A DOPPLER-SHIFT OCEAN-CURRENT METER 
by J.D. CHALUPNIK and P.$. GREEN 
Lockheed Missiles and Space Company 
Palo Alto, California 
ABSTRACT 
An ocean-current meter utilizing the Dopoler 
effect has been developed and tested. With this 
device a collimated bean of ultrasonic energy 
is projected into the water and a volume rever- 
beration signal received. The meter detects 
the difference between the transmitted and re- 
ceived frequencies, this difference being pro-= 
portional to the speed of the water past the 
meter. The device can be made to indicate sense 
as well as flow rate. 
INTRODUCTION 
Ocean=current meters commonly in use are 
mechanical devices using impellers turned by 
the dynamic pressure of the current, although 
other instruments which measure (1) dynamic 
pressure on static members, (2) electromotive 
force generated by the conducting liquid flow- 
ing in a magnetic field, (3) cooling effect of 
the current on hot wires, and (lh) time required 
for a sound pulse to travel a specified dis- 
tance have been tried. 1* 
The impeller devices respond slowly to 
changing flows and operate over limited ranges 
of flow rates. They are large and do not give 
continuous readings. The instruments which 
measure dynamic pressures on static members 
are limited in operating range. Hlectro- 
magnetic current meters are limited in oper- 
ating range and are expensive. Hot-wire 
anemometer=type devices are difficult to use 
and require frequent cleaning due to films 
forming on the wires. Ultrasonic current 
meters which have been reported prior to this 
meeting have been electronically complicated 
and expensive. A paper being presented at 
this meeting by F. J. Suellentrop describes an 
improved version of this instrument which gives 
speed-of-sound information as well as flow rate. 
This paper describes a new instrument 
which makes use of the Doppler frequency shift 
to measure flow rates in ocean water and other 
liquids containing inhomogeneities. 
THEORY OF OP#RATION 
When a beam of ultrasonic energy is pro= 
jected into an inhomogeneous liquid, it is 
scattered by irregularities in the liquid and 
some of the energy is returned in the direction 
of the transmitter. This returned signal is 
called volume reverberation. The volume re- 
verberation signal is found to shift in fre- 
quency due to the Doppler effect, provided 
there is net movement of the inhomogeneities 
along the axis of the beam.2 If the scatterers 
are stationary with respect to the liquid, then 
the observed Doppler shift is proportional to 
the speed of the liquid relative to the meter. 
The Doppler-shift ocean-current meter is a 
continuous-tone sonar device which detects the 
volume reverberation signal with a receiving 
transducer located adjacent to a transmitting 
transducer, then detects any shift in frequency 
between the transmitted and received signals. 
It is assumed that the vast majority of the 
contributing scatterers are nearly neutrally 
buoyant and move with the water. 
The application of the Doppler-shift prin- 
ciple to measuring currents in the ocean ap= 
peared to be feasible, provided enough scat-= 
terers were present in the water. Since Ray= 
leigh scattering increases with the fourth 
power of frequency, only high frequencies were 
investigated, 2.5 and 10 megacycles being 
chosen as favorable operating frequencies. 
Most considerations indicated that the higher 
frequency should be used, the principal objec- 
tion being the inherent difficulties encount- 
ered in high-frequency transistor circuitry. 
At 10 mc the number of scatterers one wave- 
length or greater (A = .15mm) in size is 
quite large, with small marine organisms, 
particulate matter, and minute bubbles abound- 
Inge 
For a stationary transducer-pair and moving 
target (scatterers), the frequency of the re- 
* Superior numbers refer to similarly numbered references at the end of this paper. 
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