Very Large Scale Aerial Photography for Rangeland Monitoring

Ecological assessment of ground cover by conventional on‐the‐ground point sampling is labor intensive, expensive, and biased by access. Historically, motion blur has prevented high‐resolution aerial photography from being used for ground cover measurements. To reduce motion blur we used a fixed‐wing, 225‐kg (empty weight) airplane flown at 72 km/hr ground speed 100 m above ground level with both a modified Hulcher 70 mm camera (500 mm lens, Kodak Aerocolor HS SO‐846 film, 1/4,000‐second shutter speed), and a Canon 11. 1 ‐megapixel, automatic, digital single lens reflex, color camera (420 mm focal‐length lens). The resulting very‐large scale aerial (VLSA) photography had resolutions of 5.0 and 2.1 mm GSD (Ground Sample Distance) for the scanned film and digital‐camera images, respectively. Motion blur was minimal. The cost for obtaining 450 VLSA photographs over a 70,800‐ha watershed was $0.07 ha. We found our methods well adapted for extensive aerial surveys to monitor the ecological condition of rangeland watersheds.