Wolff, Tatro, and Megehee 



amplitude of approximately 1/2 meter per second (PUP, 1963). The 

 first question which must be answered, then, is to what extent this 

 microstructure in the sea affects the path of sound. To answer this, 

 a measured profile was carefully digitized using 120 points in depth 

 which preserved all the "wiggles" and a Ray Trace run as far as the 

 first convergence zone. Then the same profile was digitized using 54 

 data points, and finally 20 data points corresponding to standard 

 oceanographic depths. Figure 4 shows a section of the basic profile 

 and how it was smoothed by successively fewer data points. The 

 range to the first convergence zone agreed in all three cases within 

 less than 150 yards. It was concluded from this that a fairly smooth 

 average profile for a point in space and time is sufficient to describe 

 the sound field at that point. 



CONVERGENCE ZONE RANGE PREDICTION 



The presence or absence of a convergence zone and the range to 

 the zone when one exists are tactically useful pieces of information. 

 It has been shown that the ray trace program is capable of determining 

 a very precise range; however, to run this program for enough points 

 to adequately cover the area of interest to the Navy on a daily basis 

 would be prohibitive in terms of computer time required. What is 

 needed is a simpler method of prediction. It was decided to attack 

 this problem by a variation of parameters scheme. First a rather 

 standard "typical" temperature trace was determined. Figure 5 shows 

 this profile. The parameters which were considered to be of 

 importance were (1) the sea surface temperature (SST) , (2) the mixed 

 layer depth (MLD) , (3) the thermocline gradient (^T) and (4) the 400 

 meter temperature (T400). These parameters were varied, one at a 

 time, while holding the others constant. 



First five profiles were determined which had sea surface 

 temperatures ranging from 14°C to 22°C (Figure 6). These were run 

 through the ray trace program to determine the convergence zone 

 range for a 60 foot source depth. Figure 7 shows a plot of range vs. 

 temperature for these profiles. 



Next the basic profile was modified to cover a variety of mixed 

 layer depths, varying from 20 meters to 200 meters (Figure 8). The 

 convergence zone ranges for these profiles were plotted on the range 

 vs. temperature plot determined earlier, and an "equivalent tempera- 

 ture change" was determined for each layer depth. Figure 9 shows a 

 plot of equivalent temperature change (ATMLD) versus layer depth. 



The next step was to modify the basic profile to cover a range of 



200 



