How are forest fires detected by the AVHRR satellite sensor?
The most important AVHRR channel for fire detection is the mid-infrared channel, which measures a combination of reflected and thermal energy at wavelengths around 3.7 µm. This channel is highly sensitive to objects that are emitting thermal energy at high temperatures (over 200°C), such as vegetation fires. For this reason, the AVHRR sensor can detect fires that cover only a fraction (less than 0.1% or 1200 m²) of a 1.2-km² AVHRR pixel. Since other types of objects, such as cloud edges and exposed soil, also produce a large response in the mid-infrared channel, information from other AVHRR channels is required to filter out extraneous data (“false alarms”). The AVHRR fire detection algorithm used in Fire M3 was developed and tested specifically for boreal forest fires. It is described in publications by Li et al. (2000b,2000c).
