50 research outputs found
Observing and Modeling the Pacific Ocean [Video]
Marine scientists incorporate a wide array of observations and models to understand the oceans, their dynamics, and the life they support. The development of new sensing technologies such as satellites, gliders, and robotic floats, as well as increasing public interest and funding for projects to investigate the oceanâs role in climate change, has transformed marine sciences into "big data" sciences. But the observational scientist still faces numerous obstacles in measuring ocean characteristics such as sea surface height, currents, temperature, salinity, water color, ocean chemistry, and undersea life: electromagnetic radiation does not readily penetrate its waters, which makes it harder to conduct observations and communicate with underwater instruments, and because oceans are full of life, so called "biofouling" is a challenge to observing, especially in the sun-lit layers near the surface. Nevertheless, new technologies such as robotic vehicles and new sensors are enabling observations throughout the ocean water column. These technologies, coupled with rapidly advancing ocean models, are revolutionizing our understanding of the marine biosphere.
Video available: https://vimeo.com/52739734
Direction finding and likelihood ratio detection for oceanographic HF radars
Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of the Atmospheric and Oceanic Technology 39(2), (2022): 223â235, https://doi.org/10.1175/JTECH-D-21-0110.1.Previous work with simulations of oceanographic high-frequency (HF) radars has identified possible improvements when using maximum likelihood estimation (MLE) for direction of arrival; however, methods for determining the number of emitters (here defined as spatially distinct patches of the ocean surface) have not realized these improvements. Here we describe and evaluate the use of the likelihood ratio (LR) for emitter detection, demonstrating its application to oceanographic HF radar data. The combined detectionâestimation methods MLE-LR are compared with multiple signal classification method (MUSIC) and MUSIC parameters for SeaSonde HF radars, along with a method developed for 8-channel systems known as MUSIC-Highest. Results show that the use of MLE-LR produces similar accuracy, in terms of the RMS difference and correlation coefficients squared, as previous methods. We demonstrate that improved accuracy can be obtained for both methods, at the cost of fewer velocity observations and decreased spatial coverage. For SeaSondes, accuracy improvements are obtained with less commonly used parameter sets. The MLE-LR is shown to be able to resolve simultaneous closely spaced emitters, which has the potential to improve observations obtained by HF radars operating in complex current environments.This work was supported by the National Science Foundation (NSF) under Grant OCE-1658475. Computing resources were provided by the UCSB Center for Scientific Computing through an NSF MRSEC (DMR-1720256) and NSF CNS-1725797
Do oil and gas platforms off California reduce recruitment of bocaccio (Sebastes paucispinis) to natural habitat? An analysis based on trajectories derived from high-frequency radar
To investigate the possibility that oil and gas platforms may reduce recruitment of rockfishes (Sebastes spp.) to natural habitat, we simulated drift pathways termed âtrajectoriesâ in our model) from an existing oil platform to nearshore habitat using current measurements from high-frequency (HF) radars. The trajectories originated at Platform Irene, located west of Point Conception, California, during two recruiting seasons for bocaccio (Sebastes paucispinis): May through August, 1999 and 2002. Given that pelagic juvenile bocaccio dwell near the surface, the trajectories estimate transport to habitat. We assumed that appropriate shallow water juvenile habitat exists inshore of the 50-m isobath. Results from 1999 indicated that 10% of the trajectories represent transport to habitat, whereas 76% represent transport across the offshore boundary. For 2002, 24% represent transport to habitat, and 69% represent transport across the offshore boundary. Remaining trajectories (14% and 7% for 1999 and 2002, respectively) exited the coverage area either northward or southward along isobaths. Deployments of actual drifters (with 1-m drogues) from a previous multiyear study provided measurements originating near Platform Irene from May through August. All but a few of the drifters moved offshore, as was also shown with the HF radar-derived trajectories. These results indicate that most juvenile bocaccio settling on the platform would otherwise have been transported offshore and perished in the absence of a platform. However, these results do not account for the swimming behavior of juvenile bocaccio, about which little is known
Improving surface current resolution using direction finding algorithms for multiantenna high-frequency radars
Author Posting. © American Meteorological Society, 2019. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of the Atmospheric and Oceanic Technology 36(10), (2019): 1997-2014, doi: 10.1175/JTECH-D-19-0029.1.While land-based high-frequency (HF) radars are the only instruments capable of resolving both the temporal and spatial variability of surface currents in the coastal ocean, recent high-resolution views suggest that the coastal ocean is more complex than presently deployed radar systems are able to reveal. This work uses a hybrid system, having elements of both phased arrays and direction finding radars, to improve the azimuthal resolution of HF radars. Data from two radars deployed along the U.S. East Coast and configured as 8-antenna grid arrays were used to evaluate potential direction finding and signal, or emitter, detection methods. Direction finding methods such as maximum likelihood estimation generally performed better than the well-known multiple signal classification (MUSIC) method given identical emitter detection methods. However, accurately estimating the number of emitters present in HF radar observations is a challenge. As MUSICâs direction-of-arrival (DOA) function permits simple empirical tests that dramatically aid the detection process, MUSIC was found to be the superior method in this study. The 8-antenna arrays were able to provide more accurate estimates of MUSICâs noise subspace than typical 3-antenna systems, eliminating the need for a series of empirical parameters to control MUSICâs performance. Code developed for this research has been made available in an online repository.This analysis was supported by NSF Grants OCE-1657896 and OCE-1736930 to Kirincich, OCE-1658475 to Emery and Washburn and OCE-1736709 to Flament. Flament is also supported by NOAAâs Integrated Ocean Observing System through Award NA11NOS0120039. The authors thank Lindsey Benjamin, Alma Castillo, Ken Constantine, Benedicte Dousset, Ian Fernandez, Mael Flament, Dave Harris, Garrett Hebert, Ben Hodges, Victoria Futch, Matt Guanci, and Philip Moravcik for assistance in building, deploying, and operating the radars.2020-04-1
High Frequency Radar Wind Turbine Interference Community Working Group Report
Land-based High Frequency (HF) Radars provide critically important observations of the coastal ocean that will be adversely affected by the spinning blades of utility-scale wind turbines. Pathways to mitigate the interference of turbines on HF radar observations exist for small number of turbines; however, a greatly increased pace of research is required to understand how
to minimize the complex interference patterns that will be caused by the large arrays of turbines planned for the U.S. outer continental shelf. To support the U.S.âs operational and scientific needs, HF radars must be able to collect high-quality measurements of the oceanâs surface inand around areas with significant numbers of wind turbines. This is a solvable problem, but given the rapid pace of wind energy development, immediate action is needed to ensure that HF radar wind turbine interference mitigation efforts keep pace with the planned build out of turbines
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Subtidal inner-shelf circulation near Point Conception, California
We discuss connections between innerâshelf and midâshelf circulation near Point Conception, California, as well as the wind forcing of innerâshelf circulation. Point Conception marks the southern edge of a major upwelling zone that extends from Oregon to central California. The coastline makes a sharp eastward turn at Point Conception, and the Santa Barbara Channel to the east is generally assumed to be an upwelling shadow. Consistent with this regional division, innerâshelf currents are strongly correlated with wind north of Point Conception, but not in the Santa Barbara Channel. One exception to this generalization is a location in the Santa Barbara Channel, near a pass that cuts through the coastal mountains, where local winds have a dominant crossâshore component and directly drive crossâshore currents over the inner shelf. Innerâshelf currents in the Santa Barbara Channel, when compared with midâshelf currents in that area, are weaker, but strongly correlated. By contrast, innerâshelf currents north of Point Conception show a far greater incidence of poleward flow than is seen over the midâshelf in that area. Poleward flow events, lasting 1â5 days, transport warm water from the Santa Barbara Channel around Point Conception to the central California coast. These events are associated with relaxation of the generally equatorward wind, but not always with midâshelf flow reversals
Decrease in natural marine hydrocarbon seepage near Coal Oil Point, California, associated with offshore oil production
Prolific natural hydrcarbon seepage occurs offshore of Coal Oil Point in the Santa Barbara Channel, California. Within the water column above submarine vents, plumes of hydrocarbon gas bubbles act as acoustic scattering targets. Using 3.5 kHz sonar data, seep distribution offshore of Coal Oil Point was mapped for August 1996, July 1995, and July 1973. Comparison of the seep distributions over time reveals more than 50% decrease in the areal extent of seepage, accompanied by declines in seep emission volume, in a 13 km2 area above a production oil reservoir. Declines in reservoir pressure and depletion of seep hydrocarbon sources associated with oil production are the mechanisms inferred to explain the declines in seep and emission volume
Poleward propagating subinertial alongshore surface currents off the U.S. West Coast
The article of record as published may be found at http://dx.doi.org/10.1002/jgrc.20400The 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(100â300) 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.National Research Foundation (NRF)Ministry of EducationHuman Resources Development of the Korea Institute of Energy Technology Evaluation and Planning (KETEP)Ministry of Trade, Industry and EnergyRepublic of Koreano. 2013R1A1A2057849no. 2011403020004
Evaluating Connectivity between Marine Protected Areas Using CODAR High-Frequency Radar
To investigate the connectivity between central California marine protected areas (MPAs), back-projections were calculated using the network of high-frequency (HF) radar ocean surface current mapping stations operated along the California coast by the member institutions of the Coastal Ocean Currents Monitoring Program with funding provided by California voters through Propositions 40 & 50 and administered by the State Coastal Conservancy. Trajectories of 1 km resolution grids of water particles were back-projected from ten MPAs each hour, out through 40 days in the past, from each day in 2008, producing a map of where surface waters travel over a 40-day period to reach the MPAs - and visualizations of the length of time the waters travel along these paths. By comparing the travel times of those back-projected track-points that crossed between MPA regions, the connection time between MPAs along the State\u27s central coast was assessed. Repeating these calculations resulted in a connectivity matrix between the MPAs in the region, and may be useful for assessing connectivity for the important invertebrate and fish larvae that are restricted to the surface ocean during a fraction of their lifecycle
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Water mass subduction and the transport of phytoplankton in a coastal upwelling system
Observations during the Coastal Transition Zone (CTZ) experiment in summer 1988 reveal the
presence of deep phytoplankton layers in a coastal upwelling system. The layers occur throughout the
CTZ study area, including a strong baroclinic jet which was present over the period of the experiment.
On the basis of a variety of bio-optical, hydrographic, and geochemical indicators, it is concluded that
the water masses associated with the layers result from subduction processes. Criteria are developed
for identification of subducted water masses based on the beam attenuation coefficient, chlorophyll
fluorescence, and distribution of light in the water column. Temperature-salinity characteristics are
consistent with two source regions for the subducted layers, one nearshore and a second farther
offshore. Most of the layers correspond to the inshore source which is apparently distributed
alongshore. Subducted water masses are found in all six grid surveys of the CTZ experiment and
probably result from a variety of physical processes. One of these is flow along sloping isopycnal
surfaces due to advection and mixing processes. Advection time scales for flow out the axis of the jet
range from a few days to a few weeks, depending on the depth of a particular surface, and the
bio-optical indicators for subduction processes persist over these time scale