The height of the instrument above the water surface and the inclination
determine area on the surface that is covered by the radar beam. This measurement
area should be clear of any obstacles. The structure holding the instrument (pole, bridge
fence, etc.) must be solid and without vibrations. There should be no vegetation
between the radar and the measurement area because it could affect measurement
accuracy.
Water surface direct below the sensor should be clean of vegetation, rocks, sand
deposition or other obstacles that could affect measurement.
Surface velocity radar beam will cover an elliptical area on the water surface.
The radar reports average surface velocity of the covered area and instrument uses
complex Kalman filters with physical modelling of the water flow to give stable
measurements even under turbulent conditions. However even the moderate waviness of
the water surface will improve the measurement, if the water flow is strongly turbulent,
fluctuations in measured data could be expected as well as somewhat reduced
measurement accuracy. If strongly turbulent flow can be expected at monitoring site,
then the filter length of the radar should be configured to 120 or more.
4.2. Measurement quality indicator
Geolux RSS-2-300W instrument is constantly calculating various parameters of the
signal in the signal processing algorithms and will continuously with measurement data
report also measurement quality. Quality indicator value is in range from 0 (the best
quality) to 3 (the worst quality) and can be used to interpret data in the analysis
software with better understanding and confidence.
For example, when radar is mounted on the railway bridge, one of common
applications, measurements will be very good quality most of the time except when train
is passing the bridge due to the extensive vibrations. In this case radar will still report
measurements but values could be quite wrong, but also measurement quality indicator
value will go up to the higher value. It is up to every user to interpret quality indicator
value for their application, but general recommendation is that measurements with
quality indicator 3 cannot be trusted, value 2 could be questionable and values 1 and 0
are very good and accurate.
4.3. Rain and wind
Geolux RSS-2-300WL instrument have integrated internal software filters to
filter out effects of rain, fog or wind both for surface velocity and for radar distance
sensor. These filters however have some limitations. Majority of measurement
inaccuracies caused by environmental factors can be solved by proper sensor installation.
For rain and snow suppression, the most effective solution is to mount the radar so that
it points upstream and the water flows towards the radar. As rain falls down and the
radar is tilted downwards, rain droplets will move away from the radar, while the water
flows towards the radar. The radar can then easily distinguish the water movement
