352 REFRACTION AND REFRACTIVE INDEX MODELS 



N,-AT TWO ANTENNAS 



Figure 8.26. Range difference fluctuations observed over a 460-m in-line baseline, 



Boulder Creek-Green Mountain path, Colo. 



4.15-hr run, 460 meter in-line baseline, target height = 688 m apparent range 15.5 km, May 9-11, 1961 



on Green Mountain at an elevation of 2242 m and a receiving antenna 

 located near Boulder Creek at an elevation of 1554 m, the true target 

 height thus being 688 m. 



The apparent range fluctuations, expressed in parts per million of the 

 15.5-km path length (with an arbitrary zero since the total range was not 

 measured), are plotted as a function of the surface value of the refractive 

 index taken at a point quite close to the lower terminal. Quite good 

 agreement is seen between the simple linear regression of the observed 

 AT^e values on N s and the predicted linear relationship obtained from 

 the CRPL Standard Sample. Note that both hues have statistically 

 equal standard errors of estimate with respect to the observed data. 



Figure 8.26 shows the results of the range difference measurements 

 made over a 460-m baseline essentially in line with the transmission path, 

 where the second antenna was farther from the target beacon than the 

 primary antenna. Here the range difference fluctuations (again with an 

 arbitrary zero) have been plotted as a function of the mean value of N s 

 measured at each end of the baseline. The zero point on the graph is set 

 by the predicted mean of the sample. In this case there seems to be some 

 discrepancy between the regression of the data and the predicted slope; 



