Fig. 14,2 Unusually long range visibility is shown from this camera and a line ot targets. 4-liter bottles spaced 10 teet apart, photographed at a depth of 600 feet under ambient light 

 ofl Key West Flonda from STAR III The depth of field exceeds 100 feet and honzontal visibility was estimated at over 200 feel (NAVOCEANO) 



device to warn of obstacles in their line of 

 flight — e.g., cliffs, wrecks, cables, etc. — be- 

 yond the limits of visibility. Two approaches 

 to obstacle avoidance have been taken: The 

 first incorporates a conventional echo soun- 

 der transducer mounted on the bow and look- 

 ing directly forward; the second involves a 

 horizontally trainable transducer mounted 

 forward and atop the vehicle which operates 

 similar to radar and displays targets on a 

 cathode ray tube scope inside the vehicle and 

 which provides range and relative bearing of 

 a target from the submersible (Fig. 14.3). A 

 number of companies produce this latter sys- 

 tem. The Straza Model 500 CTFM Sonar is on 

 several submersibles and its range is from 10 



to 1,500 yards. Both the forward-looking echo 

 sounder and the CTFM have served admira- 

 bly; the characteristics of these are dis- 

 cussed in Chapter 10. From a safety view- 

 point, none have demonstrated an advantage 

 over the other. 



Life Support Monitors 



Most, but not all, submersibles carry auto- 

 matic or manual devices to measure pressure 

 hull oxygen and carbon dioxide content. The 

 manual devices are easily obtainable off-the- 

 shelf instruments, the automatic devices are 

 also stock items but more expensive. The 

 general practice is to take or observe cabin 

 oxygen and carbon dioxide content at peri- 



657 



