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JANUARY 2010 - TD 220a DEPLOYMENT GUIDE, RDCP600
For
Timing Configurations
, open
Start menu
→
Deployment Setup
→
Edit
→
Timing.
Set the
Ocean current duration
and the
Acoustic
wave duration
, refer Figure 2-6.
The
Recording Interval
will be the sum of the
Ocean current duration and the Acoustic wave
duration.
The instrument alternates between current
measurements and wave measurements.
In the example above the current measurements
are set up with a ping activity of 350ms (the
instrument pings once every 350ms), while the
Acoustic wave duration is set up with a ping
activity of 500ms.
2.2.2
Important Considerations
The minimum wave period that the RDCP600 can measure is restricted by the design of the
transceiver head and the Nyquist sampling theorem.
The Nyquist sampling theorem states that the minimum sampling rate required to avoid aliasing
is twice the highest frequency contained within the signal, hence the length of the wave (in
meters) must be at least twice the distance between two opposite transducer beams at the
surface.
Relationship between the deployment depth and the wave period:
The RDCP600 transducers are tilted 25
off the
vertical axis. The acoustic signal from each
transducer propagates into the water, forming all
together four propagation beams used as the basis
for the current measurements, refer figure. Due to
the transducer tilting, the distance between the four
beams increases with the propagation distance; if the
instrument is deployed 20 meters below the surface,
the distance between two opposite beams is about 20
meters:
m
20
20
25
tan
2
.
Figure 2-6 Acoustic wave duration.
