RESEARCH ON TERRAIN EFFECTS ON OPTICAL TURBULENCE GENERATION.
WHITE SANDS MISSILE RANGE NM INSTRUMENTATION DIRECTORATE
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The turbulence-generating potential of various surfaces was investigated by measuring the temperature profile from 0.5 to 24 feet above each surface. Surfaces investigated include sparselyvegetated desert, a shallow lake, white sand, and vegetation. An attempt was made to determine a quantitative relationship between optical resolution and lapse rate by simultaneously measuring the temperature profile and photographing a target pattern through a 120 cm lens at one of the sites. Results of the temperature-profile measurements indicate that higher lapse rates exist over the vegetation tested than over the desert. The lapse rates over white sand and over water are appreciably lower than that over the desert. Due to the high scatter in the optical data, no mathematical expression for the optical resolution as a function of the lapse rate was determined. However, the results demonstrate that the optical turbulence increases rapidly with increasing lapse rate. Resolution-loss rates as high as twenty lines per millimeter per degree Centigrade temperature-difference, measured between points six inches and eighteen feet above the surface, were recorded. The relationship between the optical resolution and the lapse rate, together with the difference in lapse rate occurring over areas with different surfaces, demonstrate that when selecting a location for optical instrumentation the lapse-rate characteristics of the surface layer should be taken into account. Author