SECT. 4] 



SOUND SCATTERING BY MARINE ORGANISMS 



511 



recorder. When sound-scatterers appear on the echo-sounder record at an 

 appropriate range, the camera is triggered. Data taken with such a system, not 

 in deep scattering layers but in relatively near-surface waters of the deep ocean, 

 show a high correlation between images of small fishes and the presence of 

 strong echo-sequences on the echo-sounder record (Johnson, Backus, Hersey 

 and Owen, 1956). An example of such data is shown in Fig. 10. The chief 



:CHO sequence/ L^,^^^ 



)F SCATTERER/ ff^^'k- 



ECHO SEQ 

 CALIBRAT 



UENCE OF j 

 ION BALL I 



PICTURE TAKEN 



30 g 



u. 



UJ 

 40 O 



5 seconds 



Fig. 10. An example of data collected by a suspended echo-sounder-camera apparatus 

 showing simultaneously taken echo-sounder record and 35 mm photograph (see text). 

 The fish in the photograph is the gempylid. Nealotus tripes Johnson, and was identified 

 with the aid of specimens collected at a nearby depth. (After Johnson, Backus, 

 Hersey and Owen, 1956.) 



design problem in such an instrument is that of making the echo-sounder 

 system directional enough so as to be certain that scatterers seen on the echo- 

 sounder record are within the purview of the camera. A refinement of the 

 equipment described above has recently been constructed, at the Woods Hole 

 Oceanographic Institution, which overcomes this problem and in which the 

 echoes received from the mid-water scatterers directly trigger the underwater 

 camera. At the same time photography of an oscilloscope in the ship's labora- 

 tory records data for the computation of the acoustical cross-section of the 

 scatterer. 



