Publications

Export 44 results:
Sort by: Author Title Type [ Year  (Desc)]
2018
Cimino, M, Colin P, Schramek T, Lindfield S, Domeier M, Terrill E.  2018.  Oceanographic, acoustic, and remote approaches reveal the spatio-temporal dynamics of blackfin snapper at an aggregation site in Palau. Marine Ecology Progress Series. 601:185-201.   10.3354/meps12651   AbstractWebsite

Forming spawning aggregations is a critical life-history activity for fish, but it is unclear what physical conditions are associated with fish behavior at specific sites. The habitat, movements and distribution of blackfin snapper Lutjanus fulvus at a monthly aggregation site in Palau were studied using a combination of instruments and approaches, including active/passive acoustics, time-lapse cameras, an autonomous underwater vehicle, current profilers, and high resolution bathymetry. We found that L. fulvus predictably form a large pre-spawning aggregation of an estimated 15 000 fish in a small zone (10s of m) in a tidally forced channel. The aggregation spans 125 m along the northern channel wall, with the highest densities of fish from 9 to 13 m and <15 m from the wall where current velocities are <0.25 m s(-1). The aggregation occurs within an indent in the channel wall where an abrupt change in bathymetry creates a visible eddy-like feature during outgoing tides. The aggregation forms year-round, for 6 d each moon cycle, starting 1 d before the full moon to 4 d after. During the study, 4 tagged fish returned to the site for 6 consecutive lunar cycles; however, residency times within aggregation periods was similar to 1.5 d on average. Densely aggregated fish were present during the day, but migration patterns of tagged fish revealed regular evening migrations to and from the channel mouth, consistently at the highest tide of the day, a behavior assumed for spawning. These observations reveal some physical processes and biological patterns surrounding the formation and function of fish aggregations.

Wang, Q, Alappppattu DP, Billingsley S, Blomquist B, Burkholder RJ, Christman AJ, Creegan ED, de Paolo T, Eleuterio DP, Fernando HJS, Franklin KB, Grachev AA, Haack T, Hanley TR, Hocut CM, Holt TR, Horgan K, Jonsssson HH, Hale RA, Kalogiros JA, Khelif D, Leo LS, Lind RJ, Lozovatsky I, Planella-Morato J, Mukherjee S, Nussss WA, Pozderac J, Rogers LT, Savelyev I, Savidge DK, Shearman RK, Shen L, Terrill E, Ulate AM, Wendt RT, Wissss R, Woodsds RK, Xu LY, Yamaguchi RT, Yardim C.  2018.  CASPER: Coupled Air-Sea Processes and Electromagnetic Ducting Research. Bulletin of the American Meteorological Society. 99:1449-1471.   10.1175/bams-d-16-0046.1   AbstractWebsite

The objective of CASPER is to improve our capability to characterize the propagation of radio frequency (RF) signals through the marine atmosphere with coordinated efforts in data collection, data analyses, and modeling of the air-sea interaction processes, refractive environment, and RF propagation.

Pozderac, J, Johnson J, Yardim C, Merrill C, de Paolo T, Terrill E, Ryan F, Frederickson P.  2018.  X-band beacon-receiver array evaporation duct height estimation. Ieee Transactions on Antennas and Propagation. 66:2545-2556.   10.1109/tap.2018.2814060   AbstractWebsite

Recent experimental campaigns provided the opportunity to measure radio wave propagation and atmospheric conditions with the X-band beacon-receiver (XBBR) array system. The system consists of vertical arrays of transmitters and receivers for measuring the X-band propagation. Measurements near the sea surface can be used to obtain information regarding the refractivity profile of the lower atmosphere. Since ducted propagation acts as a leaky waveguide, the vertical array elements in various transmit and receive height combinations effectively observe differing combinations of the modal components propagating in the duct, the use of multiple combinations improves the estimation of duct properties. The aforementioned measurement campaigns occurred near the coast of southern California; the SoCal 2013 experiment and the Scripps Pier Campaign. During both campaigns, the propagation loss recorded at each of the receivers from each of the transmitters, standardized by the total received power, was compared to variable terrain radio parabolic equation model predictions in order to estimate the evaporation duct height (EDH). Point meteorological data were recorded and used with the Navy Atmospheric Vertical Surface Layer Model to obtain in situ measurements of the EDH. Comparisons show strong correlation between EDH values inferred from XBBR measurements and meteorological information.

Sinnett, G, Feddersen F, Lucas AJ, Pawlak G, Terrill E.  2018.  Observations of nonlinear internal wave run-up to the surfzone. Journal of Physical Oceanography. 48:531-554.   10.1175/jpo-d-17-0210.1   AbstractWebsite

The cross-shore evolution of nonlinear internal waves (NLIWs) from 8-m depth to shore was observed by a dense thermistor array and ADCP. Isotherm oscillations spanned much of the water column at a variety of periods. At times, NLIWs propagated into the surfzone, decreasing temperature by approximate to 1 degrees C in 5 min. When stratification was strong, temperature variability was strong and coherent from 18- to 6-m depth at semi-diurnal and harmonic periods. When stratification weakened, temperature variability decreased and was incoherent between 18- and 6-m depth at all frequencies. At 8-m depth, onshore coherently propagating NLIW events had associated rapid temperature drops (Delta T) up to 1.7 degrees C, front velocity between 1.4 and 7.4 cm s(-1), and incidence angles between -5 degrees and 23 degrees. Front position, Delta T, and two-layer equivalent height z(IW) of four events were tracked upslope until propagation terminated. Front position was quadratic in time, and normalized Delta T and z(IW) both decreased, collapsing as a linearly decaying function of normalized cross-shore distance. Front speed and deceleration are consistent with two-layer upslope gravity current scalings. During NLIW rundown, near-surface cooling and near-bottom warming at 8-m depth coincide with a critical gradient Richardson number, indicating shear-driven mixing.

2017
Terrill, E, Moline M, Scannon P, Gallimore E, Schramek T, Nager A, Hess R, Cimino M, Colin P, Pietruszka AJ, Anderson M.  2017.  Project Recover: Extending the Applications of Unmanned Platforms and Autonomy to Support Underwater MIA Searches. Oceanography. 30:150-159.   10.5670/oceanog.2017.237   Abstract

An estimated 70,000 US servicemen remain missing from World War II, with approximately two-thirds of those losses from the Pacific Theater. Many of the missing were lost in the maritime environment. Historically, attempts to locate remains in this environment were deemed too difficult, as water-based searches can be labor intensive, logistically cumbersome, and technically difficult to execute. Ironically, despite these challenges, underwater sites are often better preserved than terrestrial sites, as they are less subject to human disturbance and negative environmental conditions. Technological advances in unmanned platforms, autonomy, sensors, underwater navigation and communications, forensic oceanography, search methodologies, and data processing are now enabling the discovery of crash sites associated with losses and stimulating new research that combines oceanography, unmanned systems, historical research, and forensic archaeological methods. Project Recover began as a two-year program funded by the US Office of Naval Research, designed to serve as a testbed for unmanned technologies and public outreach. Now, through public and private sponsorship, it has grown into providing a global survey capability.

Terrill, EJ, Moline MA, Scannon PJ, Gallimore E, Schramek T, Nager A, Hess R, Cimino M, Colin PL, Pietruszka A, Anderson MR.  2017.  Extending the Applications of Unmanned Platforms and Autonomy to Support Underwater MIA Searches. Oceanography. 30:150-159.   10.5670/oceanog.2017.237   AbstractWebsite

An estimated 70,000 US servicemen remain missing from World War II, with approximately two-thirds of those losses from the Pacific Theater. Many of the missing were lost in the maritime environment. Historically, attempts to locate remains in this environment were deemed too difficult, as water-based searches can be labor intensive, logistically cumbersome, and technically difficult to execute. Ironically, despite these challenges, underwater sites are often better preserved than terrestrial sites, as they are less subject to human disturbance and negative environmental conditions. Technological advances in unmanned platforms, autonomy, sensors, underwater navigation and communications, forensic oceanography, search methodologies, and data processing are now enabling the discovery of crash sites associated with losses and stimulating new research that combines oceanography, unmanned systems, historical research, and forensic archaeological methods. Project Recover began as a two-year program funded by the US Office of Naval Research, designed to serve as a testbed for unmanned technologies and public outreach. Now, through public and private sponsorship, it has grown into providing a global survey capability.

Centurioni, LR, Hormann V, Talley LD, Arzeno I, Beal L, Caruso M, Conry P, Echols R, Fernando HJS, Giddings SN, Gordon A, Graber H, Harcourt RR, Jayne SR, Jensen TG, Lee CM, Lermusiaux PFJ, L'Hegaret P, Lucas AJ, Mahadevan A, McClean JL, Pawlak G, Rainville L, Riser SC, Seo H, Shcherbina AY, Skyllingstad E, Sprintall J, Subrahmanyam B, Terrill E, Todd RE, Trott C, Ulloa HN, Wang H.  2017.  Northern Arabian Sea Circulation Autonomous Research (NASCar): A research initiative based on autonomous sensors. Oceanography. 30:74-87.   10.5670/oceanog.2017.224   AbstractWebsite

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.

Campana, J, Terrill EJ, de Paolo T.  2017.  A new inversion method to obtain upper-ocean current-depth profiles using X-band observations of deep-water waves. Journal of Atmospheric and Oceanic Technology. 34:957-970.   10.1175/jtech-d-16-0120.1   AbstractWebsite

A new method for estimating current-depth profiles from observations of wavenumber-dependent Doppler shifts of the overlying ocean wave field is presented. Consecutive scans of marine X-band backscatter provide wave field measurements in the time-space domain that transform into the directional wavenumber-frequency domain via a 3D fast Fourier transform (FFT). Subtracting the linear dispersion shell yields Doppler shift observations in the form of (k(x), k(y), Delta omega) triplets. A constrained linear regression technique is used to extract the wavenumber-dependent effective velocities, which represent a weighted depth average of the Eulerian currents (Stewart and Joy). This new method estimates these Eulerian currents from the effective velocities via the inversion of the integral relationship, which was first derived by Stewart and Joy. To test the effectiveness of the method, the inverted current profiles are compared to concurrent ADCP measurements. The inversion method is found to successfully predict current behavior, with a depth-average root-mean-square (RMS) error less than 0.1 m s(-1) for wind speeds greater than 5 m s(-1) and a broad wave spectrum. The ability of the inversion process to capture the vertical structure of the currents is assessed using a time-average RMS error during these favorable conditions. The time-averaged RMS error is found to be less than 0.1 m s(-1) for depths shallower than 20 m, approximately twice the depth of existing methods of estimating current shear from wave field measurements.

Pawlak, G, Moline MA, Terrill EJ, Colin PL.  2017.  Hydrodynamic influences on acoustical and optical backscatter in a fringing reef environment. Journal of Geophysical Research-Oceans. 122:322-335.   10.1002/2016jc012497   AbstractWebsite

Observations of hydrodynamics along with optical and acoustical water characteristics in a tropical fringing reef environment reveal a distinct signature associated with flow characteristics and tidal conditions. Flow conditions are dominated by tidal forcing with an offshore component from the reef flat during ebb. Measurements span variable wave conditions enabling identification of wave effects on optical and acoustical water properties. High-frequency acoustic backscatter (6 MHz) is strongly correlated with tidal forcing increasing with offshore directed flow and modulated by wave height, indicating dominant hydrodynamic influence. Backscatter at 300 and 1200 kHz is predominantly diurnal suggesting a biological component. Optical backscatter is closely correlated with high-frequency acoustic backscatter across the range of study conditions. Acoustic backscatter frequency dependence is used along with changes in optical properties to interpret particle-size variations. Changes across wave heights suggest shifts in particle-size distributions with increases in relative concentrations of smaller particles for larger wave conditions. Establishing a connection between the physical processes of a fringing tropical reef and the resulting acoustical and optical signals allows for interpretation and forecasting of the remote sensing response of these phenomena over larger scales.

2016
Campana, J, Terrill EJ, de Paolo T.  2016.  The development of an inversion technique to extract vertical current profiles from X-band radar observations. Journal of Atmospheric and Oceanic Technology. 33:2015-2028.   10.1175/jtech-d-15-0145.1   AbstractWebsite

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 radm 21. This agreement when observations successfully capture the broadband wavefield suggests the X-band backscatter is a viable means of remotely estimating current shear.

2015
Harada, AE, Lindgren EA, Hermsmeier MC, Rogowski PA, Terrill E, Burton RS.  2015.  Monitoring spawning activity in a Southern California marine protected area using molecular identification of fish eggs. Plos One. 10   10.1371/journal.pone.0134647   AbstractWebsite

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 spill-over 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.

Terrill, EJ, Taylor GRL.  2015.  Entrainment of air at the transoms of full-scale surface ships. Journal of Ship Research. 59:49-65.   10.5957/josr.59.1.140014   AbstractWebsite

We 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 RN Revel le and 2004 from RN 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 CFD codes and initialize far-field, bubbly wake CFD models.

Rogowski, PA, Terrill E, Schiff K, Kim SY.  2015.  An assessment of the transport of southern California stormwater ocean discharges. Marine Pollution Bulletin. 90:135-142.   10.1016/j.marpolbul.2014.11.004   AbstractWebsite

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. (C) 2014 Elsevier Ltd. All rights reserved.

2014
Rogowski, P, Terrill E, Chen JL.  2014.  Observations of the frontal region of a buoyant river plume using an autonomous underwater vehicle. Journal of Geophysical Research-Oceans. 119:7549-7567.   10.1002/2014jc010392   AbstractWebsite

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. Key Points Wind-driven processes in the nearshore can enhance mixing of discharge plumes Synoptic observations are key to understanding the structure of dynamic plume discharges Choosing appropriate hydrodynamic model parameters can be accomplished using AUV data

Lund, B, Collins CO, Graber HC, Terrill E, Herbers THC.  2014.  Marine radar ocean wave retrieval's dependency on range and azimuth. Ocean Dynamics. 64:999-1018.   10.1007/s10236-014-0725-6   AbstractWebsite

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.

2013
Rogowski, P, Terrill E, Otero M, Hazard L, Middleton W.  2013.  Ocean outfall plume characterization using an autonomous underwater vehicle. Water Science and Technology. 67:925-933.   10.2166/wst.2012.635   AbstractWebsite

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.

2012
Rogowski, P, Terrill E, Otero M, Hazard L, Middleton W.  2012.  Mapping ocean outfall plumes and their mixing using autonomous underwater vehicles. Journal of Geophysical Research-Oceans. 117   10.1029/2011jc007804   AbstractWebsite

This paper reports on developing autonomous underwater vehicle (AUV) survey methods for ocean outfall discharge plumes and new insights gained on plume mixing. Unique to the study is mapping the discharge mixing using colored dissolved organic matter (CDOM) calibrated for effluent dilution. AUV mission planning methodologies for discharge plume sampling, plume characterization using onboard temperature, salinity and optical sensors, and comparison of observational data to model results are presented for the Point Loma Ocean Outfall offshore of San Diego, CA. The results are expected to be applicable to the general theme of mixing of submerged buoyant discharges. In the near-field, the plume is found to mix to a height consistent with the predictions of buoyant jet engineering models. At the far-field, the fine spatial scales of the plume resolved by the vehicle suggests that shear instabilities caused by internal waves can enhance plume mixing and elevate the discharge plume above the predicted equilibrium rise height. These results suggest that even under variable oceanic conditions, properly planned missions for AUVs equipped with an optical CDOM sensor in addition to traditional physical oceanographic sensors, can accurately map the mixing of ocean outfall plumes at resolutions not possible with traditional boat-based techniques. Variations of oceanic conditions are found to influence the mixing and fate of the plume at time scales generally not considered in the design of these discharges.

2011
Kim, SY, Terrill EJ, Cornuelle BD, Jones B, Washburn L, Moline MA, Paduan JD, Garfield N, Largier JL, Crawford G, Kosro PM.  2011.  Mapping the U.S. West Coast surface circulation: A multiyear analysis of high-frequency radar observations. Journal of Geophysical Research-Oceans. 116   10.1029/2010jc006669   AbstractWebsite

The nearly completed U. S. West Coast (USWC) high-frequency radar (HFR) network provides an unprecedented capability to monitor and understand coastal ocean dynamics and phenomenology through hourly surface current measurements at up to 1 km resolution. The dynamics of the surface currents off the USWC are governed by tides, winds, Coriolis force, low-frequency pressure gradients (less than 0.4 cycles per day (cpd)), and nonlinear interactions of those forces. Alongshore surface currents show poleward propagating signals with phase speeds of O(10) and O(100 to 300) km day(-1) and time scales of 2 to 3 weeks. The signals with slow phase speed are only observed in southern California. It is hypothesized that they are scattered and reflected by shoreline curvature and bathymetry change and do not penetrate north of Point Conception. The seasonal transition of alongshore surface circulation forced by upwelling-favorable winds and their relaxation is captured in fine detail. Submesoscale eddies, identified using flow geometry, have Rossby numbers of 0.1 to 3, diameters in the range of 10 to 60 km, and persistence for 2 to 12 days. The HFR surface currents resolve coastal surface ocean variability continuously across scales from submesoscale to mesoscale (O(1) km to O(1000) km). Their spectra decay with k(-2) at high wave number (less than 100 km) in agreement with theoretical submesoscale spectra below the observational limits of present-day satellite altimeters.

2010
Harlan, J, Terrill E, Hazard L, Keen C, Barrick D, Whelan C, Howden S, Kohut J.  2010.  The Integrated Ocean Observing System High-Frequency Radar Network: Status and Local, Regional, and National Applications. Marine Technology Society Journal. 44:122-132. AbstractWebsite

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 1 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.

Kim, SY, Cornuelle BD, Terrill EJ.  2010.  Decomposing observations of high-frequency radar-derived surface currents by their forcing mechanisms: Decomposition techniques and spatial structures of decomposed surface currents. Journal of Geophysical Research-Oceans. 115   10.1029/2010jc006222   AbstractWebsite

Surface current observations from a high-frequency radar network deployed in southern San Diego are decomposed according to their driving forces: pure tides and their neighboring off-band energy, local winds, and low frequency. Several superposed ocean responses are present as a result of the complicated bottom topography and relatively weak winds off southern San Diego, as opposed to coastal regions where circulation can be explained by a dominant forcing mechanism. This necessitates an application of a statistical decomposition approach. Surface currents coherent with pure tides are calculated using harmonic analysis. Locally wind-driven surface currents are estimated by regression of observed winds on observed surface currents. The dewinded and detided surface currents are filtered by weighted least-squares fitting assuming white noise and three colored signal bands: low-frequency band (less than 0.4 cycles per day) and near-tidal peaks at the diurnal (K-1) and semidiurnal (M-2) frequencies. The spatial and temporal variability of each part of the decomposed surface currents is investigated in terms of ocean response to the driving forces. In addition, the spatial correlations of individual components exhibit Gaussian and exponential shapes with varying decorrelation length scales.

Kim, SY, Cornuelle BD, Terrill EJ.  2010.  Decomposing observations of high-frequency radar-derived surface currents by their forcing mechanisms: Locally wind-driven surface currents. Journal of Geophysical Research-Oceans. 115   10.1029/2010jc006223   AbstractWebsite

The wind impulse response function and transfer function for high-frequency radar-derived surface currents off southern San Diego are calculated using several local wind observations. The spatial map of the transfer function reflects the influence of the coast on wind-current dynamics. Near the coast (within 20 km from the shoreline), the amplitudes of the transfer function at inertial and diurnal frequencies are reduced due to effects of coastline and bottom bathymetry. Meanwhile, the amplitude of low-frequency currents increases near the coast, which is attributed to the local geostrophic balance between cross-shore pressure gradients against the coast and currents. Locally wind-driven surface currents are estimated from the data-derived response function, and their power spectrum shows a strong diurnal peak superposed on a red spectrum, similar to the spectra of observed winds. Current magnitudes and veering angles to a quasi-steady wind are typically 2-5% of the wind speed and vary 50 degrees-90 degrees to the right of the wind, respectively. A wind skill map is introduced to present the fractional variance of surface currents explained by local winds as a verification tool for wind data quality and relevance. Moreover, the transfer functions in summer and winter are presented to examine the seasonal variation in ocean surface current response to the wind associated with stratification change.

2009
Hoteit, I, Cornuelle B, Kim SY, Forget G, Kohl A, Terrill E.  2009.  Assessing 4D-VAR for dynamical mapping of coastal high-frequency radar in San Diego. Dynamics of Atmospheres and Oceans. 48:175-197.   10.1016/j.dynatmoce.2008.11.005   AbstractWebsite

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. (C) 2008 Elsevier B.V. All rights reserved.

Kim, SY, Terrill EJ, Cornuelle BD.  2009.  Assessing Coastal Plumes in a Region of Multiple Discharges: The US-Mexico Border. Environmental Science & Technology. 43:7450-7457.   10.1021/es900775p   AbstractWebsite

The San Diego/Tijuana border region has several environmental challenges with regard to assessing water quality impacts resulting from local coastal ocean discharges for which transport is not hindered by political boundaries. While an understanding of the fate and transport of these discharged plumes has a broad audience, the spatial and temporal scales of the physical processes present numerous challenges in conducting assessment with any fidelity. To address these needs, a data-driven model of the transport of both shoreline and offshore discharges is developed and operated in a hindcast mode for a four-year period to analyze regional connectivity between the discharges and the receiving of waters and the coastline. The plume exposure hindcast model is driven by surface current data generated by a network of high-frequency radars. Observations provided by both boat-based CTD measurements and fixed oceanographic moorings are used with the Roberts-Snyder-Baumgartner model to predict the plume rise height. The surface transport model outputs are compared with shoreline samples of fecal indicator bacteria (FIB), and the skill of the model to assess low water quality is evaluated using receiver operating characteristic (ROC) analysis.

Kim, SY, Cornuelle BD, Terrill EJ.  2009.  Anisotropic Response of Surface Currents to the Wind in a Coastal Region. Journal of Physical Oceanography. 39:1512-1533.   10.1175/2009JPO4013.1   Abstract

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 degrees +/- 2 degrees 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 degrees +/- 4 degrees (71 degrees +/- 3 degrees) 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.

Piskozub, J, Stramski D, Terrill E, Melville WK.  2009.  Small-scale effects of underwater bubble clouds on ocean reflectance: 3-D modeling results. Optics Express. 17:11747-11752.   10.1364/OE.17.011747   AbstractWebsite

We examined the effect of individual bubble clouds on remote-sensing reflectance of the ocean with a 3-D Monte Carlo model of radiative transfer. The concentrations and size distribution of bubbles were defined based on acoustical measurements of bubbles in the surface ocean. The light scattering properties of bubbles for various void fractions were calculated using Mie scattering theory. We show how the spatial pattern, magnitude, and spectral behavior of remote-sensing reflectance produced by modeled bubble clouds change due to variations in their geometric and optical properties as well as the background optical properties of the ambient water. We also determined that for realistic sizes of bubble clouds, a plane-parallel horizontally homogeneous geometry (1-D radiative transfer model) is inadequate for modeling water-leaving radiance above the cloud. (C) 2009 Optical Society of America