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VEGETATION - 2000

Lake Maggiore - Italy, 3-6 April 2000


Monitoring of forest ecosystems at regional scale using VEGETATION daily-data : First results on the Landes maritime pine forest (SW France)

Jean-Pierre Lagouarde 1,Dominique Guyon 1, Benoît Duchemin 2
(1) INRA, Unité de Recherche en Bioclimatologie, BP81, F-33883 Villenave d’Ornon Cedex
(2) CESBIO, 18 Av. Ed.Belin, F-31055 Toulouse Cedex

Paper (pdf file, 189 k)

Previous studies carried out within the framework of Vegetation Preparatory Program on coniferous and deciduous forests using VEGETATION data simulated from AVHRR/NOAA and Landsat TM time-series. They demonstrated the potential of VEGETATION daily-data for monitoring large-scale spatial heterogeneity and temporal changes of biophysical variables which determine surface-vegetation-atmosphere transfer, net primary production (NPP), forest growth, forest yield and other environmental processes: phenological cycle duration, albedo, fraction of photosynthetic radiation absorbed (fAPAR) by forest canopy, trees-cover fraction…

We present here applications performed with actual VEGETATION daily-data for estimating these variables. The study is based on a VEGETATION daily-data set acquired during one cycle of vegetation (31 March to 7 November 1998) on the Landes maritime pine forest. It is complemented by ground measurements of forest biophysical variables and land-use geographical data base, on the test site of NEZER which covers about 3000 hectares.

The directional variations of reflectance in visible (VIS), near infrared (NIR) and middle infrared (SWIR) are analysed. A semi-empirical model of BRDF (Rahman model) already tested in the ‘pre launch’ phase of the preparatory program is fitted. Applications for the normalisation of reflectances, the estimation of albedo and fAPAR are presented and the consequences of the sampling of the BRDF during only one year discussed.

The spatial variations of reflectance and their sensitivity to forest structure parameters are also studied. VEGETATION reflectances are compared to tree-cover fraction estimated at 1km² scale from ground measurements. The practical interest of vegetation indices including the SWIR reflectance to reduce the seasonal sensitivity to phenological properties of undergrowth is analysed.