A note on ADCP-based indirect observations of turbulence

A 70-day data set from bottom-mounted ADCPs on the two sides of the Faroe-Bank Channel was analysed using the recorded flow variance and echo intensity in the deeper reaches of the passage as proxies for turbulence. A consistent picture emerged, not least since the data losses (which were ascribed to turbulence-induced activation of the fish-elimination option in the ADCP software) could be shown to co-vary with the internal M-2 tide affecting the vertical shear, which in turn proved to be correlated with the flow variance

Simulations to benchmark time-varying connectivity methods for fMRI

Published: May 29, 2018There is a current interest in quantifying time-varying connectivity (TVC) based on neuroimaging data such as fMRI. Many methods have been proposed, and are being applied, revealing new insight into the brain’s dynamics. However, given that the ground truth for TVC in the brain is unknown, many concerns remain regarding the accuracy of proposed estimates. Since there exist many TVC methods it is difficult to assess differences in time-varying connectivity between studies. In this paper, we present tvc_benchmarker, which is a Python package containing four simulations to test TVC methods. Here, we evaluate five different methods that together represent a wide spectrum of current approaches to estimating TVC (sliding window, tapered sliding window, multiplication of temporal derivatives, spatial distance and jackknife correlation). These simulations were designed to test each method’s ability to track changes in covariance over time, which is a key property in TVC analysis. We found that all tested methods correlated positively with each other, but there were large differences in the strength of the correlations between methods. To facilitate comparisons with future TVC methods, we propose that the described simulations can act as benchmark tests for evaluation of methods. Using tvc_benchmarker researchers can easily add, compare and submit their own TVC methods to evaluate its performance.WHT acknowledges support from the Knut och Alice Wallenbergs Stiftelse (SE) (grant no. 2016.0473, http://kaw.wallenberg.org). PR acknowledges support from the Swedish Research Council (Vetenskapsrådet) (grants no. 2016-03352 and 773 013-61X-08276-26-4) (http://vr.se) and the Swedish e-Science Research Center (http://e- science.se/). CGR acknowledges financial support from the Spanish Ministry of Economy and Competitiveness, through the ªSevero Ochoaº Programme for Centres/Units of Excellence in R&Dº (SEV-2015-490, http://csic.es/)

Simultaneous Trajectory Estimation and Mapping for Autonomous Underwater Proximity Operations

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 state estimation during an autonomous underwater docking mission. Docking 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 use factor graphs to generalize the underlying estimation problem for arbitrary underwater prox-ops. To showcase our framework, we use this factor graph approach to model an underwater homing scenario with an active target as a Simultaneous Localization and Mapping problem. Using basic AUV navigation sensors, relative Ultra-short Baseline measurements, and the assumption of constant dynamics for the target, we derive factors that constrain the chaser's state and the position and trajectory of the target. We detail our front- and back-end software implementation using open-source software and libraries, and verify its performance with both simulated and field experiments. Obtained results show an overall increase in performance against the unprocessed measurements, regardless of the presence of an adversarial target whose dynamics void the modeled assumptions. However, challenges with unmodeled noise parameters and stringent target motion assumptions shed light on limitations that must be addressed to enhance the accuracy and consistency of the proposed approach.Comment: 19 pages, 14 figures, submitted to the IEEE Journal of Oceanic Engineerin

A modelling evaluation of electromagnetic fields emitted by buried subsea power cables and encountered by marine animals : considerations for marine renewable energy development

Part of this work was supported by the Bureau of Ocean Energy Management (contract number M14PC00009).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.PostprintPeer reviewe

Offshore exposure experiments on cuttlefish indicate received sound pressure and particle motion levels associated with acoustic trauma

Recent findings on cephalopods in laboratory conditions showed that exposure to artificial noise had a direct consequence on the statocyst, sensory organs, which are responsible for their equilibrium and movements in the water column. The question remained about the contribution of the consequent near-field particle motion influence from the tank walls, to the triggering of the trauma. Offshore noise controlled exposure experiments (CEE) on common cuttlefish (Sepia officinalis), were conducted at three different depths and distances from the source and particle motion and sound pressure measurements were performed at each location. Scanning electron microscopy (SEM) revealed injuries in statocysts, which severity was quantified and found to be proportional to the distance to the transducer. These findings are the first evidence of cephalopods sensitivity to anthropogenic noise sources in their natural habitat. From the measured received power spectrum of the sweep, it was possible to determine that the animals were exposed at levels ranging from 139 to 142¿dB re 1¿µPa2 and from 139 to 141 dB re 1¿µPa2, at 1/3 octave bands centred at 315¿Hz and 400¿Hz, respectively. These results could therefore be considered a coherent threshold estimation of noise levels that can trigger acoustic trauma in cephalopods.Postprint (published version

Spatial and temporal variability of ambient underwater sound in the Baltic Sea

During last decades, anthropogenic underwater sound and its chronic impact on marine species have been recognised as an environmental protection challenge. At the same time, studies on the spatial and temporal variability of ambient sound, and how it is affected by biotic, abiotic and anthropogenic factors are lacking. This paper presents analysis of a large-scale and long-term underwater sound monitoring in the Baltic Sea. Throughout the year 2014, sound was monitored in 36 Baltic Sea locations. Selected locations covered different natural conditions and ship traffic intensities. The 63 Hz, 125 Hz and 2 kHz one-third octave band sound pressure levels were calculated and analysed. The levels varied significantly from one monitoring location to another. The annual median sound pressure level of the quietest and the loudest location differed almost 50 dB in the 63 Hz one-third octave band. Largest difference in the monthly medians was 15 dB in 63 Hz one-third octave band. The same monitoring locations annual estimated probability density functions for two yearly periods show strong similarity. The data variability grows as the averaging time period is reduced. Maritime traffic elevates the ambient sound levels in many areas of the Baltic Sea during extensive time periods

Monitoring Guidance for Underwater Noise in European Seas- Part II: Monitoring Guidance Specifications

This document has been prepared by the Technical Subgroup on Underwater Noise and other forms of Energy (TSG Noise), established in 2010 by the Marine Directors, i.e. the representatives of directorates or units in European Union Member States, Acceding Countries, Candidate Countries and EFTA Member States dealing with or responsible for marine issues. In December 2011, the Marine Directors requested the TSG Noise to provide monitoring guidance that could be used by Member States in establishing monitoring schemes to meet the needs of the Marine Strategy Framework Directive indicators for underwater noise in their marine waters. This document presents the recommendations and information needed to commence the monitoring required for underwater noise.JRC.H.1-Water Resource

Monitoring Guidance for Underwater Noise in European Seas - Part I: Executive Summary

This document has been prepared by the Technical Subgroup on Underwater Noise and other forms of Energy (TSG Noise), established in 2010 by the Marine Directors, i.e. the representatives of directorates or units in European Union Member States, Acceding Countries, Candidate Countries and EFTA Member States dealing with or responsible for marine issues. In December 2011, the Marine Directors requested the TSG Noise to provide monitoring guidance that could be used by Member States in establishing monitoring schemes to meet the needs of the Marine Strategy Framework Directive indicators for underwater noise in their marine waters. This document presents the key conclusions and recommendations that support the implementation of the practical guidance to commence the monitoring required for underwater noise.JRC.H.1-Water Resource

Ljud från pålning av vindkraftfundament : påverkan på fiskbeteende

Studier av effekter av konstruktionsljud från havsbaserade vindkraft på fisk har helt nyligen aktualiserats av forskare, myndigheter och av industrin. När ett fundament pålas ner i botten genererar väldigt höga ljudnivåer som potentiellt kan hindra fisk från att nå lekområden, hitta föda eller partners. Detta kan på lång sikt påverka reproduktion och andra biologiskt viktiga parametrar. Dessutom kan fisk reagera med ett undvikande beteende från viktiga fiskeområden vilket leder till minskad fångst om den akutiska störningen blir för stor. Men hur fisk reagerar på pålningsljud och vid vilka ljudnivåer en beteendereaktion kan uppstå är i stort sätt okänt i dagsläget. Denna studie beskriver ett experiment där inspelat pålningsljud återspelades med hjälp av en stor undervattenshögtalare för torsk (Gadus morhua) och plattfisken sjötunga (Solea solea) hållna i två stora nätburar med en diameter på 40 m. Fiskarnas rörelse registrerades med ett telemetrisystem varefter deras beteendemönster analyserades. Ljudnivåer av både ljudtryck och partikelrörelse mättes under experimentet som utfördes i en bukt i västra Skottland med låg nivå av bakgrundsbrus. Av studiens resultat framgår att båda arterna visade tydliga beteendereaktioner på ljudet, redan vid relativ låga ljudnivåer (sjötunga: 144–156 dB re 1μPa(toppvärde); torsk: 140–161 dB re 1 μPa(toppvärde); partikelrörelse mellan 6,5 10-3 och 8,6 10-4 m/s2 (toppvärde)). Sjötunga reagerade med en signifikant ökad simhastighet under perioden då de utsattes för ljudet jämfört men de tysta perioderna innan och efter ljudexponering. Torsk reagerade på liknade sätt men resultaten var inte signifikanta eftersom reaktionerna varierade stort mellan de olika individerna. Torsk reagerade även med att ”stelna till” (eng. freezing response) när ljudbilden förändrades. Det fanns indikationer på att en del individer av båda arterna simmade bort från högtalaren när ljudet sattes på. Resultaten visar även en viss reduktion i reaktioner efter upprepade exponeringar, dock ej signifikant. Generellt sett varierade beteendereaktionerna på ljuduppspelningarna hos olika individer av samma art. Detta är den första studien som visar en tydlig beteendereaktion hos fisk som utsätts för uppspelning av pålningsljud av hög intensitet. Resultaten visar att beteendereaktioner kan uppstå inom ett intervall av olika nivåer av ljudtryck och partikelrörelser och inte vid ett specifikt tröskelvärde. Detta betyder att dessa reaktioner kan uppstå inom en relativ stor omkrets vid en pålningsaktivitet. Varför fiskar reagerar och vad det har för betydelse på längre sikt måste undersökas ytterligare även om delar av resultaten i denna studie kan påvisa en eventuell tillvänjning till ljuduppspelningarna. Resultaten från denna studie kan användas vid planering av och under byggnationen av havsbaserad vindkraft för att minska miljöpåverkan. Vi föreslår även att våra gränsvärden för beteendereaktioner beaktas i bedömningarna av effekter av havsbaserad vindkraft. Ytterligare förebyggande åtgärder bör diskuteras för att minska utsläpp av akustisk energi i vattenmassan och på så sätt minska påverkan på fisk. I framtiden bör fler studier undersöka hur fisk reagerar på ljud vid kritiska tidpunkter (t.ex. parning och lek) och om effekterna av pålning kan påverka fiskarnas akustiska kommunikation. Man bör även studera om fisk kan vänja sig vid ljud och vad detta har för betydelse på lång sikt för att kunna förutse och minska eventuella skadliga effekterna av pålningsljud på fisk