Vertical air photo: A11569-201
Flight height: 7,920 feet a.s.l.; lens focal length: 152.4 mm
Scale: 1:14,700 (approx.)
Date: August 18, 1948
Location: Township 18, Range 21 WI
Map sheets: 1:250,000: 62K Riding Mountain
1:50,000: 62 K/9 Elphinstone
In this area of hummocky ground moraine topography, numerous small lakes (sloughs) can be seen. In the centre and north they are dark-toned 1 whereas in the southeast they are light-toned 2. The light tone is a result of the relationship between the camera angle, the sun angle, and the water surface, a phenomenon known as specular reflection. The diagram below shows the conditions under which specular reflection occurs. Objects at E would show the effect whereas objects at F would not.
The very light-toned lake in the west 3 is probably a dried up lake with a salt surface resulting from evaporation. The same process seems to be starting at another lake further south 4, which was obviously once much larger 5 and now has white deposits along its shore 6.
The photo also illustrates the interpretation criterion “texture.” The central lake 7 is uniformly dark-toned and has a smooth texture whereas wooded areas to the north 8 and south 9 have variable tones resulting from the way light falls on tree crowns and sides. The result is a mottled texture.