Photography
Introduction

ES 555 Small Format
Aerial Photography

James S. Aber

Table of Contents
Basic cameras Film & digital
Aerial photos Related sites

Basic cameras

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. Conventional film cameras are designed to accept film of certain format or width--for example 35 mm, 70 mm, 5 inches, or 9 inches. Most popular cameras are for 35-mm film, whereas professional photographers tend to employ 70-mm format cameras. The larger formats are utilized mainly for scientific and engineering applications.

Compact, point-and-shoot, 35-mm (film) camera--see Olympus Stylus Epic.
Compact, point-and-shoot, digital camera--see Canon Digital Elph.
Single-lens reflex, high-resolution digital camera--see Canon Digital Rebel.
Complete, 70-mm format, film & digital camera systems--see Hasselblad.

Most people are familiar with 35-mm film cameras and compact digital cameras. There is a geometric relationship between the lens focal length, the area (angle) of view, and the amount of light that enters the camera. Some common lens focal lengths are given in the following table for 35-mm format film and typical cameras. Many cameras are now equiped with zoom lenses that allow the user to vary the focal length.

Focal lengths for 35-mm film and digital cameras.
Focal length
35-mm film 		Focal length
Digital CCD* 		Field of view Light
15 mm 9 mm Fish eye High
19 mm 12 mm Super wide High
28 mm 18 mm Wide angle High
50 mm 31 mm Standard Moderate
200 mm 125 mm Telephoto Low

*Approximate ratio of 1.6 to 35-mm film format.

Photographic film and digital

Photochemical imagery 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 chemical 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. Most digital cameras are limited to visible light, although a few special digital cameras extend into near-infrared radiation.

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.

Color photograph in visible light of ghost town at La Veta Pass, Colorado with Mount Maestas in the background. Taken in late May with active grass and conifer trees (pine & spruce).
Tetracam ADC color-infrared photograph of approximately same scene as above. Grass is more reflective in near-infrared (pink) compared with conifer trees (red) in this standard false-color format.

During the 1990s, digital still cameras were developed for popular and scientific use. These cameras employ a charged couple device (CCD) to sense light. A CCD is essentially a microscopic array of semiconductors that measure light intensity in a raster grid. The picture is made up of many small dots--also called cells or pixels (picture elements). Early digital cameras could not deliver the high resolution possible with conventional film. However, within the past few years, digital cameras with megapixel CCDs have come on the market at moderate cost. These cameras produce images that rival the sharp detail of 35-mm and 70-mm film. Digital cameras are quickly becoming more popular, and their capabilities are increasing dramatically. Digital technology rapidly is replacing film for most applications, except for the low-end disposable-camera market and special high-end applications.

See basic cameras and film.
Glossary of photographic terms.

Aerial photography

Conventional aerial photography is done from specially equiped airplanes nowadays. Large-format cameras take photographs on 9-inch (23 cm) wide film or large-format digital cameras. In either case, the camera, lens, film spools, and accessory equipment weigh several 100 kg and require considerable cargo space in the plane. Normally a twin-engine airplane is necessary. Small-format aerial photography (SFAP), in contrast, is typically done with 35-mm or 70-mm film or with small video or digital cameras. This allows use of light-weight equipment that can be lifted in a variety of manned or unmanned platforms.

  • Great Plains kite aerial photography.
  • Hot-air blimp and kite airphotos--MoGul project.
  • Kite and balloon aerial photography (French).
  • Unmanned, powered drone for aerial photography.
  • Manned digital infrared SFAP.

    • 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), property management, reclamation, transportation, urban planning, zoning and tax appraisal, etc.

    Related sites

    Return to SFAP schedule.
    ES 555 © J.S. Aber (2010).