Le bulletin Theia est sorti !

De la part de Sophie Ayoubi, chargée de la communication de Theia

Le 8ème numéro du bulletin du pôle de données et de services surfaces continentales Theia vient de paraître.

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MUSCATE news : 50000 L2A products from Sentinel-2A and 2B

Since it became operationnal in December last year, MUSCATE has produced 50 000 level 2A products from Sentinel-2A. Let's recall what has been processed so far :
  • For 550 tiles, we have processed all Sentinel-2A data acquired since December 2015.
  • For 100 tiles, mainly in South America, and in Italy, we have processed all Sentinel-2A data from December 2016. We are currently catching up the backlog for Italy, and later on, for South American sites.
  • For all these 650 tiles, we are producing all Sentinel-2 data (Sentinel-2A and Sentinel-2B) in near real time. I think THEIA is the only place where you can download Sentinel-2B L2A data so far. ESA has not started that production yet (nah, nah, nah :) )
  • For all these 650 tiles, we have processed all Sentinel-2B data since beginning of October 2017. We will soon catch-up with the Sentinel-2B data acquired from July 2017.

 

 

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Map of the 650 tiles currently processed in near real time (in red). The blue tiles will be added beginning of next year.

 

All these products are available from https://theia.cnes.fr

 

Let's recall that MUSCATE uses the MAJA L2A processor, which uses multi-temporal criteria to perform a high quality cloud detection and atmospheric correction. Despite the recent installation of version 2.4, MUSCATE still regularly suffers from instability as soon as CNES High Performance Computer is overloaded. The problem does not lie in MAJA, but in the information exchanges between all the components of MUSCATE which need to respect an accurate timing (sorry, I am not able to explain better).

 

The exploitation team just installed a new version of MUSCATE (v 2.4.16.p2 (!)), which is expected to increase stability. But that's the theory, let's see if it works in the coming days and if we are able to increase our production rate.

 

 

La mission Sentinel-2 va vraiment bientôt fournir des données tous les 5 jours, partout !

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Mise à jour : L'ESA progresse rapidement, les acquisitions de toutes les terres ayant défilé sous S2B étaient disponibles sur PEPS le 12 Novembre.

 

La mission Sentinel-2, qui se compose de deux satellites jumeaux, S2A et S2B, a été déclarée opérationnelle par l'ESA au début du mois d'Octobre, même si chacun des satellites n'observait en fait que sur une orbite sur deux, sauf en Europe et en Afrique. Résultat, la répétitivité de 5 jours n'était disponible que sur ces deux continents, et passait à 10 jours ailleurs. Heureusement, dans le dernier Sentinel-2 mission status report, l'ESA a annoncé cette excellente nouvelle :

 

Sentinel-2A et -2B observent ensemble l'Europe, l'Afrique et le Groenland avec une répétitivité de 5 jours. Le reste du monde est observé tous les 10 jours. L'observation complète et systématique de toutes les terres tous les 5 jours sera obtenue quand la liaison EDRS deviendra opérationnelle. Ceci est attendu pour décembre 2017 à la fois pour S2A et S2B.

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Sentinel-2 mission close to start observing all lands every 5th day, really !

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Update : ESA is progressing fast. All lands overflown by Sentinel-2B were available in PEPS on November 12th, thanks to EDRS relay satellites.

The Sentinel-2 mission, made of two twin satellites S2A and S2B, has been stated "operational" since beginning of October, even if each satellite was only observing on one orbit out of two everywhere except in Europe and Africa. As a result, the 5 days revisit was only available in these two continents.  But in the new Sentinel-2 mission status report, ESA announced this very good piece of news :

Sentinel-2A and -2B are together acquiring Europe, Africa and Greenland with 5 days revisit. The rest of the World is revisited every 10 days jointly by the two satellites. Full systematic 5-day revisit everywhere will be reached once EDRS downlink becomes available operationally, assumed during December 2017 for both S2A and S2B.

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[MUSCATE News] Le traitement des données Sentinel-2B L2A a démarré

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L'ESA a déclaré Sentinel-2B opérationnel a la fin du mois d'Octobre, même si des données préliminaires étaient déjà disponibles depuis juillet. Depuis hier matin, MUSCATE distribue aussi les produits Sentinel-2B de niveau 2A en utilisant le processeur MAJA (les produits L2A sont exprimés en réflectance de surface après correction atmosphérique et sont munis d'un masque de nuage de bonne qualité). La production actuelle a démarré à partir des acquisitions du 1er octobre 2017 et se poursuivra en temps réel. De plus, nous ajouterons progressivement les produits Sentinel-2B acquis depuis juillet 2017.

 


Premiers produits S2B disponibles sur https://theia.cnes.fr

 

Comme toujours, les données peuvent être téléchargées gratuitement depuis https://theia.cnes.fr

Voici un petit exemple de série temporelle près de Baotou, en Chine, acquises en alternance par Sentinel-2A et Sentinel-2B. Les images se ressemblent beaucoup, excepté là ou la surface a clairement changé, dans la vallée Est-Ouest au centre de l'image.

Sentinel-2A Sentinel-2B Sentinel-2A

 

 

Comme le traitement MAJA est multi-temporel, sa précision bénéficiera de la répétitivité doublée des acquisitions, ce qui devrait avoir un effet sur nos résultats de validation à venir. A partir des productions de qualification de la nouvelle version, nous avons déjà vérifié que les réflectances fournies par les deux capteurs sont assez proches et concordent bien avec les mesures in situ obtenues avec la station de mesure de réflectance de surface du CNES à La Crau (Provence, France). Quelques exemples de résultats sont fournis ci-dessous.

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[MUSCATE News] Processing of Sentinel-2B L2A products begins

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ESA declared Sentinel-2B operational at the beginning of October, although preliminary data were already available. Since this morning, MUSCATE is producing and distributing Sentinel-2B Level 2A products using the MAJA processor (the L2A products are expressed in surface reflectance after atmospheric correction and are provided with a good quality cloud mask). The current production starts from the first of October 2017 and will go on in real time, and we will progressively add the Sentinel-2B products acquired since July 2017.

 

First S2B products available for download from https://theia.cnes.fr

 

As always, the data can be freely downloaded from https://theia.cnes.fr

 

Here is a little example of time series of iimages acquired over Baotou, China, alternatively by Sentinel-2A and Sentinel-2B, here again, the images look the same, except where something has clearly changed on the ground, in the east-west irrigarted valley in the image center.

Sentinel-2A Sentinel-2B Sentinel-2A

 

As MAJA processing is multi-temporal, its accuracy will benefit from the doubled repetitivity of acquisition, which should have an effect on our validation results. Using the production we did to check our  parameters, we have already checked that the reflectances provided by both sensors are quite close, and agree well with in situ measurements obtained with CNES surface reflectance measuring station in La Crau. The results are provided below.

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Yellow skies look grey from above

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 ?

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[Muscate news] temporary slowlyness

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.

Venµs' moon

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Well, the audience of our blog is still steady increasing, there is no need to use explicit titles to get more connexions. And although I mainly use space to look down, I do not think the planet has a natural satellite. So why this title ?

The Venµs satellite actually showed us the moon, and not only to provide a nice title in this blog. Our Israeli colleagues from MBT really worked hard to obtain it, as a very good pointing accuracy is needed to image it from a quickly rotating satellite : the moon is far from here !

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Quand Venµs nous montre la lune

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Non, non, la fréquentation de ce blog n'est pas en baisse au point qu'il nous faille attirer une nouvelle clientèle pour compenser une perte de revenus financiers issus de la publicité. (La fréquentation augmente régulièrement d'ailleurs, mais les revenus financiers sont nuls...)

Le satellite Venµs nous a vraiment montré la lune, et ce n'est pas seulement pour proposer une belle image et un titre accrocheur sur le blog du CESBIO. Nos collègues israéliens de MBT se sont d'ailleurs donné beaucoup de peine pour l'obtenir, car il faut une très bonne précision de pointage pour l'observer : la lune est loin !

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