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cited By 9; International audience; Ocean surface winds, currents, and waves play a crucial role in exchanges of momentum, energy, heat, freshwater, gases, and other tracers between the ocean, atmosphere, and ice. Despite surface waves being strongly coupled to the upper ocean circulation and the overlying atmosphere, efforts to improve ocean, atmospheric, and wave observations and models have evolved somewhat independently. From an observational point of view, community efforts to bridge this gap have led to proposals for satellite Doppler oceanography mission concepts, which could provide unprecedented measurements of absolute surface velocity and directional wave spectrum at global scales. This paper reviews the present state of observations of surface winds, currents, and waves, and it outlines observational gaps that limit our current understanding of coupled processes that happen at the air-sea-ice interface. A significant challenge for the coming decade of wind, current, and wave observations will come in combining and interpreting measurements from (a) wave-buoys and high-frequency radars in coastal regions, (b) surface drifters and wave-enabled drifters in the open-ocean, marginal ice zones, and wave-current interaction "hot-spots," and (c) simultaneous measurements of absolute surface currents, ocean surface wind vector, and directional wave spectrum from Doppler satellite sensors.

Background Detecting tagged animals in coastal environments is often limited to stationary arrays of acoustic receivers that can decode transmissions from tags on animals. However, mobile autonomous platforms are becoming important tools that support the science of understanding biophysical relationships because they can concurrently detect tagged individuals and measure properties of their ocean habitat. To assess the effectiveness of these emerging platforms, proper validation and range detection studies are necessary. Here, we report on the deployment of a wave powered unmanned surface vessel, the Liquid Robotics Wave Glider SV3, equipped with a forward- and backward-facing acoustic receiver (VR2W) and transceiver (VR2Tx) at 4 m depth. Surveys were conducted around two stationary moorings equipped with receivers, transceivers or tags emitting signals with different power outputs. Results During our study, the sea state was mild with low wind speeds ( 0.5 km and the maximum range was 0.5–1.2 km. The forward-facing receiver had almost half the detection efficiency of the backward-facing transceiver, suggesting a backward configuration is optimal to reduce the influence of the moving platform. The higher power output transmitters had a 20% detection efficiency to ranges of ~ 0.5 km (153 dB) and ~ 0.8 km (160 dB). Distance between the receiver and transmitter was the main factor affecting detection probability, with background noise, receiver heading, angle between transmitter and receiver and wave height also being important. Wind speed, water temperature, mooring line tilt angle and vehicle dynamics were found not to be as important over the limited range of conditions over which our study was conducted. Conclusions Wave Gliders equipped with receivers can provide useful data and can be an effective biotelemetry asset that could supplement stationary arrays of acoustic receivers or act as an exploratory technology to search for biologically important areas.

The influence of wave–current interactions on time series of marine X-band radar backscatter maps at the mouth of the Columbia River (MCR) near Astoria, Oregon, is examined. The energetic wave environment at the MCR, coupled with the strong tidally forced currents, provides a unique test environment to explore the limitations in accurately determining the magnitude and vertical structure of upper-ocean currents from wavefield measurements. Direct observation in time and space of the wave-induced radar backscatter and supporting acoustic Doppler current profiler (ADCP) current measurements provide a rich dataset for investigating how currents shift the observed wave dispersion relationship. First, current extraction techniques that assume a specific current–depth profile are tested against ADCP measurements. These constrained solutions prove to have inaccuracies because the models do not properly account for vertical shear. A forward solution using measured current profiles to predict the wavenumber–Doppler shift relationship for the range of ocean waves sensed by the radar is introduced. This approach confirms the ocean wavefield is affected by underlying vertical current shear. Finally, a new inversion method is developed to extract current profiles from the wavenumber-dependent Doppler shift observations. The success of the inversion model is shown to be sensitive to the range of wavenumbers spanned by observed Doppler shifts, with skill exceeding 0.8 when wavenumbers span more than 0.1 rad m−1. This agreement when observations successfully capture the broadband wavefield suggests the X-band backscatter is a viable means of remotely estimating current shear.

In this study, we expand previous large eddy simulation (LES) modeling investigations of Langmuir turbulence (LT) to real ocean conditions using field observations collected under the multi-platform field campaign “Coupled Air–Sea Processes and Electromagnetic (EM) ducting Research (CASPER-East)”. The measurement site has strong local variabilities of temperature and salinity and experienced large variations in wind forcing and several cooling events. Although LT enhances the turbulence in the water column and deepens the mixed layer during most of the simulation period, being consistent with previous studies, strong reduction of turbulent kinetic energy (TKE) in the mixed layer is observed in the simulation with Stokes drift compared to that without Stokes drift during a short period. Analysis of the meteorological forcing and the TKE budget have revealed that in the circumstance of swell dominated wave fields with young wind seas, the presence of Stokes drift reduces shear production more than the Stokes production it generates, and a reduction of total TKE in the mixed layer may be expected whether or not the Stokes drift is aligned with the wind. Weak reduction of TKE due to the inclusion of Stokes drift is also observed beneath the mixed layer during a cooling event possibly due to the fact that the upwelling associated with Langmuir circulation at the base of the mixed layer counteracts on the downwelling associated with the deep convection and reduces the total turbulence level in the water column. While both resolved Reynold stresses and the bulk eddy viscosity decrease with the increase of wind-wave misalignment angle θ w w and become smaller than that in the case without Stokes drift when θ w w exceed 60°, the subgrid scale (SGS) part of the momentum flux increases with the increase of θ w w , suggesting that the LES solutions in cases with large wind-wave misalignment become more sensitive to the SGS models used and need to be dealt with caution.

To facilitate sensor integration and provide a testbed for autonomous sense and react research, an onboard sensor processing and autonomy system has been developed for the REMUS 100 AUV using the Robot Operating System (ROS) and the REMUS RECON interface, which provides backseat control of the vehicle. An interface library, pyREMUS, has been developed to handle the REMUS RECON interface, and a ROS package, ros_remus, uses this library to provide a deep level of interoperability between the REMUS vehicle computer and other ROS-based subsystems. This system has been deployed on multiple REMUS 100 vehicles and it is currently used operationally for field research programs. Vehicles outfitted with this system have seen numerous deployments, where they have been used for seabed surveys, sensor evaluation, and engineering tests.

“Chirp”-style sidescan sonar systems, which use pulse-compressed signals, provide advantages over pulsed continuous-wave sidescan sonar systems, including increased imaging range, resolution, and image fidelity. Marine Sonics (Yorktown, VA) has recently released a system, the “Arc Scout”, using modern electronics in a form factor suitable for installation on small autonomous underwater vehicles (AUVs). A number of these systems have been integrated into REMUS 100 AUVs, and their performance imaging archaeological targets on the seabed has been evaluated. Targets were surveyed under a variety of conditions at four different sonar center frequencies: 600 kHz, 900 kHz, 1200 kHz, and 1800 kHz. The results were analyzed to provide performance assessments for selecting the sonar operating characteristics based on area search rate and target size. The hardware and software integration required for the retrofit installation of these sonar systems the REMUS 100 vehicle is detailed.

Observations from around the main island group of Palau, located in the tropical Western Pacific, exhibit a persistent presence of baroclinic coastally trapped waves. The signals are found in records of temperature that were sustained on the fore-reef for seven months, May to December 2013, with the strongest signal from Typhoon Haiyan which passed over Kayangel Atoll, along with the northern most Palauan islands, in November of 2013. This strong forcing led to a large near- and sub-inertial response both in temperature and nearshore currents. We use semi-analytical models, such as the vertical structure equation and Brink and Chapman's (1985) model, to compute propagating modes for this oceanographic region providing a benchmark for comparison with the observations. These models provided a framework to account for the influence of local stratification, topography and the local Coriolis parameter on the wave guide around Palau. We found the maximum vertical displacements over the course of a 22-day period that included Typhoon Haiyan were 35.5 m and 45.7 m at the 57 m and 90 m isobaths, respectively, where temperatures ranged by 4.1 °C and 9.0 °C over that same period at those respective depths. The apparent omnipresence of coastally trapped waves throughout the observational window provide a regular cycling of temperature at depth, potentially conditioning benthic communities living on the outer reef slope to temperature swings.

The authors report on the results from a series of full-scale trials designed to quantify the air entrainment at the stern of an underway vessel. While an extremely complex region to model air entrainment due to the confluence of the breaking transom wave, bubbles from the bow, turbulence from the hull boundary layer, and bubbles and turbulence from propellers, the region is a desirable area to characterize and understand because it serves as the initial conditions of a ship's far-field bubbly wake. Experiments were conducted in 2003 from R/V Revelle and 2004 from R/V Athena II using a custom-built conductivity probe vertical array that could be deployed at the blunt transom of a full-scale surface ship to measure the void fraction field. The system was designed to be rugged enough to withstand the full speed range of the vessels. From the raw time-series data, the entrainment of air at speeds ranging from 2.1 to 7.2 m/s is computed at various depths and beam locations. The data represent the first such in-situ measurements from a full-scale vessel and can be used to validate two-phase ship hydrodynamic computational fluid dynamics (CFD) codes and initialize far-field, bubbly wake CFD models.

The dominant source of coastal pollution adversely affecting the regional coastal water quality is the seasonally variable urban runoff discharged via southern California’s rivers. Here, we use a surface transport model of coastal circulation driven by current maps from high frequency radar to compute two-year hindcasts to assess the temporal and spatial statistics of 20 southern California stormwater discharges. These models provide a quantitative, statistical measure of the spatial extent of the discharge plumes in the coastal receiving waters, defined here as a discharge’s “exposure”. We use these exposure maps from this synthesis effort to (1) assess the probability of stormwater connectivity to nearby Marine Protected Areas, and (2) develop a methodology to estimate the mass transport of stormwater discharges. The results of the spatial and temporal analysis are found to be relevant to the hindcast assessment of coastal discharges and for use in forecasting transport of southern California discharges.

The Arabian Sea circulation is forced by strong monsoonal winds and is characterized by vigorous seasonally reversing currents, extreme differences in sea surface salinity, localized substantial upwelling, and widespread submesoscale thermohaline structures. Its complicated sea surface temperature patterns are important for the onset and evolution of the Asian monsoon. This article describes a program that aims to elucidate the role of upper-ocean processes and atmospheric feedbacks in setting the sea surface temperature properties of the region. The wide range of spatial and temporal scales and the difficulty of accessing much of the region with ships due to piracy motivated a novel approach based on state-of-the-art autonomous ocean sensors and platforms. The extensive data set that is being collected, combined with numerical models and remote sensing data, confirms the role of planetary waves in the reversal of the Somali Current system. These data also document the fast response of the upper equatorial ocean to monsoon winds through changes in temperature and salinity and the connectivity of the surface currents across the northern Indian Ocean. New observations of thermohaline interleaving structures and mixing in setting the surface temperature properties of the northern Arabian Sea are also discussed.

The Coupled Air–Sea Processes and Electromagnetic Ducting Research (CASPER) project aims to better quantify atmospheric effects on the propagation of radar and communication signals in the marine environment. Such effects are associated with vertical gradients of temperature and water vapor in the marine atmospheric surface layer (MASL) and in the capping inversion of the marine atmospheric boundary layer (MABL), as well as the horizontal variations of these vertical gradients. CASPER field measurements emphasized simultaneous characterization of electromagnetic (EM) wave propagation, the propagation environment, and the physical processes that gave rise to the measured refractivity conditions. CASPER modeling efforts utilized state-of-the-art large-eddy simulations (LESs) with a dynamically coupled MASL and phase-resolved ocean surface waves. CASPER-East was the first of two planned field campaigns, conducted in October and November 2015 offshore of Duck, North Carolina. This article highlights the scientific motivations and objectives of CASPER and provides an overview of the CASPER-East field campaign. The CASPER-East sampling strategy enabled us to obtain EM wave propagation loss as well as concurrent environmental refractive conditions along the propagation path. This article highlights the initial results from this sampling strategy showing the range-dependent propagation loss, the atmospheric and upper-oceanic variability along the propagation range, and the MASL thermodynamic profiles measured during CASPER-East.

To characterize the transitional region from the near-field to far-field of a river plume entering coastal waters, we conducted four surveys using an autonomous underwater vehicle (AUV) to target the outflow of the New River Inlet, North Carolina, during maximum ebb tide. The utilization of a mobile sensor to synoptically observe current velocity data in tandem with natural river plume tracers (e.g., colored dissolved organic matter, salinity) was essential in understanding the mechanisms driving the observed circulation and mixing patterns within these waters. We find that this region is regularly impacted by two primary processes: (1) the interaction of an old dredged channel plume with the main discharge and (2) the recirculation of the discharge plume by an eddy that persistently forms between the old channel and main discharge location. Wind-driven processes in the nearshore can enhance the interaction of these two plumes resulting in unstable regions where mixing of the merged plume with the receiving waters is accelerated. We also conduct comparisons between AUV velocity observations from two surveys and their corresponding velocity outputs from a parallelized quasi-3-D model. We conclude that the ability to observe the estuarine outflow transitional region at near-synoptic temporal scales and resolutions discussed in this paper is key in providing the mechanisms driving local circulation which is essential for proper parameterization of high-resolution numerical coastal models.

Knowledge of the nearshore ocean environment is important for naval operations, including military and humanitarian applications. The models used by the US Navy for predicting waves and circulation in the coastal regions are presented here. The wave model of choice for coastal regions is the Simulating WAves Nearshore (SWAN) model, which predicts wave energy as a function of frequency and direction. SWAN is forced by winds as well as waves at the offshore boundaries. For coastal circulation, Delft3D, composed of a number of different modules that can be coupled with each other, is presently used. Most applications for daily operational predictions use only the Delft3D-FLOW module, which predicts currents, mean water levels, temperature, and salinity. Inputs to the model include winds, tides, general ocean circulation, waves, daily river discharges, temperature, and salinity. Delft3D-FLOW is coupled with the Delft3D-WAVE module for areas where wave effects are of importance. A four-dimensional variational assimilation (4DVar) system based on SWAN, the SWANFAR system, is under development for nearshore wave predictions. It will improve wave predictions by using regional wave observations. We present several case studies that illustrate the validation and diverse applications of these models. All operational systems are run at the Naval Oceanographic Office.

The strength of the surface wave signal in marine X-band radar (MR) images strongly depends on range and azimuth (i.e., the angle between antenna look and peak wave direction). Traditionally, MR wave analysis is carried out in a set of rectangular windows covering the radar field of view (FOV). The FOV is typically partially obstructed, e.g., due to the coastline or ship superstructures. Especially for ships that are subject to regular course changes, this results in an increased variability or error associated with wave parameters. Using MR measurements from R/P FLIP, acquired off California during the 2010 US Office of Naval Research (ONR) high resolution air–sea interaction (Hi-Res) experiment, this study quantifies the dependency of the radar-based 2D wave spectrum and parameters on range and azimuth. With the help of reference data from a nearby Datawell Waverider buoy, we propose empirical methods to remove the dependency and we illustrate their efficacy.

[1] The network comprising 61 high-frequency radar systems along the U.S. West Coast (USWC) provides a unique, high resolution, and broad scale view of ocean surface circulation. Subinertial alongshore surface currents show poleward propagating signals with phase speeds of O(10) and O(100–300) km d −1 that are consistent with historical in situ observations off the USWC and that can be possibly interpreted as coastally trapped waves (CTWs). The propagating signals in the slow mode are partly observed in southern California, which may result from scattering and reflection of higher-mode CTWs due to curvature of shoreline and bathymetry near Point Conception, California. On the other hand, considering the order of the phase speed in the slow mode, the poleward propagating signals may be attributed to alongshore advection or pressure-driven flows. A statistical regression of coastal winds at National Data Buoy Center buoys on the observed surface currents partitions locally and remotely wind-forced components, isolates footprints of the equatorward propagating storm events in winter off the USWC, and shows the poleward propagating signals year round.

Estimates of surface currents over the continental shelf are now regularly made using high-frequency radar (HFR) systems along much of the U.S. coastline. The recently deployed HFR system at the Martha’s Vineyard Coastal Observatory (MVCO) is a unique addition to these systems, focusing on high spatial resolution over a relatively small coastal ocean domain with high accuracy. However, initial results from the system showed sizable errors and biased estimates of M2 tidal currents, prompting an examination of new methods to improve the quality of radar-based velocity data. The analysis described here utilizes the radial metric output of CODAR Ocean Systems’ version 7 release of the SeaSonde Radial Site Software Suite to examine both the characteristics of the received signal and the output of the direction-finding algorithm to provide data quality controls on the estimated radial currents that are independent of the estimated velocity. Additionally, the effect of weighting spatial averages of radials falling within the same range and azimuthal bin is examined to account for differences in signal quality. Applied to two month-long datasets from the MVCO high-resolution system, these new methods are found to improve the rms difference comparisons with in situ current measurements by up to 2 cm s−1, as well as reduce or eliminate observed biases of tidal ellipses estimated using standard methods.

A national high-frequency radar network has been created over the past 20 years or so that provides hourly 2-D ocean surface current velocity fields in near real time from a few kilometers offshore out to approximately 200 km. This preoperational network is made up of more than 100 radars from 30 different institutions. The Integrated Ocean Observing System efforts have supported the standards-based ingest and delivery of these velocity fields to a number of applications such as coastal search and rescue, oil spill response, water quality monitoring, and safe and efficient marine navigation. Thus, regardless of the operating institution or location of the radar systems, emergency response managers, and other users, can rely on a common source and means of obtaining and using the data. Details of the history, the physics, and the application of high-frequency radar are discussed with successes of the integrated network highlighted.

The problem of dynamically mapping high-frequency (HF) radar radial velocity observations is investigated using a three-dimensional hydrodynamic model of the San Diego coastal region and an adjoint-based assimilation method. The HF radar provides near-real-time radial velocities from three sites covering the region offshore of San Diego Bay. The hydrodynamical model is the Massachusetts Institute of Technology general circulation model (MITgcm) with 1 km horizontal resolution and 40 vertical layers. The domain is centered on Point Loma, extending 117 km offshore and 120 km alongshore. The reference run (before adjustment) is initialized from a single profile of T and S and is forced with wind data from a single shore station and with zero heat and fresh water fluxes. The adjoint of the model is used to adjust initial temperature, salinity, and velocity, hourly temperature, salinity and horizontal velocities at the open boundaries, and hourly surface fluxes of momentum, heat and freshwater so that the model reproduces hourly HF radar radial velocity observations. Results from a small number of experiments suggest that the adjoint method can be successfully used over 10-day windows at coastal model resolution. It produces a dynamically consistent model run that fits HF radar data with errors near the specified uncertainties. In a test of the forecasting capability of the San Diego model after adjustment, the forecast skill was shown to exceed persistence for up to 20 h.

Analysis of coastal surface currents measured off the coast of San Diego for two years suggests an anisotropic and asymmetric response to the wind, probably as a result of bottom/coastline boundary effects, including pressure gradients. In a linear regression, the statistically estimated anisotropic response explains approximately 20% more surface current variance than an isotropic wind–ocean response model. After steady wind forcing for three days, the isotropic surface current response veers 42° ± 2° to the right of the wind regardless of wind direction, whereas the anisotropic analysis suggests that the upcoast (onshore) wind stress generates surface currents with 10° ± 4° (71° ± 3°) to the right of the wind direction. The anisotropic response thus reflects the dominance of alongshore currents in this coastal region. Both analyses yield wind-driven currents with 3%–5% of the wind speed, as expected. In addition, nonlinear isotropic and anisotropic response functions are considered, and the asymmetric current responses to the wind are examined. These results provide a comprehensive statistical model of the wind-driven currents in the coastal region, which has not been well identified in previous field studies, but is qualitatively consistent with descriptions of the current response in coastal ocean models.

Ecosystem function will in large part be determined by functional groups present in biological communities. The simplest distinction with respect to functional groups of an ecosystem is the differentiation between primary and secondary producers. A challenge thus far has been to examine these groups simultaneously with sufficient temporal and spatial resolution for observations to be relevant to the scales of change in coastal oceans. This study takes advantage of general differences in the bioluminescence flash kinetics between planktonic dinoflagellates and zooplankton to measure relative abundances of the two groups within the same-time space volume. This novel approach for distinguishing these general classifications using a single sensor is validated using fluorescence data and exclusion experiments. The approach is then applied to data collected from an autonomous underwater vehicle surveying >500 km in Monterey Bay and San Luis Obispo Bay, CA during the summers of 2002–2004. The approach also reveals that identifying trophic interaction between the two planktonic communities may also be possible.

Oil-spill fate and transport modeling may be used to evaluate water column hydrocarbon concentrations, potential exposure to organisms, and impacts of oil spills with and without dispersant use. Important inputs to transport modeling for such analyses are current velocities and turbulent dispersion coefficients. Fluorescein dye studies off San Diego, California, were used to calibrate an oil transport model by hindcasting movement and dispersion of dye. The oil spill model was then used to predict subsurface hydrocarbon concentrations and potential water column impacts if oil were to be dispersed into the water column under similar conditions. Field-collected data included surface currents calculated from high-frequency radar data (HF-Radar), near-surface currents from drifter measurements drogued at several depths (1m, 2m, 4m or 5m), dye concentrations measured by fluorescence, spreading and dye intensity measurements based on aerial photography, and water density profiles from CTD casts. As the dye plume quickly extended throughout an upper mixed layer (7–15m), the horizontal dye movements were better indicated by the drifters drogued to a depth near the middle of that layer than the HF-Radar, which measured surface (∼top 50 cm) currents (including wind drift). Diffusion rates were estimated based on dye spreading measured by aerial photography and fluorescence-depth profiles. The model used these data as inputs, modeling of wind-forced surface water turbulence and drift as a function of wind speed and direction (based on published results of fluid dynamics studies), and Stokes law for droplet rise/sinking rates, to predict oil transport and dispersion rates within the water column. Use of such diffusion rate data in an oil fate model can provide estimates of likely dispersed oil concentrations under similar conditions, which may be used to evaluate potential impacts on water column biota. However, other conditions with different patterns of current shear (due to background currents, tidal currents, and wind stress) should be examined before these results can be generalized.

The California Department of Fish and Game Office of Spill Prevention and Response (CA OSPR) is utilizing oil-spill fate and transport modeling to develop the time and spatial scales, and equipment needs, for a formal Dispersed Oil Monitoring Plan (DOMP). When fully implemented, the DOMP will aid in documenting hydrocarbon concentrations in the water column, potentially exposed organisms (zooplankton), and the impacts of entrained oil and dissolved hydrocarbons with and without dispersant applications. Fluorescein dye studies off San Diego, California (USA) have been completed to test the operational framework for repeated sampling of dispersed oil plumes as outlined in the DOMP, to allow evaluation of high-frequency radar (HP-Radar) for providing surface current input data to oil spill models, and to provide verification of model-predicted movement of subsurface oil (dye) by comparison with drogue movement and measured dye concentrations over three dimensions and time. Aerial photodocumentation, subsurface drogues, dye transport, and HF-Radar were used to measure near-surface current fields at varying depths. High-resolution subsurface dye-plume structure was mapped using an in situ GPS-coupled towed fluorometer equipped with pressure sensors to provide dye concentration data as a function of time, position, and depth. In addition, data from the more traditional Special Monitoring of Applied Response Technology (SMART) protocols utilized by the U.S. Coast Guard (USCG) were compared with the in situ towed-fluorometer measurements, and conventional CTD data were collected to determine the mixed layer depth, an important variable in monitoring dispersion of oil in the water column. As a result of these efforts, significant progress has been made on developing and testing sampling protocols for the DOMP, and nearly continuous and synoptic data have been obtained from seven cruises conducted over a 12-month period. These data sets (available on-line through the Coastal Response Research Center (CRRC) website: http://www.crrc.unh.edu/) are being analyzed and integrated to support oil spill model development and verification with direct applicability to spill response decision making, net environmental benefit analysis, natural resource damage assessments, and educating the spill community and public.

Stormwater river plumes are important vectors of marine contaminants and pathogens in the Southern California Bight. Here we report the results of a multi-institution investigation of the river plumes across eight major river systems of southern California. We use in situ water samples from multi-day cruises in combination with MODIS satellite remote sensing, buoy meteorological observations, drifters, and HF radar current measurements to evaluate the dispersal patterns and dynamics of the freshwater plumes. River discharge was exceptionally episodic, and the majority of storm discharge occurred in a few hours. The combined plume observing techniques revealed that plumes commonly detach from the coast and turn to the left, which is the opposite direction of Coriolis influence. Although initial offshore velocity of the buoyant plumes was ∼50 cm/s and was influenced by river discharge inertia (i.e., the direct momentum of the river flux) and buoyancy, subsequent advection of the plumes was largely observed in an alongshore direction and dominated by local winds. Due to the multiple day upwelling wind conditions that commonly follow discharge events, plumes were observed to flow from their respective river mouths to down-coast waters at rates of 20–40 km/d. Lastly, we note that suspended-sediment concentration and beam-attenuation were poorly correlated with plume salinity across and within the sampled plumes (mean r 2 =0.12 and 0.25, respectively), while colored dissolved organic matter (CDOM) fluorescence was well correlated (mean r 2 =0.56), suggesting that CDOM may serve as a good tracer of the discharged freshwater in subsequent remote sensing and monitoring efforts of plumes.

A skill analysis of the Multiple Signal Characterization (MUSIC) algorithm used in compact-antenna-style HF radar ocean current radial velocity/bearing determination is performed using simulation. The simulation is based upon three collocated antennas (two cross loops and a monopole with ideal gain patterns) in a geometry similar to the 25-MHz SeaSonde HF radar commercially available from Coastal Ocean Dynamics Applications Radar (CODAR) Ocean Sensors, Palo Alto, California. The simulations consider wind wave/current scenarios of varying complexity to provide insight to the accuracy of surface current retrievals and the inherent limitations of the technique, with a focus on the capabilities of the MUSIC algorithm itself. The influence of second-order scatter, interference, and stationary target scatter are not considered. Simple error reduction techniques are explored and their impacts quantified to aid in operational system configuration and encourage areas of further research. Increases in skill between 55% and 100% using spatial averaging, and between 14% and 33% using temporal averaging, are realized, highlighting the utility of these techniques. When these error-flagging and averaging techniques are employed, individual range cell skill metrics are found to be as high as 0.94 for simple currents at a high signal-to-noise ratio (SNR), while more complex currents achieve a maximum skill metric of 0.72 for the same SNR. These simulations, conducted under ideal conditions, provide insight to understanding the variables, which influence the accuracy of surface currents retrieved using MUSIC.

Dense arrays of surface drifters are used to quantify the flow field on time and space scales over which high-frequency (HF) radar observations are measured. Up to 13 drifters were repetitively deployed off the Santa Barbara and San Diego coasts on 7 days during 18 months. Each day a regularly spaced grid overlaid on a 1-km2 (San Diego) or 4-km2 (Santa Barbara) square, located where HF radar radial data are nearly orthogonal, was seeded with drifters. As drifters moved from the square, they were retrieved and replaced to maintain a spatially uniform distribution of observations within the sampling area during the day. This sampling scheme resulted in up to 56 velocity observations distributed over the time (1 h) and space (1 and 4 km2) scales implicit in typical surface current maps from HF radar. Root-mean-square (RMS) differences between HF radar radial velocities obtained using measured antenna patterns, and average drifter velocities, are mostly 3–5 cm s−1. Smaller RMS differences compared with past validation studies that employ current meters are due to drifter resolution of subgrid-scale velocity variance included in time and space average HF radar fields. Roughly 5 cm s−1 can be attributed to sampling on disparate time and space scales. Despite generally good agreement, differences can change dramatically with time. In one instance, the difference increases from near zero to more than 20 cm s−1 within 2 h. The RMS difference and bias (mean absolute difference) for that day exceed 7 and 12 cm s−1, respectively.

The Coupled Boundary Layer Air–Sea Transfer (CBLAST) field program, conducted from 2002 to 2004, has provided a wealth of new air–sea interaction observations in hurricanes. The wind speed range for which turbulent momentum and moisture exchange coefficients have been derived based upon direct flux measurements has been extended by 30% and 60%, respectively, from airborne observations in Hurricanes Fabian and Isabel in 2003. The drag coefficient (CD) values derived from CBLAST momentum flux measurements show CD becoming invariant with wind speed near a 23 m s−1 threshold rather than a hurricane-force threshold near 33 m s−1 . Values above 23 m s−1 are lower than previous open-ocean measurements. The Dalton number estimates (CE) derived from CBLAST moisture flux measurements are shown to be invariant with wind speeds up to 30 m s −1 which is in approximate agreement with previous measurements at lower winds. These observations imply a CE/CD ratio of approximately 0.7, suggesting that additional energy sources are necessary for hurricanes to achieve their maximum potential intensity. One such additional mechanism for augmented moisture flux in the boundary layer might be “roll vortex” or linear coherent features, observed by CBLAST 2002 measurements to have wavelengths of 0.9–1.2 km. Linear features of the same wavelength range were observed in nearly concurrent RADARSAT Synthetic Aperture Radar (SAR) imagery. As a complement to the aircraft measurement program, arrays of drifting buoys and subsurface floats were successfully deployed ahead of Hurricanes Fabian (2003) and Frances (2004) [16 (6) and 38 (14) drifters (floats), respectively, in the two storms]. An unprecedented set of observations was obtained, providing a four-dimensional view of the ocean response to a hurricane for the first time ever. Two types of surface drifters and three types of floats provided observations of surface and subsurface oceanic currents, temperature, salinity, gas exchange, bubble concentrations, and surface wave spectra to a depth of 200 m on a continuous basis before, during, and after storm passage, as well as surface atmospheric observations of wind speed (via acoustic hydrophone) and direction, rain rate, and pressure. Float observations in Frances (2004) indicated a deepening of the mixed layer from 40 to 120 m in approximately 8 h, with a corresponding decrease in SST in the right-rear quadrant of 3.2°C in 11 h, roughly one-third of an inertial period. Strong inertial currents with a peak amplitude of 1.5 m s−1 were observed. Vertical structure showed that the critical Richardson number was reached sporadically during the mixed-layer deepening event, suggesting shear-induced mixing as a prominent mechanism during storm passage. Peak significant waves of 11 m were observed from the floats to complement the aircraft-measured directional wave spectra.

As the US Integrated Ocean Observing System (IOOS) high frequency (HF) radar network (HFRNet) approaches its tenth year of existence, we highlight the growth and enhancements that have occurred. High frequency radar systems measure the speed and direction of ocean surface currents in near real time. Starting with about 30 radars in 2005, the network has grown to over 130 radars with 33 participating organizations and approximately ten million radial files sent via the network. A key component of the network has been the data ingest, processing and distribution system that is the core of the national HF radar data servers. Due to the scalability that was designed into it, this IOOS HF radar data management system has kept pace with the network growth and continues to have high reliability. We will show how the gridded vector velocity data have repeatedly proven their value in a number of operational applications including offshore search and rescue, oil spill response and water quality monitoring.

The surface current observations made by HF radar systems are increasingly being relied on to support decision-making by coastal ocean users and managers. Thus, the need for high quality data with defined error characteristics has never been higher. Building on previous efforts, this paper examines the use of ‘radial metrics’, the ancillary output of the direction finding algorithm used by the SeaSonde radar system, to improve both accuracy and error characterization. The radial metrics provide non-velocity based parameters that can be used to eliminate low-quality data and or weight the contribution of individual returns on the resulting spatially averaged radial velocity. While their effects on the data are different, both thresholding and weighted averaging based on the metrics are shown here to significantly increase the accuracy and reduce the error of the resulting velocity estimates. Thus, we suggest that operators should take advantage of these advancements to improve the accuracy of existing systems.

Aeronautical engineering design projects involving rigid wingsail vehicles are described. Wingsail technology is appropriate for study by undergraduate aeronautical engineering students because it encompasses a range of topics that are already treated within the curriculum. Aeronautical engineering programs must prepare graduates to have knowledge of aerodynamics, materials, structures, propulsion, flight mechanics, and stability and control. The projects described in this paper are arranged to demonstrate how they meet many of the student outcomes required for aeronautical engineering program accreditation.

This paper presents a new method to measure the near-surface currents' vertical shear by marine X-band radar (MR). The data used here were acquired from R/V Roger Revelle during the Impact of Typhoons on the Ocean in the Pacific (ITOP) field campaign in 2010. Existing techniques use MR surface wave signatures to retrieve a single near-surface current vector per analysis period. In essence, this is done by measuring the phase velocity of a wave on a current, which is then compared with the known still-water linear dispersion relationship. The resulting current corresponds to a depth-weighted average over the near-surface ocean layer. We introduce a new method that yields multiple estimates as a function of ocean wavenumber. The “effective” depth of the radar current measurement increases with the length of the ocean wave it was derived from. Our wavenumber-dependent near-surface currents thus provide information on vertical current shear. This method is analogous to an approach that has already proven successful for multi-frequency high-frequency (HF) radars. Here, we present first results which are put into the context of shipboard wind, surface wave, and background current measurements.

The collection and processing of X-Band radar backscatter in the frequency-wavenumber domain holds promise for extracting information about ocean surface currents and vertical shear. The ability to sense this information remotely has potentially significant impacts on scientific, navigational, and military operations, especially in areas of energetic currents. We present results from an experiment conducted in a shallow, tidally forced river inlet. First, X-Band observations of wave dynamics in the highly energetic region of the Columbia River Inlet (OR, USA) are presented. Second, a bulk current retrieval technique is discussed. Finally, the presence of vertical current shear is shown to affect X-Band observations in the wavenumber dependence of current-induced Doppler shifts.

High resolution spatial and temporal observations are essential in determining mechanisms driving dynamic ocean processes. Mobile oceanographic sensors are often used to observe these processes at spatial resolutions unattainable by cast-based techniques. By undulating the sensor path (seesaw pattern), ocean parameters (e.g., velocity, salinity, colored dissolved organic matter (CDOM)) are profiled synoptically and utilized to characterize the process of interest. We present the methods employed to estimate velocity fields observed by a Doppler Velocity Log (DVL) deployed on an Autonomous Underwater Vehicle (AUV) during two field campaigns at New River, North Carolina, and Huntington Beach, California. In addition, we discuss the utilization of synoptic observations to characterize (1) the mixing region of the New River Inlet discharge during maximum ebb tide and (2) the nearshore discharge region of a wastewater outfall. The AUVs sampling resolution, adaptive sampling capabilities, and suite of instruments were key in determining the mechanisms of these processes.

This paper will primarily focus on the value of high-resolution wave measurements and high-frequency (HF) radar–derived surface currents on maritime operations, and the contributions of the Coastal Data Information Program (CDIP) and the Coastal Observing Research and Development Center (CORDC) on those measurements, respectively. Use case scenarios are presented to demonstrate operational applications utilizing wave and surface current measurements. Both CDIP and CORDC are based at the Scripps Institution of Oceanography and rely on multiple partnerships and collaborations. CDIP, primarily funded by the United States Army Corps of Engineers, manages and ingests data from over 60 coastal wave buoys, many of them at entries to ports and harbors, supporting near shore navigation. CORDC manages the data acquisition and near real-time processing of the U.S. High Frequency Radar network (HFRNet), a network that includes numerous participating organizations. These programs work in partnership with the U.S. Integrated Ocean Observing System (IOOS ® ). IOOS provides vital collaborations enabling tracking, predicting, managing, and adapting to changes in our ocean, coastal, and Great Lakes environment. Discussions continue with the commercial and recreational maritime community as to which types of observational products are needed in order to improve safety and efficiency. Both the wave and surface current data are available through web services and the IOOS regional organizations, such as the Southern California Coastal Ocean Observing system (SCCOOS).

In order to protect the diverse ecosystems of coastal California, a series of marine protected areas (MPAs) have been established. The ability of these MPAs to preserve and potentially enhance marine resources can only be assessed if these habitats are monitored through time. This study establishes a baseline for monitoring the spawning activity of fish in the MPAs adjacent to Scripps Institution of Oceanography (La Jolla, CA, USA) by sampling fish eggs from the plankton. Using vertical plankton net tows, 266 collections were made from the Scripps Pier between 23 August 2012 and 28 August 2014; a total of 21,269 eggs were obtained. Eggs were identified using DNA barcoding: the COI or 16S rRNA gene was amplified from individual eggs and sequenced. All eggs that were successfully sequenced could be identified from a database of molecular barcodes of California fish species, resulting in species-level identification of 13,249 eggs. Additionally, a surface transport model of coastal circulation driven by current maps from high frequency radar was used to construct probability maps that estimate spawning locations that gave rise to the collected eggs. These maps indicated that currents usually come from the north but water parcels tend to be retained within the MPA; eggs sampled at the Scripps Pier have a high probability of having been spawned within the MPA. The surface transport model also suggests that although larvae have a high probability of being retained within the MPA, there is also significant spillover into nearby areas outside the MPA. This study provides an important baseline for addressing the extent to which spawning patterns of coastal California species may be affected by future changes in the ocean environment.

The maneuverability of autonomous underwater vehicles (AUVs) equipped with hull-mounted arrays provides the opportunity to actively modify received acoustic fields to optimize extraction of information. This paper uses ocean acoustic data collected by an AUV-mounted two-dimensional hydrophone array, with overall dimension one-tenth wavelength at 200-500 Hz, to demonstrate aspects of this control through vehicle motion. Source localization is performed using Doppler shifts measured at a set of receiver velocities by both single elements and a physical array. Results show that a source in the presence of a 10-dB higher-level interferer having exactly the same frequency content (as measured by a stationary receiver) is properly localized and that white-noise-constrained adaptive beamforming applied to the physical aperture data in combination with Doppler beamforming provides greater spatial resolution than physical-aperture-alone beamforming and significantly lower sidelobes than single element Doppler beamforming. A new broadband beamformer that adjusts for variations in vehicle velocity on a sample by sample basis is demonstrated with data collected during a high-acceleration maneuver. The importance of including the cost of energy expenditure in determining optimal vehicle motion is demonstrated through simulation, further illustrating how the vehicle characteristics are an integral part of the signal/array processing structure.

This paper describes the methods presently used to produce unaveraged radial velocity maps from radar voltage cross spectra measured by a SeaSonde, including a discussion of the multiple signal classification (MUSIC) algorithm as it is applied to SeaSonde data and methods employed to alleviate difficulties associated with the use of measured antenna patterns. We also describe internal consistency checks including visual observation of the radial velocity map, consideration of the computed uncertainties and quantitative tests of radial velocities measured by two radars along the baseline between the systems. Baseline analysis is illustrated by application to two SeaSonde networks, with contrasting results that lead to a better understanding of SeaSonde output

The Rough Evaporation Duct (RED) experiment was performed off of the Hawaiian Island of Oahu from late August to mid-September 2001 to test the hypothesis that a rough sea surface modifies the evaporation duct. Two land sites were instrumented, one with microwave receivers and the other with an infrared receiver. Two bouys were deployed, a small boat was instrumented and two aircrafts flew various tracks to sense both sea and atmospheric conditions. It was observed that waves do modify the scalars within the air-sea surface layer. There was a lack of agreement of the scalar profile constants and those typically observed over land. Furthermore, evidence was obtained indicating that the Monin-Obukhov similarity theory, combined with high-quality meteorological measurements, can be used by propagation models to accurately predict microwave signal levels.

Breaking waves at the ocean's surface inject bubbles and turbulence into the water column. During periods of rough weather the scales of wave breaking will increase with increasing sea states and result in mixing of the surface waters and the turbulent transport of bubbles to depth. Depending on their concentrations and size distribution, the entrained bubbles can significantly change the optical properties of water, introducing potentially significant errors in retrieval of remotely sensed hyperspectral data products. In this paper, the effects of bubbles on optical scattering in the upper ocean are investigated through optical scattering calculations based on field measurements of bubble populations. The field measurements were obtained offshore Point Conception, California, in June 1997, using an acoustical technique which measured the bubble size distribution at 2 Hz from a surface buoy designed to follow the longer waves. The effects of the bubbles on the bulk optical scattering and backscattering coefficients, b and bb, respectively, are determined by using the acoustically measured size distributions, and size-dependent scattering efficiencies based on Mie scattering calculations. Time series of the bubble distributions measured in rough conditions (wind speed, U10 = 15 m/s, significant wave height, H1/3 = 3.2 m) suggest that the bubble contribution to light scattering is highly variable near the ocean surface, with values spanning roughly 5 decades over time periods of O(10) minutes. Bubble size distributions measured at a 0.7-m depth indicate that the optical effects of the bubbles on bb, and hence the remote sensing reflectance, will be significant at bubble void fractions above 10−6 and that the bubble contribution to total bb will exceed values of 10−2 m−1 inside bubble clouds.

The development of a broadband sound velocimeter that allows the simultaneous measurement of sound speed and attenuation over a wide range of frequencies is described. The velocimeter measures the attenuation and dispersion of a broadband acoustic pulse over frequencies ranging from 4 to 100 kHz across a fixed pathlength using a two-transducer system. The resulting data are inverted to arrive at bubble size distributions over bubble radii in the range 30‐800 mm. The instrument was tested in the large wave channel at the Hydraulics Laboratory of Scripps Institution of Oceanography. The channel can generate breaking waves of O(1 m) height using a hydraulically driven wave generator, giving bubble size distributions similar to those found in the field. The presence of the bubbles significantly changes the acoustical properties of the water. Internal consistency checks of the acoustic data and measurements of bubbles using an independent optical sizing technique support the accuracy of the acoustic system in measuring bubble size distributions. A field test of the system was performed off Scripps Pier in water of approximately 6-m depth. Observations demonstrate that bubble transport events with significant temporal and spatial variability are associated with rip currents and introduce significant vertical gradients in the acoustical properties of the water. The performance of the system in the field was found to be comparable to that found in the laboratory.

Wave breaking at the surface of the ocean entrains bubbles, significantly modifying the phase speed and attenuation of acoustic waves propagating through the resulting two-phase medium. An autonomous buoy system was developed that directly measures sound speed at 3.33, 5, and 10 kHz at seven depths ranging from 0.7 to 7 m through the use of a travel-time technique. Simultaneous measurements at each depth are obtained at a 2-Hz rate, allowing observation of the unsteady sound-speed field from individual bubble injection events, as well as the calculation of mean sound speeds. The travel-time technique allows a direct measurement of the sound speed, eliminating the uncertainties common with inferring sound speeds from bubble population data. The sound speed buoy was deployed in the North Atlantic during the winter of 1993–94 as part of the Acoustic Surface Reverberation Experiment (ASREX). Our aim was to characterize the highly variable near-surface sound-speed field under varying environmental conditions. ...

Principal research goals are to characterize the physics and fluid dynamics which exist at the Mouth of the Columbia River. Coming from the relatively benign environment of the New River Inlet (RIVET I), this DRI will provide much stronger flows, larger waves, and more dynamic signals for our remote sensing instruments to observe. A by-product of the observational program will be the development of sensing capabilities that may have Naval interest.

Our long term goals are to improve our ability to characterize and forecast ocean surface waves. Most all at-sea Naval operations depend on knowledge of the conditions of the sea surface in one form or another. This includes the forecasting of EM/RF propagation near the ocean-surface as sea surface roughness has a profound influence on transmission characteristics. The world s oceans are data poor with respect to in-situ wave observations that are suitable for assimilation into, and verification with, operational global wave models (WAM, WaveWatch III). Data that is routinely available to models are satellite-based and have their own set of challenges. For example, remote sensing of the surface wave field using techniques such as radar altimetry or synthetic aperture radar (SAR) provides some measure of bulk wave properties, such as significant wave height or mean wave direction, and can be used to adjust global wave models. However, the techniques suffer from several issues: poor spectral resolution (e.g., differentiating swell vs. seas); the estimation of wave height is dependent on semiempirical models or modulation transfer functions that have inherent errors: and the satellite repeat time over a particular region of the ocean is too long to reliably improve. Global wave models suffer additional challenges as the wind forcing terms are derived from models (COAMPS, NOGAPS) that have their own set of data sparse challenges, and wave-current interactions are typically neglected due to poor measurements of ocean surface currents.

Full scale measurements of wave impact loads and their statistics in real sea states are desirable for validation of numerical simulations and for application to marine engineering design problems. Measuring and/or estimating wave forces on flat plates are especially problematic due to statistics of large waves in a given sea state, the intermittent statistics of wave breaking, the sensitivity of the loading relative to the phase of the incoming wave and scaling issues when translating from model scale data to full-scale. To increase our understanding of wave hydrodynamic pressures on a flat plate, an instrumented plate was deployed from the Scripps Institution of Oceanography's research pier. The instrumented plate is exposed to a wide range of wave conditions with a significant wave height (Hs) ranging from 3-4 m in the winter and Hs in the 1-2 m range in the summer. The instrumented flat plate is composed of three discrete modules each containing 6 pressure gages. Data are being collected over an extended period, nominally 12 months, to characterize extreme value distributions due to wave impact loading. Preliminary analysis of the data is presented and discussed.

A monitoring mission to map and characterize the Point Loma Ocean Outfall (PLOO) wastewater plume using an Autonomous Underwater Vehicle (AUV) was performed on 3 March 2011. The mobility of an AUV provides a significant advantage in surveying discharge plumes over traditional cast-based methods, and when combined with optical and oceanographic sensors, provides a capability for both detecting plumes and assessing their mixing in the near and far-fields. Unique to this study is the measurement of Colored Dissolved Organic Matter (CDOM) in the discharge plume and its application for quantitative estimates of the plume's dilution. AUV mission planning methodologies for discharge plume sampling, plume characterization using onboard optical sensors, and comparison of observational data to model results are presented. The results suggest that even under variable oceanic conditions, properly planned missions for AUVs equipped with an optical CDOM sensor in addition to traditional oceanographic sensors, can accurately characterize and track ocean outfall plumes at higher resolutions than cast-based techniques.

A non-membrane, micro-hole, potentiostatic oxygen sensor was designed and tested for use on an oceanic CTD. The sensor consists of three electrodes: a carbon-fiber cathode, a Ag/ AgC1 reference and a platinum anode; all are mounted in a plexiglass flow duct. The carbon-fiber cathode is a bundle of 1000 carbon fibers recessed in epoxy and electroplated with platinum. The sensor calibrates to oxygen concentration (02), not partial pressure. The effect of temperature on sensor output can be modelled with an activation energy term. Pressure decreases current output of these sensors 5% over 5000 dbar. Ten calibration casts were performed as part of the Hawaii Ocean Time Series (HOTS) sampling program in the Pacific Ocean north of Oahu, Hawaii. Vertical profiles of O2 were calibrated using 18–23 Winkler determinations from each cast. The coefficient of determination (r2) for the calibrations ranged from 0.9979 to 1.0000. The standard deviation of the unexplained error between predicted O2 and Winkler OZ ranged from 0.49 to 3.6 μM, with a mean value of 1.3 μM.

This paper reports on our experiences developing methods to survey an ocean outfall discharge plume using an Autonomous Underwater Vehicle (AUV). . The mobility of an AUV provides a significant advantage in surveying discharge plumes over traditional boat-based methods, and when combined with optical and oceanographic sensors, provides a capability for both detecting plumes and assessing their mixing in both the near and far-fields. Unique to this study is the optical sensing of of the presence of Colored Dissolved Organic Matter (CDOM) in the discharge plume for quantitatively assessing the dilution ratio of the plume water. This capability is demonstrated for two Publicly Operated Treatment Works (POTWs) located offshore San Diego, California that have significantly different environmental settings and operating parameters. The first is the South Bay Ocean Outfall (SBOO) operated by the International Boundary Water Commission (IBWC) whose discharge is located in approximately 30m deep water at a flow rate of 28 million gallons per day (MGD). The second discharge is the Point Loma Ocean Outfall (PLOO) which discharges at approximately 90m with a nominal volume flow rate of 250 MGD. The methodologies for planning the AUV missions to sample the discharge plume, characterizing the plume using the signals measured by the onboard oceanographic and optical sensors, and use of those data in predictive models is outline. The results suggest that even in variable oceanic conditions, properly planned missions for AUVs equipped with appropriate sensors can accurately characterize and track ocean outfall plumes with high spatial resolution more effectively than traditional methods.

In this paper we evaluate different methods to retrieve wind information from marine radar data. In contrast to traditional in-situ sensors, marine radar wind data cover a large area and therefore are much less susceptible to air flow distortion by the platform. Unlike previous studies that have been limited to fixed-platform data, this study includes data from a quasi-stationary and moving platform. Images collected with a standard marine HH-polarized X-band radar operating at grazing incidence angle exhibit a single intensity peak in the upwind direction. Marine radar images that are averaged over about 1 min may also show wind streaks, which are usually well-aligned with the mean surface wind direction. Here, we use both phenomena to retrieve wind directional information and compare results to determine the best approach under the given conditions. To retrieve wind speeds, an empirical model function which relates average backscatter intensity to wind speed is developed.

Full scale measurements of wave impact loads and their statistics in real sea states are desirable for validation of numerical simulations and for application to marine engineering design problems. Measuring and/or estimating wave forces on flat plates are especially problematic due to statistics of large waves in a given sea state, the intermittent statistics of wave breaking, the sensitivity of the loading relative to the phase of the incoming wave and scaling issues when translating from model scale data to full-scale. To increase our understanding of wave hydrodynamic pressures on a flat plate, an instrumented plate was deployed from the Scripps Institution of Oceanography’s research pier. The instrumented plate is exposed to a wide range of wave conditions with Hs ranging from 3–4 m in the winter and with Hs in the 1–2 m range in the summer. The instrumented flat plate is composed of three discrete modules containing 6 pressure gages. Data are being collected over a extended period, nominally 12 months, to characterize extreme value distributions due to wave impact loading.Copyright © 2012 by ASME