Aerial Films and Solar Angles: Influences on Silver Sagebrush Inventory

Abstract

Aerial photos in Alberta are generally acquired according to topographic mapping and forestry specifications. The parameters for interpreting rangeland vegetation, such as silver sagebrush (Artemisia cana-Pursch), need to be explored and condensed into an operational specification. Five aerial films and 3 solar angles were evaluated by 7 photo interpreters to determine the optimal conditions for interpreting silver sagebrush at a scale of 1:20,000. Interpreter accuracy and preference are determined for the 2 experimental conditions as to determine operational specifications. Kodak Panatomic-X 2412 achieved the highest interpretation accuracies for silver sagebrush cover detection and plant density estimation (91.0% and 94.4% respectively), while Kodak Aerochrome Infrared 2443 and Agfa Avicolor H100 performed best for estimating plant vigor (92.7% and 93.7% respectively). Photo interpreters also chose Kodak Panatomic-X 2412 as the preferred film for interpreting silver sagebrush (7.7 on a scale of 10). Positive correlations were obtained between combinations of interpretation accuracy, interpreter film preference and photographic density range measurements, indicating the trends for higher accuracy and preference are associated with higher density ranges. Solar angles of 20 degrees, 37 degrees and 54 degrees were evaluated by photo interpreters with significant preference shown for 20(.). Recommendations for modifying Alberta's air photo operational specifications to include high resolution (Kodak Panatomic-X) imagery and decreasing the acceptable lower boundary for the operational solar angle from 30 to 20 degrees for interpreting silver sagebrush at the 1:20000 scale are proposed.