Methodologies for measuring underwater noise output from wave energy converters have
been developed. These acoustic noise measurement methodologies have been proposed
for two general classes of wave energy convertor device that may be present at the EMEC
site: mobile systems and static systems (fixed position but distributed throughout the water
column). Both methodologies employ the use of long term recording systems designed to
assess long term variance in acoustic output due to device operation status, weather, tidal
conditions etc. Multiple recording systems will be deployed at different ranges on single
transects for the device to allow assessment of local propagation loss conditions, and
therefore estimate ‘at source’ absolute levels. In addition, multiple aspect angles of the
systems will be measured simultaneously to assess potential directivities of the source. It is
identified that long term recordings at the complete hearing bandwidth of all potential
receptors (~150 kHz) is often a limited compromise of bandwidth versus record time. It is
anticipated that the majority of signals of interest will be for frequencies below 48 kHz (with
higher frequencies more highly attenuated with range). Several systems exist that can be
used to make continuous recordings at these lower bandwidths for periods of days to allow
assessment of long term operational and environmental noise variation. However it is also
felt important to sample higher bandwidth (up to 150 kHz) at regular intervals. In this case
two technical solutions are proposed these include bottom mounted high-bandwidth
recorders with a suitable duty cycle and/or the use of wide bandwidth ‘drifting systems’.
Either solution can be used simultaneously with a longer term recording system to augment
long term data sets with sampled wideband data.