceux d'entre vous qui attendent nos produits. La production de MUSCATE est arrêtée. Les équipes travaillent d'arrache pied pour la remettre en route.
Mise à jour: les problèmes rencontrés se produisent lors de l'envoi des données au serveur de distribution. Une requête en base prend un temps infini, et le système finit par s'arrêter. La production vient de redémarrer à pleine vitesse, mais l'envoi des données pour la distribution a été désactivé, en attendant que la solution en cours de test soit validée.
Land cover map validation is a complex task. If you read French, you can check this post by Vincent Thierion which shows how the 2016 LC map of France produced by CESBIO stands with respect to data sources independent from those used for its production. But this is only one aspect of the validation. A land cover map is a map, and therefore, there are other issues than checking if individual points belong to the correct class. By the way, being sure that the correct class is known, is not so easy neither.
In this epoch of machine learning hype , it is easy to fall in the trap of thinking that optimising a single metric accounts for all issues in map validation. Typical approaches used in machine learning contests are far from enough for this complex task. Let's have a look at how we proceed at CESBIO when we assess the quality of a LC map produced by classification.
As you have probably noticed, our production rate has been very low these days and we are more than 10 days late in our delivery of L2A and snow cover products.
This seems to be due to an intervention on CNES cluster end of December to add new nodes and disk space. MUSCATE sometimes loses communication with the platform that handles the databases and crashes. As it also happened when CNES was closed for Christmas, we really lost a lot of time. All the teams are on the deck to try to solve this issue and catch the delay up. We are very sorry for that inconvenience.
The Sentinel-2 mission status document, edited by ESA, is a very interesting reading. On its last edition of 2017, ESA announced very discretely that the spectral bands of Sentinel-2 had been revised, following a review of the pre-flight measurements. Very few details are provided on the nature of the error contained in the previous version, and on the validation of the new ones. But still, a new version of the spectral response function is available here,, since the 19th of December 2017. The site provides an excel file with the spectral response functions.
All the visible and near infrared bands have changed a little, even if only three bands have significant changes, B1, B2 and B8: B2 equivalent wavelength changes by 4 nm, B1 by 1 nm, and B8 by 2 nm. The SWIR bands did not change.
Old and new versions of five VNIR S2A spectral bands, together with that of S2B.
Most users should not use bands B1 and B2, as they are affected by atmospheric effects. So I do not think much of you will have to change the coefficients in your methods. But for us, who take charge of the atmospheric correction, and heavily rely on B1 and B2, it probably has an effect, and we are changing our look-up tables to account for that. Stay tuned for the results.
May this new year bring you happiness, and not only related to image time series !
As usual, this beginning of year brings the opportunity to summarize 2017. Here is what I would record, in our field of interest :
- the consecration of Copernicus program and of the Sentinel satellites. Since 2015, more than 110,000 people have registered to access the data since 2015! In my opinion, this success is due to the combination of several factors: the data are free and easy to access, the observations are repetitive, regular and frequent worldwide, and the data are of high quality. Congratulations to ESA and the EU, not to mention the contribution of CNES for the quality of Sentinel-2 images and the calibration of Sentinel-3. Continue reading
Que cette nouvelle année vous apporte joie et bonheur, et pas seulement dans l'utilisation de séries temporelles !
Sans aucune originalité, ce début d'année est l'occasion de faire un petit bilan de l'année 2017. Voici, dans notre domaine, quelques uns des faits que je retiendrai :
- la consécration du programme Copernicus, et des satellites Sentinel. Plus de 110 000 personnes se sont inscrites pour accéder aux données depuis 2015 ! A mon avis, ce succès est dû à la combinaison de plusieurs facteurs : les données sont gratuites et faciles d’accès, les observations sont répétitives, régulières et fréquentes sur le monde entier, et les données sont de grande qualité. Un grand bravo à l'ESA et à l'UE, sans oublier la contribution du CNES pour la qualité des images de Sentinel-2 et l'étalonnage de Sentinel-3. Continue reading