Aerial Imagery: Data

Development

Aerial photographs are the first type of aerial imagery. The first known aerial photograph was taken from a hot balloon by the French photographer Felix Tournachon, who used the nom de plume Nadar, in 1858. One of the earliest aerial photographs taken in the United States is the Balloon View of Boston, taken in 1860 by James Wallace Black. Photography from aircraft was widely applied during World War I. The early aerial photographs are typical nondigital photographs and in black and white. Data are usually stored in films or prints. The American Society of Photogrammetry was founded in 1934 to advance aerial photography. The U.S. Geological Survey began using aerial photographs for mapping in the 1930s.

Aerial photography evolved to a high level of sophistication during World War II and the Korean War. Since then, color infrared photography has become important in identifying vegetation types, detecting disease, and quantifying biomass. Multispectral aerial imagery, taken at the same time with different portions of the electromagnetic spectrum, was developed and tested with the data of true-color and false-color aerial photographs. Data are saved in magnetic, optical, solid-state media with digital images of the matrix of numbers, using the technology of digital photography. Now, most aerial imagery is stored in digital image format.

Innovation

The most important innovations in the development of aerial imagery are black-and-white film, color film, conventional cameras, multiband cameras, digital cameras, aerial hyperspectral imagery, side-looking airborne radar (SLAR), and aerial light detection and ranging (LIDAR). The black-and-white film traditionally used in aerial imagery is panchromatic black-and-white film, which is often used for a wide range of resolutions, gradations, and sensitivities. Compared with color film, an advantage of black-and-white film is that it can be combined with appropriate filters for bad weather, such as a misty day.

Color film includes color diapositive film, color negative film, and color infrared film. Color diapositive film is typically used in large-scale and medium-scale photogrammetry for mapping and interpretation. Color negative film, which results in a high geometric resolution, is suitable for all types of applications. Color infrared film, also called false-color film, is typically used to generate a color photograph of yellow, green, and the red of the near-infrared spectrum, which offers the most useful information in vegetation analysis.

Traditional cameras include mapping frame cameras, frame reconnaissance cameras, panoramic cameras, and strip cameras. A multiband camera is used for capturing images in a variety of wavelength bands and usually consists of a set of three or more cameras to suit a specific spectrum. A digital camera is used to record and store photographic images in digital format. Images are usually created through a photosensor with a charge-coupled device (CCD). The captured images can be stored in the camera or directly uploaded on a computer. Images also can be archived on a photographic disc or external hard drive. Currently, digital cameras often have a liquid crystal display (LCD) for viewing both captured and archived images. With the help of Web-based instruments, aerial imagery can be proofed by clients immediately.

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