The detection and interpretation of Alaskan fire-disturbed boreal forest ecosystems using ERS-1 SAR imagery

AVHRR data have been used to determine area and location of Alaskan fire scars in the 1990 and 1991 fire seasons. The detectability of fire scars as well as the estimates of area burned using AVHRR data are limited by the coarse resolution of the sensor (1 km). While such coarse resolution data are necessary for large area analysis, finer resolution sensors are preferable for more detailed studies of smaller regions. Initial observations of the European ERS-1 C-VV SAR satellite imagery have resulted in detection of recent (1-5 year old) Alaskan fire scars. These recently burned areas have a brighter radar return in the ERS-1 SAR imagery (3-6 dB brighter) than adjacent unburned forests. The enhanced radar return from fire scars has been found to vary spatially across a fire scar as well as temporally throughout a season. The purpose of this study is to analyze this variability and to determine the best season in which to detect fire scars and to estimate the area burned. Since the ERS-1 SAR has much finer resolution (30 m) than the AVHRR sensor, area estimates of burn should be substantially more accurate. This study focuses on several fire scars throughout the interior of Alaska from the 1980s and 90s. Seasonal ERS-1 data of these fire scars were obtained from 1991 to 1994. Area estimates of the burned regions in the ERS-1 imagery are calculated through the use of a GIS database. This GIS database also contains burn boundaries mapped by the Alaska Fire Service (AFS). An evaluation of the ERS-1 area estimates is made through comparisons with AFS records and estimates obtained using the AVHRR sensor.