132 



DEEP-WATER TRANSMISSION 



in reference 14 to give average curves. The curves for 

 a shallow hydrophone (16 to 30 ft) are reproduced in 

 Figure 49. The curves are again plotted for different 

 values of D^^. 



To illustrate the scatter of the individual observa- 

 tions, all individual anomalies averaged to give the 

 curve for D^ between 20 and 40 ft are shown in Fig- 

 ure 50. The open circles represent the anomalies for 

 MIKE patterns, the solid circles those for CHARLIE 

 patterns; no systematic difference is apparent be- 

 tween these two sets of points. The upper and lower 

 quartiles of the distribution are shown by dashed 

 lines. The increase of spread with increasing range is 

 very marked and is an evidence of the unpredicta- 

 bility of transmission conditions for such shallow 

 isothermal layers. The quartile spread at short range 

 is much smaller and represents the more normal 

 scatter, apparent also in Figures 15 and 41. 



o 



lOCX} 2000 



RANGE IN YARDS 



3000 



Figure 51. Average transmission anomalies for Di 

 between 20 and 40 feet. 



The change of transmission anomaly with changing 

 hydrophone depth has not been analyzed separately 

 for MIKE, NAN, and CHARLIE patterns. The 

 average results for D2 between 20 and 40 ft, combin- 

 ing results for all three patterns, is shown in Figure 

 51. The change with depth down to 200 ft is negligi- 

 ble, but at greater depths an appreciable increase in 

 sound intensity is noted. This change is greater than 

 the probable error of each curve resulting from the 

 internal scatter of the points and is therefore probably 

 significant, even though different temperature pat- 

 terns were present when different hydrophone depths 

 were used. 



The corresponding plot for D2 between 40 and 80 ft 

 has already been given in Figure 30. For such tem- 

 perature structure, the intensity first decreases with 

 increasing depth as the hydrophone goes below the 



thermocline, and then increases. As pointed out in 

 Section 5.3.4, the transmission anomaly below a sharp 

 thermocline is likely to show better correlation with 

 the depth and sharpness of the thermocline than with 

 the temperature code used in Figures 49 and 51. In 

 fact the limited results available are consistent with 

 the belief that for MIKE and CHARLIE patterns in 

 general the average transmission anomaly below a 

 thermocline is approximately given by equation (13) 

 in Section 5.3.4. 

 -20 



z 

 o 



33 



23 



13 



20 



40 

 -20 



20 



1000 2000 



RANGE IN YARDS 



3000 



Figure 52. Average transmission 

 hydrophone 50 to 100 feet deep. 



anomalies for 



An example of the way in which transmission 

 anomalies change with changing temperature struc- 

 ture is shown by the set of average curves for hydro- 

 phones between 50 and 100 ft deep shown in Figure 

 52, again taken from reference 14. Most of the data 

 used in these curves were actually obtained with 

 hydrophones at 50 ft. The curves are in terms of the 

 digits in the temperature-depth code explained in 

 Section 5.1.4. The successive curves may be inter- 

 preted as follows : 



13 Temperature decreases to 0.3 F below surface tem- 

 perature between 5 and 10 ft; between 20 and 40 ft it 

 has decreased to 1 F below surface temperature. This is 

 a moderately sharp NAN pattern with the sharp 

 gradient extending practically up to the surface, and 



