Release of the first version of SPOT4 (Take5) data

 

Phew ! These last days were quite intense, but we did it (almost) ! We are very proud to announce that the first version of SPOT4 (Take5) will be released on Monday the 15th of July at the following site : https://www.ptsc.fr/en/products/spot4-take5. The data format is explained here.


It will be possible to download the whole time series by clicking on 1C and 2A buttons. However downloading a whole series might take some time. Several small issues have been observed but not yet corrected (see this paragraph), but we still think it is useful that you start working on our data despite the few bugs that affect them. Downloading a data set requires the user to accept a licence. With the current version of the web site, you will need to accept this license each time you download a file.

In our initial schedule, we had announced a distribution of data during the month of June, but we are just a bit late, and happy to have done it, accounting for the numerous tasks we had to fulfil.

 

  • We had to obtain the experiment decision, which was done by the 11th of December 2012, and we had to implement it. The last data were acquired less than one month ago, and they will be available with the whole time series.
  • We had to modify and tune the processing chains, and the geometry  kept us busy for several weeks (and still does over equatorial forests). The level 2A processor worked quite well from the beginning, thanks to Mireille Huc (CESBIO) !
  • It was the first production of the French Land Data Center. The ground segment was built and implemented simultaneously to the data acquisition, its development team did a very nice work (namely, Dominique Clesse from CAP GEMINI, Hassan Makhmara and Joelle Donadieu at CNES). The data processing in this changing environment was perfectly managed by the exploitation team, Nicolas Prugent, Karl Rodriguez (Steria), Eric Faucher (CNES)...
  • A simple but very nice data server was set up in a very short time by Jerome Gasperi and Bernard Specht (CNES). The result is very simple and convenient (it helped us finding the last bugs...)

Issues and bugs

The products on the data server should be considered as a preliminary version of the processing. Other versions will be distributed, because the data sets still have a few defects :

 

  • Because of a little bug, the overlapping sites (Midi-Pyrénées East and West, and Britanny) were badly processed. These sites will be processed again and released in about 10 days. For the same reason, Maricopa site (USA) could not be processed, it will be released probably in September.
  • One image at the south of Languedoc site is always missing. We do not know why yet, but there is no doubt it will be corrected shortly.
  • Some Level 1A  products were not provided by Spot Image (25 out of 1600). We will need to reprocess the affected sites.
  • For all sites, the reference image for ortho-rectification were taken from LANDSAT  5 or 7. From our point of view, their location accuracy is a little insufficient. On the next version, we will replace LANDSAT data in FRANCE by the GeoSud high resolution cover from 2009. Out of France, we will replace them by LANDSAT 8 data whenever possible.
  • Data ortho-rectification often fails on some uniform equatorial forest sites (in particular for Congo(2), Gabon, Borneo, Sumatra). As  a result several dates are missing and those available are not perfectly registered.
  • On the level 2A, atmospheric corrections were performed with a constant aerosol model globally. We will use different aerosol models depending on the location in a future version.

 

Finally, we want to draw your attention to the fact that SPOT4 data are coded on 8 bits and can be saturated. SPOT system uses a data base of histograms to determine the gains to use depending on the location and date. This database is far from perfect and saturated data are quite common. For sites resulting from the merger of several images, it is also possible that the saturation thresholds differ between the left and the right half of the site. We provide you, within Level 1C and level 2A products with a mask saturations that you really should use.

 

Despite these few defects, we wish that this data set will be useful for you, and that you will obtain good results for your experiment and for your preparation for the arrival of Sentinel-2.

 

Many of the SPOT4(Take5) team will leave for vacations in the coming weeks, this blog will b much less active as I leave today !

 

 

 

 

 

Posted under: In English, Sentinel-2, SPOT4 (Take 5), THEIA

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