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Aerial Photographs
The Environmental Photographic Interpretation Center (EPIC) acquires both historical and current aerial photographs in order to depict the status, condition, and change of sites over time. Archived historical aerial photographs may come in various forms since the goal is to obtain and analyze whatever aerial photo records exist which may help to characterize an area or site. Historical photos, therefore, may be at different scales, film types, formats, or seasons (dates) of collection. For new overflights EPIC can set the specifications for each of these factors in order to obtain optimal photo coverage.
Photo Scale - aerial photo scale is controllable when obtaining new coverage by selecting the appropriate aircraft flying height and camera lens focal length. Scale may range from small (e.g., flying at a high altitude in order to cover a large area) to large (e.g., flying at a lower altitude to cover a smaller area) in order to perform either a regional assessment of an area or a detailed site characterization, respectively.
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High Altitude, Small Scale for Large Area or Regional Coverage
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Medium Altitude,
Moderate Scale for Large Site Coverage
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Low Altitude, Large
Scale for Detailed Site Analysis
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Film Type - film type refers to either panchromatic (black and white), natural color, or color infrared film. Skilled image analysts can extract different information from each of these film types. Panchromatic film can offer useful information on land use and land cover and site details, but may not be as effective as natural color film for differentiating between, for example, vegetation types, spills on the ground surface or into water bodies, or other features which have a unique or distinguishing color. Natural color aerial photographs are useful for differentiating between unique colors of features or areas which might go un-noticed if presented as black and white or gray tones only. Natural color is very good for detecting differences in water body colors which may be suggestive of water quality differences, and has excellent water penetration for looking at shallow water bottoms or submerged vegetation in clear water. Color infrared, or false color film, displays vegetation as shades of red, can be used to differentiate between vegetation types, can detect vegetation which is stressed, has good atmospheric penetration in areas covered by haze, and aids in differentiating between land and water boundaries. Color infrared film detects the reflective or near infrared portion of the electromagnetic spectrum and is not sensitive to temperature differences of objects.
Panchromatic B&W Aerial Photograph
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Natural Color Aerial Photograph
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Color Infrared Aerial Photograph
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Film Formats - EPIC uses the standard 9"x9" square film format whenever possible. Most 9"x9" format aerial film has been collected using metric mapping cameras and with overlapping exposures to provide stereoscopic (3-D) viewing. However, there are other film formats which may exist in aerial photo archives and which might provide the only available useful film coverage for an area or site. Aerial photos may thus be available in 35mm, 70mm or other formats or elongated as strips. Some film may not be available in stereoscopic form. If the film is of a non-standard format, but contains useful information about site status, condition, or change, it will be obtained and included as part of a site characterization project.