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A . Check for wind effect occurring on the water surface . Wind can
affect the measurement of low velocities, as example below 2 fps
( .60 m/s) . If possible, make the measurement in two directions,
one of the water flowing toward the gun and one away from the
gun . Try to make the measurement by pointing at the same spot .
Q . I’m making a measurement during a flooding condition . The
water is flowing very fast and is very turbulent and rough with a
lot of debris and floating material . Is the gun giving me a good
measurement?
A . YES, turbulent water with floating material on the surface
provides a good return signal to the radar . Note that in these
conditions, the radar gun reads many different velocities
occurring in numerous directions . The radar gun measures all
these velocities and provides one averaged velocity value .
Q . While making a measurement, the value is changing every 5
seconds .
A . The radar gun measures the velocity in 60-second intervals .
When the first measurement value appears on the display, it is a
result of the radar gun sampling the surface velocity numerous
times . (The radar gun puts the data values in a type of first-in,
first-out memory buffer .) As the radar gun continues to take
samples, it discards and replaces the older velocity values with
newer samples then averages the values again . The sampling
process takes place every 5 seconds within this 60-second
period . This is because the hydraulics of the water can change .
The radar samples the surface water and provides ten averaged
values of surface velocity, each sampled in a 5-second period .
After 60 seconds, the radar gun averages the ten values together
to provide a final velocity value .
Q . When I make measurements, the readings seem to change from
high to low velocities to high velocities, etc .
A . Make sure you hold the gun steady when you take a
measurement . The tilt sensor that compensates for vertical
(pitch-down) cosine error in velocity is very sensitive . Vibration or
jerky movements of the gun cause incorrect angle readings .
