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A low-cost [$30 (U.S. dollars)] consumer grade GPS receiver with a sideways-mounted antenna has been applied to measure tidal water levels at a mesotidal coastal site using an interferometric reflectometry approach. The proofof- concept system was installed approximately 16m above mean sea level in close proximity to a conventional bubbler tide gauge that provided validation data. The received signal-to-noise ratios (SNR) for the satellites in view were recorded for several months during two successive years and the observed frequencies of the interferometric oscillations used to calculate the difference in elevation between the receiver and the water surface. Comparisons with concurrent and historic in situ tide gauge data at the site initially helped to identify a calibration issue with the in situ gauge. The GPSbased measurements were shown to be in excellent agreement with the corrected in situ gauge, exhibiting a root-meansquare difference of 5.7 cm over a tidal range exceeding 3m at spring tides and a daily averaged RMS of 1.7 cm. The SNR data from the low-cost GPS receivers are shown to provide significantly higher-quality data for this purpose compared with high-end geodetic grade receivers at similar sites. This low-cost, widely available technology has the potential to be applied globally for monitoring water levels in a wide variety of circumstances and applications that would otherwise be cost or situation prohibitive. It could also be applied as an independent cross check and quality control measure for conventional water-level gauges. [ABSTRACT FROM AUTHOR]

Despite rapid development of marine renewable energy, relatively little is known of the immediate and future impacts on the surrounding ecosystems. Quantifying the behavior and distribution of animals around marine renewable energy devices is crucial for understanding, predicting, and potentially mitigating any threats posed by these installations. The Flow and Benthic Ecology 4D (FLOWBEC) autonomous seabed platform integrated an Imagenex multibeam echosounder and a Simrad EK60 multifrequency echosounder to monitor marine life in a 120 ^\circ sector over ranges up to 50 m, seven to eight times per second. Established target detection algorithms fail within MRE sites, due to high levels of backscatter generated by the turbulent physical dynamics, limiting and biasing analysis to only periods of low current speed. This study presents novel algorithms to extract diving seabirds, fish, and fish schools from the intense backscatter caused by turbulent dynamics in flows of 4 m s$^{{-1}}$. Filtering, detection, and tracking using a modified nearest neighbor algorithm provide robust tracking of animal behavior using the multibeam echosounder. Independent multifrequency target detection is demonstrated using the EK60 with optimally calculated thresholds, scale-sensitive filters, morphological exclusion, and frequency-response characteristics. This provides sensitive and reliable detection throughout the entire water column and at all flow speeds. Dive profiles, depth preferences, predator–prey interactions, and fish schooling behavior can be analyzed, in conjunction with the hydrodynamic impacts of marine renewable energy devices. Coregistration of targets between the acoustic instruments increases the information available, providing quantitative measures including frequency response from the EK60, and target morphology and behavioral interactions from the multibeam echosounder. The analyses draw on deployments at a tidal energy site in Scotland to compare the presence and absence of renewable energy structures across a range of physical and trophic levels over complete spring-neap tidal cycles. These results can be used to inform how animals forage in these sites and whether individuals face collision risks. This quantitative information can de-risk the licensing process and, with a greater mechanistic understanding at demonstration scales, its predictive power could reduce the monitoring required at future arrays. [ABSTRACT FROM AUTHOR]

The Atlantic killer whale ( Orcinus orca) is a top-level marine predator with a global range, being found in all of Earth's oceans. The potential interaction between killer whales and marine renewable energy projects requires surveillance and monitoring efforts that call for new technologies, with marine radar showing promise in the field. Marine radar images recorded at the European Marine Energy Centre ( EMEC) were used to track a pair of male killer whales undertaking Surface Active Behavior ( SAB) with visual observations used as validation. Using a tidal prediction model, the tide-adjusted, radar-derived target speeds between SAB events provide estimates of swim speeds averaging 4 m/s and time between SAB events of 30 s. The similarities between the radar signatures of the animals and sea clutter, combined with their low occurrence compared to other imaged phenomena renders automatic detection with this system difficult. However, the combination of opportunistic radar imagery and independent visual observation has allowed the radar signature of one form of killer whale SAB to be documented. It is hoped that with a greater number of validated observations such as these that automated, radar-based identification and the benefits it will bring to long-term observations at MRE sites will be possible. [ABSTRACT FROM AUTHOR]

Mapping the morphology of intertidal areas is a logistically challenging, time consuming and expensive task due to their large expanse and difficulties associated with access. A technique is presented here that uses standard marine navigational radar operating at X-band frequency. The method uses a series of time-exposure radar images over the course of a two-week tidal cycle to identify the elevation of the wetting and drying transitions at each pixel in the radar images, thereby building up a morphological map of the target intertidal area. This “Temporal Waterline” method is applied to a dataset acquired from Hilbre Island at the mouth of the Dee Estuary, UK, spanning March 2006 to January 2007. The radar gathered data with a radial range of 4 km and the resulting elevation maps describe the intertidal regions of that area. The results are compared with airborne LiDAR data surveyed over the same area and within the radar survey time period. The residual differences show good agreement across large areas of beach and sandbanks, with concentrations of poor estimations around points that are shadowed from the radar or likely to suffer from pooling water. This paper presents the theoretical framework of the method and demonstrates its stability and accuracy. The Temporal Waterline radar method is aimed at providing a useful tool for the monitoring and operational management of coastlines. [ABSTRACT FROM AUTHOR]

The drive towards sustainable energy has seen rapid development of marine renewable energy devices (MREDs). The NERC/Defra collaboration FLOw, Water column and Benthic ECology 4-D (FLOWBEC-4D) is investigating the environmental and ecological effects of installing and operating wave and tidal energy devices. The FLOWBEC sonar platform combines several instruments to record information at a range of physical and multitrophic levels for durations of two weeks to capture an entire spring-neap tidal cycle. An upward-facing multifrequency Simrad EK60 echosounder is synchronized with an upward-facing Imagenex Delta T multibeam sonar. An acoustic Doppler velocimeter (ADV) provides local current measurements and a fluorometer measures chlorophyll (as a proxy for phytoplankton) and turbidity. The platform is self-contained, facilitating rapid deployment and recovery in high-energy sites and flexibility in gathering baseline data. Five 2-week deployments were completed in 2012 and 2013 at wave and tidal energy sites, both in the presence and absence of renewable energy structures at the European Marine Energy Centre (EMEC), Orkney, U.K. Algorithms for target tracking have been designed and compared with concurrent, shore-based seabird observations used to ground truth the acoustic data. The depth preference and interactions of birds, fish schools and marine mammals with MREDs can be tracked to assess whether individual animals face collision risks with tidal stream turbines, and how animals generally interact with MREDs. These results can be used to guide marine spatial planning, device design, licensing and operation, as different device types are tested, as individual devices are scaled up to arrays, and as new sites are considered. [ABSTRACT FROM PUBLISHER]

All existing examples of current measurements by spaceborne synthetic aperture radar (SAR) along-track (AT) interferometry (ATI) have suffered from short baselines and corresponding low sensitivities. Theoretically, the best data quality at X-band is expected at effective baselines on the order of 30 m, i.e., 30 times as long as the baselines of the divided-antenna modes of TerraSAR-X. In early 2012, we had a first opportunity to obtain data at near-optimum baselines from the TanDEM-X satellite formation. In this paper, we analyze two TanDEM-X interferograms acquired over the Pentland Firth (Scotland) with effective AT baselines of 25 and 40 m. For comparison, we consider a TerraSAR-X dual-receive-antenna (DRA)-mode interferogram with an effective baseline of 1.15 m, as well as velocity fields obtained by Doppler centroid analysis (DCA) of single-antenna data from the same three scenes. We show that currents derived from the TanDEM-X interferograms have a residual noise level of 0.1 m/s at an effective resolution of about 33 m × 33 m, while DRA-mode data must be averaged over 1000 m × 1000 m to reach the same level of accuracy. A comparison with reference currents from a 1-km resolution numerical tide computation system shows good agreement in all three cases. The DCA-based currents are found to be less accurate than the ATI-based ones but close to short-baseline ATI results in quality. We conclude that DCA is a considerable alternative to divided-antenna mode ATI, while our TanDEM-X results demonstrate the true potential of the ATI technique at near-optimum baselines. [ABSTRACT FROM AUTHOR]

The simultaneous measurement of current flow and suspended sediment concentration in the marine environment is central to the study of sediment transport processes. In view of this, two acoustic approaches for measuring flow were tested in a tidal estuary to assess their capabilities in this environment. A coherent Doppler velocity profiler and a cross-correlation velocity profiler were assessed using conventional current meters and a commercially available acoustic Doppler velocimeter. Mean velocity profiles were obtained up to a range of 1.47 m in 0.046-m range bins over a number of flood tides. The measurements compared well with the reference instruments and regression analysis produced gradients close to unity. Turbulent velocities measured with the coherent Doppler profiler were comparable with turbulent fluctuations measured with the acoustic Doppler velocimeter. The cross-correlation velocity profiler was shown to be unable to measure turbulent velocities. The backscattered signals received on the cross-correlation transducers were also used to compute the sediment concentration profiles using an explicit solution to the acoustic backscatter equation. Combining the concentration and flow measurements enabled sediment flux profiles to be obtained, the results of which compared favorably with flux measurements obtained from the conventional current meters and pumped sampling. [ABSTRACT FROM AUTHOR]

The article focuses on the development of marine energy devices to harvest tidal energy resources in Great Britain. Topics discussed include challenges with marine energy harvesting including costs and risks of operating the marine energy devices, Engineering and Physical Sciences Research Council (EPSRC)'s focus on the resources and challenges, and Natural Environment Research Council (NERC) and the Department for Environment, Food and Rural Affairs (DEFRA)'s projects on marine energy.