Central African Forest Cover and Cover Change Mapping

the 1930’s following the completion of the first botanical and ecological studies. These mapping efforts were based on aerial photography interpretations coupled with numerous groundbased observations. National and regional maps were mainly derived from the compilation of local studies, resulting in compatibility problems such as the matching of contiguous map edges. Th e UNESCO/ AEFTAT/UNSO (White, 1983) potential vegetation map of Africa is the result of a long effort to mosaic existing maps and standardize existing documents with local experts. The vegetation map of Africa produced by the Institut de la carte internationale de la vegetation is also based on the compilation of information existing at the national level, and on the interpretation of Landsat mosaics for transition zones. For the past ten years, Central African vegetation maps, and forest cover changes estimates, have been primarily derived from satellite imagery, which provides undeniable benefits: simultaneous data acquisition over very large areas, repeated acquisition (for a better monitoring of seasonal and inter-annual ecosystem evolution), better geographic accuracy, and observations in wavelengths beyond the visible range (increase of thematic information). These innovative projects have demonstrated not only the possibilities for improving vegetation mapping, but also revealed limitations that need to be taken into consideration when mapping Central Africa. • In particular, the quasi-permanent cloud coverage over numerous areas of the Basin (Atlantic Coast, South Congo) poses difficulties for accurate mapping. There are two options to overcome cloud coverage: daily acquisition of coarse resolution optical data (SPOT VEGETATION, MERIS, MODIS) or radar observation (ERS, JERS, Radarsat) that are not affected by cloud coverage. • Coverage of the region from high-resolution polar orbiting sensors is rare. • Another limitation is the absence of a permanent receiving station in the region. Mobile receiving stations, portable acquisition systems, and on-board recorders can provide potential solutions to this problem (Box 9.1). • Difficult access to the field due to limited infrastructure impedes validation efforts. • Vegetation seasonal effects require the use of systems with high temporal acquisition frequency (optical systems with coarse spatial resolution).JRC.H.3-Global environement monitorin