A GIS BASED METHODOLOGY FOR SMALL-SCALE MONITORING OF TROPICAL FORESTS - A CASE-STUDY IN SUMATRA

A Geographical Information System based methodology was developed in t he framework of global survey of tropical vegetation using satellite d ata; it was tested on the forests of Sumatra with time series of NOAA AVHRR GAC and LAC data of 1982, 1988 and 1989. After some geometrical registration and radiometric optimization, these data are processed th rough a mono-date approach for minimizing the strong and highly variab le atmospheric effects. Final results are derived from superimposing s ingle-date classification outputs. Due to the low resolution of satell ite data and the small size of local systems, adequate reliability for sampling and classification processes require the introduction of geo graphical information (topography, soils, bio-climates); iterative int eractive procedures are used for that approach. Elevation is especiall y useful due to the altitudinal zonation of natural vegetation. Differ ent classification rules based on satellite and geographical informati on are tested and compared for assessing the potential of NOAA AVHRR d ata for small-scale survey of tropical forests. Finally, the vegetatio n maps of Sumatra in 1982 and 1988 are obtained, and the on going defo restation rate is estimated.