The extreme values of the sound velocity profile can be obtained by con- 

 structing the envelope of the profiles existing in a given area. A deter- 

 minati on of these envelopes has been coiranenced by the US Naval Oceanographic 

 Office. The results are contained in NavOceanO Technical Report No. TR-171, 

 "An Interim Report on the Sound Velocity Distribution in the North Atlaintic 

 Ocean", March 1965. 



Using this report we have constructed the six regions, or oceanographic 

 provinces, shown in Figure 2. (The original report contained a finer sub- 

 division of the provinces for each of four seasons.) The shaded areas 

 represent transition zones that change from season to season. Each of the 

 six regions in Figure 2 has associated with it an envelope of the sound- 

 velocity profiles existing in that region. This partitioning of the North 

 Atlantic Ocean is of course an interim result. Additional data is needed 

 in many areas. This additional data would very likely alter the presenta- 

 tion in Figure 2. The modification, however, could only be expected to 

 deliniate the zones more accurately. The size of the zones, and their 

 general location are, it is felt, well established by the above-mentioned 

 NavOceanO report. 



In Figure 3 there are two sound velocity profiles labeled T-, and Pj 

 which are indicated by heavy black lines. These two profiles were con- 

 structed by taking the envelope of all profiles measured in Zone 2 (Fig 2), 

 i.e. the North American Basin. These two sound velocity profiles represent 

 in essence the extreme conditions which the environment can assume in 

 Zone 2. 



It will later be shown that the errors associated with the predictions 

 increase as the envelope increases. An improvement in the prediction of 

 the sound velocity envelope at any given moment can be made through a better 

 knowledge of the behavior of water nasses. Thus, for instance, it is known 

 that large positive gradients tend to be unstable. This instability is also 

 a function of depth. Studies performed by Vitro Laboratories in conjunction 

 with the ASIi/EPS program indicated that an upper bound to the positive gradi- 

 ents existing in the first 100 feet of Zone 2 is O.OU ft/sec/ft. An upper 

 bound to positive gradients existing below 100 feet in this area was found 

 to be 0,0175 ft/sec/ft. This information, in conjunction with the known 

 value of surface velocity , permits a sound velocity profile to be con- 

 structed that intersects the value of sound velocity at the surface and the 

 profile P^ (Fig 3). The profile P2 which borders the shaded region on the 

 right and the profile P^ can now be used as the environmental inputs to the 

 computations. 



Variation of Acoustic Parameters 



A schematic depiction of the variation in the acoustic parameters at 

 a fixed value of sonar range are shown in Figure U(b) through U(f). Figure 

 U(a) shows a graph of normalized range /ij^ versus a normalized Snell's index, 

 I/, The values of slant range, s, and travel time, t, are also normalized. 



49 



