See TM 5-246 for technical information on stereopairs. Concealment provided by cover of darkness may be of no value where night photography is possible. An object which measures approximately .0125 inches on a photograph can usually be identified. A foxhole with a parapet made of spoil is 7 to 8 feet in diameter. The intensity of sound at the source and the enemy's means of intercepting it are major effective factors.
Sound carries well at night, in mist, fine rain, and on water.
Both lack of wind and wind blowing from the camouflaged object favor sound-carrying. Wind blowing from the observer to the camouflaged object detracts from sound-carrying. Heavy and thundery weather have the effect of subduing sound. These influences must be considered. Diameter of foxhole, including spoil, is 0.018 inch on photograph.