Detection and impact assessment of impulsive underwater noise

Detection and impact assessment of impulsive underwater nois

Measurement and modeling of the acoustic field near an underwater vehicle and implications for acoustic source localization

The performance of traditional techniques of passive localization in ocean acoustics such as time-of-arrival (phase differences) and amplitude ratios measured by multiple receivers may be degraded when the receivers are placed on an underwater vehicle due to effects of scattering. However, knowledge of the interference pattern caused by scattering provides a potential enhancement to traditional source localization techniques. Results based on a study using data from a multi-element receiving array mounted on the inner shroud of an autonomous underwater vehicle show that scattering causes the localization ambiguities side lobes to decrease in overall level and to move closer to the true source location, thereby improving localization performance, for signals in the frequency band 2–8 kHz. These measurements are compared with numerical modeling results from a two-dimensional time domain finite difference scheme for scattering from two fluid-loaded cylindrical shells. Measured and numerically modeled results are presented for multiple source aspect angles and frequencies. Matched field processing techniques quantify the source localization capabilities for both measurements and numerical modeling output. © 2007 Acoustical Society of America

Unmanned Aerial Systems (UAS) for marine mammal detection and underwater noise assessment

Conventional underwater based acoustic deployment platforms, such as boats, drifting systems or moored long term acoustic data loggers are often expensive, complex and are usually deployed in dangerous environments. A novel alternative involving the use of a waterproof Unmanned Aerial System (UAS) for the deployment of underwater acoustic sensors is presented. The system has the capability of overcoming the limitations of current deployment methods, while also being able to self-deploy and self-retrieve, and will improve deployment and redeployment times

Use of Unmanned Aerial Vehicles (UAV’s) for underwater noise assessment [Poster]

The underwater and airborne acoustic environment forms a critical part of many marine mammals life cycles. Assessment and development of understanding of these acoustic soundscapes is often vital in understanding many marine life and human operation interactions as well as species to species interactions in the natural acoustic environments. Traditional passive acoustic methodologies used for underwater sound and noise measurements include static hydrophones, autonomous loggers, boat-based deployments, towed arrays, drifter systems etc. Most of these systems however also rely on expensive and sometimes hazardous deployments and retrieval methods. The rapid growth in Unmanned Ariel Vehicles (UAV) technologies in recent years has lead to investigation of these platforms to act as enhanced aerial visual platforms for observing marine mammal behaviour, abundance estimation etc. These systems are however often limited by battery life to relatively short in flight deployments. However these platforms can also offer the opportunity for rapid deployment of smart hydrophone systems over a relatively large spatial areas to include acoustic behaviours and sound scape analysis by flying to a site landing on the water and then deploying underwater sensors. Whilst on the waters surface relative power consumption is significantly lower than in-flight allowing significantly longer deployments. Smart systems will then return to some base point with minimal human interaction. A prototype multi-rotor system has been developed and tested in an open water site, capable of flying to site, landing on the water, deploying a wideband hydrophone for underwater noise assessment and then returning to base. Measurements include underwater noise self-noise analysis in-flight, landing, static and take-off and potential implications to marine wildlife. These developments and trials have demonstrated the overall feasibility of wide-scale rapid hydrophone deployment using UAVs for sound field and marine mammal behaviour analysis

Evaluation of UAVs as an underwater acoustics sensor deployment platform

Marine surveys carried out by Passive Acoustic Monitors conventionally use towed hydrophone arrays, which requires dedicated surface observation boats. This is a costly and slow process, which could be made cheaper and quicker by using Unmanned Aerial Vehicles (UAVs). Presented in this paper are the initial findings from using UAVs to capture underwater acoustic signals from an acoustic test tank

Unmanned aerial system for use in environmental monitoring of water body wave motion

This paper details the research conducted on an open source flight controller for the use of monitoring surface and wave motion of water bodies. Testing was preformed on an industrial FANUC robotic arm, where a Pixhawk 2 was tested using pre-preprogrammed circles of varying sizes to mimic the amplitude of sinusoidal waveforms. Results show good to excellent comparability between the circle radii programmed, and the calculated displacement from the Pixhawk's reported acceleration. This was achieved through the use of Fourier Transforms, filtering and integration of the acceleration logged by the Pixhawk during tests. Such a system is envisaged to be used in the reduction of flow noise a hydrophone experiences from surface deployments, where real time monitoring of the surface would raise and lower a deployed hydrophone in the water column to reduce or eliminate flow noise. Further to this, this system could be used for an early warning tsunami detection system, which could compliment systems already deployed, as well as being a cost effective solution for areas where no systems are currently in place

Designing practical on-site calibration protocols for acoustic systems: key elements and pitfalls

Although acoustic systems are increasingly being used for environmental and noise surveys of marine energy devices, there are currently no standard protocols for the on-site full bandwidth calibration of these systems. Reports often include little or no information on the methods of calibration used before, during or after surveys. Without proper calibration, the sound levels may be far from accurate, leading to skewed reporting and inaccurate conclusions. Hydrophone calibrations from internationally recognised standardisation centres, such as NPL, allow providers to reference their systems to international standards. Marine renewable energy devices, however, are often deployed in remote areas and it is not always practical or cost-effective to send every acoustic system to be independently tested before every deployment. On-site referencing of multiple units to a single standardised system can help improve calibration traceability. Although this may at first appear relatively simple, the production of an accurate, full-spectrum calibration, particularly in real-world test sites, is surprisingly difficult

Acoustic assessment of SIMRAD EK60 high frequency echo sounder signals (120 & 200 kHz) in the context of marine mammal monitoring

The use of active high frequency echo sounders for commercial activities and marine research has been increasing in recent years. Compared to other anthropogenic noise sources, high frequency echo sounders have received little attention in terms of their potential impacts on marine life. However, while these devices typically operate at centre frequencies outside the hearing range of most marine species, recent work has demonstrated that they may produce unintended energy at lower frequencies. These lower frequencies may extend into the audible range for several species of marine mammals and have the potential to affect their behaviour (Deng et al. 2014). Given the theoretical detectability of these lower frequencies by marine mammals, both signal types have the potential to elicit behavioural responses towards them. This should be considered in environmental impact assessments of activities using these devices and when planning marine mammal monitoring studies alongside ecosystem studies using active acoustic sonar systems

Autonomous recording system for simultaneous long-term ambient noise and marine mammal monitoring

There has be significant growth in recent year in the requirement for high quality long-term underwater acoustic data acquisition. One of the primary drivers has been the assessment of long-term trends in noise in our oceans and potential impacts from anthropogenic noise on marine wildlife. These recorders usually fulfill a number of key roles in this sector. These include providing acoustic data on long-term trends in ambient or background noise, data on trends in system or device noise of interest and data on vocalizing marine species and potential associated behaviors. Many marine sectors now routinely use these data types to assess any impact from their operations and commonly they form part of ocean operators consenting processes. However no single technology is widely available to perform all of these functions efficiently within a single deployment package

Preliminary investigations into the response of O+ twaite shad (alosa fallax) to ultrasound and its potential as an entrainment deterrent

Water is abstracted from riverine, estuarine and marine environments to supply potable water, power stations, hydroelectric facilities and industry. Such abstractions inevitably carry with them the risk of fish entrainment, defined as „the drawing in of fish of any life stage at a water intake‟ (Turnpenny & O‟Keeffe, 2005). It is possible, however, that entrainment losses can be reduced to an acceptable level with the use of appropriate fish screening technologies. Fish protection solutions for water intakes are manifold and include: alterations to intake design; management of the abstraction regime; modification of existing screens to make them “fish friendly”; provision of fish return systems; and the installation of physical screens or behavioural deterrents to prevent or minimise entrainment. There are however a range of site specific constraints which influence the suitability of each solution