Comparison of computed with observed atmospheric refraction

Ray tracing methods have been applied in the computation of atmospheric refraction for a path at White Sands Missile Range, N. Mex., with a range of about 48 miles and an elevation angle of 14.5 milliradians. The atmosphere was assumed to be horizontally stratified. Refractive index profiles were derived from meteorological data obtained from surface observations, wiresondes, radiosondes, and airborne refractometer soundings. The profiles were classified "A", "B," or "C," in descending order of reliability, prior to radar refraction computations. The classification system considered the variety of data available, the time lag between radar and weather observations, and the proximity of the sounding to the propagation path. A good correlation between observed and computed angles resulted and the correlation was directly related to the classification. Radar observations were made in the
X
-band and instrumental precision maintained to within 0.25 milliradian. Total bending ranged between 0.56 and 2.23 millirardians, with standard deviation 0.38 milliradian. The rms deviation of computed from observed angles ranges from 0.19 to 0.41 milliradian for Class A and Class C data, respectively. The correlation coefficient ranges from 0.81 to 0.13. It is concluded that within the limits of this experiment: a)ray tracing methods are justified, b) horizontal stratification may be assumed and c) the accuracy of bending predictions is increased by improving the meteorological data.