Digital reproduction of historical aerial photographic prints for preserving a deteriorating archive

Aerial photographyfrom the 1920s and 1930s is a unique record of historical information used by government agencies, surveyors, consulting scientists and engineers, lawyers, and individuals for diverse purposes. Unfortunately, the use of the historical aerial photographic prints has resulted in their becoming worn, lost, and faded. Few negatives exist for the earliest photography. A pilot project demonstrated that high-quality, precision scanning of historical aerial photography is an appealing alternative to traditional methods for reproduction. Optimum sampling rate varies from photograph to photograph, ranging between 31 and 42 ,um/pixel for the USDA photographs tested. Inclusion of an index, such as a photomosaic or gazetteer, and ability to view the imagery promptly upon request are highly desirable. The Problem Aerial photography from the 1920s and 1930s is becoming increasingly recognized as a unique record of historical information. This historical aerial photography is used by government agencies, land surveyors, consulting scientists and engineers, lawyers, and individuals for diverse purposes. The Illinois State Geological Survey is a frequent user of the historical aerial photography. Common applications include identifying