The underwater acoustic environment is known for its unpredictability, making it challenging to establish configuration parameters for acoustic modems before network deployment. When the modems are configured for robustness, potential throughput is often sacrificed; meanwhile, opting for high-rate links can result in communication failures in highly dynamic acoustic conditions. Given these challenges, this article presents an adaptation framework for networked underwater acoustic modems. Its primary objective is to let modems adaptively select communication links that balance information rate and reliability. It is assumed that the modems provide a set of preconfigured links with monotonically increasing information rate and decreasing reliability. The framework is developed specifically for flooding-based routing protocols, which efficiently handle sudden changes in network topology. By leveraging existing network traffic and implicit acknowledgments, the framework achieves link adaptation with minimal network overhead, necessitating only the addition of a “previous node” address field in the packet headers. Field experiments were conducted by deploying six acoustic modems in a time-varying acoustic environment. A well-known flooding-based protocol, DFlood, was used for routing in the experiments. The network's throughput with the adaptation framework was compared to that when only robust links were permitted. Results of the framework, using modems configured with four different links, show an increase in the average information per packet by a factor of up to 12, and a reduction in network transmission times of 25%–50%, demonstrating DLink's ability to enhance channel utilization, outperforming configurations that rely solely on robust links.

The Marine Strategy Framework Directive (MSFD) (Directive 2008/56/EC) promotes sustainable use of the seas by requiring member states to achieve and maintain Good Environmental Status (GES), including underwater noise as one of of the eleven specific criteria for evaluating GES. In 2022, the EU established quantitative threshold values for addressing the consequences of impulsive underwater noise input into the marine environment. In this chapter, a data-driven stepwise approach is introduced for the implementation of an MSFD compatible assessment methodology. Corresponding standardized practices are presented. For the data-driven evaluation of regional requirements and of the applicability of harmonized methodologies within EU regions, exemplary regional case studies were performed for the Baltic Sea, North Sea, and Mediterranean Sea. Further, the estimation of effect ranges and corresponding risks of adverse effects is important for an impulsive noise assessment. Regional differences in the marine environment were addressed. Main challenges of impulsive noise propagation modelling were identified based on both numerical and analytical/empirical propagation modelling. Finally, recommendations for the impulsive noise registries are presented.

The knowledge of the noise characteristics stemming from recreational boats is scarce, and the amount of studies is too small to draw any conclusions on impact and recommend any measures. To close this gap, it is necessary to measure the underwater radiated noise (URN) from boats and estimate their source level. This chapter aims to describe the development of a methodology for source-level estimations of recreational boats based on classification society’s guidelines and test it in field trials. Three boats with different engine, propeller, and fuel types, including one electric motor, were used. Parameters such as speed, measurement depth, distance, and propagation loss estimations are varied, aiming to study their effect on the estimated source level. By combining the GPS position of the boats and sound data from a hydrophone system, successful measurements of the boats’ radiated noise were conducted, and their source levels were estimated. The source spectra of all boats showed clear tones, stemming from the rotational frequencies of the engines and propellers. Finally, a measurement guideline was developed for estimation of the source level from recreational boats that can be used for comparison with published scientific studies and environmental impact studies and as input to source models.

The Marine Strategy Framework Directive (MSFD) has been an important driver for progress in monitoring and assessment of impulsive underwater noise in the marine environment of the European Union. An important achievement of the MSFD implementation was the development of regional noise registries, providing the data basis for assessments. Recently, the EU has made tremendous efforts to propose harmonized assessment approaches and first-of-their-kind regional quantitative thresholds for impulsive underwater noise. In light of these newly developed thresholds values, we analyze the suitability of the available data in the noise registries for assessment purposes under the MSFD and review sources of uncertainties regarding quantitative results. We present three regional case studies located in the North Sea, the Baltic Sea and the Mediterranean Sea. For each of these regions, a sound-intensive activity was selected that aligned with a realistic impulsive noise event reported for the region. We made use of available data in the noise registries and applied the EU Guidance recommended for the description of impulsive noise sources, but also used alternative approaches and observations as comparison. The case study analysis includes the evaluation of data availability, data quality and data accuracy in the noise registries, and identifies corresponding consequences of the data for the uncertainty and interpretability of assessment results, especially for the quantitative evaluation of habitat areas impacted by noise. Finally, we make suggestions for the improvement of the data basis in the noise registries and the optimization of the assessment accuracy.

A calibration technique with potential for low frequencies and sizeable systems of underwater transducers is being developed at the Swedish Defence Research Agency. The technique is based on the three-transducer spherical wave reciprocity method for use in an ice-covered lake with a depth of 220 m in the Swedish arctic zone. The calibration is performed at a depth of approximately 100 m with inter-transducer separations of 50 m, 86.6 m, and 100 m, allowing for frequencies down to 59 Hz using time-gated tone burst signals. In this paper, the calibration location, system, and technique are introduced, and the calibration results of an acoustical recorder in the range of 59 Hz-1 kHz are presented. The sensitivity is varying with frequency around -148 dB re 1 V/mu Pa, and the uncertainty budget is discussed.

Measurement of particle motion from an offshore piling event in the North was conducted to determine noise levels. For this purpose, a bespoken sensor was developed that was both autonomous and sensitive up to 2 kHz. The measurement was undertaken both for unmitigated and mitigated piling. Three different types of mitigation techniques were employed. The acceleration zero-to-peak values and the acceleration exposure levels were determined. The results show that inferred mitigation techniques reduce the levels significantly as well as de-creases the power content of higher frequencies. These results suggest that mitigation has an effect and will reduce the effect ranges of impact on marine species.

This paper reports trends in the input of underwater noise source energy emission from global shipping, based on bottom-up modeling of individual ships. In terms of energy, we predict the doubling of global shipping noise emissions every 11.5 years, on average, but there are large regional differences. Shipping noise emissions increase rapidly in Arctic areas and the Norwegian Sea. The largest contributors are the containerships, dry bulk and liquid tanker vessels which emit 75% of the underwater shipping noise source energy. The COVID-19 pandemic changed vessel traffic patterns and our modeling indicates a reduction of -6% in global shipping noise source energy in the 63 Hz 1/3 octave band. This reduction was largest in the Greenland Sea, the Coastal Waters of Southeast Alaska and British Columbia as well as the Gulf of California, temporarily disrupting the increasing pre-pandemic noise emission trend. However, in some sea areas, such as the Indian Ocean, Yellow Sea and Eastern China Sea the emitted noise source energy was only slightly reduced. In global scale, COVID-19 pandemic reduced the underwater shipping noise emissions close to 2017 levels, but it is expected that the increasing trend of underwater noise emissions will continue when the global economy recovers.

The expanding marine renewable energy industry will increase the prevalence of electromagnetic fields (EMFs) from power cables in coastal waters. Assessments of environmental impacts are required within licensing/permitting processes and increased prevalence of cables will increase questions concerning EMF emissions and potential cumulative impacts. It is presumed that protecting a cable by burial, may also mitigate EMF emissions and potential impacts on species. Focussing on a bundled high voltage direct current (HVDC) transmission cable, we use computational and interpretive models to explore the influence of cable properties and burial depth on the DC magnetic field (DC-MF) potentially encountered by receptive species. Greater cable pair separation increased the deviations from the geomagnetic field and while deeper burial reduced the deviations, the DC-MF was present at intensities perceivable by receptive species. An animal moving along a cable route may be exposed to variable EMFs due to varied burial depth and that combined with an animal's position in the water column determines the distance from source and EMF exposure. Modelling contextually realistic scenarios would improve assessments of potential effects. We suggest developers and cable industries make cable properties and energy transmission data available, enabling realistic modelling and environmental assessment supporting future developments.

In this study, we present the first iteration of DPower, an energy conserving method for use in underwater acoustic networks. The method encompasses a straightforward transmission power calibration procedure and adaptive power level selection. The method was evaluated in combination with DFlood, a known and validated constrained flooding protocol developed for underwater applications. Simulations of a network with given prerequisites have shown that, with an acceptable increase in packet loss, the presented method can dramatically reduce the energy consumption and thus improve the life-time of networks. 

This is the midterm report of the project SMaRC (Swedish Maritime Robotics Centre), which is one of four industrial research centres (IRC) funded by the Swedish Foundation for Strategic Research (SSF). SMaRC is a unique collaborative research environment consisting of key industry, academia, and governmental partners in Sweden. The focus of the centre is to enable a transformational/disruptive shift towards the next generation of marine robots.The aim of this report is to describe how SMaRC will provide industrial outcomes that deliver into societal benefit areas, by linking user-defined scenarios with capabilities. This will strengthen the research focus as well as create a transparent mapping from scientific activities to end-user needs. The SMaRC project has now reached its midpoint and is running according to plan. The initial start-up process is now passed and key milestones of the project have been reached and demonstrated at the joint workshop and demonstration periods. SMaRC has already participated in very challenging Antarctic expeditions, developed and tested its own underwater robots, and demonstrated new capabilities for perception, navigation, endurance and autonomy in both simulator environments and in field experiments. For the upcoming second half of the project period, the focus will be on integration and demonstration to move closer to the industrial and end-user needs. The future research plan is connected to six targeted scenarios highlighting key capabilities to reach within the research projects. The demonstration of these scenarios also supports enhanced cooperation with both national and international partners.