COMPARISON OF FIRE DETECTION IN SAVANNAS USING AVHRRS CHANNEL-3 AND TM IMAGES

Detection of active fires in NOAA-11 AVHRR channel 3 (3.75 mu m) after noon images for an area of savannas in central Brazil was studied in r elation to fire scars in Landsat TM images. Three consecutive TM image s of the same area thus covering two periods of 16 days provided the ' ground truth' for the comparison of fire detection in AVHRR images of 15 and 14 days in each period. Using TM data as reference, 57 per cent of the new fire scars were associated with fires in channel 3 at the same places, in the first period. Seventy-four per cent of the active fires detected by AVHRR were verified in the TM imagery while the rema inder was associated mainly with agricultural areas burned before the first period. For the second period, percentages were 53 per cent and 36 per cent respectively; the high percentage of unverified fires occu rred mainly in grassland areas previously burned. Reasons for these re sults are discussed, namely, reflective soils in AVHRR's channel 3, fi re scars not detected by TM because of precipitation, wind and fast ch anges in soil surfaces, and fires not active, or covered by clouds dur ing AVHRR overpasses. A regression equation between the areas of the A VHRR fire pixels and of TM fire scars is also presented for the study area.