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VEGETATION - 2000

Lake Maggiore - Italy, 3-6 April 2000


Vegetation Action & Demonstration Plan for dry grassland monitoring in Senegal

Christian CREPEAU SCOT
Partners of the study
CSE (Centre de Suivi Ecologique), Dakar, Sénégal.
CNES, SCOT

Paper (pdf file, 2.26 M)

This study aims to demonstrate the contribution of Vegetation data for monitoring land cover in dry grassland areas in Sénégal and to identify the optimum conditions to allow Senegalese and Sahelian users to use Vegetation data and derived products in an operational mode.

Actions carried out

Acquisition, processing and photo-interpretation of VGT data concerning the 1998 and 1999 agricultural seasons. These data were provided by the CTIV in the form of ten-day synthesis (S10).

Validation using ground survey data collected by the CSE and production of chronological and differential NDVI-VGT maps.

Acquisition and processing of several AVHRR images concerning the 1998 summer in the form of ten-day synthesis provided by the CSE HRPT receiving station.

Ground survey campaign (36 sites) during the 1998 summer.

First Results

Users needs assessment, and evaluation of the AVHRR-derived products elaborated in Sénégal and in the Sahel region,

Design of new VGT-derived mapping products :

Item 1 : chronological analysis (synoptic view of the NDVI of all the dekads)

Item 2 : differential analysis (comparison between a dekade d, the previous one d-1, the same decade the year before).

Item 3 : thematical ancillary data (land use, rainfall, soils, population, altitude, crops, …) aiming to facilitate NDVI interpretation.

Quality assessment of the S10-NDVI layer. Excellent in spite of some technical problems (insufficient cloud masking, too large coastal buffer).

Interpretation of the VGT images. In the area where the NDVI value is the highest, land cover is composed of annual crops, savannah and wet forests (mangrove). In the area where the NDVI value is low (North and East) the soil is generally sandy and land cover is of rangeland type with local xerophytic woody species adapted to drought. The quality of VGT geometry and radiometry allows to identify very small features.

Conclusions:

To develop the VGT data market in Africa and within the international organisations, a second phase should be dedicated to the development of new methodologies able to produce dry lands monitoring indicators using VGT data plus climatological and socio-economical data.