In order to predict the sound field for hull-mounted sonar 

 operation, the sound speed must be known as a function of time and space. 

 The speed of sound increases with temperature at roughly 3.0 meters per 

 second per °C, with salinity at 1.3 meters per second per mille and with 

 depth at approximately 1.7 meters per second per 100 meters. In general, 

 the speed of sound in sea water varies from approximately 1460 to 1530 meters 

 per second. 



A sonar officer generally has temperature data, (i.e., tempera- 

 ture vs. depth data) for the upper part of the ocean. It is usual to 

 assume that the speed of sound varies only in the vertical direction. 

 Salinity measurements are not usually made in fleet operation, but charts 

 of "average surface salinity" as a function of latitude and longitude are 

 readily available to him. Pressure versus depth charts are also available. 

 Usually pressure is assumed to be uniquely related to depth, although 

 differences in latitude alone may introduce sound speed errors as high as 

 one meter per second. The data are usually furnished in ft- lb-sec units. 

 In order to synthesize velocity profiles then, a sonar operator depends 

 on temperature data, using the empirical relationships previously mentioned 

 which give the sound speed as a function of temperature, pressure and 

 salinity. 



The Woods Hole Oceanographic Atlas of the Atlantic Ocean 

 (Reference 4) contains both bathythermograph data and independent tempera- 

 ture and salinity measurements made by sampling techniques for identical 

 parts of the ocean. Some examples are shown in Figure 1. Nansen bottles 

 were used to obtain samples at depths from which salinities were determined; 

 reversing thermometers gave the temperatures. The estimated experimental 

 errors involved in sampling were: temperature + 0.01°C depth + 5 meters, 

 salinity +0-01 parts per thousand. The mechanical bathythermograph used had 



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