Investigation Methods and Procedures - Geotechnical Engineering Investigation - page 33

FIGURE 2.12
Stereo-pair of aerial photos (scale 1:8,000) of a portion of Figure 2.11 provides substantially more detailed
information on the soil conditions and their distribution. The spoon-shaped slide that occurred in residual soils
is clearly apparent. Its rounded forms, resulting from erosion, indicate that the slide is relatively old.
A stereo-pair at a scale of 1:40,000 is given in Figure 2.11. It shows the landform developing
in metamorphic rocks from subtropical weathering. Slump slide scars are observed on the
photos. Figure 2.12 is a stereo-pair at a scale of 1:8,000 of a portion of the area in Figure 2.11.
A geologist interpreting stereo-pairs with a stereoscope is shown in Figure 2.13.
The elements of imagery interpretation are summarized in Table 2.5. CIR ( Figure 2.8)
depicts landscapes in colors very different from those in true color photos. Healthy
vegetation, for example, appears in shades ranging from bright pink to deep-reddish
brown. Table 2.6 lists different colors of some typical surface materials as shown in CIR
photographs.
Samples of stereo-pairs of aerial photographs included in this topic are summarized in
Appendix B. Techniques of terrain analysis and air photo interpretation are described by
Way (1978), Lueder (1959), ASP (1960), Belcher (1948), and Avery and Berlin (1992), among
others.