Center for Marine Acoustics Accomplishments

Characterizing Sound Sources

The CMA and its partners are developing a strong scientific rationale as the foundation for a new regulatory framework for High Resolution Geophysical Sound Sources


High-resolution geophysical (HRG) sound sources are used in activities concerning all BOEM program areas and they require consistent, well-grounded regulation. BOEM and the National Marine Fisheries Service (NMFS) both regulate these activities, and there is room for improving regulatory regimes. For example, NMFS has required MMPA authorization for some sound source types but not others. Additional research and analyses are warranted to determine whether authorizations should be required and whether mitigation measures are appropriate, considering the risk that surveys may pose to marine life. Improved clarity on such authorizations and mitigations and a more transparent and firmer basis in science and law will be a boon to many stakeholders whose programs and interests concern the affected activities. The federal agencies involved in ocean resource mapping and use have a particular stake and include (in addition to BOEM) the U.S. Geological Survey (USGS), the National Science Foundation (NSF), the U.S. Navy and the National Oceanic and Atmospheric Administration (NOAA).

The CMA has taken the lead to tackle this problem, developing the necessary technical information and facilitating discussions across agencies through a three-pronged approach:

  • SOLUTION: Measuring commonly used HRG sound sources. Historically, HRG sound sources have not been well-calibrated, making it difficult to assess and compare their potential impact on marine species. The CMA, together with the USGS, has addressed this shortfall with a study measuring HRG sources in both the lab and the field and comparing sound propagation with model predictions.
  • SOLUTION: Developing a baseline sound source list. The CMA is developing and refining a guide for federal agencies to classify and understand the physical qualities of anthropogenic sound sources. This includes sources that produce sound on command (e.g., airguns, side-scan sonars, sub-bottom profilers) as well as sources that produce sounds incidentally (e.g., dredges, drilling platforms, vessels). This guide provides federal agencies with a common classification and description for these sources.
  • SOLUTION: Advancing scientific rationale for sound source classification. BOEM scientists contributed to technical analyses providing the scientific rationale for classification of particular sound sources. The paper delineates three categories of sources: (1) those that may be considered de minimis (“unlikely to result in take”) under the MMPA; (2) those which may be considered “unlikely to result in take when certain mitigations are applied”; and (3) those which are “likely to result in take.” This delineation will guide BOEM and NMFS staff in determining which sound sources will require an Incidental Harassment Authorization (IHA) and which will not.

Although the final products are under development, tentative agreements reflect substantial advancement in how these sources will be managed in the future. For example, many sound sources that were considered impactful will now be considered de minimis.


The CMA’s efforts will provide much-needed clarity on HRG sound source regulation and help ensure that any regulation is commensurate with actual risk. These efforts should lead to better regulatory certainty and more reasonable mitigation measures for commonly used sources.

Innovative Risk Assessment Frameworks

Before BOEM authorizes offshore activities, the bureau and industry applicants must assess the potential risk of acoustic impacts to marine species. Typically, complex acoustic propagation models and animal movement models are combined to generate a predicted number of “takes” under the ESA, MMPA or both. These estimates tend to produce very high take numbers because the assumption for calculations is highly conservative by design, and they do not incorporate other relevant information (e.g., life history, species status, and behavioral context), which is essential for realistically assessing actual impacts on population sustainability.

SOLUTION: Develop a customized, quantifiable risk assessment framework for noise-producing activities addressing biologically significant factors and cumulative effects of multiple overlapping activities and other stressors. The CMA supported the development of a customized, quantifiable risk assessment framework for reviewing the noise-producing activities (e.g., seismic surveys and pile driving) that BOEM authorizes and providing risk assessments for species and populations. This new framework integrates relevant information about species vulnerability (e.g., population size, habitat use) and other stressors (e.g., chronic noise, other environmental conditions) to provide an overall assessment of risk when a species is exposed to particular sound sources. The framework also considers the aggregate impacts of multiple overlapping activities, such as the concurrent construction of multiple offshore wind farm facilities. The result is clearer identification of higher risk areas where regulatory attention should be focused. It is a holistic assessment of risk that is not based on simple take numbers and is much more informative to decision-making.


Working with world-renowned experts, BOEM has developed a quantitative risk assessment framework that incorporates acoustic modeling. This framework more effectively interprets potential risk, highlighting where mitigation and protective measures are most needed, and thus better informs decision-making.

Guidelines for Acoustic Modeling and Sound Field Measurements for Pile-Driving

ACOUSTIC MODELING: All offshore wind Construction and Operation Plans (COPs) must include a section on acoustic modeling designed to predict the number of marine mammal “exposures” that could occur during pile-driving operations. Historically, third-party contractors have supplied most of the COPs’ acoustic modeling. This has led to inconsistent report quality and created confusion for BOEM reviewers.

SOLUTION: Develop standard third-party modeling guidelines. The CMA worked with BOEM’s renewable energy experts to develop modeling guidelines to provide offshore wind operators a list of minimum requirements for the acoustic models that should be included in a COP. Using these guidelines, BOEM will receive acoustic modeling with similar details and organizational structure, which will save time and ensure consistency across projects.


SOUND FIELD MEASUREMENTS: It is also important for operators to measure the radiated sound field during pile-driving, to ensure that the received levels at particular distances match what was modeled. These measurements allow regulators to determine the adequacy of certain mitigation and monitoring procedures.

SOLUTION: Provide a list of minimum requirements for sound field measurements. Together with BOEM’s renewable energy experts, the CMA produced guidance on the type of measurements that shall be conducted during pile-driving. Given the complexity of the marine environment, it is nearly impossible to provide universal direction that would cover every possible scenario; this document provides a list of minimum requirements to begin to fill the need.


BOEM has produced a single document that covers the requirements for acoustic modeling and sound field measurements of pile-driving sounds. As new information becomes available, these guidelines are subject to change. Third-party contractors are encouraged to communicate with NMFS and BOEM to ensure that they are following the latest guidance. Applicants should consult with other Federal and state permitting agencies on any information that may be required in addition to these guidelines.

Quantitative Assessment of Ocean Soundscapes

Soundscapes are a developing issue in marine acoustics but have the potential to significantly affect regulation and management.


Soundscapes are all the sounds - natural and anthropogenic - that exist in an environment, considered as a whole. Scientists know little about the ocean soundscape in some geographic areas; even where studies have been conducted, human contributions to marine soundscapes cover a range of frequencies and geographic scales that make them challenging for scientists to quantify. Soundscapes are still a developing issue in marine acoustics but have the potential to significantly affect regulation and management. Patterns in ocean soundscapes that occur over certain geographic areas or periods of time can be indicative of important biological activities like whale migration or fish spawning and may reveal previously unknown biological patterns. More complete information on ocean soundscapes will help BOEM and others assess the impact of noise from activities they authorize or generate.

SOLUTION: Identify and fund key projects to address soundscape needs. Working with BOEM’s regional and environmental studies experts, the bureau funded two key projects that address ocean soundscape needs.

  • ADEON Project – The Atlantic Deepwater Ecosystem Observatory Network (ADEON) project uses a series of moorings in the Atlantic to measure acoustic, physical and biological conditions to elucidate trends and contributions to Atlantic soundscapes.
  • Gulf of Mexico PAM Project – Similar to the ADEON project, the Passive Acoustic Monitoring (PAM) Program for the Northern Gulf of Mexico is collecting and analyzing data near the Mississippi Canyon to establish a baseline for ambient noise in the Gulf of Mexico against which to judge future noise impacts.


Soundscape research is a developing concept in marine acoustics. BOEM is funding two studies that will help better define how to measure soundscapes, which have the potential to significantly affect regulation and management.