102 



DEEP-WATER TRANSMISSION 



RAY DIAGRAM 



14,000 4890 4940 4990 



SOUND VELOCITY IN FT PER SEC 



2000 



6000 8000 



RANGE IN YARDS 



10,000 



12,000 14,000 



Figure 13B. Sample transmission anomaly in isothermal water. 



However, since there are no extensive measurements 

 on small-scale thermal structure in the isothermal 

 layer, no conclusions about these problems can be 

 reached at the present time. 



The straight line of best fit drawn on a plot of 

 measured transmission anomaly against range gives, 

 with moderate precision, the attenuation coefficient 

 for the time and place of the measurements. Because 

 the transmission anomaly usually approximates a 

 straight line for measurements at fixed depth in 

 isothermal water, the probable error of the attenua- 

 tion coefficient found in this way is only about 3^ db 

 per kyd, for runs extending out to about 6,000 yd. 



The detailed variation of the attenuation coefficient 

 in isothermal water from place to place and from 

 time to time has not been thoroughly explored; and 

 so it is most useful to deal with an average attenua- 

 tion coefficient. The evidence on variation of trans- 

 mission loss in isothermal water will be given in Sec- 

 tion 5.2.3. 



The most complete investigation of the average 

 attenuation coefficient at 24 kc in isothermal water is 

 apparently that presented in a report by UCDWR." 



m 

 a 



z 



o 



z 

 < 



z 

 o 

 tn 

 to 



£ 

 «o 

 z 

 < 

 a: 



10 



20 



30 



40 



50 



1000 2000 3000 



RANGE IN YARDS 



4000 



Figure 14. Average transmission anomalies in iso- 

 thermal water. 



All deep-water runs in isothermal water are analyzed 

 together. This analysis shows that if the water is es- 

 sentially isothermal to about 100 ft the measured 

 transmission anomalies do not depend on the tem- 

 perature at greater depths or on the state of the sea 

 surface, at least out to ranges of 3,000 yd. 



Transmission runs made under these conditions 

 have been combined to yield the average curves of 



