700-SDI-RADAR-300WL-Man Rev 2 11 Apr Mar 2022
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Part# 21371
The influence of the wind on the accuracy of measured data is, in most cases, small and can be
neglected. The only exception is strong wind as it will create surface waves that are traveling in a
different direction from the water flow. This can affect surface measurement accuracy.
2.4
INTERFERENCE AND MULTIPLE RADARS
The surface velocity radar operates in K band, in frequency range around 24.125 GHz. Frequency
stability and phase noise of the internal oscillator is very good and always trimmed in factory to a
precise central frequency making the likelihood of two devices working on the exact same frequency
to cause interference highly unlikely. The Doppler frequency shift caused by water in the speed
range up to 15 m/s is measured in kHz frequency shift. As this frequency shift is relatively small in
comparison to the central frequency, in most cases below 0.00005%, it will be required to keep the
difference between central frequencies of two radars in the same range to get interference.
The distance measurement radar operates in the W-band from 77 GHz to 81 GHz with continuous
linear frequency modulation within the frequency range. Interference between two or more sensors
will require precise coordination of the central frequencies with a timing synchronization in a range
of 25 ns between each other. Such synchronization is very complex to achieve so the interference
probability between several radars on the same location is very small.
Similarly, is very unlikely that other radiation sources in K band or W band in the vicinity will affect
the 300WL measurements. Some wideband radiation sources can introduce small impulse
interference for a short period of time, but this is very unlikely to affect measurements reported by
the radar.
2.5
FOGGING AND EVAPORATION
Generally, radar sensors are not affected by fog or evaporation. However, heavy evaporation with
high water density in the atmosphere can affect measurement accuracy. A very high amount of
evaporation can introduce reflections and can affect measurement on both sensors, with greater
inaccuracies seen on the surface velocity measurements.
The best solution for the surface velocity sensor measurements in heavy evaporation is to use the
outbound flow direction and to configure the sensor with only the downstream directional filter. As
evaporation is traveling upwards from the water surface, using the directional filter for water that is
inbound or approaching to the radar will solve the problem in most of the cases.
The best solution for the distance measurement is to increase the average period to get a better
average distance value. As evaporation is a naturally very turbulent event with a significant
difference in atmospheric water density over the surface area over time, averaging of the distance
measurement spectrum solves the accuracy problem.
