Type of Conventional Aerial Photographs: Black and White Photographs, Colour Infrared Film (CIR) , Ultraviolet Photography (Especially for GATE-Geospatial 2022)

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Aerial photography is typically available in:

  • Black & white (panchromatic, grayscale)
  • Natural colour (red, blue, and green)
  • Colour infrared (false colour, black and white)

Black and White Photographs

  • Black and White Photographs/Imagery exposed by visible light are also called as panchromatic photographs. It is acquired normally using filters which eliminates the ultra-violate (UV) and blue wavelength selectively, scattered by the atmosphere. These photographs ate most widely used and readily available. The application of these remote sensing products has application in compiling topographic maps, geologic surveys, crop inventories and cultural features identifications.
  • IR black and white is also a remotely sensed product, where filters are used so that only reflected infrared energy (0.7 — 0.9 µm) transmits. This has the advantage over B&W image because of higher contrast ratio and also better spatial resolution. This advantage is mainly because the filter used in IR image eliminates atmospheric scattering, pronounced in blue and UV wavelengths. It has utility in studies for vegetation types and land-water margins etc.
Black and White Photographs

Colour Infrared Film (CIR)

  • Colour infrared film is often called “false-colour” film. Objects that are normally red appear green, green objects (except vegetation) appear blue, and “infrared” objects, which normally are not seen at all, appear red. The quality of the film/camera, time of year, climatic conditions and how the film is developed influence how landscapes appear in CIR photos. The primary use of colour infrared film is for studies involving vegetation such as wetlands mapping or ecosystem monitoring.
  • Healthy green vegetation is a very strong reflector of infrared radiation and usually appears bright red on colour infrared photographs (depending on how the film is developed) . Colour Infrared (CIR) uses special film, lenses and filters to capture reflected near infrared energy (sometimes called Near IR) , NOT emitted thermal infrared (heat) .
  • A common misconception about “Infrared Photography” is that it is associated with heat - which is incorrect. Colour Infrared (CIR) photographs capture sunlight that has been reflected from the surface, NOT emitted (that՚s Thermal IR) .
Colour Infrared Film (CIR)

Ultraviolet Photography

  • UV wavelengths are the shortest of the normal photographic range of the electromagnetic spectrum; they can be acquired with standard black and white film as well as specialized film and pure lenses and filters especially manufactured for UV light. Filters for UV photography are glass only, film-based emulsion filters do not work.
  • UV aerial photography is also useful for identifying oil on the surface of the water. This is because UV wavelengths are sensitive to the smoothness of the water surface; oil on the water surface tends to smooth small capillary waves caused by wind, the smoother surface causes a contrast in reflectance with the surrounding water.
  • Nature photographers use UV photography, insects and flowering plants have been studied using UV photography. Ultraviolet aerial photography is also used to census animals in snow environments. The fur of what appear to be white animals, like the baby seals, is dark black in IN wavelengths (because their fur absorbs those wavelengths) , so they contrast very sharply against a snow background (which reflects UV) .
Ultraviolet Photography

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