Comparison of experimetal with computed tropospheric refraction

Limits of applicability of ray tracing in computing tropospheric refraction at White Sands Missile Range have been further explored. 286 comparisons were made, all for a path from radar to fixed beacon of about 45 miles and an elevation angle of 17.99 milliradians. A horizontally stratified atmosphere was assumed. Refractive index profiles were prepared from a variety of weather data, and classified A, B, C, or R, in descending order of reliability prior to ray-tracing calculations. Angle observations were made with an FPS-16 C-band radar having a quoted instrumental accuracy of 0.14 milliradian rms. Angle readings varied from 18.36 to 20.54 milliradians, with mean of 19.01 milliradians and standard deviation of 0.41 milliradians. The rms deviation of computed from experimental angles ranges from 0.28 to 0.41 milliradian for different classes of data. The ratio of this deviation to the deviation from over-all mean varies from 0.68 for Class A to 1.00 for Class R. Thus the improvement over a "standard atmosphere" varies from 32 per cent to 0, and correlates directly with quality of weather information. For this experiment it is concluded that most of the rms elevation angle error is contributed by atmospheric conditions. Although ray tracing methods provide a significant correction when sufficiently good weather information is available, there still remains a large uncertainty not accounted for by equipment.