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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 proof-of-concept system was installed approximately 16 m 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 GPS-based measurements were shown to be in excellent agreement with the corrected in situ gauge, exhibiting a root-mean-square difference of 5.7 cm over a tidal range exceeding 3 m 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.

X-band radar remote sensing of the ocean surface using ground-based installations and radar intensity imagery is a mature technology for the determination of ocean wave properties. In order to transition the analytical methods to data collected from a moving vessel the accurate geo-registration of radar images must be performed. However, finite offsets in azimuth, range and time are generated by the physical installation of equipment aboard a vessel that may not be measurable. This paper details a simple, yet robust method to “calibrate”data recorded by an arbitrary equipment installation to allow accurate geo-registration of the radar imagery. Time-integrated radar images are generated using a set of time-stamped radar intensity images and high-frequency, high-accuracy vessel heading and position information (from global satellite navigation systems and inertial navigation systems). The time-integrated image sharpness is found to be maximal for correctly determined angular, range, and time offsets. The requirements to form an operational system from the proposed method are also discussed.

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 multi-frequency echosounder to monitor marine life in a 120◦ 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 4ms−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 ren

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 ms-1 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.

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.

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.

The first small grid-connected arrays of tidal stream turbines are expected to be deployed in UK waters over the next few years, with MeyGen beginning installation operations in late 2014, and planning electricity generation by 2016. Understanding the high spatial and temporal variability of currents exhibited at such sites is of critical importance in determining turbine locations in terms of optimising predicted energy generation and device longevity. A marine radar was deployed on a remote clifftop overlooking a 4.8km radius area of the Inner Sound of Stroma in the Pentland Firth, Scotland, for 3 months during spring 2013. The area viewed by the radar includes the Crown Estate lease areas for Meygen Ltd (Inner Sound of Stroma) and Scottish Power Renewables (Ness of Duncansby). Data were post processed to extract current vector maps based on determining the Doppler shift of sea surface waves by the tidal current. This same analysis is now running operationally at the European Marine Energy Centre (EMEC) Fall of Warness Tidal Test Site producing current vector maps when there is sufficent sea clutter present.

Despite rapid development of wave and tidal marine renewable energy (MRE) devices, little is known of the environmental and ecological effects of installing and operating individual devices or arrays. The FLOWBEC project is investigating these effects at wave and tidal energy test sites in Orkney (EMEC). An upwardfacing sonar platform was developed to monitor the environment around MRE devices as a tool to guide marine spatial planning, device design, licensing and operation. The platform is self-contained, portable between sites, deployed in 20-minutes at slack tide and captures a full tidal cycle over 14 day deployments.

A marine radar was deployed on a remote clifftop overlooking a 4.8km radius area of the Inner Sound of Stroma in the Pentland Firth for 3 months during spring 2013. The area viewed by the radar includes The Crown Estate lease areas for MeyGen Ltd (Inner Sound of Stroma) and Scottish Power Renewables (Ness of Duncansby), although the data analysis has focussed solely on the MeyGen area. Data were post processed to extract current vector maps based on determining the Doppler shift of sea surface waves by the tidal current. Comparisons between current time series from two Acoustic Doppler Current Profiler (ADCP) surveys and the radar derived data are presented and show excellent correlation. The quality of the data has enabled tidal analyses to be performed and spatial variations in tidal current constituents to be mapped.

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 $times$ 33 m, while DRA-mode data must be averaged over 1000 m $times$ 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.

U.K. Sediment Initiative 2009: Developing Multidisciplinary Sediment Dynamics Research in a Strategic Context; Liverpool, United Kingdom, 27–29 April 2009; A workshop funded by the U.K. Natural Environment Research Council (NERC) brought together U.K.-based researchers, stakeholders, and policy makers with an interest in sediment processes to foster collaborative links and to help NERC theme leaders develop future Theme Action Plans (TAPs). This could be achieved only by identifying gaps in knowledge and prioritizing research needs toward formulating a U.K. sediment transport research strategy. More than 50 participants from NERC research and collaborative centers, U.K. higher education institution researchers, industry consultants, and government departments and agencies attended the workshop. The workshop was divided into three parts. First, in an introduction, guest speakers discussed the importance of sediment transport from different perspectives. The speakers included Darius Campbell (U.K. Department for Environment, Food, and Rural Affairs) on policy drivers, Richard Whitehouse (HR Wallingford, Ltd.) and David Lambkin (ABPMer, Ltd.) on industry needs, John Rees (NERC theme leader) on the NERC TAPs and possible funding opportunities, Alan Davies (University of Bangor) on the academic research perspective, and Chris Sherwood (U.S. Geological Survey) on international insight on large sediment transport projects and on developments of the U.S. National Community Sediment Transport Model project. Second, in a series of breakout sessions, participants considered the stakeholders’ needs, the different dynamic areas of the coastal ocean, and the process time scales. Third, the workshop group discussed possible funding streams and ways to better formulate a concerted research plan for presentation to funding bodies

The wave and current monitoring system WaMoS II is a remote sensing system based on a nautical X-Band radar generally used for navigation and ship traffic control. It has been used in recent years to monitor sea state information from moored platforms, coastal sites and moving vessels. A nautical radar can scan the sea surface over a large area (~ 10km2 ) with a high spatial (~7.5m) and temporal resolution (~2s). Directionalwave spectra and standard sea state parameters such as significant wave height, peak wave period and direction can be derived by analyzing the sea surface image sequences. Using the temporal and spatial evolution of the sea surface wave images it is also possible to determine high resolution current and bathymetry information. In the paper a brief introduction into the measuring principle of WaMoS II is given and results of a high resolution current and bathymetric mapping technique for shallow water areas (<20m) are presented. For validation these results are compared with model data and in-situ measurements.

Laboratory based Acoustic Doppler Velocity Profilers (ADVP) have found recent application to sediment transport and turbulence studies, due to their ability to provide vertical profiles with sub-centimetric spatial resolution at turbulent and inter-wave timescales. Adaptation of these instruments to autonomous units capable of prolonged deployment in marine environments is not straight forward due largely to the necessary reductions in power consumption, and the resulting trade off between operating frequency and signal to noise ratio, impacting upon the systems ability to de-alias ambiguous velocities over the whole profile. In the present paper, the system design, laboratory evaluation, and preliminary field trial results for an autonomous, 3-axis coherent ADVP will be presented. The system described operates at 1 MHz utilising a dual pulse repetition frequency to combat phase wrap velocity aliasing, and provides profiles over a 1.5 m range recording at 10 Hz, with a deployment duration of up to 5 weeks. In the laboratory, the instrument has been evaluated in a sediment tower, by comparing measured settling velocities obtained from spheres to theoretical estimates. The field trial was carried out in a shallow estuary, where the ADVP was evaluated relative to independent measurements of the three velocity components, and an assessment of the instruments dynamic range was conducted. The implications of the results to using autonomous ADVPs to probe sediment transport processes in marine bottom boundary layers will be discussed

Acoustic measurements of near-bed sediment diffusivity profiles are reported. The observations were made over two sandy rippled beds, classified as ‘medium’ and ‘fine’ in terms of sand grain size, under slightly asymmetric regular waves. For the medium sand, the ripples that formed had relatively steep slopes, while for the fine sand, the slopes were roughly half that of the medium sand. In the medium sand case, the form of the sediment diffusivity profiles was found to be constant with height above the bed, to a height equal approximately to the equivalent roughness of the bed, ks, while above this the sediment diffusivity increased linearly with height. For the case of the fine sand there was no constant region; the sediment diffusivity simply increased linearly with height from the bed. To understand the difference between the respective diffusivity profiles, advantage has been taken of the high temporal-spatial resolution available with acoustic systems. Using intra-wave ensemble averaging, detailed images have been built up of the variation in concentration with both the phase of the wave and also height above the bed. These intra-wave observations, combined with measurements of the bed forms and concepts of convective and diffusive entrainment, have been used to elucidate the mixing mechanisms that underlie the form of the diffusivity profiles observed over the two rippled beds. These mechanisms centre on coherent vortex shedding in the case of steeply rippled beds and random turbulent processes above ripples of lower steepness.

Bathymetric maps and tidal currents have been mapped in an estuarine environment through the analysis of marine radar image sequences to a range of 4 km and with 100 m grid spacing. the Dee estuary is located on the southern side of Liverpool Bay in the United Kingdom and contains a complex system of intertidal sand banks and channels with a peak spring tidal range exceeding 10 m. In order to understand how the estuary is evolving it would be helpful to regularly observe the positions of the sand banks and channels and the wave and current forcing driving the evolution of these features. To this end a marine radar has been deployed on an island in the estuary from which ten minute sequences of images of the sea surface are recorded once per hour. By fitting a wave dispersion equation to the observed wave behaviour it is possible to map the underlying water depth and mean current provided waves are visible on the radar images. Radar derived water depth and current maps recorded around a single high water were compared with survey data and show that in regions where the waves are feeling the sea bottom, the radar derived depths are generally witin +/-1 m of the survey data.

The bathymetry and currents in a 4km radius area of the Dee Estuary in Liverpool Bay have been mapped using a wave inversion of marine radar data without the need for any prior bathymetric data. The radar is mounted 30m above sea level on an island in the estuary and 10 minute sequences of radar images of the sea surface are recorded automatically each hour giving 360 degree coverage of the area. Several such records taken arond high tide during a moderate wave event have been processed to produce the map using a wave inversion that accounts for currents, frequency and amplitude dispersion. The results are compared to a combined LiDAR and Multibeam echosounder survey carried out in 2003, clearly identifying migrating sand banks within the estuary. The strength of this technique is in its ability to map large areas of bathymetrically complex shallow coastal waters rapidly, remotely and under storm conditions, with vertical accuracies generally better than +/-1m of survey data.

The LEACOAST2 project (http://pcwww.liv.ac.uk/civilCRG/leacoast2/) is studying the effect of a shore parallel breakwater system on the evolution of coastal morphology at Sea Palling on the east coast of England, facing the southern North Sea. Here there are strong tidal currents, and occasional storm wave conditions. The sediments are mixed with their composition ranging from coarse sand to silt supplied from the soft boulder clay cliffs to the north; these sediments are quite mobile under tide and wave stirring. The breakwaters have trapped sand in embayments, with tombolos and salients behind the breakwaters, while some sand bypassing outside the system seems to occur. As part of this project data were collected from three instrumented tripods deployed near the breakwaters, during two field campaigns (March–May 2006 and October 2006–January 2007). The instrumentation includes acoustic and optical instrumentation (ADCP, ADV, LISST and bedform scanners). Observations of waves, currents and bathymetry have also been made using an X-band radar deployed for two years to monitor the whole area over a range of several kilometers. A large dataset has been successfully obtained. Here we present an overview of the observed hydrodynamic conditions, sediment transport and bedforms from this experiment.

An acoustic profiling system designed to measure sand ripples in three dimensions has been developed and successfully deployed on benthic frames at two sites around the UK coast. The system comprises a mechanically scanning pencil beam acoustic transducer mounted on a two axis stepper motor assembly within a fully enclosed oil-filled housing. A pressure sensor, temperature sensor and conductivity sensor are also integrated with the instrument, ensuring the correct speed of sound is used for deriving distance to the bed from the time of flight of the acoustic pulses. Data recorded at two sites using the 3D-Acoustic Ripple Profiler are presented showing tidally migrating sand waves in the first case, and wave induced sand ripples evolving in response to a passing storm in the second.

The long-term goal of this research project is to improve our capability to use X-band marine radars to routinely measure waves, currents and bathymetry in coastal regions. The scientific objectives of this study are: 1. investigate the imaging mechanisms of X-band radar systems in shallow coastal waters where nonlinear wave steepening, infragravity waves, wave breaking and breaking-induced currents can affect the radar backscatter signal 2. apply high-resolution spectral analysis techniques to the estimation of directional wave spectra from X-band radar images. 3. develop improved techniques for estimating the bottom topography from X-band radar images of the sea surface in shallow water regions with highly nonlinear waves and/or strong currents., Prepared in collaboration with the Proudman Oceanographic Laboratory, Birkenhead, UK.

Image sequences of surface gravity waves are readily produced by standard marine X-band radars. These image sequences contain a great deal of information regarding wave parameters and their variation over an area. By approaching the analysis of such data, using image analysis techniques, it is possible to map the variations in wave behaviour in a shallow water area. Wave celerity and direction can be mapped, and inversion algorithms based on linear wave theory used to infer the underlying bathymetry. Knowledge of the period of the waves is necessary for the analysis, and this can also be calculated from the radar data, although there is some discrepancy between the figures derived from radar data and from an offshore S4DW instrument. These discrepancies are investigated, and the results presented. Three days of data from the Holderness II deployment during 1995 have been analysed, and estimates of the bathymetry produced. The calculated depths show a mean water level comparable to that read off an Admiralty chart for the area, and a tidal signal is also clearly superimposed on the data, giving confidence in the water depths derived using this technique.