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Multispectral systems obtain simultaneous coverage of data in several 
spectral regions--usually a portion of the ultraviolet, the visible, 
and both infrared reflectance and infrared emission regions. The data 
are collected on magnetic tape, which makes them amenable to the use 
of computer analysis techniques. Extensive research has been performed 
in using computer analysis techniques for identifying rock, soils, 
vegetation and other terrain features important for landslide investiga- 
tions. Fairly good success has been reported in identifying these 
various terrain features by computer analysis techniques, however, 
identification has been limited just to the features exposed on the 
surface. The ability to identify a feature overlain by another feature 
on the surface--e.g., identify various soils overlain by vegetative 
cover--has achieved very limited success. In conjunction with the 
analysis of multispectral data, density slicing, or image enhancing 
techniques have been applied in an attempt to isolate critical terrain 
features. McKean (6), evaluating color density slices of various film 
types achieved some success in enhancing potentially unstable slopes. 
Progressive slope failures were indicated on the enhanced images by 
anomolous geometric and vegetation patterns. These anomolous patterns 
were not identifiable on the original photography; thus, the potentially 
unstable slopes would not have been suspected by examination of the 
unsliced images alone. More research needs to be done in these areas, 
before the results achieved are consistent, repetitive and cost effec- 
tive. 
Microwave radiometers collect radiometric (temperature varying) data 
in the microwave or radar regions. The particular advantage of this 
system is that at the longer wavelengths information from subsurface 
layers is included in the data. Rib and others (11) have demonstrated 
that, under certain conditions, information on subsurface moisture 
conditions (i.e., presence of zones of high moisture level) can be 
determined by comparative evaluation of photography, nighttime infrared 
imagery, and microwave radiometry. These techniques are not described 
in detail because at this time either further development is needed or 
the systems are too costly in comparison to the level of information 
furnished. However, they do offer some future potential for landslide 
investigations. 
Radar systems offer the unique advantage of rapid coverage of large 
areas, the ability to collect data through heavy cloud cover and during 
the daytime or nighttime. Radar offers a viable alternative for perform- 
ing the small-scale regional landslide analysis, especially in inaccess- 
ible areas and areas of fairly continuous cloud cover. They are not as 
effective for detailed landslide analysis--compared to medium and 
large-scale photography--because of their small scale and poorer 
resolution.