point, and (4) It permits housing the towed vehicle In an 

 enclosed space where maintenance and equipment Installation 

 and removal can be carried out regardless of weather con- 

 ditions. 



Underwater Tracking Equipment 



The second unusual feature In MIZAR Is the Underwater 

 Tracking Equipment (UTE). (See Figure 3) Three hydrophones 

 are mounted on the ship's hull In the form of a 90 degree 

 Isocoles right triangle with 50 foot like sides. The tri- 

 angle has Its hypotenuse approximately parallel to the 

 centerllne and the other two sides roughly at 45 degrees 

 to the centerllne. A small digital computer controls the 

 system automatically. 



A sonar transponder Is planted on the ocean floor In 

 the area to be searched, and a second transponder Is mounted 

 on the submerged vehicle. In operation the fixed reference 

 transponder Is Interrogated by a coded signal. The reply 

 is received at each of the three hydrophonjes and from these 

 arrival times the location of the transponder relative" to 

 the ship in three dimensions is computed and printed out by 

 the computer (See Figure 4). Next, the submerged vehicle 

 transponder is Interrogated and its location relative to 

 the ship is computed. A simple subtraction of these two 

 numbers yields the location of the submerged vehicle relative 

 to the bottom reference transponder. This entire process is 

 repeated about twice each minute. 



Some difficulty was experienced due to the narrow-beam 

 pattern of the available hull mounted hydronhones in the first 

 portions of the search. Later, a new hydrophone with a 

 hemispherical beam pattern was obtained and used to replace 

 the original units. After this change operations were satis- 

 factorily carried out at ranges to about 3-1/2 miles in water 

 over 10,000 feet deep. The position data under these con- 

 ditions showed a scatter with a standard deviation of about 

 250 feet. 



Satellite Navigation 



The Underwater Tracking Equipment is a "relative" 

 system. The SRN-9 Satellite Navigation System was used to 

 obtain geodetic coordinates for the submerged reference. 



The satellite system was the most accurate navigation 

 system available in this area. It suffers from the fact 

 that location data are available only during the passage of 

 a satellite at an appropriate elevation. For this reason 

 passes may be as much as six hours apart. The method used 

 was to obtain the ship's position on each appropriate sat- 

 ellite pass and record the position of the ship relative to 



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