USE OF COLOR AERIAL PHOTOGRAPHY IN ENGINEERING MATERIALS SURVEYS

The opportunity to use aerial color photographs in a comprehensive construction materials survey presented itself in Yellowstone National Park (area - 3,472 sq. mi.) where a critical construction material shortage exists in certain portions of the Park. This project was undertaken by the Federal Projects Office, Region 9, U.S. Bureau of Public Roads, and was sponsored by the U.S. National Park Service. Strip aerial photographs were taken along the major highway system at a scale of 1:6,000. The aerial reversal color positive transparencies obtained were examined stereoscopically. The color transparencies at this scale proved most effective for the material survey. Special considerations in the procurement of color aerial photography are presented together with descriptions of field and office procedures. The use of aerial color photography for construction materials searches is still limited but is likely to increase due to technological improvements, reduced costs, and a general awareness by potential users of its advantages over conventional photography. Recent significant trends in aerial color films are increase in emulsion speed, a widening of exposure latitude, improvement of color reproduction, and an increase in resolution. Negative aerial color film now provides a greater variety of possible products and thus affords greater flexibility in use than reversal color film processed to a positive transparency. Areas are indicated where research on conventional color films and false color films for aerial photographic interpretation for highways is needed. /AUTHOR/