122 



DEEP-WATER TRANSMISSION 



1000 



500 1000 1500 2000 



COMPUTED RANGE IN YARDS TO SHADOW BOUNDARY 



Figure 38. Correlation between break in transmission 

 anomaly plot and computed range to shadow boundary. 



■^ 500 1000 1500 2000 



COMPUTED RANGE IN YARDS TO SHADOW BOUNDARY 



Figure 39. Correlation between Rm and computed 

 range to shadow boundary. 



of data is too limited to permit very definite con- 

 clusions. Possibly the presence of water waves on the 

 ocean surface lowers the effective level of the surface 

 and brings the shadow boundary in to closer range 

 than would be expected for a flat surface. 



A somewhat more practical quantity found from 

 the transmission curves is the range Ri^ at which the 

 sound intensity is 40 db below the intensity at 100 yd. 

 The significance of this quantity has already been 

 discussed in Section 5.3.4. A plot of ^40 against com- 

 puted limiting range is shown in Figm-e 39. The cor- 

 relation is again only fair. The dashed curve of best 

 fit was chosen visually, as in Figure 38. 



Figures 38 and 39 cannot be used to give reliable 

 average results because of the paucity of data in- 

 cluded. They indicate in a general way the correla- 

 tion that may be expected between detailed computa- 

 tions of Hmiting rays and observed transmitted sound 

 intensities. 



O 1000 2000 3000 4000 



RAN6E IN YARDS 



Figure 40. Average transmission anomalies for NAN 

 patterns, shallow hydrophone. 



Average Transmission Anomaly 



A statistical average of the measured transmission 

 anomalies for different temperature conditions is 

 given in reference 14, based on the temperature- 

 depth code described in Section 5.1.4. The data for 

 shallow hydrophones (16 to 30 ft) are discussed first. 

 Corresponding data for deeper hydrophones are given 

 in the next section. Three curves for shallow hydro- 

 phones in water with sharp temperature gradients in 

 the top 30 ft (NAN patterns) are given in Figure 40. 

 Each curve represents an average for a different value 

 of Di, the depth at which the temperature is 0.3 F less 

 than the surface temperature. An examination of the 

 bathythermograph data shows that for Z>2 less than 

 5 ft, the main thermocline in every case extended all 

 the way to the surface, resulting in very sharp down- 

 ward bending of the beam. For D^ between 5 and 

 20 ft, a layer of small gradient overlay the thermo- 

 cline, which usually extended up to within 20 ft of the 

 surface, while for Di between 20 and 30 ft the main 

 thermocline was always deeper than 20 ft and usually 

 between 20 and 30 ft from the surface. To indicate 

 the scatter of the individual points making up these 

 average curves, all anomalies for Di between 5 and 

 20 ft are plotted in Figure 41. Half of the points lie 

 within about 4 db of the mean curve. The scatter 

 shows some tendency to increase with range and is 

 significantly greater than that found with a hydro- 

 phone in deep isothermal water (see Figure 15). There 

 is no significant change either in the mean curve or 

 in the scatter if values of D2 between 5 and 10 ft and 

 between 10 and 20 ft are considered separately. The 

 curve for B-^ between 20 and 30 ft is based on rela- 



