FREQUTNCY IN CPS 



c. d. 



Fig. k. Tests at Institute of Marine Science dock May I96I to February 1962: 

 (a) oscilloscope, single sweep, 1 ms/cm, (b) Panoramic, 20 sweeps, 

 k second tape loop, (c) Panoramic. l6 sweeps, continuous segment and 

 (d) Panoramic, 60 sweeps, continuous segment. 



original tapes. In general, the audio output of 

 the Doppler meter fluctuates considerably due 

 to flow velocity variation and the number of 

 scatterers in the reverberation volume. Under 

 violently turbulent conditions the frequency 

 meter reading was fairly stable. 



Examples of extremely turbulent flow can be 

 observed in the records taken from the Institute 

 of Marine Science dock. Many local eddies were 

 observed visually around the pilings and large 

 swirling patterns from the Bear Cut bridge 

 extended to the dock. The Doppler shift fre- 

 quency, converted to an audible signal, sounded 

 complex and resembled wind in blizzard conditions. 

 When the transducer heads were positioned normal 

 to the general current flow appreciable 



Doppler shift was still produced, signifying 

 turbulent conditions . With head parallel to 

 current flow a complex wave structure was gen- 

 erated (Fig. ka) and the frequency spectrum was 

 broadband with no well defined "peak" (Figs, kb, 

 kc and Ifcl ) . 



The current meter output was recorded during 

 tests at the Stevens Institute tow tank. No 

 Doppler shift was produced until the transducers 

 were mounted 2 inches from the surface and the 

 towing arm crossed its own wake on its second 

 and subsequent revolutions. Low frequency fluc- 

 tuations modulating the sinusoidal output were 

 caused by the motion produced wavelets (Fig. 5a) . 

 The frequency spectrum of the signal is narrow 

 after a 1-second signal sweep (Fig. 5t>). There 



130 



