Airphoto Analysis of Winter Seismic Disturbance in Northeastern Alaska

Airphoto interpretation was used to quantify the extent of disturbance caused by seismic exploration on the 60,000 ha coastal plain of the Arctic National Wildlife Refuge during the winters of 1984 and 1985. The relationships of vegetation type, trail location and traffic pattern to the amount of disturbance were investigated. Approximately 20% of the seismic trails were photographed at 1:6000 scale, using color infrared film. Ground data collected at 194 sites were used to develop a photo interpretation key describing the photo signatures of seven vegetation types and four disturbance levels. Vegetation types and disturbance levels were determined for 4914 circles of 3 mm diameter on the aerial photos (18 m ground distance). Fourteen percent of the points were interpreted as having no disturbance (level 0), 57% had level 1 disturbance (low), 27% had level 2 (medium) and 2% had level 3 (high). Wet or partially vegetated areas were the least susceptible to disturbance. Vegetation types with mounds, tussocks, hummocks or high-centered polygons and dryas terraces were more heavily disturbed. Camp move trails and overlapping seismic and camp move trails created in 1984 caused more disturbance than other trail types due to multiple passes of vehicles over narrow trails. U.S. Fish and Wildlife Service monitors were more successful at minimizing disturbance the second year by requesting that vehicle operators avoid multiple passes on the same trail, sensitive vegetation types and areas of low snow cover.Key words: airphoto analysis, winter seismic exploration, seismic trails, vegetation disturbance, traffic patterns, Alaska, Arctic National Wildlife Refuge, arctic coastal plainMots clés: analyse de photographies aériennes, exploration sismique d’hiver, pistes sismiques, perturbations de la végétation, schémas de circulation, Alaska, Arctic National Wildlife Refuge, plaine côtière arctiqu