2.3 Navigation 



Survey vessel position data were acquired using OSI's 

 "Haretrack" trackline control system in conjunction with a 

 Cubic DM-40A "Auto tape" electronic positioning system. OSI's 

 "Maretrack" system consists of an Apple computer with video 

 display and left/right indicator interfaced with the 

 "Autotape" system. The "Autotape" system is comprised of 

 three components: two shore-based range responders and an 

 interrogator unit installed aboard tiie survey vessel. Range 

 measurements to each responder are acquired from the phase 

 comparison of microwave reference signals transmitted and 

 received by the responders and the interrogator. The two 

 ranges are automatically displayed in meters by the onboard 

 interrogator and are updated at a one-second rate and input 

 to the "Maretrack" system. The "Haretrack" program computes 

 vessel location, distance to beginning of line, distance to 

 end of line, vessel speed and cross-track (distance off 

 intended survey trackline) error. Additionally, "Maretrack" 

 indicates required course corrections in real-time through a 

 left/right indicator. 



In operation, the helmsman is able to locate the vessel's 

 position with respect to the survey trackline on the video 

 monitor. Once on line, he can steer the desired line 

 following the course corrections indicated on the left/right 

 display. All positional data are automatically recorded on a 

 paper tape printer for later processing. 



Where site conditions did not permit the use of the 

 "Maretrack" system, an alternate positioning method was 

 employed consisting of one range of the "Autotape" system and 

 a theodolite established on NUEL's dock. The survey vessel 

 was controlled along a bore sight representing the intended 

 survey transect by the transit operator using a hand-held VHF 



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