ECN publication
Comparative measurements of SODAR systems : Correlation with meteorological masts for onshore and offshore conditions and further measurements to compare SODARs (final draft)
Published by: Publication date:
ECN Wind Energy 1-3-2003
ECN report number: Document type:
ECN-C--02-045 ECN publication
Number of pages: Full text:
180 Download PDF  

ECN performed measurements at onshore and offshore locations to validatea MiniSODAR measurement system. A number of different measurements were done to compare the two SODARs. These were hardware test, background noise and vibration measurements. Also a comparison with a meteorology tower has been performed.
The onshore SODAR measurements are compared against a 213-metres height meteorological mast owned by the KNMI, located at Cabauw in the Netherlands. Offshore SODAR measurements are compared against a 10-metres meteorological mast owned by KNMI at the station Noordwijk, about 9 km off the coast at Noordwijk, in the Dutch part of the North Sea.
Onshore comparison is performed at different height levels and using different SODAR settings. Two different models of the MiniSODAR were used for this purpose. Offshore comparison is done at 10 metres height only (due to limitations of the available tower). A MiniSODAR model, similar to one of the models used for onshore measurements, was used offshore.
The aim of the measurements is:

  • To gain knowledge of parameters that influence the performance of the MiniSODAR;
  • To analyse the MiniSODAR?s performance under influence of external noise and vibrations;
  • To check the operation of the SODAR by comparing calibration measurements.
Correlations for measurements using a meteorological mast and a SODAR system have been derived for onshore and offshore applications. A correlation between onshore and offshore measurements using SODAR techniques is also derived.
The results of the measurements offshore are that it is important to determine the position of the SODAR by measurements and to perform regular maintenance (at least once every three months) as severe degradation of equipment has been seen. With regards to the onshore measurements the measurement results show that the mean difference between SODAR and the anemometers on the mast is 0.84 m/s (at 80 metres) and 1.73 m/s (at 80 metres) for the same SODAR with different settings. A SODAR of a different model showed a mean deviation of 1.58 m/s. The conclusion is that the SODAR performance is heavily influenced by the SODAR settings. At the moment off-the-shelf SODAR does not perform well enough to be used for wind energy purposes.

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