Manual – Starflow QSD Model 6527B and 6537A
Unidata Manual - 6527B and 6537A Starflow QSD User Manual 08 05 2023.docx
Page 99
17.2. Velocity
Histograms
The Velocity Histograms that you will see by using Velocity Trace from the Control Panel are
the Starflow QSD’s view of the channel. It is the composite of a range of factors, including
both characteristics of the equipment, the sampling method, and the velocity dynamics within
the channel. The following statistics are computed from the range of Doppler shifts
measured for each cycle.
CW-Vel Median
:
The computed median of all the Doppler shifts detected, measured in mm/sec. This is the
value presently logged.
Spread
:
A ratio of the width of the peak to the height. This can provide an indication of the “quality” of
the histogram. 10% to 80% are typical values. A transducer buried in the sand will give a
large value.
Maximum
:
The Doppler shift of the peak of the histogram, in mm/s, is indicated by the green line.
The screen will cycle, refreshing the plot and summaries each time a new set of samples are
acquired.
The following examples are shown as you would see them on your screen.
An ideal signal, when presented as
a histogram, appears as a
symmetrical peak. The x-axis
represents the velocity in mm/sec.
The y-axis indicates the relative
number of times a particular velocity
has been received. The
approximate “centre” of this peak is
the value of the velocity we are
looking for, as it will be the mean of
all the echoes received.
As the velocity changes, the peak
will be seen to move back and forth
along the x-axis.
Note:
The Velocity Trace does not
indicate Flow Direction, only Velocity
magnitude. The width of the peak
indicates that a range of velocities is
being measured with each reading. The narrowest
of peaks would be obtained in the ideal conditions
of perfectly laminar, tranquil flows in water with an
even distribution of reflective particles. These
would still be 50—100 mm/sec wide and would
appear as above.
