RSS-2-300W User Manual
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RSS-2-300W Non-Contact Surface Velocity Radar
4.4. Interference and Multiple Radars
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 precise central frequency but even with the best possible trimming and most stable
oscillators it is very unlikely that two devices will be working on the exact same frequency to
cause interference. Doppler frequency shift caused by water in 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 difference
between central frequencies of two radars in the same range to get interference.
Similarly, as interference from two or more surface velocity radars on the same location it is
very unlikely that other radiation sources in K band will also affect radar measurements. It is
possible that some wideband radiation sources can introduce small and impulse interference
for the short period of time, but this should not, or is very unlikely to affect measurements
reported by radar sensor continuously.
4.5. Fogging and Evaporation
Generally, radar sensors are not affected by fog or evaporation of water unless very heavy
evaporation is present and water density in the air is very high. Very high amount of
evaporation can introduce reflections and can affect measurement on surface velocity sensor.
In the case of evaporation, the best solution for surface velocity sensor problem solving is to
use outbound flow direction and to configure sensor with only downstream directional filter.
As evaporation is traveling upwards from the water surface, inbound or approaching to the
radar, directional filter will solve the problem in most of the cases.
4.6. Reflections
Water is very reflective medium for the radar waves and most of the power transmitted from
radar transmitter will be reflected from the water surface. Reflections of the radar transmitted
power beam follow the same physical laws as in optics and every time radar beam hits the
surface part of the power is reflected away from the radar, part of the power is reflected
towards the radar and only a small part of power is absorbed by the water. Depending on
the surface roughness and incident angle ratio between power reflected in the direction away
from the radar and direction back towards the radar can significantly vary.
Ratio between reflections is determined by water surface roughness and rule of thumb
can be applied where more rough water surface will lead to stronger reflection inbound
the radar thus easier detection and greater SNR (signal to noise) ration on the radar which
enables more accurate measurement. Geolux surface velocity radar is designed with special
techniques to achieve accurate measurements even in the very small SNR environments so the
required surface roughness of 1 mm is usually enough for the precise measurements.
Summary of Contents for RSS-2-300W
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