No / The Shetland Islands are well known for their archaeology, with many features from later prehistory surviving to an exceptional degree, with brochs being an excellent example. Less is known of submerged prehistoric sites, though the offshore profile of the islands means that ancient occupation of the current submerged zone was likely, and also that the sites are likely preserved. One such archaeological site, previously identified, occurs near Semblister. The site has been known locally, and is recorded as a broch in the local Historic Environment Records, however, its dimensions and location do not strongly suggest that it is a broch. Combining satellite imagery – the site is in relatively shallow water and visible – with targeted side-scan sonar survey and data processing, will aid the development of a process approach to the re-classification / confirmation of historically recorded sites, and archaeological prospection in the shallow water zone. / University of Bradford

ITC/USA 2006 Conference Proceedings / The Forty-Second Annual International Telemetering Conference and Technical Exhibition / October 23-26, 2006 / Town and Country Resort & Convention Center, San Diego, California / This paper describes the design and successful development of an acoustic modem for potential use in underwater ecological sensor networks. The presentation includes theoretical study, design and development of both software and hardware, laboratory experiments, full-scale field tests, and the documentation and analysis of field-test results.

Anthropogenic noise in the sea is now classed as a pollutant alongside chemical pollution and marine litter in accordance with the Marine Strategy Framework Directive. Noise from shipping is a major contributor to the ambient noise levels in the ocean, particularly at low (<300Hz) frequencies. The properties of sound propagation in shallow waters are highly influenced by the marine physical environment. Ocean modelling plays an important role in underwater noise studies since it can provide high resolution water column parameters over large geographic areas. This study investigates the noise patterns and their temporal variations in the Celtic Sea by using a coupled ocean model (POLCOMS) and an acoustic model (HARCAM). A method to predict noise exposure experienced by marine animals is then developed, following an application for diving seals. The ocean model is applied in the Celtic Sea to provide high-resolution 3D hourly temperature and salinity fields for the acoustic model. The model is validated against in-situ and satellite observations, giving high skills to simulate the water column structures. Sensitivity studies of modelled results to different atmospheric forcing are carried out in order to improve the accuracy of the model. The results show that the modelled sea surface temperature, stratification and water column structures are highly sensitive to the choice of surface forcing, especially in the summer time. The increase in resolution of surface forcing does not necessarily lead to more accurate results. The tidally frontal position is, however, insensitive to the forcing. The variability of noise propagation is studied using the coupled model, demonstrating high dependence on oceanographic conditions, geographic location of sound source and its depth. In summer, when the source of sound is on the inshore side of the bottom front, the sound energy is mostly concentrated in the near-bottom layer. In winter, the sound from the same source is distributed more evenly in the vertical. When the source is on the seaward side of the front, the sound level from a shallow source is nearly uniform in the vertical and the transmission loss is significantly greater (~16dB at 40km distance) in summer than in winter. In contrast, sound energy from a deep source is trapped in the bottom cold water, leading to a much lower transmission loss (~20dB) in summer than in winter. Note that ~10dB fluctuation of sound energy is found during the deterioration of the thermocline in late autumn. Shallow sources (e.g. ships) are sensitive to the surface heat flux as it changes significantly the vertical temperature gradient, while tides play an important role in determining the TL variability of deeper sources (e.g. pile driving) since they cause adjustments of positions of subsurface fronts. The seasonal noise patterns radiated by a large cargo ship are modelled by relating the AIS ship track data and the coupled model, showing a clear influence of the seasonal thermocline and associated bottom fronts on shipping noise distribution. The noise propagates much further (tens of kilometres) in winter than in summer. The predicted shipping noise exposure perceived by grey seals shows strong step changes in the sound level during their descent/ascent through the water column. Since grey seals tend to be benthic foragers, a hypothesis that the step change in sound exposure may have negative impacts on their foraging behaviour is proposed for biological specialists.

ITC/USA 2005 Conference Proceedings / The Forty-First Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2005 / Riviera Hotel & Convention Center, Las Vegas, Nevada / Underwater acoustic (UWA) telemetry requires wideband waveforms for anti-multipath which are simultaneously easy to equalize and demodulate. The Walsh/m-sequence waveforms proposed here are robust to multipath and with appropriate time-guard bands do not require equalization. For example, in the UCSB prototype acoustic modem, a data rate of 133 bps is achieved using 8-ary Walsh signaling with an 11.2 msec. symbol duration. Demodulation is performed using noncoherent detection, and hence accurate phase tracking, which is difficult to achieve in the UWA channel, is not required. However, telemetry from unmanned underwater vehicles (UUVs) is more problematic due to large Doppler shifts resulting from platform motion. A new receiver algorithm based on Matching Pursuits is proposed which combines channel and Doppler shift estimation. Symbol-error rate (SER) simulation results are presented for the UWA modem under realistic Doppler/multipath conditions.

Underwater sound from anthropogenic sources such as seismic surveys, marine renewable device installations and naval exercises has the potential to disturb and cause injury to a variety of marine species. There is particular concern for the potential effects upon marine mammals, which utilise sound to communicate, hunt and navigate. Observed effects include behavioural changes and reduced sighting rates, with unknown consequences for individuals or populations over time. Potential effects on marine mammals include sound induced damage to auditory systems, altered diving behaviour potentially resulting in decompression sickness, stranding and death. The aim of the thesis was to develop a framework of best practice measures relating to mitigating the potential effects of underwater sound on marine mammals during offshore exploration and development operations. In order to mitigate the potential effects of underwater sound, regulatory guidelines have been developed and implemented around the world, principally for seismic surveys. These guidelines limit the activation of seismic sources when in proximity to marine species, and involve the use of specially trained personnel on survey vessels known as Marine Mammal Observers (MMOs). A critical review of the guidelines identified variation in the level of precaution applied to measures, such as the distance at which species can be sighted before reducing sound output from the operation. MMOs collect sighting information for all encounters with marine species, resulting in large volumes of data detailing species occurrence and behaviour. A sample dataset was found to be subject to variation in quality due to the different academic backgrounds and training levels of personnel. The data highlighted significant differences in relation to sighting distance while the sound source is active or inactive, though lacked detail with regard to behaviours, likely due to the lack of ethological expertise among the observers. A questionnaire was conducted to determine any differences of opinion regarding current mitigation practice and the underlying issue between stakeholder groups. There was no difference of opinion between stakeholders regarding the importance of underwater sound compared to other environmental issues facing marine species such as fisheries by-catch and overfishing. Areas of consensus were evident, with most stakeholders finding current mitigation practice to be only ‘somewhat’ effective, and that sightings data collected by MMOs should be better utilised, with it being more useful for adding to our knowledge of marine mammal distributions than for determining the effects from operations. A framework for enhancing the collection, use and dissemination of MMO data is described with recommendations for the development of a Global Positioning System (GPS) enabled smartphone/ tablet based field data collection system, linked to an internet based geographical information system to enhance species distribution analysis. By coupling this with a simplified mitigation methodology, the outcome would enhance the risk management of operations in relation to where species are known to occur, with mitigation aimed at reducing exposure at critical times or in critical habitats. Simplifying mitigation and enhancing data collection and use will benefit stakeholders in managing essential operations responsibly.

A considerable corpus of information regarding the formation of terrestrial archaeological deposits exists which is not matched by studies of deposit formation in coastal waters. Similarly, there is a disjunction between strident calls for minimal disturbance investigation, with conservation in situ, and knowledge of how this might actually be achieved in the marine environment. The manner in which the investigation of deposit formation can complement the study of in situ conservation is considered An approach is proposed which combines selected elements of Schiffer's Transformation Theory with a method of studying changes to deposits outlined by Wildesen. It is suggested that, although sufficient regularities can be detected in the influence of formation processes to allow their influence to be recognised and inference refined accordingly, there are case specific limitations on the extent to which the precise influence of each process can be described and evaluated. A case study is presented which investigates casual depredation as a formation process. Commercial fishing activity and marine burrowing activity are the subject of detailed consideration. New insights into these processes result from this study and specific recommendations concerning in situ conservation of deposits subject to their influence are made. The need to consider fishing practice as well as the mechanical properties of fishing gear in the study of deposit formation and protection is emphasised. The excavation of a 16th century wreck in Studland Bay, Dorset, is used to demonstrate the pervasive influence of burrowing activity and the problems associated with mitigation of this process. Recommendations are made regarding future study of formation processes and the development of policy related to the management of the submerged archaeological resource.

Acoustical interactions with ocean sediments effect a wide range of sonar applications in littoral environments. An important factor in understanding the acoustical behavior of the ocean bottom is how the sediment density changes with depth. Although there are existing techniques for obtaining information about sediment gradients, these methods are unable to provide direct measurements of the sediment density gradient without significantly disrupting the test site and requiring significant diver support for installation and implementation. The proposed X-Ray Attenuation Measurement (XRAM) device aims to improve upon these existing techniques with the goal of being a portable diver operated device that can perform direct in situ measurements of sediment density gradients without significant disruption of the ocean bottom. To accomplish this, the XRAM utilizes the attenuation of x-rays passing through the sediment to measure the density as a function of depth, and is arranged in a compact, portable design that can be deployed and operated by a single diver. The layout and basic design of the XRAM device is discussed, and a physical model of its operation is developed. Results of experimental testing on homogeneous liquid samples and liquid/solid mixtures to evaluate the effectiveness of the XRAM device in measuring density gradients are presented. Based on the analysis of these results, recommendations of improved performance for future development are given. / text

Three-dimensional acoustic propagation in shallow water waveguides is studied using the longitudinally invariant finite element method. This technique is appropriate for environments with lateral variations that occur in only one dimension. In this method, a transform is applied to the three-dimensional Helmholtz equation to remove the range-independent dimension. The finite element method is employed to solve the transformed Helmholtz equation for each out-of-plane wavenumber. Finally, the inverse transform is used to transform the pressure field back to three-dimensional spatial coordinates. Due to the oscillatory nature of the inverse transform, two integration techniques are developed. The first is a Riemann sum combined with a wavenumber sampling method that efficiently captures the essential components of the integrand. The other is a modified adaptive Clenshaw-Curtis quadrature. Three-dimensional transmission loss is computed for a Pekeris waveguide, underwater wedge, and Gaussian canyon. For each waveguide, the two integration schemes are compared in terms of accuracy and efficiency. / text

300 million pictures are uploaded everyday on Facebook alone. We live in a society where photography, filming and self-documentation are a natural part of our lives. But how does it inflict on our experiences when we always are considering camera angles, filters and compositions? We might very well ruin the experiences we so badly want to save. Scuba diving is a special experience. We enter a world with another space of movement, surroundings and animal life. An experience that can only be experienced for a limited time. An adventure one want to remember, save and share. But what implications does it have on ones experience if one also have to focus on documenting it? JACQUES is a product that enables the diver´s to document their dive as a memory to re-experience later and share with others while still leaving them fully immersed in their diving experience. With relatively simple technology such as sonar and video object recognition Jacques can film the diver´s underwater adventure and adept to their behavior without the diver even noticing it. And by being focused on the actual dive one also becomes a better and safer diver.

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