At comparable sound levels, impulsive noise is generally more hazardous than non-impulsive noise for marine mammals’ hearing.  However, this study showed a decrease in impulsive characteristics as sounds travel further away from the source.

After an extensive literature review, assessment of field data, and the development of a framework (software tool) estimating hearing damage impact ranges from impact pile driving from offshore wind on marine mammals, the RaDIN project concluded that:

• The assumptions used in noise impact assessments may result in an overestimation of the auditory injury impact ranges, as data from 44 real world hammer logs indicated a 57% median reduction in permanent hearing threshold shift (PTS) impact area, when compared to a standardised baseline (that mirrors current EIA applications for wind farms to be constructed in coming years).
• Increasing time between subsequent pile strikes in the first 45 minutes of piling has the largest potential to significantly reduce the estimates of hearing damage onset ranges, compared to characteristics such as the total duration of piling.
• The viability of such approaches could be determined via discussions among engineers, developers, decision makers and supported by scientists.
• Finally, the transition from impulsive to non-impulsive noise must occur within 5 km from the source to have a meaningful effect on the permanent hearing damage impact ranges, when factors such as animal fleeing speed, transmission loss, and source level are standardised.

The framework developed by RaDIN – which allows flexibility for the user to input soundscape modelling, animal reactions, and distance thresholds – could be used to help design installation blow temporal patterns to help minimise impacts at the design or pre-consent stage of an offshore wind farm.