James S. Aber
Traditional film 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 chemically developed into a visible picture. The spectral sensitivity of conventional photography ranges from near-ultraviolet to near-infrared wavelengths (~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. Similar limits apply to digital cameras, which have largely replaced film for remote sensing.
|Digital color-visible photograph. Sunken garden on the campus of Emporia State University in late summer. Note normal appearance of vegetation, flags, and other objects in the view. Photo © J.S. Aber.|
|Digital color-infrared photograph of same scene. Active vegetation appears red and pink. Also some synthetic fibers and dyes are highly reflective for near-infrared, as shown by the flags. Photo © J.S. Aber.|
Airphotos of the Earth's surface are not maps. Photographs are single-point perspective views, and as such they contain geometric distortions. In vertical airphotos, for example, tall objects appear to lean away from the center. This phenomenon is called relief displacement and is particularly obvious toward the edges of the scene.
|Relief displacement demonstrated by trees in a a conifer forest at Kojšovská hol'a, Slovakia (left) and cemetery tombstones at Liebenthal, Kansas (right). Note the person (*) for scale. Kite airphotos © S.W. and J.S. Aber.|
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.
|Great Plains kite aerial photography|
|UAS applications for soil degradation|
|Helium blimp aerial photography|
|Rocket 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), archaeology, 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, wind energy, etc.
|Quantum Spatial||National Aerial Photography Program—NAPP|
|Midwest Aerial Photography||National High Altitude Photography NHAP|
|Col-East, Inc.||Digital orthophoto quadrangles—DOQ|
Return to course schedule.
EB/ES/GE 351 © J.S. Aber (2016).