What different types of aerial photographs are available through the USGS?
The aerial photographs date as far back as the 1940's for the United States and its territories. Availability of specific coverage, film type, and acquisition dates vary from agency to agency.
The Earth Resources Observation and Science Center (EROS) in Sioux Falls, SD has digitized over 6.4 million frames of aerial film, creating medium-resolution digital images (400 dpi) and associated browse images for online viewing. Products can be downloaded at no cost through EarthExplorer or GloVis. Several kinds of aerial photos are available.
- CIR (color infrared) film, originally referred to as camouflage-detection film, differs from conventional color film because its emulsion layers are sensitive to green, red, and near-infrared radiation (0.5 micrometers to 0.9 micrometers). Used with a yellow filter to absorb the blue light, this film provides sharp images and penetrates haze at high altitudes. Color infrared film also is referred to as false-color film.
- Black-and-white panchromatic (B/W) film primarily consists of a black-and-white negative material with a sensitivity range comparable to that of the human eye. It has good contrast and resolution with low graininess and a wide exposure range.
- Black-and-white infrared (BIR) film, with some exceptions, is sensitive to the spectral region encompassing 0.4 micrometers to 0.9 micrometers. It is sometimes referred to as near-infrared film because it utilizes only a narrow portion of the total infrared spectrum (0.7 micrometers to 0.9 micrometers).
- Natural color (also referred to as conventional or normal color) film contains three emulsion layers which are sensitive to blue, green, and red (the three primary colors of the visible spectrum). This film replicates colors as seen by the human eye.
Photographic reproduction of images from the USGS film archives ceased on September 3, 2004. For those who specifically need paper or film products, there is a list of USGS Business Partners who provide aerial photographic research and image printing services.