PART II: SYSTEM CONFIGURATION 



Sonar Components 



5. Components of an SSS system typically include, as a minimum: a tow- 

 fish; a control/processing/display/recording/power unit; and a speed log (see 

 Figure 1). The towfish is a streamlined body that houses the transducers, one 

 on each side. The transfer of signals between the fish and the control unit 

 occurs through an electrical cable that may serve a dual function as the tow- 

 ing cable. Forward speed of the transducer- -used in automatic correction of 

 along-track speed variation distortion of the record- -can be measured by a 

 separately towed speed log or by a speed log built into the towfish. The 

 speed of the towing vessel can be input directly to the control unit. 



6. Vertical elevation of the fish above the bottom- -used for correction 

 of across-track (slant-range) distortion- -is determined using a directly 

 downward -pointing separate acoustic transducer or is obtained from a downward- 

 directed portion of the side-looking transducer's beam. Various optional and 

 auxiliary equipment that might be added to the basic system include: data 

 processing software/hardware modules for automatic corrections, image enhance- 

 ment, digital recording, etc.; alternative display options (e.g. dry paper 

 plotter, color CRT); separate DC power supply; annotation keyboard for placing 

 marks and messages on the image; and position- fixing equipment. 



Platform Types and Means of Deployment 



7. The type of problem to be studied, the site conditions, and the 

 resources available will dictate the choice of platform. An advantage of the 

 modern SSS systems is that they are small enough to be deployed in a variety 

 of ways . 



8. Most commonly, the SSS system will be deployed from a boat. In 

 shallow water under calm conditions, a boat as small as an outboard-powered 

 inflatable could be used (a further discussion of vessel requirements is found 

 in paragraphs 12 through 27) . In addition to the common deepwater deployment 

 method where the fish is towed from the stern, deployment from the bow or the 

 side of the boat near midships, possibly using a boom to extend the cable away 

 from the hull, may be advantageous in both shallow and rough waters. In 



