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PHOTOGRAPHY OF LUMINOUS EXTENDED OBJECTS AGAINST A TWILIGHT SKY
GEOPHYSICS CORP OF AMERICA BOSTON MA
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Clouds of sodium, lithium, and potassium vapor are used to determine wind velocity and the coefficient of expansion for various heights in the upper atmosphere. These materials scatter sunlight radiation incident upon the cloud by a resonance process. The resulting scattered light is nearly monochromatic and is characteristic of the scattering atom. The vapor is released from a carrier-rocket during twilight periods at times when the cloud will be sunlit, but the background will be as low as possible. For optimum photographic registration of the cloud characteristics, filters and film types are used to augment as far as possible the ratio of light scattered by the cloud to background light. A discussion of filter and film types for discrimination of the various wavelengths is given. Developing techniques to insure the required contrast and photographic latitude are considered. Film calibration and processing for subsequent densitometry is described. Consideration is given to the changing background intensities encountered during twilight, and to the optimum exposure under these various conditions. Author
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