How are smoke plumes detected by the AVHRR satellite sensor?
Smoke plumes from forest fires tend to be highly reflective and therefore are often difficult to distinguish from cloud. Yet AVHRR imagery does provide some information that can be used to effectively distinguish thick smoke from cloud cover. Thick smoke and the underlying land surface are generally warmer than cloud and therefore produce a larger signal in the thermal infrared channels. In addition, smoke plumes tend to have a smoother spatial texture than many cloud types at a 1-km² scale. A recent study by Li et al. (2000a) examined various techniques for identifying smoke using AVHRR, including artificial neural networks and multiple threshold tests. For smoke detection in Fire M3, a multiple threshold approach has been adopted. The thresholds are designed to be conservative, in that false smoke pixels are kept to a minimum, while only the more optically thick smoke is detected. Note that even this conservative approach to smoke detection can lead to false smoke pixels. Smoke plume
