Film Types
Before the birth of digital photography, aerial cameras had to be pre-loaded with a roll of film before a mission could begin. Traditionally, this roll of film would be panchromatic, with colour becoming more common in the last two decades of the 20th century. For specialist survey projects, film sensitive to light reflected at infra-red wavelengths could be used.
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PANCHROMATIC
Panchromatic film is sensitive to the full spectrum of visible light and renders this in shades of grey. This produces an image which appears realistic to the human eye, although the eye can only differentiate 26 of the 256 shades of grey.
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COLOUR
Colour film is sensitive to visible light and renders this in shades of red, green and blue. The human eye can differentiate between millions of shades of colour. Colour film therefore makes it easier for the human eye to differentiate between similar vegetation types, for example, than would be the case with panchromatic film.
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FALSE-COLOUR INFRA-RED
Infra-red film is sensitive to light in the near-infra-red part of the electromagnetic spectrum, not visible to the human eye. Since the human eye finds it difficult to discriminate between shades of grey or green, colour infra-red film makes vegetation appear red, which the eye can more easily differentiate. This film records the infra-red reflectance of chlorophyll in living plants, so while healthy vegetation reflects more infra-red and appears bright red, unhealthy or dying foliage, with less chlorophyll, appears less red or pink.
Colour infra-red imagery is commonly used for environmental monitoring and crop management.
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