ECN publication
Noise and Vibrations Measurements: External noise and vibrations measurements for offshore SODAR application
Published by: Publication date:
ECN Wind Energy 1-10-2003
ECN report number: Document type:
ECN-C--03-109 ECN publication
Number of pages: Full text:
47 Download PDF  

The partners in the WISE project investigate whether application ofthe SODAR measurement technique in wind energy experimental work is feasible as a replacement for cup anemometers, wind direction sensors and tall meteorological masts. In Work Package 2 of the WISE project extensive controlled experiments with the SODAR are performed. For example SODAR measurements are compared with measurements from nearby masts and different brands of SODARs are compared. Part of the work package is the measurement of vibration and noise on an offshore SODAR system. The results of these measurements are presented in this report.

ECN performed measurements at an offshore location to investigate the influence of noise and vibrations on the performance of a MiniSODAR measurement system. The aim of the measurements is to quantify the effect of these external noise and vibrations disturbances on the MiniSODAR?s performance. Measurements on an identical SODAR system onshore are carried out to compare the disturbances of offshore and onshore external conditions.

The effect of background noise on SODAR operation has clearly been established in literature. Therefore, measurements have been performed only to establish the absolute sound pressure levels. This is done at the Measuring Platform Noordwijk (MPN) located in the North Sea, nine kilometres out of the coast at Noordwijk, The Netherlands, and at two locations onshore. At the MPN-platform, the SODAR has been moved from the middle deck to the upper deck to diminish the influence of the diesel generator needed for the electric powering of the island. Although the absolute sound pressure level became higher at the new location, this level became lower at the most important frequencies inside the SODAR, due to the use of absorbing foam. With regards to the sound pressure level the move improved the situation. The sound pressure levels measured offshore were 6 to 15 dB higher than for the two locations measured onshore. Therefore, under offshore conditions a negative effect of the background noise on the SODAR measurements is expected.

The vibrations in the metal structure of the offshore island are expected to have an influence on the SODAR performance. The vibration measurements showed that the effects are negligible with regards to the normal SODAR measurement uncertainties.

A recommendation is to limit negative effects of background noise offshore by performing noise measurements in advance and by choosing a position for the SODAR equipment based on these measurements. It is recommended to select the best position on an offshore island using instruments and not just by listening.

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