TNO: Measuring and modelling particle motion

by Christ de Jong, TNO

This news article is part of Issue 2 of our annual newsletter, which chronicles our research in 2022. To view more articles describing our research progress from our second year, read the newsletter in full here.

The Netherlands organisation for applied scientific research, TNO, is involved in a variety of tasks in the SATURN project, including the provisionof acoustic support to biologists and maritime researchers.

Deployment of the sound particle motion measurement rig from the RHIB.

Mapping and Measuring Particle Motion

In SATURN Task 2.3, TNO and JASCO are jointly developing the capability to create maps that represent the particle motion component of underwater sound from ships. This is relevant for evaluating the impact of shipping sound on fish and invertebrate species, that are sensitive to particle motion. Different models for sound particle motion havebeen applied and verified through a process of benchmarking. The results were presented by Victor Oppeneer (TNO) at the International Conference on Underwater Acoustics (ICUA 2022) in Southampton.

To be able to validate these models against field data, for a realistic offshore location in shallow water, TNO deployed its particle motion measurement rig at a location in the North Sea, in the The Hague offshore test area. The rig was deployed from a rigid-hull inflatable boat (RHIB), on the seabed at about 15 depth. It collected data from the sound produced by a small controlled airgun source during various runs with the RHIB at different distances from the rig. In addition to these measurements for model validation, the rig continuously recorded sound pressure and sound particle acceleration over the three deployment days. These data will provide typical signals from passing ships that can be compared with models, as well as provide insight on background noise levels, including flow-noise and noise from surface wave breaking and rain.

Harmonised Test Signals

A key highlight of our activities in 2022 was the completion of the development of a suite of artificially synthesized ship sound signals for use in future laboratory studies. These signals are considered suitable for the assessment of harmful underwater noise characteristics in the sense that they are relevant for the impact on marine life as well as subject to technically achievable mitigation measures. Using harmonized test signals for the different bioacoustics playback studies facilitates the comparability of results. These signals are offered as a standard reference for external stakeholders and future projects. They were presented at the Aquatic Noise 2022 conference in Berlin and are available from https://www.saturnh2020.eu/resources-1/ harmonised-test-signals.

ISO Standard Development

Another highlight was the completion of the Committee Draft (CD) for a new ISO standard procedure for measurements of ships in shallow water (ISO 17208-3). This was developed by an international group of experts, led by Christ de Jong (TNO) with support from SATURN. The CD passed the ISO balloting process, and the working group is now working on the comments towards the next stage, aiming at submission of a Draft International Standard for ballot in 2023. The proposed measurement procedure was tested by TSI in the November 2022 sea trials carried out by TSI (SATURN Task 2.2).

Developing DEPONS

Together with SATURN partner Aarhus University, TNO supported the development of a proper and efficient implementation of ship acoustic modelling in the DEPONS model for assessing population effects of disturbances on marine populations. Various discussions were held concerning the analysis of D-tag and satellite tag data and acoustic modelling of ship sound emission and propagation for the scenarios studied to derive dose-response relationships for relevant vessel noise metrics.