Measuring snow depths by aerial photography

Aerial photogrammetry is used to measure snow depth over a 100 acre study basin in southwestern Idaho. This procedure was demonstrated successfully and shown that the same procedures used in modern aerial topographic mapping can be applied to snow covered terrain. However, some additional problems are introduced. A base control system is necessary to develop a point grid system for subtracting the soil surface elevations from the newly derived snow surface elevations. The latest model of aerial photo plotting machine is used for this work. Other problems arise in the photographic exposure and development film. Some difficulty is experienced with using filter lenses to bring out the definition of the snow surface of new fallen snow that appears always flat in certain lights without shadows, and wrinkled wind blown surfaces create a problem at times. Newly available data on processing equipment and computer techniques will aid materially in soling some of these minor problems.