EB/ES 351 Aerial
Photography

James S. Aber

Introduction to Cameras and Film

Photography is one of the oldest and most versatile forms of remote sensing of the Earth's surface. All photographic cameras have certain basic components: lens, diaphragm, shutter, viewfinder, and image plane. Geometry of the lens and film format determine the scene area focused onto the image plane. The diaphragm and shutter control the amount of light to expose each photograph.

Photography is based on the reaction to light of silver halide crystals, which undergo a chemical change when exposed to ultraviolet, visible or near-infrared radiation. This photochemical change can be "developed" into a visible picture. The spectral sensitivity of photography ranges from about 0.3 µm to 0.9 µm. The lower limit is based on available ultraviolet energy and strong atmospheric scattering; film sensitivity determines the upper limit.

Color photograph in visible light. Cottonwood River at Cottonwood Falls, Kansas. Note normal appearance of vegetation, water, and other objects in the view. Photo date 5/98; © J.S. Aber.
Color-infrared photograph of Cottonwood River at Cottonwood Falls, Kansas. Active vegetation appears red and pink. Photo date 5/98; © J.S. Aber.

Different parts of the spectrum may be photographed by using various combinations of films and filters. Photographs are routinely taken in b/w panchromatic, b/w minus blue, b/w infrared, color-visible, color-infrared, and multiband types. For example, color-infrared film is exposed to green, red, and near-infrared wavelengths, which are depicted as blue, green and red in the photograph. This shifting of bands to visible colors is called false-color. Ultraviolet photography is also possible for special applications.

See basic cameras and film.
Glossary of photographic terms.

Modern aerial cameras.

Aerial Photography

Aerial photographs may be taken in vertical, low-oblique or high-oblique positions; standard air photos are vertical views of the ground. Vertical photographs are normally acquired in overlapping pattern, so as to create a stereoscopic effect when adjacent pairs are viewed together. The overlapping views of the same ground area produce a parallax effect, which is also the basis for depth perception in human vision. This ability to perceive depth is quite useful for visual interpretation of air photos.

Examples of aerial photographs--see Aero-Metric.

Airphotos of the Earth's surface are not maps. Photographs are single-point perspective views, and as such they contain geometric distortions. For example, the scale of an airphoto is determined by lens focal length (f) and flying height above the ground (H):

photo scale = f ÷ H
f & H must be in same units

Flying height varies with topography, however, so scale is not constant throughout a photograph. Vertical air photos can be used for ground measurements and map making. Photogrammetry is the art and science of accurate measurements based on photographs. Dimensions and locations of objects, height differences, and absolute elevations may be determined accurately. Modern topographic maps are usually produced on the basis of air photos.

Aerial photography is typically done from specially equiped airplanes or helicopters nowadays. However many other manned or unmanned platforms may be utilized to hold the camera above the ground, including balloons, tethered blimps, kites, radio-controlled model planes, and rockets--see Project Corona.

Low-Height Unmanned
Aerial Platforms
Great Plains kite aerial photography
Hot-air blimp aerial photography
Helium blimp aerial photography

Applications of Aerial Photography

Aerial photographs are routinely employed for all manner of mapping and evaluation of natural and cultural resources, including agriculture (crops and soils), archeology, biology (habitat, wildlife census), forestry, geology, geomorphology, engineering, hydrology, industrial development, military (camouflage detection, espionage, terrain models), mineral and oil prospecting, pollution (air, land, water), reclamation, transportation, urban planning, etc.

U.S. Sources for Aerial Photographs
Commmercial U.S. Government
Western Air Maps U.S. aerial photography overview
MJ Harden/GeoEye Selecting NAPP & NHAP photographs
Col-East Digital orthophoto quadrangles--DOQs

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EB/ES 351 © J.S. Aber (2007).