APPENDIX A - SURFACE WAVE HEIGHT DATA OBTAINED BY THE 

 SONIC SURFACE SCANNER 



A. Digital Recording and Playback of Sonic Surface Scanner Data 



An example of a sea surface profile obtained by Sonic Surface Scanner is presented 

 in Reference 8. The Sonic Surface Scanner consists of ten transducers mounted on the 

 deck. These are spaced 33 feet apart (Fig. 1). The transducers are mounted face 

 upward and are essentially Inverted echo sounders. Each transducer in turn measures 

 distance between itself and the sea surface directly above in a 3° cone. By sequencing 

 from one transducer to the next aft along the deck of the submarine, a wave profile, 

 comparable to the length of the submarine, is obtained. The complete sequence takes 

 approximately 0.7 seconds „ The Sonic Scanner was designed to provide an accuracy 

 to the nearest foot . 



The output of all ten transducers are available, but the primary Interest In this 

 report is the power spectra of the output of one transducer. A recording from one 

 transducer Is, therefore, the instantaneous height of the sea surface above the submarine 

 as a function of time. This is given in terms of the two-way travel time required for a 

 sound wave front to travel from the transducer to the sea surface and return. 



Assume the velocity of sound in ocean waters to be 5000 ft/sec (the resulting error 

 in this assumption is very small). Travel time per foot can be expressed: 



1 -3 



sec ./ft. = 0.2 x 10 sec ./ft. = 0.2 mil Usee ./ft. 



5000 



Since we are concerned with a two-way travel time (the time required for the 

 sound beam to go from the submarine transducer to the sea surface and return), the 

 effect is the same as if the travel time were doubled. Thus, the effective travel time 

 per foot is: 



t = 0.4 ml I Usee ./ft. 



For convenience In counting, t is expressed ass 



t = 10mIllisec./25 ft. 



In this way, changes in the height of sea surface above the submarine are measured 

 in terms of the two-way travel time. These changing values of sea surface height above 

 the submarine are recorded as pulses on an AM channel of a tape recorder every 0.7 

 seconds. 



49 



