b. Bivouacs are nonpermanent encampments of short durations in which troops are
rested under improvised shelter and prepared for further movement. Bivouacs of small
transitory units dispersed near the front line have little target value, but may be valuable
sources of intelligence about unit movements. Larger bivouacs of a more permanent
nature, particularly those in rear areas, are more valuable as targets. Larger bivouacs are
an important indication of large-scale troop and equipment movement. There are several
identification factors which lead to the discovery of bivouac areas:
(1) Equipment. It is very hard to hide large quantities of vehicles. Trucks,
trailers, tanks, artillery, and engineer equipment are bulky and can be detected when
studied on imagery under the stereoscope if they are not properly dispersed, or if the tree
cover is too thin.
(2) Spoil. A large amount of digging is done at bivouac sites. The excess earth
is usually piled up around each hole or ditch. This newly turned dirt will show up on
imagery in different tones and shades than the surrounding soil.
(3) Tracks. When large quantities of vehicles are moving in the area, the track
activity left by the vehicles will show up on imagery. It is almost impossible to hide track
activity (Figure 2-8).
(4) Litter. Troops occupying an area usually leave small holes, broken shrubs,
uprooted trees, crushed grass, paper, and other odds and ends, which cause an untidy
appearance and are easily detected on imagery (Figure 2-8).
(5) Shelters vary from slit trenches or fighting positions covered with individual
tents or tree branches to fairly elaborate shelters or bunkers, depending upon the length
of the occupancy.
(6) Related features. Bivouacs contain garbage pits, latrines, field kitchens,
and sometimes large recreation tents and headquarters shelters. The extent of these
features will depend upon the size of the unit and the length of occupancy.