YSI ADV6600 - Manual (Page 111)

ADV6600
Y S I
Environmental
Page 101
Section 9. Principles of Operation
9-1. Acoustic Doppler Velocimeter (ADV)
The ADV6600 measures the velocity of water using a physical principle called the Doppler effect.
If a source of sound is moving relative to a receiver, the frequency of the sound at the receiver is
shifted from the transmit frequency.
F
doppler
= -F
source
(V / C)
where:
F
doppler
= Change in received frequency (Doppler shift)
F
source
= Frequency of transmitted sound
V = Velocity of source relative to receiver
C = Speed of sound
The velocity (V) represents the
relative speed between source and
receiver (motion that changes the
distance between the two).
• If the distance between the two
objects is decreasing, frequency
increases.
• If the distance is increasing,
frequency decreases.
• Motion perpendicular to the line
connecting source and receiver
does not introduce a Doppler
shift.
The ADV6600 is a bistatic Doppler
current meter. Bistatic means
separate acoustic transducers are used
for transmitter and receiver. The
transmitter generates sound concentrated in a narrow beam. The receivers are sensitive to sound
coming from a narrow beam. The receivers are mounted such that the beams intersect at a volume
of water located a fixed distance from the tip of the probe, typically 6.8 cm (4 in). The beam
intersection determines the location of the sampling volume, which is the volume of water in which
measurements are made.
The ADV6600 measures velocity by emitting a short pulse of sound at a known frequency from the
transmitter. The sound travels through the water along the transmitter beam axis. As the pulse
passes through the sampling volume, sound is reflected in all directions by particulate matter