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.