Statistiques de téléchargements des données SPOT4(Take5)

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Trois mois et demi après le début de la diffusion des produits de l'exprience  SPOT4(Take5), nous pouvons examiner les statistiques des téléchargements effectués depuis le site de distribution du pôle THEIA : http://spirit.cnes.fr/take5/

 

  • 160 utilisateurs différents provenant de nombreux pays ont téléchargé des données, .
  • 75% des téléchargements concernent des produits de niveau 2A, et les utilisateurs qui ont téléchargé des produits de niveau 1C ont aussi, en général, téléchargé des données de niveau 2A.
  • 40% des téléchargements concernent des séries temporelles entières pour un site, 60% concernent des images mono-date. Si on tient compte du fait que les séries temporelles comportent en moyenne 14 dates, on en déduit que 90% des acquisitions sont téléchargées à partir de séries entières.
  • Chaque série temporelle a été téléchargée 12 fois en moyenne.
  • Deux utilisateurs (Français, je présume) prétendent s'appeler Titi et Toto.

Nombre de téléchargements de séries entières par site

 

Nous pouvons aussi obtenir un classement des 45 sites en fonction du nombre de téléchargements, et nous pouvons remarqué que chacun des 45 sites a été au moins téléchargé une fois. Ceci dit, même si les sites du CESBIO arrivent premiers, ce classement est probablement biaisé car certains laboratoires centralisent les télléchargements, alors que d'autres téléchargent plusieurs fois les données (parmi lesquels le CESBIO). Le dernier site de la liste a été ajouté récemment à la liste des sites.

 

Le nombre de communications ou de papiers par site sera bien plus intéressant, mais pour le moment, le compteur est bloqué à trois, pour autant que je sache (3 communications au Living Planet Symposium). Rappelez vous que la licence des données demande que chaque communication basée sur ces données soit envoyée au CNES (à Sylvia Sylvander et moi-même)

 

PS : ces informations sont obtenues grâce au formulaire saisi par chaque utilisateur, celui-ci est collecté dans la base de données mise en place par Jérome Gaspéri, et chaque mois, Bernard Specht, du CNES m'envoie les résultats.

SPOT4(Take5) data downloads statistics

Three and a half months after the first release of SPOT4 (Take5) products, we can draw a first analysis of the SPOT4(Take5) data downloads (from THEIA distribution website : http://spirit.cnes.fr/take5/)

 

  • 160 different users have downloaded data, from all over the world.
  • 75% of downloads are Level 2A products, and most of the users who downloaded Level 1C products also downloaded Level 2A.
  • 40% of downloads concern whole time series, 60% concern mono-date images, which means that, with an average number of 14 dates per site, about 90% of product downloads are downloaded as whole time series.
  • Each time series has been downloaded 12 times on average.
  • Two users (I would bet they are French) are named Titi and Toto

Number of downloads per site (only whole site archives)

We have also obtained a ranking of the 45 sites versus the number of downloads, and notice that all 45 sites where at least downloaded once. Well, although CESBIO sites come first (!), this is not a competition, and it is probably biased, as some well organised user groups centralise their downloads, while other labs (among which CESBIO...) have downloaded their sites several times. The least demanded site (Rennes), was added very recently to the list.

 

The number of communications or papers per site will be much more interesting, but as far as I know, the counter is still set to 3 (3 communications at the Living Planet Symposium). Please remember that users are requested to send us all their communications based on SPOT4(Take5) data.

 

PS : this information is gathered thanks to the information provided by users at each download, which is collected on the download site data base (designed by J.Gasperi (CNES)), and then provided to me each month by B.Specht (CNES).

SPOT4 (Take5) users's day presentations

Voici les présentations de la Journée SPOT4 (Take5) du 2 octobre, qui a réuni une centaine de personnes au CNES pour faire un bilan des acquisitions et des produits distribués, et prendre connaissance des premiers retours des utilisateurs. J'en profite pour remercier les deux organisatrices, Sylvia Sylvander et Danielle Barrère, du CNES (DCT/ME/OT), les 23 orateurs qui nous ont proposé de brillantes présentations, et le photographe (Gérard Dedieu) qui n'a oublié que 3 orateurs.

 

J'ai rédigé pour le CNES un bref compte rendu en Français. Pour voir les présentations, cliquez sur les liens dans le tableau ci dessous.

 

Here are the presentations from SPOT4 (Take5) users day on October the 2nd. 100 people attended this meeting at CNES, which aimed at making an assessment of the acquisition and products, and obtain a first feedback from users. I would like to thank a lot the two organizers, Sylvia Sylvander and Danielle Barrère from CNES, the 23 speakers, who delivered brilliant presentations, and the photographer (Gerard Dedieu), who only forgot 3 speakers.

 

The table below gives access to all the slides of the presentations.

 

 

O. Marsal

CNES Introduction
S. Sylvander CNES Preparation and progress of Take 5 experiment
O. Hagolle CNES/CESBIO Justification of Take 5 experiment, site selection and data access
M. Leroy CNES The THEIA Land Data Centre
O. Hagolle CNES/CESBIO First results
M. Claverie NASA GSFC Consistency of SPOT4 (Take 5) surface reflectance data: Comparison with MODIS surface reflectance data.
C. Szczypta CESBIO Application of remote sensing to snow modelling in the Pyrenees
JP. Dedieu LTHE/CNRS Grenoble Snow cover monitoring in the French Alps
B. Koetz ESA ESA preparatory activities for Sentinel-2 exploitation - Agriculture, Land Cover Change, Costal Monitoring & Forest Mapping
C. Corbane / F. Güttler UMR TETIS Contribution of remote sensing data with high repetitivity for the identification and monitoring of natural habitats - Application to Lower Aude Valley Natura 2000 site.
A. Govind INRA/Bordeaux High resolution mapping of LAI using SPOT-4 data for spatially explicit modeling of Carbon and Water Fluxes in the Landes de Gascogne
D. Jacques UCL Preparing for the exploitation of Sentinel-2 observations for agriculture monitoring
V. Gond CIRAD Phenological monitoring of tropical forest ecosystems (North of Congo)
E. Bartholome JRC First observations from SPOT 4 Take 5 data over intertropical regions
 

A. Jacquin / A. Roumiguié

EI Purpan Use of multitemporal series of high and medium spatial resolution for forest and biomass monitoring
D. Courault INRA Monitoring of the evolution of agri-hydrosystems in a mediterranean region
V. Lafon EPOC, Univ. Bordeaux Contribution of Sentinel-2 to coast management
S. Battiston SERTIT First results of Take Five experiments over the Alsatian Plain (France) and Chinese lakes in term of biodiversity, forestry and hydrology
M. Le Page CESBIO, UCAM, ORMVAH, INAT Preliminary results of a real time irrigation experiment in Morocco and first results in Tunisia
M. Battude CESBIO Contribution of optical multitemporal satellite imagery for the cartography of irrigated areas
Y. Justeau Exelis VIS Take 5 GeoProcessing with ENVI Services Engine
D. Giaccobo ASTRIUM-GEO Potential use of Take5 data for the ESA DREAM Data Quality Web Service

Les N2A perdent du poids

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C'est Mireille Huc qui a vu ce bug discret qui embêtait pourtant tous les utilisateurs des données de SPOT4 (Take5), sans qu'ils le sachent, depuis deux mois : les produits de N2A avaient une taille deux fois plus grande que nécessaire. Le bug s'est produit lors de la transformation des données au format Geotiff, uniquement sur la machine de production et pas sur les machines de test. Des données inutiles étaient ajoutées aux fichiers, qui ne nous empêchaient pas de lire les données utiles normalement.

 

Les données ont été corrigées et chargées sur le serveur de distribution dès le 10 octobre. Nous vous conseillons de les télécharger à nouveau, elles prendront beaucoup moins de place sur vos disques.

A new version of the SPOT4(Take5) products is available.

Here are the thumbnails from the China(2) site, for which several dates were missing on the version 1.0. Please note that on the server, you may download all the dates at once by clicking on the 1C or 2A buttons.

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The CNES teams of the THEIA Land Data Center have reprocessed the SPOT4 (Take5) data, in order to take into account a large number of images that were not processed in the first place, because some data had not been yet received or because their processing had failed due to a few little bugs.

 

The same processors and parameters were used and the only difference is the increased number of available dates, but as the L2A methods are multi-temporal and recurrent, when we add an image, the results on the subsequent images are also changed. It is thus advisable that you download again all the products of the sites you are interested in, from the following address : http://spirit.cnes.fr/take5

 

On this prototype ground segment, our management of product versions is basic, and only takes the processors into account. As the processors are unchanged, the new version 1.1 products are still identified as level 1.0 products in the Metadata. We are sorry for this inconvenience, you will need to pay attention not to mix them with the older version.

 

A few missing images

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I just took a work break in the middle of my holidays, but as I was away, we received a few feedbacks from users, and CNES PTSC teams, with Mireille's help at CESBIO verified the data sets released on July the 16th, in quite a rush...

 

They found out that a few scenes were missing. For some of them, it was due to the late arrival of some images (just as for planes at the airport). These images have already been added to the server.

And there were a couple of bugs that mostly affected the sites made of several SPOT images (CNES and NASA sites), and ESA Chinese site. These glitches have been corrected and the reprocessing started. The whole data set will be updated before end of August, which will constitute the version 1.1 of the SPOT4(Take5) data set.

 

Keep posted on this blog, we will update it as soon as the data are available. Meanwhile, version 1 is still accessible here, and the format described there.

 

Quelques données manquantes

J'ai pris une petite semaine de travail de travail au milieu de mes vacances, mais pendant ce temps, nous avons reçu quelques retours d’utilisateurs, et les collègues de l'équipe d'exploitation et de l'équipe de développement du PTSC au CNES, avec l'appui de Mireille au CESBIO, ont vérifié les données qui avaient été mises à disposition le 16 juillet, un peu "à l'arrache", il faut le dire...

 

Ils se sont aperçus qu'il manquait un petit nombre de scènes, par-ci par là. Pour certaines d'entre elles, c'était dû à la réception tardive des données (comme ils disent quand les avions sont en retard). Ces données ont déjà été remises à disposition, discrètement, sur le serveur.

 

Et puis il y avait un petit bug, qui faisait que les sites composés de plusieurs images (les sites du CNES et de la NASA), perdaient quelques dates. Le site Chinois de l'ESA a aussi été victime d'un autre bug. Ces bugs ont été corrigés, et les traitements viennent d'être relancés. Nous mettrons les données à jour d'ici la fin du mois d'août. Ce sera bientôt la version 1.1 des données.

 

Nous vous informerons donc sur ce blog dès que ces informations seront disponibles.En attendant, les données de la version 1. sont toujours disponibles ici et le format des données, .

 

 

 

 

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 !

 

 

 

 

 

L1C registration performances for SPOT4(Take5) V1 products

Now that all SPOT4(Take5) images have been processed (pfew !), we can make an appraisal of the performances. Let's start by the geometry, which caused us a lot of trouble :

  • SPOT4 has a location accuracy around 400 mètres, but during the experiment, it went through a fifteen day period when the location errors could reach 1500 m.
  • We seek a multi-temporal registration performance of 0.3 pixel RMS. This performance is difficult to measure because the measurement technique itself (correlation image matching) is not perfectly accurate.
  • We provide as a criterion the maximum registration error observed for the 50% best results or for the 80% best results. It is likely that the last criterion includes less inaccurate measurements.

 

Here are the observed performances for 3 very different sites :

  • CMaroc site, which is an arid site with a green period in march, a lot of blue sky, and high mountains (the Atlas). performances are excellent, with errors lower than 0.3 pixels for 50% of the measurementsl.

 

  • CBretagneLoireE site, which is a rather flat coastal area with large tides, and is often very cloudy. In that case, performances are still better than 0.5 pixels. The worse dates correspond to images with a large cloud cover, for which it is not easy to automatically collect accurate ground control points.

 

  • JSumatra site is a very flat area, covered with very uniform equatorial forest, and a large river whose limits change with time. In that case, the performance is really bad, with registration errors up to 10 pixels. This uniform site does not enable to find good control points, and the ones that are found are often along the river whose contour changes with the water level.

 

Conclusions

We have obtained very good results for most sites, with registration errors below 0.5 pixels (10m) even when the initial location error reaches 1500m. However, 4 sites are resisting to this processing. These 4 sites correspond to flat forest sites covered by equatorial forest : JSumatra, JBorneo, EGabon, ECongo. The ECongo site is even so uniform that it is not possible to measure its registration performance.

These sites will be distributed with the others in a few days with the first version of the products, but you should use them cautiously.

Finally, if the registration of 95% of images is good, the location performance is inherited from our reference images, ie LANDSAT (5 et 7). The next versions will be based on Geosud (IGN) images in France and on LANDSAT 8 data elsewhere. Performances should be enhanced in the next versions.

All the quicklooks

Before the distribution starts at the land data center (before mid July, or even sooner), I have updated all the quicklooks of all the images taken during the experiment. I have checked in the catalog to see if a few images had not been forgotten. I found about 20 images (on a total of 1600). These images will be processed soon.

 

You may find all the SPOT4 (Take5)  quicklooks following the links below, or via the SPOT4 (Take5) menu.