Contrast transmission in rain

Document Type

Article

Publication Date

9-22-1983

Abstract

While the propagation of visible and infrared radiation in adverse weather has been studied by many investigators, the effect of rain on contrast transmission or visual range have received little attention. A theoretical and experimental program examining contrast transmission in adverse weather will be described in this paper. Measurements of contrast transmission were made using bar targets consisting of parallel flourescent light bulbs. The bulb spacing is four times the bulb diameter. Data is obtained by photographing the target from a distance of two hundred meters using a camera fitted with an eight-hundred millimeter lens under both clear and obscured conditions. The negatives are then analyzed using a microdensitometer and contrast is defined by C = (I MAX - i MAX + i MIN)-1 where I-MAX and I-MIN are the intensity maximum and minimum, respectively. In addition to contrast measurements, simultaneous measurements of atmospheric transmission, snow particle phase function, and all relevant weather parameters are made. A computer model, based on scattering theory, has been developed for predicting contrast transmission. The model computes zero, first and second order scattering contributions in a three-dimensional atmosphere using phase function computations based on Mie theory. © 1983 SPIE.

Publication Title

Proceedings of SPIE - The International Society for Optical Engineering

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