THE LIMITATIONS AND POTENTIAL OF AVHRR GAC DATA FOR CONTINENTAL-SCALEFIRE STUDIES

Global Area Coverage (GAC) data from the Advanced Very High Resolution Radiometer (AVHRR) arc available on a daily basis, dating back to Jul y 1981. The AVHRR's 3.55- 3.93 mum channel is suitable for detection o f terrestrial hot spots, such as bushfires. The long-term archives and global cover make the GAC a potentially valuable data source for larg e scale fire studies. However, these data are sampled spatially throug h a combination of line skipping and averaging. This study shows that the sampling affects the sensitivity of GAC for fire detection in rela tion to ecosystem and season. The GAC are found to provide a reasonabl e measure of fire activity in grassland and open bush savannah, but to perform poorly in the forest margins. Overall at least 79 per cent of fires detected with non-sampled AVHRR data are missed by the GAC. Thi s severely limits the use of GAC data for quantitative fire studies. T he GAC does appear to provide a reasonable measure of fire calendar (i .e., variations in fire activity with time) and on a continental scale successfully identifies the main regions of fire activity. The potent ial of these data for continental scale fire studies is illustrated th rough the preliminary analysis of 277 GAC mosaics of Africa for the pe riod September 1988 to August 1989.