Vegetation characterization and land cover mapping with NOAA‐AVHRR data in the wet tropics

Abstract

Abstract The 1 km resolution of NOAA (National Oceanic and Atmospheric Administration) AVHRR (Advanced Very High Resolution Radiometer) data, has been found suitable to study forested/non‐forested areas. These data are however, strongly affected by atmospheric conditions in the equatorial tropics. This paper examines the problem of identifying and characterizing spectral contrasts between the evergreen rain forest, and contiguous vegetation cover types (various forms of secondary or degraded formations) in Sumatra (Indonesia), and the problem of establishing a typology of forest/non‐forest interfaces as seen at the resolution of AVHRR data. Time series of NOAA AVHRR Local Area Coverage (LAC) and High Resolution Picture Transmission (HRPT) data of the 1990 period have been processed. Some ancillary data such as vegetation maps have been digitized. The analysis of the data set is based mainly upon radiometric transects, the advantage of combining the NDVI (Normalized Difference Vegetation Index) and the middle infra‐red channel is demonstrated. To assess the forest/non‐forest cover with AVHRR data, a methodology for coping with the amount of data, cloud cover and spectral discriminants is tested. Finally, the AVHRR output classes are closed evergreen forest, degraded/fragmented forest and non‐forest. Classification results are presented and compared with existing maps. The systematic regroupement of the degraded/fragmented forest with the forest class leads to an overestimation of the forest cover. The analysis procedure described in the paper gives a basic indication of how the AVHRR data can be used and proposes a typology of forest/non‐forest dealing with the problem of interfaces over the wet tropics.