SONAR 

 HYDROPHON 



a 



PROJECTOR 



SONAR 



CABLES ^-,- 



OELTICr? : 

 ANALYZER 



EDTsu 



SONAR 



RECORDING 

 EQUIPMENT 



POWER 

 PPLY 



UOv.o.c, 

 POWERLINE 



\ 



POLYVINYL 



BAG 



ENCLOSURE 



■ DIRECTION OF 

 ROTATION FOR 

 LOADING SPECIMEN 



Figure 5. — Top view of test site Mission Bay Yacht Club pier. 



limited to the technique of presenting informa- 

 tion on the Doppler effect of the fish, a process 

 by which the signal return could be removed 

 in the presence of the surface and bottom 

 reflections. 



Preliminary tests in air and pools of the 

 Doppler portion of the sonar equipment had 

 been made at the Straza sonar laboratory. 

 The operation was fo\ind to be extremely good; 

 the low-frequency presentation which was 

 possible with the Doppler technique went to at 

 least 2 Hz, and was capable of operation in the 

 lOth's of Hz of Doppler information. A live, 

 76-cm. yellowtail ( Seriola dorsalis ) was pur- 

 chased from one of the commercial fishing 

 boats and brought to the Mission Bay Yacht 

 Club pier. This fish was placed in the new 

 6-foot-diameter (1.8 m.) bag. During this 

 test, the Doppler unit was used to determine 

 the feasibility of operation in the shallow 

 water. The tape recordings made at this test 

 were observed visually on a Tektronix oscil- 

 loscope and aurally. The information that a 

 fish was in the enclosure showed up as 

 differences in the appearance of the waveforms 

 and changes in pitch of the aural signals. 



Sophisticated techniques for data reduction 

 were required to extract from the taped infor- 

 mation the signals from the fish and those 

 from the surface motion of the water. This 

 point is covered in a separate section--Data 

 Evaluation and Reduction. The tests at the 

 Mission Bay Yacht Club pier were concluded 

 and preparations for a deep, open-water test 

 were begun. Deep water was required because 

 ripples on the surface of the water and the 

 reflection from surface and bottom caused too 

 great problems. The intent was to make a test 



in water deeper than 50 feet (15.2 m.) and 

 thus eliminate the problem of surface and 

 bottom return and at the same time permit 

 the operation of both the CTFM sonar and the 

 Doppler equipment, 



Catalina Tests 



A test site at Catalina Island was selected 

 for several reasons: (1) clarity of the water 

 that would permit films to be made of the 

 fish during the test; (2) availability of a large 

 number of fish in the size range of interest in 

 the area; (3) depth of the water sufficiently 

 great to eliminate most of the problems from 

 surface and bottom reflections. 



Both the CTFM and Doppler sonar equip- 

 ment were taken to Catalina. These tests had 

 many operational difficulties owing to the 

 operation of breadboard equipment on the 

 45 -foot (13.7 m.) charter boat Duchess which 

 was used at Catalina Island (and engineer's 

 mal de mer). Three SCUBA divers set up the 

 equipment on the bottom. The arrangement of 

 the equipment and the checkout and operation 

 went smoothly--all systems checked perfectly 

 and on the second day the television equipment 

 offered by the U,S. Naval Ordnance Test 

 Station, Pasadena, and all the sonar equipment 

 were functioning perfectly. During the second 

 day the divers obtained abalone and placed 

 them on the chumming platforms so that fish 

 would accumulate in the beam of the sonar as 

 depicted in figure 6. The sonar returns were 

 recorded on one track of a Magnecord tape 

 recorder. Data runs were taken for 1-1/2 

 days with both the CTFM sonar and the 

 Doppler sonar equipment. A series of 14 film 



