As an aid to forest resource management, DNR Forestry acquires color infrared aerial photographs of forested counties on a rotating basis, covering each county about once every 8 years. Taken from 7900 feet above ground, the photos in their original form are highly detailed, showing individual trees, buildings and vehicles. Each covers an area slightly larger than four square miles. They are taken with 60% stereoscopic overlap for three-dimensional viewing. DNR airphotos appear predominantly red because they are taken with color infrared (CIR) film, which displays healthy vegetation in red rather than green tones. On CIR film, clear water usually looks black, turbid water looks blue, and paved surfaces are usually blue-gray. DNR photos are normally taken during fall, to capture leaf color changes that help distinguish vegetation types. Conifers (pines, spruces, firs) normally appear darker red than broadleaved trees.
When a new set of aerial photos is taken, we scan the resulting prints, which have a scale of 4 inches per mile, at the rate of 400 pixels per inch (or 300 pixels per inch for photos taken before 2002) to produce digital images. This captures a great deal of detail (each picture element measures just 1 square meter on the ground), but it creates a substantial 38-megabyte file.