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The altitude of Landsat is ~ 570 miles. Identification of 
objects having dimensions as small as 60-70 meters is ob- 
tainable. Under high contrast conditions smaller objects 
can be identified. 
The Skylab satellite imagery is similar to Landsat; 
however, Skylab orbited the earth at a somewhat lower alti- 
tude in a relatively narrow sinusoidal swath and had a 
short life span. Skylab camera imagery however, has a higher 
revolution than was attainable from Landsat's multispectral 
scanners. 
Conventional black and white aerial photography and 
color or color infrared photography are also used in siting 
studies. In addition to the stereoscopic image afforded, 
photography also provides very high resolution. However, 
except for extremely high altitude missions (60,000 feet 
or more) it does not provide a synoptic view and it is subject 
to vagaries of weather and sun angle which frequently produce 
spurious tonal variations. 
Side Looking Airborne Radar (SLAR) is useful in areas 
having persistent cloud cover or heavy vegetative ground 
cover. Unlike other sensors, SLAR is an active system in 
that it projects a signal. Because of the oblique projection 
angle of the radar antenna the return signal exaggerates 
the height of any surface irregularity it encounters and 
can therefore be useful in identifying subtle topographic 
features which might be missed by other sensors. 
Aeromagnetic and gravimetric sensors detect a force 
field rather than sampling the electromagnetic spectrum; 
however, they do provide supplemental data useful for 
analysis of geologic features. 
Role of Remote Sensing Investigations 
Starting with small scale Landsat and Skylab imagery 
subtle as well as obvious features are visually identified 
for further study. Succeedingly larger scale maps are 
then prepared from other acquired remote sensor data to 
provide greater definition and an increased measure of the 
validity of the features. It cannot be too strongly em- 
phasized that data base acquisition is the principal role 
of remote sensing and should be the initial step, after a 
literature search in acquiring a detailed data base.