Statistical Relationship Between Median Visibility and Conditions of Worst-Case Manmade Impact on Visibility

摘要

A study was conducted of the statistical relationships between median visibility and the levels of visibility associated with worst-case manmade impacts. The data base for the study consisted of midday visibility recordings for the years 1974-1976 at 28 suburban/nonurban airports throughout the United States. The visibility recordings were converted to estimates of extinction coefficients with the use of the Koschmeider formula. The data were sorted according to meteorology in order to eliminate days that were obviously dominated by natural causes of poor visibility. Three approaches were used for relating worst-case (90th through 99th percentile) extinction to median extinction. The first approach was based upon frequency distribution functions. The second used observed ratios of upper percentile to median extinction. The third employed regression techniques. All of the relationships were formulated and evaluated with the 1974-1976 data on a national/annual basis as well as regional/quarterly basis. Performance tests were also run against 1954-1956 data at 11 of the 28 sites. Simple ratio relationships are recommended for use in translating median visibility impacts into worst-case impacts. The errors associated with these ratio models are approximately 30%, which is less than the error typically associated with mathematical dispersion models. (ERA citation 05:038655)