A guidance on measurement and evaluation methods for underwater sounds focusing on offshore windfarms

Abstract

Carbon neutral is the global agenda in these years. Offshore windfarm is expected to be the major renewable energy sources. During construction and operation, intensive pulse noise and long-term continuous noise are radiated due to pile driving and windmill rotation. In 2021, we proposed a guidance on measurement and evaluation methods for underwater sounds based on discussion among a study group organized by Marine Acoustics Society of Japan. The guidance focuses on the method of underwater noise measurement and assessment of the effect of noise on aquatic animals. Long-term recording using a fixed recorder is recommended to identify the background noise level and its seasonal changes in the potential construction site. Measurement of received sound levels to three directions from the pile up to 6 km is recommended to know the asymmetric noise field due to complicated shallow water propagation. The distance at the background noise level masks radiated sound is defined as "safe distance". Noise impact assessment should be conducted in the area within this distance. This guidance is not completed yet. It should be revised according to the field tests. In addition, noise exposure criteria for each species in the ocean is required.