Mark Otero

Interpretation of Coastal HF Radar–Derived Surface Currents with High-Resolution Drifter Data

Abstract 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 wi...

Mapping ocean outfall plumes and their mixing using autonomous underwater vehicles

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.

Ocean outfall plume characterization using an Autonomous Underwater Vehicle.

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 plumes 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.

National IOOS high frequency radar search and rescue project

The U.S. Integrated Ocean Observing System (IOOS®) partners have begun an effort to extend the use of high frequency (HF) radar for U.S. Coast Guard (USCG) search and rescue operations to all U.S. coastal areas with HF radar coverage. This project builds on the success of an IOOS and USCG-supported regional USCG search and rescue product created by Applied Science Associates (ASA), Rutgers University and University of Connecticut for the mid-Atlantic region. We describe the regional product and the expanded national products two main components: optimally-interpolated velocity fields and a predicted velocity field.

DISPERSED OIL TRANSPORT MODELING CALIBRATED BY FIELD-COLLECTED DATA MEASURING FLUORESCEIN DYE DISPERSION

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. Fieldcollected 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 fluorescencedepth 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.

Chapter 10 – How High-Resolution Wave Observations and HF Radar–Derived Surface Currents are Critical to Decision-Making for Maritime Operations

Abstract 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).

Observations of Shelf Exchange and High‐Frequency Variability in an Alaskan Fjord

High-frequency observations collected over 3 years are used to describe upper-ocean variability in Behm Canal, a nonglacial fjord in Southeast Alaska. The fjord is sheltered by surrounding topography and connected to the outer continental shelf by a 400-m-deep strait. Summer conditions are characterized by strong near-surface stratification, a sea breeze wind regime, and tidally dominated flows. In nonsummer months, baroclinic subinertial flows exceeding 0.5 m/s dominate the velocity record. The flow events represent a wind-driven response to low-pressure systems that impact the coast as they propagate across the Gulf of Alaska. The observations suggest that the storm systems generate downwelling events that propagate into the fjord with a mode-one-like vertical structure in the upper 60 m. Following the initial up-fjord current pulse lasting approximately a day, a down-fjord flow occurs lasting several days, the duration of the downwelling anomaly. These subinertial downwelling events likely are the dominant mechanism of shelf-fjord exchange, with estimated fjord-flushing times of 50 days. The downwelling events are accompanied by enhanced near-inertial shear, which exhibits downward energy propagation. Evidence for enhanced energy near the maximum buoyancy frequency in the thermocline suggests high-frequency internal wave trapping, with the primary energy source in the semidiurnal band associated with tidal and wind forcing. The observations highlight the importance of shelf-fjord coupling through meteorological forcing and the existence of internal wave energy at a range of frequencies, which have implications for mixing and transport within the fjord.

The Integrated Ocean Observing System HF radar network

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.

FIELD MEASUREMENTS OF FLUORESCEIN DYE DISPERSION TO INFORM DISPERSED-OIL PLUME SAMPLING AND PROVIDE INPUT FOR OIL-TRANSPORT MODELING1

ABSTRACT 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,...