72 REPORT OF COMMISSION VII 
cially at high latitudes, and in winter time when the sun is low, it is possible, 
thanks to the shadows, to follow solitary ski tracks, even when the photos were 
taken at as great an altitude as say 33,000 ft. (about 10,000 m.). Very well 
camouflaged vehicles are as a rule revealed by their wheel tracks, as is also the 
case with gun positions carefully concealed in woods. Generally speaking, tracks 
and paths, which do not conform to the natural lines of the terrain, always 
  
Fic. 14. An interpreted aerial photograph (vertical) of positions in a partially woody district 
on both sides of a sound. 
A—A —antitank ditch with crossing-place at I 
B—B =barbed wire belts, with openings, among others, at I 
C—C =infantry trenches 
D =flanking weapons (probably machine guns) which flank a part of the barbed wire belt 
E =machine gun nest, flanking before D, probably with a secondary field of fire towards the 
bridge and road 
F —2.9" (7.5 cm.) A.A. battery with probable task, among others, to defend the bridge 
G =emplacements for 4.7” (12 cm.) mortar battery 
H =40 and 20 mm. A.A. gun towers with probable mission to supplement the fire from the 2.9” 
A.A. battery at F 
I—I =vehicle tracks. 
tend to betray and to give the interpreter the possibility of discovering troops 
even in wooded country. Every day spent there makes it easier for him to re- 
veal them. In summer, or otherwise when the ground is green, tracks of vehicles 
and human beings, and perhaps even the direction in which they have gone, may 
be discovered because blades of grass have been bent or broken, thus reflecting 
light in a different way. Barbed wire is similarly detected; the nearby vegetation 
usually remains undisturbed by humans as well as by animals, while on the 
other hand, adjacent crops are usually cut or the fields are used as pastures. 
The vegetation density often is greater within the barbed wire area, among 
other reasons because of greater moisture round the posts and the wire fastenings