348 



REFRACTION AND REFRACTIVE INDEX MODELS 



T3 

 O 



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CAPE KENNEDY, FLA 



MEAN APPARENT ELEVATION ANGLE =0.7 mrad 

 RANGE = 17. 1 km 

 1EAN TARGET HEIGHT = l3 7m 



Figure 8.22. Elevation angle fluctuations from phase differences taken across a 24-ft 

 vertical baseline, at Cape Kennedy, Fla. 



Figure 8.22 shows some results of measurements taken at Cape 

 Kennedy, Fla., on November 1-3, 1959, at a very low elevation angle, 

 about 0.7 mrad or 0.04°. These are "instantaneous" measurements, 

 taken at half-hourly intervals, of the phase difference fluctuations between 

 the signals from a beacon as they arrived at the upper and lower terminals 

 of a vertical 24-ft baseline, thus being very closely equivalent to a meas- 

 urement of the fluctuations in the angle of arrival of the wave front at the 

 centerpoint of the baseline (the altitude difference between this point and 

 the target beacon is referred to as the "mean" target height). Since only 

 the fluctuations and not the total phase differences were measured, only 

 the slope and scatter of the elevation angle errors as a function of the 

 observed N s data can be compared with the predicted values from the 

 CRPL Standard Sample. The zero point on the graph is set by the pre- 

 dicted mean value for the sample. The correlation coefficient is, as ex- 

 pected, only 0.57. In this case the scatter of the observed data is well 

 inside the limits of the standard error of estimate of the regression for the 

 standard sample, even at this very small elevation angle where horizontal 

 changes in the A'^ profile can exert a large effect on elevation angle errors. 



