Effect of scan angle on AVHRR fire detection accuracy in interior Alaska

Some AVHRR fire detection studies have excluded pixels that exceeded an arbitrary scan angle. This exclusion seems to be based on the distortion of pixels at high scan angles and the well-documented effects of scan angle on the Normalized Difference Vegetation Index. However, excluding high scan angle pixels reduces the temporal resolution of an AVHRR fire detection system, especially at high latitudes. High scan angle pixels may be less obscured by smoke compared to near-nadir pixels. We tested the effect of scan angle on AVHRR fire detection by comparing scan angle classes of less than and greater than 25 degrees from sixteen AVHRR images of interior Alaska. At scan angles under 25 degrees, 35/86(40%) of fire observations were detected. At scan angles over 25 degrees, 24/53 (45%) of fire observations were detected. For interior Alaska, where cloudy, low-fuel conditions exist, and 8-12 AVHRR images are available daily, we recommend not excluding high scan angle pixels for wildfire detection.