Noise generating activities such as, oil and gas developments, sand and gravel extraction and construction of offshore wind farms are regulated by the Environmental Impact Assessment Directive (85/337/EEC (as amended by 97/11/EC)). This Directive requires Member States to perform an Environmental Impact Assessment (EIA) if projects are likely to have significant effects on the environment. In the cases of the oil and gas industry and offshore wind farms, several guidance documents have been published to assist developers and regulators in the consenting process.

Mitigation measures have been developed and implemented for offshore wind farm construction and the prospecting of hydrocarbons. They include, the avoidance of undertaking work during specific periods, the application of a soft start-procedure (gradually increasing the sound level to provide animals with time to leave the impact area), and the use of observers that scan a safety zone where no marine mammals should be present prior to the commencement of activities.

The most expedient approach to completing noise related EIA work is to compile a noise propagation model, based on measurements, including all acoustic events forming part of the future development and, when possible, identifying noise sources associated to other operating activities and, beyond that, the marine species that are potentially affected by the development proposal.

To assist developers in managing underwater noise throughout the project life cycle of offshore activities, SONSETC is pleased to offer a range of specialist services including:

• Desk-based review of device/environment/marine organism interaction;

• Environmental impact assessment based on latest available knowledge of:

- Background noise levels
- Source levels associated with devices
- Models of sound propagation underwater
- Hearing sensitivity of marine receptors including marine mammals, invertebrates and fishes
- Predictions of impact zones and definition of exclusion zones
- Assessment on mitigation requirements and monitoring conditions

The following two clips show the masking effect on the signal of a dolphin at a frequency of 5 kHz by a merchant vessel. The environment shown here uses a Mediterranean summer deep-water sound speed profile using information from the NOAA World Ocean Database. The dolphin source level was set to 165 dB re 1 uPa @ 1 m. The ship source level and directivity pattern was based on measurements made in the SILENV project. Propagation was performed using the Ocean Acoustic Library; the simulation uses X3D with the H3D API and NumPy for computations. The translucent areas in the clips show the areas where the dolphin whistle may be masked by the background noise and where communication with other dolphins may not be possible. The grid has a 1 km spacing.

 

The last video shows masking of sperm whale clicks (5 kHz component) in the same environment using 186 dB as the source level.

Towed arrays or autonomous recorders produce large amounts of data; these datasets are often time consuming to manually analyse for particular acoustic events. SONSETC can assist in off-line analysis of data with custom software that searches for specific features, substantially reducing the time for post-processing of the data.

SONSETC can advice on noise measurement protocols for areas where noisy activities are planned or for conservation purposes in marine protected areas. When requested, SONSETC can perform noise measurements, either spot measurements or continuous measurements for a period of time.

Additionally, SONSETC can provide source level measurements for ships, platforms, turbines, or similar sources and can create noise maps to assess the acoustic environmental impact of the source at a particular location.

When a customer already has a suitable data acquisition system running, SONSETC can provide custom software for the analysis and on-line representation of the data stream.