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Frontier areas, particularly, lend themselves to initial phase study via remote sensing imagery. The many types of satellite imagery have the advantage that large areas of the earth's surface may be studied quickly, cheaply, and thoroughly enough to lead directly into more detailed photogeology and/or surface mapping. Imagery can be acquired in various spectra, the most useful of which are normal color, normal black and white, color infrared, black and white infrared, and side-looking radar. Perhaps the best single imagery for most geological mapping is the band 7 "False Color" infrared, at the scale of 1:250,000. Each photo measures approximately 29 in.2 (187 cm2) and covers 115 mi (185 km) on a side; the cost in 1982 was $80 per photo.
Using the 1:250,000 band 7 color infrared images, good sharpness and color contrast are retained, yet enough magnification is present to allow visual recognition of roads, small towns, smaller lakes and streams, railroads, and agricultural features. Recognition of such physical features is necessary for satisfactory ground control.
Geologic and geomorphic features such as tonal, color, and drainage anomalies, linears, and more direct features such as actual geologic structures, faults, and regional structural dip directions often may be recognized. In areas of sparse well control and/or limited geophysical data, recognition of such features and geological data is of extreme importance and is a good beginning step in studying remote areas.
I have selected two 1:250,000 band 7 color infrared images from central and north-central Montana to display the variety of geologic, geomorphologic, and physical features that may be determined. Easily denoted features include regional dip; domal and anticlinal structures; tonal, drainage, and color anomalies; regional lineations; fault traces, and igneous activity. Subtle features are shown such as noses, subtle anticlines, and radial and concentric fracture patterns associated with the Bearpaw and Little Rockies uplifts. Follow-up work was performed using 1:20,000 stereo pairs, and several examples are available for inspection. In many situations, the leads from color infrared imagery subsequently proved to be bonafide geologic features.
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