Aerial Films for Forest Inventory: 0ptimizing Film Parameters

Abstract

Recent advances in aerial film emulsions and processing techniques have not been evaluated to determine their suitability to forest inventory operations. Five black-and-white films (Kodak's Double-X 2405, Infrared 2424, and Panatomic-X 2412; Agfa's Aviphot Pan 200; and Ilford's FP3) and two color films (Kodak's Aerocolor 2445, and Aerochrome Infrared 2443 processed as a positive and as a negative) were evaluated for their accuracy and user preference for forestry photo interpretation at a scale of 1:20,000. The black-and-white films were also exposed and processed at three average gradients (1.0, 1.4, 1.8) except for the Panatomic-X (1.8, 2.0, 2.2) and Ilford FP3 (1.4 only). Species composition, crown closure, stems per hectare, and height were examined collectively to determine photointerpretation accuracy for each film/average gradient combination. The highest interpretation accuracies were attained when average gradients produced densitometric range measurements of 0.11 to 0.17 (0.12-mm aperture) in mixed coniferous-deciduous forest stands. The Panatomic-X emulsion achieved the highest interpretation accuracy (83 percent) and Aerocolor 2445 attained the lowest (68 percent). Interpreter preference was highest with Aerochrome I.R. 2443 positive processing (7.2 on a scale of 1 to 10) and lowest with Aerochrome I.R. 2443 negative processing (4.1 on a scale of 1 to 10). Higher interpreter preferences were associated with increasing spectral sensitivity to the infrared. There was no correlation, however, between interpreter accuracy and preference for the 16 average gradient/film combinations. Using Panatomic-X film in forest inventory entails practical trade-offs between gains in interpretation accuracy and its requirements for proper exposure. Panatomic-X is a fine-grained, slow speed film with narrower exposure latitude, narrower photo acquisition windows (day and season) relative to other panchromatic films, and likely requires image motion compensation for optimal exposure at a scale of 1:20,000