Now that Sentinel-2A has started to acquire time series over Europe, we have been able to try our MACCS Level 2A processor to perform atmospheric corrections. As you probably know if you have been following this blog, MACCS works with time series to detect clouds, shadows, water and estimate aerosols optical thickness. Our processor therefore requires at least a couple of images to get a good initialization, .
Beatrice Petrucci, from CNES, launched the first processing with a time series of L1C images obtained near the Pyrenees. The L1C data were produced at CNES with the Ground Processing Prototype, which is used to define and validate the processing methods, and also produces all the data needed for the commissioning phase.
The results obtained on these L2A data are just great, with a very good detection of clouds and shadows, as you may see on the attached quicklooks. On the joined images, the detected clouds are circled in red, while the shadows are circled in black and water is in blue. You will need to click on the images to see them at 100 m resolution (we had to reduce it to let you download them quickly). You might wonder why on the top of the image of 26/7 some clouds are circled in black and not in red. There is no error in MACCS mask detection, but when cloud mask and shadow mask overlap exactly, the red contour is hidden by the black contour.
The atmospheric correction also looks fine, but of course needs to be validated scientifically.
These excellent results have been found with a first set of parameters coarsely tuned on the basis of our experience with other sensors; we expect to have even better results when the fine tuning of the parameters will be completed using much more images...
During the summer, the processing of SPOT5 (Take5) started to be updated weekly by THEIA processing Center in CNES. There is now a production lag of only 3 weeks, and the latest date available on the server was acquired on the 12th of August.
If you have been using these data, and had interesting preliminary results, or if you did an in-situ campaign, it would be very nice to send us your early results to be added on this blog. You just need to send me only one text page with one or two images, either in French or English, I would translate it.
Here is an example of a very interesting time series with the quickest changes I have ever seen. It is due to rice mono culture, in the Shandong region in China. End of May (May the 28th), the rice is green, end of July (July the 27th), the rice is also green, but meanwhile, it has been cropped and sowed again. With a lower repetitivity, one might miss the images in the middle, and think it is a long lasting crop cycle.
Twice a year, there is a Landsat Science Team meeting, organised by USGS. One day is dedicated to LANDSAT news, and one or two days to the science team presentations. And what is good, is that the slides are made available just after the meeting. It is a good way to get news from LANDSAT, and even from Sentinel-2, and to see how LANDSAT data are used in the USA mainly, but also around the world.
Here is the address : http://landsat.usgs.gov/science_LST_Team_Meetings.php
The question is : will there be a Sentinel-2 Science Team ? There is a Sentinel-2 Mission Advisory Group, but the carefully selected members (I am one of them...) were only reunited twice during Sentinel-2 development phase, and the slides are not available. Even if there were also two Sentinel-2 symposiums (and two SPOT (Take5) workshops, with the slides here and there), the level of discussions and feedback with the project team is not the same as in a science team with a reduced size.
Please remember that the next SPOT (Take5) workshop will be held within the Living Planet Symposium in Prague, next May.
Number of LANDSAT scenes processed and delivered by USGS. More than 700 000 Landsat scenes were distributed in March 2015, which makes quite a difference with the period when LANDSAT data were not free, until 2008 (source USGS)
Le CNES vent de décider de prolonger l'expérience SPOT5 (Take5) d'une semaine, jusqu'au 15 septembre. Cette prolongation généreuse compensera les deux pertes de données rencontrées au cours de l'expérience.
- La première perte a été dûe à un problème technique sur la station de réception d'Airbus DS, et a occasionné la perte d'un cycle de 5 jours de données acquises entre le 29 mai et le 2 juin compris.
- Le second évènement est plus récent : c'est un bug du système de programmation dans un cas qui n'avait pas encore été testé, qui a causé la perte de deux jours de programmation, du 1er Août à 21:26:22 au 3 août à 22:25:44.
Grâce à cette prolongation, nous aurons bien 5 mois de données pour chaque site, et environ 30 acquisitions par site. A l'issue de l'expérience, Sentinel-2 devrait prendre le relais, au moins sur l'Europe. La programmation est déjà systématique depuis fin juillet et la zone observée devrait être étendue progressivement.
CNES just decided to extend the SPOT5 (Take5) experiment by one week until the 15th of September. This extension is a generous compensation for the loss of two periods of acquisition :
- the first one was due to a failure of the receiving station, and resulted in the loss of a complete cycle of data, from May the 29th to June the 2nd.
- the second and recent one was related to a bug in the programming software in a configuration that had not been tested yet. This one resulted in the lost of two days of acquisition, from August the 1st,, 21:26 :22 to August the 3rd, 22:25:44.
Thanks to this extension, we will still get 5 complete months of data for each site, and about 30 acquisitions per site, every 5 days. After that, Sentinel-2 will soon take over from SPOT5 (Take5) acquisitions. Sentinel-2 acquisitions started to be almost systematic above Europe at the end of July, and the programmed zone will be extended progressively.
The programming of the 2nd and 3rd of August acquisitions failed for a complex reason which is now understood, and should not happen again. Please remember that the programming is done fully manually, as SPOT5 is not on its nominal orbit and that it requires a lot of work from the teams at CNES to program 150 images every 5 days..
As a result, no data were acquired from the 01/08/2015, 21:2 :22 to the 03/08/2015, 22:25:44. The missing data correspond to the days 2 and 3 of SPOT5 (Take5) cycle. We are very sorry for those of you who counted on these data and who did in situ measurements on these days.
While most CNES personnel is on vacation, the THEIA exploitation team is still producing data. A new batch of L1C and L2A SPOT5 (Take5) data has been uploaded to the server. All the data acquired until the 8th of July are now available. Have fun (either with your holidays, or with the Take5 data !)
Alors que les trois quarts des personnels du CNES sont en vacances, l'équipe THEIA continue à produire les données SPOT5 (Take5). Un nouveau lot, contenant les données L1C et L2A jusqu'au 8 juillet vient d'être mis à disposition sur le serveur. Amusez vous bien (avec les données ou en vacances !).