New paper ! An active learning cloud detection tool to generate reference cloud masks for Sentinel-2. Application to the validation of MAJA, Sen2cor and FMask cloud masks

20/02/2019 Reply

Example of reference cloud mask generated by ALCD, and comparison with the cloud masks generated by three operational processors (Sen2cor, FMask and MAJA). True positive invalid pixels appear in blue, true negative in green, false negative in red and false positive in purple..

It is not that frequent when the work of a trainee ends up as a peer reviewed publication, but Louis Baetens was a brilliant trainee. In a six months training period at CESBIO, funded by CNES, here is what Louis Baetens did:

  • developed an active learning method to generate reference cloud masks for Sentinel-2, using multi-temporal data as input
  • validated the quality of the produced masks (around 99% overall accuracy)
  • generated cloud and shadow masks covering 32 entire Sentinel-2 images
  • produced these same scenes with Sen2cor 2.5.5, FMask 4.0 and MAJA 3.3
  • evaluated the results using ALCD masks
  • wrote a report and a user manual for ALCD
  • released the masks and tools on open access platforms
  • And wrote (with Camille and myself) a scientific publication

 

The publication was just released by remote sensing :

Baetens, L.; Desjardins, C.; Hagolle, O. Validation of Copernicus Sentinel-2 Cloud Masks Obtained from MAJA, Sen2Cor, and FMask Processors Using Reference Cloud Masks Generated with a Supervised Active Learning Procedure. Remote Sens. 2019, 11, 433.

 

The remaining of the post provides a plain language summary (but it's better to read the paper !)

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A pause in MUSCATE production, end of February

19/02/2019 Reply

The MUSCATE production centre will be offline for a week from February 25th to March 4th (or maybe the week after, please see Theia's RSS feed to see the exact date). This pause will be necessary to upgrade the processing centre to V2.5. As a result, we will not be able, for a week, to process Sentinel-2 data in real time, and hope it will not be too inconvenient to you. In case you need some data urgently, you can ask PEPS to produce MAJA L2A data for you during that period.

 

The main change regards the internal format used by MUSCATE for Sentinel-2 Level 2A products. This internal format is different from the external format that we distribute, and this results in unnecessary product format conversions, as well as the necessity to develop drivers for the various formats (internal and external) for the processors that use Sentinel-2 L2A data within MUSCATE. To enable this modification, it will be necessary to convert all the L2A data from the internal format to the external format, which will take a whole week.

 

MUSCATE V2.5 will bring other improvements, such as the integration of MAJA 3.1, with possibility to use Copernicus Atmosphere data, or a new version of LIS, the processor that delivers the snow maps.

MUSCATE  V2.6 is also ready and queuing to be installed, with MAJA 3.2, WASP and the possibility to process Venµs L2A data within MUSCATE and not externally on Venµs ground segent.

 

 

 

Black snow in Prokopyevsk

18/02/2019 Reply

The snow cover is not always white. Sometimes it is orange, sometimes it is black. The images below were captured by Sentinel-2 in Prokopyevsk, Russia.

According to the Siberian Times the deposition of black dust on snow in February 2019 was due to the failure of a filtering system in a coal processing plant. Looking at the picture below, I have the feeling that this kind of event was not exceptional in Prokopyevsk this winter...

Pictures from Kemerovo region by Orlovprklife, Willravilov, Typical Kemerovo

Source: Siberian Times 15 Feb 2019. Pictures from Kemerovo region by Orlovprklife, Willravilov, Typical Kemerovo

Thanks to François Tuzet for pointing this to me!

Apport des images radar et optiques pour la cartographie des surfaces irriguées

12/02/2019 Reply

(English version below)

Dans le cadre du projet Simult’eau (partenaires : Arvalis, CACG, Chambres d’Agriculture du Tarn et des Hautes-Pyrénées, financement CASDAR) nous avons testé l’apport d’une utilisation combinée des images radar et optiques pour la cartographie des surfaces irriguées (maïs et soja) dans le Sud-Ouest de la France. Les résultats publiés dans Remote Sensing (https://www.mdpi.com/2072-4292/11/2/118) ont révélé que l’utilisation d’images radar Sentinel-1 combinées aux images optiques (Landsat-8) permettait de détecter les surfaces irriguées plus précocément qu’avec les images optiques seules. En effet ces dernières sont souvent perturbées par la présence de nuages qui rendent la détection impossible à certaines périodes de l'année. Ce résultat, qui doit être confirmé par des études complémentaires (autres lieux et autres dates), est très encourageant. Il ouvre de nouvelles perspectives pour une gestion "optimisée" des ressources en eau notamment pour des organismes tels que la CACG (Compagnie d'Aménagement des Coteaux de Gascogne) ou les Organismes de Gestion Collective de l’eau (OUGC). Les cartes produites sont en libre accès sur le site Theia: http://www.theia-land.fr/fr/ces-surfaces-irriguees.


Ces recherches se poursuivent actuellement dans le cadre de la thèse de
Yann Pageot financée par le CNES, l'Agence de l'Eau Adour-Garonne et la CACG.

 
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Diffusion d'un premier lot des données Sentinel-2A de niveau 2A sur le Sahel

06/02/2019 2 Comments

Il y a quelques semaines, nous annoncions la sélection d'une nouvelle zone de production de données Sentinel-2 au niveau 2A par Theia, au Sahel. La production a démarré, et Theia a déjà produit les tuiles de la zone UTM28 (à l'ouest). Les tuiles en vert foncé existaient déjà, mais nous avons rajouté celles en vert clair, qui permettent de couvrir l'ensemble du Sénégal, la Gambie,  une partie de la Guinée Bissau, de la Guinée, et le nord de la Sierra Leone.

 

Les données disponibles ont été traitées du premier janvier 2017 à hier, soit plus de deux ans de données. Les nouvelles données seront maintenant traitées en temps réel au fur et à mesure de leur arrivée.

Nous procéderons de même avec les différentes zones  de l'ouest vers l'est : UTM29, UTM30...

 

Our blog's audience in 2018

04/02/2019 Reply

A seventh year begins for the "Séries temporelles" blog, and as usual, it is an opportunity to review its audience, and to get a little self-satisfaction. We usually publish this post early January, but it seems there was no January this year (or was I too busy ?). The blog is still receiving more visits every year, with a sharp growth this year : +35% of visits ...

Blog traffic from December 2012 to January 2019

Blog traffic from December 2012 to January 2019 (the trends were computed using the Theil–Sen estimator), computed by Simon Gascoin.

So, if we look at the trends on the plots above, the audience growth is remarkably linear, but if we sum-up everything per year, we see a sharp increase. The cause is that outlier in the top-right corner or each graph above, related to a big buzz in Japan for SImon's article about Xe-Namnoy lake dam failure in July, that flooded several villages, and killed too many people.

 

2013 2014 2015 2016 2017 2018
Number of visits 13985 22928 34723 47773 57692 79243
Number of viewed pages 30922 46940 66947 89555 105846 131846

 

French visitors only counted for 25% of visits, much less than the other years. Japan ranked second with 16%,  United States ranked third, followed by European countries (UK, Germany, Italy, Spain) and by India, Canada and Morocco.

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