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Geo-location assessment of MERIS Globcover ortho-rectified products

P. Bicheron(1), V. Amberg(2), L. Bourg(3), B. Miras(1), C. Brockmann(4), S. Delwart(5), Ph. Goryl(6), F. Ranéra(6), O. Hagolle(7) and O. Arino(6,6)

(1) MEDIAS-France, CNES, Bpi 2102, 31401 TOULOUSE Cedex 9, France
(2) MAGELLIUM, 24 rue Hermès, BP 12113, 31521 Ramonville Saint Agne, France
(3) ACRI-ST, 260 route du Pin Montard, BP 234, 06904 Sophia-Antipolis Cedex, France
(4) Brockmann Consult, Max-Planck-Strasse 1, D-21502 Geesthacht, Germany
(5) ESA-ESTEC, Keplerlaan 1, Noordwijk, Netherlands
(6) ESA/ESRIN, via Galileo Galillei, 00044 Frascati, Italy
(7) CESBIO, 18 avenue Edouard Belin, 31401 Toulouse Cedex 9, France


The GLOBCOVER product from the European Space Agency (ESA) provides a land cover map using as its main source of data the fine resolution (300m) mode data (FRS) to be acquired over the full year 2005 by the MERIS sensor on-board the ENVISAT satellite. Distinction in land cover types at global scale uses primarily the seasonal characteristics of vegetation generally based on the temporal dynamics of spectral information and derived from the compositing of multiple single orbits into a single dataset. Relative geo-location at a high level accuracy is therefore a critical step for each orbit as well as an absolute geo-location for studies in a geographical scope.

The initial accuracy specifications for MERIS absolute geo-location was 2000m with an operational goal of ±150m at nadir corresponding to about the half size of a ground pixel. Initial geo-location performance was significantly worse than required because of sensor attitude inaccuracies. Regular improvements concerning the MERIS pointing as well as the attitude on–board software have been made. The recent development of Accurate Meris Ortho-Rectified Geo-location Operational Software–AMORGOS (Bourg et al., 2007) provides a geo-location information for every image pixels and not anymore at one pixel per 64 in the Full Resolution product.

Our objective is therefore to evaluate whether the requirements of 150meters (absolute geo-location error) are fulfilled on a global basis after the geo-location AMORGOS and the cartographic projection module. These assessments are performed by correlating these output products with a reference database through the processing of disparity measurements in column and line shifts. Initial results are very satisfactory with an absolute geo-location error of 77 meters and a relative geo-location error of 51 meters.


Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry