SOUND VELOCITY 



The speed of sound at intervals 

 throughout the water column is computed 

 from measurements of temperature, 

 salinity, and pressure. In addition, 

 various sound velocity meters have been 

 tested and used. Some meters were 

 mounted on tower carts for vertical 

 sound-velocity structure measurements, 

 while others were attached to a tripod 

 out from the tower for long-period re- 

 cording. 



The meters normally utilize sing- 

 around circuits which produce a fre- 

 quency proportional to the sound velocity. 

 The frequency is recorded digitally and 

 later converted to sound velocity. The 

 data are used for acoustic transmission 

 studies when precise values are required. 

 In other studies, sound velocity is ob- 

 tained indirectly. 



Variable-depth sound velocity meter transmits a 

 pulse of sound. When the pulse is received it triggers 

 a new pulse. This process is continuously repeated 

 over a^iven path. The pulse repetition frequency is 

 a direct measure of the sound velocity. The signals 

 are carried to digital recorders in the instrument 

 house and the recordings are later converted by 

 machine to correct sound velocity. 



58 



