By Christ de Jong and Boudewijn van den Bosch (TNO)
Members of the EU-funded SATURN project at OCEANOISE 2023.
2024 was another busy year for TNO in the SATURN project. The core of our work is in WP2 where TNO and JASCO are jointly developing the capability to create maps that represent the particle motion component of underwater sound from ships, to enable quantifying the potential impact of shipping sound on fish and invertebrate species that are more sensitive to sound particle motion that to sound pressure. This work was presented and discussed at the Oceanoise 2023 conference in Villanova I la Geltrú, Spain.
2022 Particle motion Measurements
The results from the 2022 particle motion measurements in the shallow coastal water outside the port of Scheveningen were analysed. Measurements with a controlled sound source (airgun) were compared against model predictions. Figure 1 below shows an example of modelled propagation loss for sound pressure and sound particle velocity for the airgun measurements. This illustrates that the radial sound particle velocity field is very similar to the sound pressure field. At most locations, not too close to close to the source, the water surface or the seabed, the radial sound particle velocity can be estimated by scaling the sound pressure with a constant factor (the characteristic impedance of sea water). At distance not too close to the source, the vertical sound particle velocity is much smaller (the propagation loss much higher) than the radial sound particle velocity.
Figure 1: Modelled propagation loss for sound pressure (top: PL re 1 m2), and sound particle velocity in radial (middle: PVPLr re 1 (µPa m)²/(µm/s²)²) and vertical (bottom: PVPLz re 1 (µPa m)²/(µm/s²)²) at a frequency of 500 Hz, along a track away from a source at 6 m below the water surface. The seabed along the track is indicated by the green line.
Status of ISO 17208-3
SATURN WP2 also supports the ISO working group that is developing a new standard procedure for measurements of ships in shallow water (ISO 17208-3). The international group of experts, led by Christ de Jong (TNO), produced a Draft International Standard (DIS) that was distributed for ballot by the participating ISO members in October 2023. All members voted in favour of this DIS, so that the group can now start processing the remaining comments towards publication of the standard.
Migradome Tests
We worked on the development of the SATURN terminology standard (in T2.1) and contributed to the analysis of the ship URN measurements in (T2.2). With Pablo Pia (UPC) we worked on a manuscript on the design and testing of the AquaVib (T3.1). And together with Kees te Velde (IBL) we carried out measurements of sound pressure and sound particle motion in the newly built Migradome (T3.2) (see adjacent figure), at the site of the manufacturer. These measurements were made to characterize the acoustic response of the Migradome fish swim tunnel and to design the appropriate setup for future sound playback studies.
Together with Laia Rojano Doñate (Arhus University) and Dominik Nachtsheim (TIHO) we analysed the sound recordings from porpoise and seal tags (T3.3), demonstrating that the single decidecade band sound pressure levels used in the analysis provided a good proxy for the audibility of the sound to the animals.
Publications and Reports
Our TNO partners worked with Caitlin Frankish on the preparation and publication of:
The DEPONS report (T3.5)
Frankish et al., 2023. Ship noise causes tagged harbour porpoises to change direction or dive deeper. Marine Pollution Bulletin, 115755. Read more.