Multispectral Photography: From Single to Multi-Spectrum Designs (Especially for GATE-Geospatial 2022)

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Limitations of Single Spectrum Photography

From the review of the applications of different types of non-panchromatic and colour photography, it has become increasingly clear that no single film-type is ideal for all purposes. One type of film may exhibit some advantages in certain aspects, but limitations in others. Although the true-colour film has been regarded as being capable of more general use, it suffers too much from the necessity to maintain correct colour fidelity which is highly elusive depending on how the weather changes. If cost is unimportant, the combined use of all the different film types will certainly yield more information than any one of these as our terrestrial environmental facets are so highly varied.

Using a Multispectral Array with MATLAB, Part 2 – MATLAB Rec …

It has already been mentioned that infra-red photographs, when used in conjunction with panchromatic photographs, can yield more information than when each is used alone. This fact has also been stressed by Colwell, who demonstrated the complementary nature of these two types of photography in rural land-use interpretation. 8 ′ For example, on panchromatic and infra-red aerial photographs of a rural area in the Sierra Nevada foothills of California taken on the same date, he noted the superiority of the panchromatic photography in discerning dry stream channels, field boundaries, vegetation boundaries and roads and, on the other hand, the superiority of the infra-red photography in discerning moist stream channels, vegetation boundaries, wet soil and rocky hummocks in the same area. This is the underlying principle of ′ multi-spectral ′ or ′ multiband ′ photography.

What is Multispectral Photography?

Multispectral photography involves sensing simultaneously different portions of the electromagnetic spectrum (known as spectral regions) in order to accumulate more information. This exploits the fact that ′ transmission, reflection, absorption, emission and scattering of electromagnetic energy by any kind of matter are selective with regard to wavelength and are specific for that particular kind of matter, depending primarily upon its atomic and molecular structure. This means that each object has its own ′ spectral signature ′ .

Equipment for Multispectral Photography?

In practice, a multiband camera is employed by means of which several photographic film-filter combinations, each especially suited to sensing in its own spectral band, are used to obtain photographs of the same area at the same time.

Multi-Camera and Multi-Lens Designs

Both the multi-camera and the multi-lens designs are possible.

  • The multi-camera design involves the use of several identical cameras each with its own lens and film whilst the multi-lens design makes use of only one camera body with several lenses and one or more rolls of film. The multi-camera type is more popular from the geographical point of view because of its flexibility in film-filter combinations and its lower cost, and only small frame (70mm) cameras need to be used.
  • There are four-, six- or nine-lens cameras; and usually, for the nine-lens type, photographs are obtained with panchromatic film for six of the wavebands and with infra-red film for three. One important example of the multispectral photographic system in use today is the nine-lens camera produced by the company of Itek in the United States. This is really a multi-lens design, with all the nine lenses mounted on a single lens cone, each lens covering a 70mm format. The camera magazine contains three spools of 70mm film on each of which are projected three images. This is more flexible than the other multi-lens design in that each channel can be used with a different type of film if greater flexibility in spectral sensitivity is desired, and spectral filters can also be placed in each of the nine lenses to obtain a simultaneous recording of a scene in nine bands. Each is a 152m f/2.8 Schneider Xenotar lens chromatically corrected for the band in use. Image motion compensation is provided. A further advantage is that the camera can be fitted with a magazine containing a 23cm film (i.e. standard format) to obtain at nine bands recording separately on one photograph.

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