A pinhole camera for the evaluation of atmospheric haze
Howell, Hutson Koger
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The purpose of this paper is to describe the research on design, construction, and preliminary testing of a pinhole camera for evaluation of the relative distribution of scattered light from atmospheric haze. The camera is designed for airborne use, and intended to make photographs covering a field angle of 120 degrees, at a series of altitudes. The introduction includes a brief discussion of haze and the theory of scattering, also the effect of sun position and altitude upon the scattered light distribution as well as the effect of haze upon aerial photography. The camera, as it was designed to meet the requirements set up for it, is shovm in photographs and assembly drawings. The camera will provide photographs which, upon analysis, show the variation in the superimposed scattered light upon an average terrain reflectance over a field angle of 120 degrees. To achieve this average terrain reflectance the exposure is made of sufficient duration to blur all image detail in the film, while the aircraft maintains a constant heading with respect to the sun. To compensate for the increased exposure time, a neutral density filter is used with the pinhole. To translate the densities of the photograph into terms of relative illumination incident on the film, a sensitometric exposure is included on each film; from this, the densities can be translated into terms of relative exposure. Values so obtained will include the fall-off of illumination due to the physical characteristics of the camera. These inherent losses are due to Lambert's law, vignetting of the off-axis beam because of the thickness of the material in which the pinhole is made, and the absorption and reflection characteristics of the neutral density filter. These losses are calculated, and correction tables and graphs are shown that are used in separating the desired haze effect from the inherent illumination fall-off. Graphs of pinhole effective f/no. and exposure time versus pinhole diameter are included, also a photograph made in the laboratory to demonstrate the extreme wide angle of the camera. Readings and a graph of a test film are presented and discussed. The method is a new approach to making measurements of scattered light in the atmosphere. If carried through an organized program of flights and analysis, may prove to be an important tool for the scientist.
Thesis (M.A.)--Boston University This item was digitized by the Internet Archive.
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