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Appendix to the INT. ARCHIVES OF | 
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| P'IOTOGPAMMETPY, Vol. XiE4, 19561] 
STATUS OF COLOR AERIAL PHOTOGRAPHY IN GEOLOGIC STUDIES 
OF THE U.S. GEOLOGICAL SURVEY* 
ee ————————— 
by 
Bion H. Kent 
U.S. Geological Survey 
INTRODUCTION 
In 1955 the U.S, Geological Survey obtained full- 
color vertical aerial photographs of thirteen test areas in 
the States of California, Nevada, and Utah. Field evaluation 
studies of one of these areas, the Purnace Creek Wash test 
area (Fig. 1), Death Valley, California, were made between 
October 25 and November 10, 1955, Panchromatic, infrared, 
and color aerial photographs were available for the test area. 
All photographs were vertical photographs at approximately 
1:10,000 scale. 
In order to evaluate photograph colors with respect 
to ground colors, observation points were occupied 1n the 
field. The field areas generally were observed in direct 
sunlight so that the clearest impression of ground colors 
could be obtained,  Traverses within the field areas were made 
in company with field personnel, and many of the stratigraphic 
units were examined, primarily in terms of thelr ground colors. 
This report concerns the preliminary results of these 
field studies. 
OBJECTIVES OF THE FIELD STUDIES 
The field studies had a two-fold objective: 1) to 
outline specific geologic uses of color aerial photographs, 
and 2) to study ground colors and their relationship to 
colors as seen at a distance and/or recorded upon color film. 
The second objective also involved studies of the effects of 
atmospheric haze, altitude of terrain photographed, sun 
angles, viewing distances, and flight altitudes. 
*Publication authorized by the Director, U.S. Geological Survey