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4. Diurnal temperature changes that oc^ur in soil masses (these 
provide clues to the soil-water mass conditions). 
Tanguay and Chagnon (16) demonstrated the value of infrared imagery and 
aerial photography for evaluating the moisture and drainage regime asso- 
ciated with a landslide. A flow slide had occurred within the crater of 
a former slide in clay lake beds in the vicinity of St. Jean-Vianney, 
Canada. To plan a drilling program to evaluate the potential of further 
movements required that the areas of seepage, water runoff, and wet 
soils be identified. By means of photography alone, these features 
could not be uniquely separated from areas of standing water, topographic 
shadows, and dense vegetation (brush and forested zones), because they all 
produced similar dark tonal patterns. However, the combination of photo- 
graphy and daytime and nighttime imagery made it possible to separate 
these various features and identify the critical items for planning the 
drilling program. 
Figures 4 and 5 show some of the results reported by Tanguay and Chagnon. 
Figure 4 shows daytime thermal infrared imagery obtained in the 8 to 
l4-um band and black-and-white infrared photographs of a portion of the 
aroa shown in the imagery. Several of the seepage areas (points a and 
b) interpreted from this figure were drilled and indicated very deep 
and soft clay starting from the surface. The c points indicate both 
seepage and runoff in a farm field; and d points show standing water 
coming from snowmelt and surface drainage; and the e points depict the 
boundary of the recent slide. Point f indicates the uppermost boundary 
of an older slide surface. In this figure, Seepage areas, runoff, and 
standing water are dark on both images. On the predawn infrared 
imagery in Figure 5, standing water (points a and f) is warmer and has 
light tones while seepage zones and runoff (points c and d) are cooler 
and have darker tones. On the photography, all of these areas have 
dark tones.  Vegetated areas occurring between the areas of standing 
water in this figure have a medium tone on the imagery and appear as 
white specs on a dark background on the photography. 
Figure 6 shows a nighttime (predawn) infrared image of an area along a 
railroad line being investigated for locating potential areas for land- 
slides. The railroad had been plagued for years with landslide problems. 
The circled darker areas were interpreted as zones of seepage and high 
moisture levels--potential for landslides. Based on this analysis, the 
circled areas were drained, and no further slides have occurred in those 
areas. 
Other systems 
Other remote sensing systems such as multispectral imagery, microwave 
(radar) and microwave radiometry offer potential for indicating the 
presence of landslides. The application of these systems are just 
briefly summarized because at this time, either further development 
is needed, or the systems are too costly in comparison to the level of 
information furnished.