I . INTRODUCTION 



1 .1 Purpose and Scope . The acoustical experiment that forms the subject of 

 this report, was planned as a joint program of Codes 3185 and 3190, US Navy 

 Electronics Laboratory, San Diego, California. The object of the experiment 

 was to determine the effects of internal waves on acoustical transmission in a 

 quasi -isothermal ocean surface layer. The experiment was performed in De- 

 cember 1964. The analysis of the experimental results is presented in this 

 report . 



1 .2 Description of the Experiment . The USS Marysville, under the direction 

 of Code 3190, performed a thermal survey using its thermistor chain, in areas 

 200-300 miles SW of Los Angeles. Two areas were selected as experimental 

 stations (Figure 1). The areas were similar in that both possessed well defined 

 surface layers as described in the report by Lee, Reference (1) . They differed 

 in that Area I was located at the unstable boundary between Eastern North Pacific 

 Central Water and Transition Water flowing southward from the Sub-Arctic, 

 whereas Area II was located further to the east in the more stable Transition 

 Water. The thermal survey of the area was completed 10-24 hours before the 

 performance of the acoustical transmission experiment. (See Appendix A for 



a detailed chronology of the experiment, in particular Table A-l for the times 

 involved .) The information on thermal structure obtained by the Marysville is 

 discussed in Appendix B, and presented in Figures B-l and B-2 . 



The acoustical experiment was performed by USS Rexburg and USNS Charles H. 

 Davis under the direction of Code 3185. At each station the experiment was the 

 same and consisted of the Davis making three radial runs ranging from 2 to 35 

 kiloyards from the Rexburg. The Davis transmitted a sequence of acoustical 

 pings at 700 cps, 1300 cps, and 3000 cps . One run was distinguished from 

 another by the projector depth (25 or 50 feet, 80 feet and 300 feet) . The Rex- 

 burg's receiving hydrophones were suspended at approximately 50 feet, 80 feet 

 and 300 feet. At the Rexburg, the received signals were recorded on magnetic 

 tape for later analysis . Details of the experimental program are provided in 

 Appendix A and of the recording equipment and methods in Appendix C . During 

 the acoustical experiment the Rexburg and Davis made regular bathythermograph 

 casts. As discussed in Appendix B, this data provided the basis for the calcula- 

 tion of the acoustic velocity profiles used in the theoretical calculations. 



arthur ai.HittleJnr. 



