The global expansion in offshore renewable energy, primarily through offshore wind, is associated with the proliferation of subsea power cables (SPCs) throughout marine and coastal benthic environments. The transmission of electrical power through these SPCs will introduce electromagnetic fields (EMFs) into the seabed and the adjacent water column, which raises questions regarding the potential impact on benthic fauna, particularly during critical developmental early-life stages for which research considering the effects of both the electric and magnetic components of SPC EMFs is lacking. We conducted an experiment on three benthic egg-laying species, – the elasmobranch Scyliorhinus canicula, the cephalopod Loligo vulgaris, and the cephalopod Sepia officinalis – found in areas under consideration for the routing of SPCs. We exposed the embryos to realistic EMF levels (magnetic field 4–6 μT) recreated in the laboratory using an AC power cable set-up that simulated the EMF conditions, and examined the morphological, physiological, and behavioural responses. Our findings indicate subtle responses to EMF exposure in S. canicula and L. vulgaris with faster growth rates and morphometric differences, but no responses in S. officinalis. Our results highlight the value of a multiple end point approach to determine the potential influence of chronic exposure to EMFs on embryogenesis in benthic fauna and provide a baseline for future studies to build upon. Although our study cannot extrapolate the consequences of individual-level effects to population-level impacts, it does underscore the necessity of realistic and longer-term studies to assess the potential consequences of EMFs to marine fauna.

Open data are scarce in underwater robotics, making it more difficult for researchers to develop new methods that address real-world problems. In this work, we present the experimental design, execution, and curation of three datasets that represent different conditions in a realistic underwater dynamic proximity operation. The raw datasets gathered during the deployments are post-processed to improve consistency. We detail and use a joint batch optimization technique that uses a probabilistic approach to iteratively search for the set of optimal agent trajectories that are in best agreement with the relative measurements provided by a USBL positioning system and optical pose measurements from a fiducial light array. Error analysis of the relative measurements with respect to the baseline and optimized trajectories validate our results, effectively providing ground-truth trajectories of the agents. The resulting datasets, together with their documentation, are publicly available at github.com/aldoteran/asko_2024_datasets

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.

Due to the challenges regarding the limits of their endurance and autonomous capabilities, underwater docking for autonomous underwater vehicles (AUVs) has become a topic of interest for many academic and commercial applications. Herein, we take on the problem of relative navigation for the generalized version of the docking operation, which we address as proximity operations. Proximity operations typically involve only two actors, a chaser and a target. We leverage the similarities to proximity operations (prox-ops) from spacecraft robotic missions to frame the diverse docking scenarios with a set of phases the chaser undergoes on the way to its target. We emphasize the versatility on the use of factor graphs as a generalized representation to model the underlying simultaneous trajectory estimation and relative navigation problem that arises with any prox-ops scenario, regardless of the sensor suite or the agents’ dynamic constraints. To emphasize the flexibility of factor graphs as the modeling foundation for arbitrary underwater prox-ops, we compile a list of state-of-the-art research in the field and represent the different scenario using the same factor graph representation. We detail the procedure required to model, design, and implement factor graph-based estimators by addressing a long-distance acoustic homing scenario of an AUV to a moving mothership using data sets from simulated and real-world deployments; an analysis of these results is provided to shed light on the flexibility and limitations of the dynamic assumptions of the moving target. A description of our front- and back-end is also presented together with a timing breakdown of all processes to show its potential deployment on a real-time system.

Current autonomous underwater vehicles generally use multibeam sonars and Doppler velocity logs to aid their inertial navigation systems. While effective, these active acoustic systems can reveal the presence of a vehicle, making them unsuitable for covert operations. This report presents the key findings from a research project investigating the feasibility of using a quantum magnetometer array as a substitute or complement to active sonar sensors in autonomous underwater vehicles. Field and sea trials demonstrate that the magnetic field near the Earth’s surface exhibits significant spatial variations, enabling speed estimation and absolute positioning using quantum magnetometer arrays. Theoretical analysis shows that temporal variations in the Earth’s magnetic field, rather than sensor noise, set the fundamental performance limit for estimating vehicle speed using a magnetometer sensor array. However, if a continuous forward communication link with a rate of ∼ 10 bits/s is available, the temporal variation can, to a large extent, be removed by transmission of correction data. Temporal variations also make map-matching-based positioning challenging. But by estimating the magnetic-field gradient using a magnetometer array, temporal variations can be effectively canceled, making gradient-based magnetic-field map-matching a promising approach. Further work is needed to quantify the effects of platform-induced disturbances and map imperfections. 

Autonomous underwater docking is of the utmost importance for expanding the capabilities of Autonomous Underwater Vehicles (AUVs). Due to a historical focus on underwater docking to only static targets, the research gap in underwater docking to dynamically active targets has been left relatively untouched. We address the state estimation problem that arises when trying to rendezvous a chaser AUV with a dynamic target by modeling the scenario as a factor graph optimization-based Simultaneous Localization and Mapping problem. We present a set of boundary factors that aid the inference process by seamlessly transitioning the target’s state between the different observability stages, intrinsic to any dynamic docking scenario. We benchmark the performance of our approach using the Stonefish simulated environment.

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.