Manual – Starflow QSD Model 6527B and 6537A
Unidata Manual - 6527B and 6537A Starflow QSD User Manual 08 05 2023.docx
Page 101
The Doppler shift measured is the velocity component
along the line between the particle and the transmitter,
so this changes by 5% as the particle traverses the
beam.
17.5.
Measuring Errors Due To “Signal Noise”
“Signal Noise” is a convenient term used to classify any Doppler shifts that cannot be
explained as legitimate measurements of water velocity. The Starflow QSD measures tiny
signals echoed back from small particles along a path scattered with many other particles, all
in motion. The returned signals are sometimes echoes of echoes, vague and ambiguous
and can be misinterpreted by the measuring circuits resulting in an incorrect Doppler shift.
These result in frequency shifts being measured that are outside the range of velocities
expected. They can represent several percent of measurements in a scan but are typically
widely distributed. They are usually statistically irrelevant because of the signal analysis
techniques used to define the median.
17.6.
Channel Characteristics Affecting the Signal
All signals are affected by the factors discussed above. Additional factors related to channel
and flow characteristics can influence the measured velocity. These result in a widening of
the histogram base because of the broader spread of Doppler shifts measured.
