Camera Components: Parts, Assembly, Multi-Spectral Cameras, Large Spectral Camera, Film and High-Quality GIS Camera (Especially for GATE-Geospatial 2022)

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The main difference between aerial camera systems and traditional cameras is the need for aerial systems to be spatially accurate. Metric precision is necessary because aerial photography is often used to measure very small distances, and to create high-resolution elevation models from stereo imagery. For these purposes, it is necessary to have photography that is extremely accurate. It is possible to do your own photo reconnaissance by pointing a regular camera out the window of a plane and taking a picture of the ground, but to make a reliable measurement, you need a more stable setup. Certified “metric quality” cameras are expensive sensitive devices but necessary if precise/accurate measurements are required.

Aerial Cameras Consist of Essentially Six Components

  • Lens Assembly: 3.5,6, 8.25 and 12 inches are typical focal lengths. The lenses of aerial systems have the focus fixed at infinity.
  • Focal Plane: this is a perfectly perpendicular plate aligned with the axis of the lens, a vacuum system is used to fix the film to the plate so the focal plane is perfectly flat during exposure.
Illustration 2 for Aerial_cameras_consist_of_essen …

Schematic diagram of an aerial camera, cross-sectional view

  • Lens Cone: this holds the lens and filter, and covers the front part of the camera preventing light from leaking into the camera body.
  • Body: encloses the camera, the mounting bolts and stabilization mechanism.
  • Drive Assembly: the guts of the camera, the winding mechanism, shutter trigger, the vacuum pressure system and motion compensation.
  • Magazine: holds the roll of unexposed film, advances the film between exposures, holds the film in place and winds-up the exposed film.

Aerial camera systems also have a mounting bracket, power supply, vacuum lines, heating jackets, filters, forward motion compensation (FMC) and an Inertial Motion Unit (IMU) . Also, part of the system is a viewfinder for targeting the camera, an intervalometer that determines the rate at which exposures are taken (the amount of overlap) as the plane flies along the flight path, a navigation control system and an exposure control system. Computers have assumed many of these tasks which were once manual/mechanical. Global Positioning Systems (GPS) are now integrated into the camera system to provide very precise in-flight positional control.

Multi-Spectral Cameras

Multi-spectral cameras were the precursor to the development of digital multi-spectral satellite remote sensing systems. Different configurations of cameras, lenses, filters and film types were experimented with to determine optimal wavelength regions for the remote sensing of different landscape features. These experiments led to the selection of the multi-spectral wavelength ranges, or “bands” that were later used for satellite-based remote sensing systems.

Large Format Camera

The Large Format Camera (LFC) was a high-altitude aerial mapping camera scaled up to operate from the Space Shuttle. It was used on one mission in October 1984. The camera weighs about half a ton and a single frame covers 23,400 square miles at about 10 - 20 m resolution.

High-Quality Photographic Systems and the Digital Modular Camera

Aerial cameras manufactured by Carl Zeiss and LH Systems are of the highest quality and are the most widely used. Z/I Imaging (Intergraph - Carl Zeiss) introduced the Digital Modular Camera (DMC) . The advantages of an all-digital camera system are extremely precise planar coordinate registration, reliability, and the automation of manual tasks, such as triangulation, which is typically expensive and time-consuming.

Films

On the most basic terms, the three layers in the film can be thought of as three black and white emulsions containing metal halide grains layered onto a flexible base. The layers consist of a blue-sensitive layer (yellow dye) , a green sensitive layer (magenta dye) and a red sensitive layer (cyan dye) . The amount of dye released by the light passing through each of the layers is inversely proportional to the amount of light of a particular wavelength (colour) is received from the scene, i.e.. the more blue there is the less yellow dye is released by the blue sensitive layer and since these layers are on top of each other, there will be more magenta and cyan in the layer՚s underneath. The more green there is the less magenta dye, and consequently more yellow and cyan. The three dye layers, when added together, produce the colours we see blue, green and red. These are called “colour reversal films” .

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