Figure 12. DM-UO Cubic Autotape Interrogator, 

 Direct digital readout is in meters. 



the vessel is easily determined on a plotting board by intersecting arcs 

 struck by the ranges scaled from the respective plotted responder sites. 

 This manual method is used only as an aid in piloting the vessel. The 

 Autotape is electrically coupled to the on-board analyzer of the mobile 

 detection system for direct correlation of vehicle position with the 

 parameters of time and count rate. 



A knowledge of bottom topography is essential to a realistic analysis 

 of littoral transport patterns. In addition, the operating depths should 

 be known while towing the detector vehicle. Prior to the field tracer 

 test, hydrographic and topographic surveys are conducted on ranges per- 

 pendicular to the shoreline. A transit operator with a portable radio 

 occupies a point on shore and directs the vessel in on the range line. 

 A second instrumentman, at a measured distance up or downcoast , plots the 

 survey vessel's position using a plane table with an alidade on radio 

 command from an operator on the boat . Depths are constantly recorded on 

 the boat with a portable precision recording fathometer. Later the re- 

 corded depths are plotted on cross-section paper as a function of the 

 distance from a baseline to form profiles of the sea bottom. 



The heart (and most vulnerable part) of a fathometer is the trans- 

 ducer unit which is a 2-way energy conversion device. It transmits sonic 

 energy waves (200 kilohertz) to the bottom and receives echoes of these 

 waves reflected back from the bottom. The time lapse between transmission 

 and reception, mainly a function of the distance the signal travels through 

 the water, determines the water depth. Depths are visually displayed and 

 recorded on electrosensitive paper. Calibrations are made for variations 

 in water temperature, salinity and turbidity by measuring depths (at 10- 

 foot increments) to a metal bar lowered below the boat. At the end of 



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