Inter-comparison of SEVIRI/MSG and MERIS/ENVISAT biophysical products over Europe and Africa
F. Javier García-Haro(1), Fernando Camacho-de Coca(2) and Joaquín Meliá Miralles(1)
(1) University of Valencia, Dr. Moliner 50, 46100 Burjassot, Spain
(2) EOLAB SPAIN, Pol. La Coma s/n, 46980 Paterna, Spain
The scope of the Satellite Application Facility on Land Surface Analysis (LSA SAF) is the development and implementation of algorithms, which take full advantage of remotely sensed data from EUMETSAT geostationary (MSG, Meteosat 8-10) and polar orbiting (MetOp series) satellites. The vegetation products are the fractional vegetation cover (FVC), the leaf area index (LAI) and the fraction of Absorbed Photosynthetically Active Radiation (FAPAR). The user may access via the Land-SAF web page to daily estimates of these parameters, generated on a pixel-by pixel basis at the SEVIRI/MSG resolution over Europe, Africa and South America since January 2006. The products will be disseminated via EUMETCast in short, particularly for the benefit of African and European users.
The validation is a challenging task particularly regarding the extent of the products, the spatial resolution, as well as the dynamics of the vegetation. Different validation exercises have been carried out in parallel to the development of the different versions of the Land-SAF algorithm for retrieving FVC, LAI and FAPAR through an inter-comparison with other programs, particularly MERIS/ENVISAT, VEGETATION/SPOT and MODIS/TERRA. In this study, MERIS TOAVEG (FVC, LAI and FAPAR) and MERIS MGVI FAPAR products from two different algorithms delivered by ESA have been processed from MERIS-1km TOA data obtained from an ESA cat-1 project over a two-year period. MODIS collection 5 (LAI and FAPAR) recently released products have been used as a reference. In addition, the consistency of Land-SAF products against ground measurements representing different continental biome types and conditions has been demonstrated.
A strategy has been developed to obtain temporal composites of MERIS vegetation products over Europe and Africa, with a frequency of production of 10 days. A semi-Gaussian filter function was used to enhance the stability of the MERIS products and fill in the gaps due to MERIS observations affected by clouds. The MERIS vegetation fields were then compared against Land-SAF vegetation v2.1 products for the same period (January 2006 – March 2008). Land-SAF FVC presents a reasonably good agreement with MERIS FVC over Europe and North Africa, with resulting RMS of about 0.14 and 0.10, respectively. The main differences are found in South Africa due to a systematic bias. In addition, the Land-SAF, MERIS and MODIS LAI products have compared reasonably well over Europe and Africa. The observed deviations between Land-SAF and equivalent products are in the order of 0.10-0.15 for FVC, 0.5-0.8 for LAI and about 0.10 for FAPAR. This result proves that Land-SAF and MERIS vegetation products are highly consistent spatially and temporally.
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,