acoustic signal is usually of ultrasonic frequency, perhaps several megacycles. 



Combinations of these systems are sometimes used in experiments 

 for comparison of the data measured by each. S.V.T.P. systems (e.g., 

 Reference 2) measure salinity, sound speed velocity, temperature and 

 pressure; and "birdcage" systems have been used consisting of Nansen bottles 

 and velocimeters in a protective enclosure. 



B. Requirements for Tactical Situations and Prediction 



The problem of using active sonar to best advantage involves 

 analysis of the ocean environment in order to decide the optimum operation 

 modes and probable detection ranges. The shape of the velocity profile 

 is of prime importance and so the requirement is principally for relative 

 accuracy. A detailed discussion of accuracy requirements for range pre- 

 diction is given in Reference 3. 



Several kinds of information are typically available to a sonar 

 officer. Echo sounders give bottom depth and variability. In general, 

 successful bottom bounce operation is not possible when the bottom slope 

 exceeds a few degrees. Elementary geometry suffices to predict approxi- 

 mate detection ranges for various beam depressions. Thus if 



(j) = sonar beam depression angle 



R = range 



z = depth of the bottom 



then 



R = 2z 



Arthur ZD.1Littlc.3nr. 



