Applied Ocean Physics and Engineering (AOP&E)

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The Department is a major center for research in fluid mechanics, coastal processes, ocean mixing, acoustics, air-sea interaction, deep submergence, ocean systems and moorings, remote sensing, robotics, certain biological processes, image processing, signal processing and estimation, control theory, and the dynamics of ocean cables.


Recent Submissions

Now showing 1 - 20 of 1408
  • Article
    Approximation of modal wavenumbers and group speeds in an oceanic waveguide using a neural network
    (Acoustical Society of America, 2023-06-12) Varon, Arthur ; Mars, Jerome ; Bonnel, Julien
    Underwater acoustic propagation is influenced not only by the property of the water column, but also by the seabed property. Modeling this propagation using normal mode simulation can be computationally intensive, especially for wideband signals. To address this challenge, a Deep Neural Network is used to predict modal horizontal wavenumbers and group velocities. Predicted wavenumbers are then used to compute modal depth functions and transmission losses, reducing computational cost without significant loss in accuracy. This is illustrated on a simulated Shallow Water 2006 inversion scenario.
  • Article
    Greenland Subglacial Discharge as a driver of hotspots of increasing coastal chlorophyll since the early 2000s
    (American Geophysical Union, 2023-05-18) Oliver, Hilde ; Slater, Donald ; Carroll, Dustin ; Wood, Michael ; Morlighem, Mathieu ; Hopwood, Mark J.
    Subglacial discharge emerging from the base of Greenland's marine‐terminating glaciers drives upwelling of nutrient‐rich bottom waters to the euphotic zone, which can fuel nitrate‐limited phytoplankton growth. Here, we use buoyant plume theory to quantify this subglacial discharge‐driven nutrient supply on a pan‐Greenland scale. The modeled nitrate fluxes were concentrated in a few critical systems, with half of the total modeled nitrate flux anomaly occurring at just 14% of marine‐terminating glaciers. Increasing subglacial discharge fluxes results in elevated nitrate fluxes, with the largest flux occurring at Jakobshavn Isbræ in Disko Bay, where subglacial discharge is largest. Subglacial discharge and nitrate flux anomaly also account for significant temporal variability in summer satellite chlorophyll a (Chl) within 50 km of Greenland's coast, particularly in some regions in central west and northwest Greenland.Runoff and modeled nitrate upwelling can explain temporal variability in surface cholorophyll in some coastal areas in west Greenland
  • Article
    Joint trans-dimensional inversion for water-column sound speed and seabed geoacoustic models
    (Acoustical Society of America, 2023-06-09) Dosso, Stan E. ; Bonnel, Julien
    This letter considers joint estimation of the water-column sound-speed profile (SSP) and seabed geoacoustic model through Bayesian inversion of ocean-acoustic data. The inversion is formulated in terms of separate trans-dimensional models for the water column (as an unknown number of nodes of a piecewise-continuous SSP) and seabed (as an unknown number of uniform layers) to intrinsically parameterize each according to the information content of the data. The inversion estimates marginal posterior probability profiles, quantifying the resolution of water-column and seabed structure. To validate the proposed method, modal-dispersion data from the New England Mud Patch, collected using hand-deployable systems, are considered.
  • Article
    Seismo-acoustic coupling in the deep atmosphere of Venus
    (Acoustical Society of America, 2023-03-20) Averbuch, Gil ; Houston, Reyna ; Petculescu, Andi
    The extreme conditions at the surface of Venus pose a challenge for monitoring the planet's seismic activity using long-duration landed probes. One alternative is using balloon-based sensors to detect venusquakes from the atmosphere. This study aims to assess the efficiency with which seismic motion is coupled as atmospheric acoustic waves across Venus's surface. It is, therefore, restricted to the immediate neighborhood of the crust-atmosphere interface. In order to account for supercritical conditions near the surface, the Peng-Robinson equation of state is used to obtain the acoustic sound speed and attenuation coefficient in the lower atmosphere. The energy transported across the surface from deep and shallow sources is shown to be a few orders of magnitude larger than on Earth, pointing to a better seismo-acoustic coupling. For a more realistic scenario, simulations were made of the acoustic field generated in the lower atmosphere by the ground motion arising from a vertical array of subsurface point-force sources. The resulting transmission loss maps show a strong epicentral cone accompanied by contributions from leaky surface waves. Results at 0.1 Hz and 1 Hz confirm that the width of the epicentral cone is larger at lower frequencies.
  • Article
    Shortfalls in the protection of persistent bull kelp forests in the USA
    (Elsevier, 2023-06-03) Arafeh-Dalmau, Nur ; Olguín-Jacobson, Carolina ; Bell, Tom W. ; Micheli, Fiorenza ; Cavanaugh, Kyle C.
    Kelp forests are one of the most productive ecosystems on earth, providing critical ecosystem services. Despite their global importance, their persistence in the face of human pressure and climate change is uncertain. We present a 38-year quarterly time series of satellite imagery that maps the distribution and persistence of surface canopy-forming kelp (dominated by the bull kelp, Nereocystis leutkeana) forests along eleven degrees of latitude in the western Pacific of the USA. We estimate kelp persistence as the fraction of years occupied by kelp canopy in the time series and evaluate the representation of kelp in marine protected areas (MPAs). While 3.6 % of kelp habitat is fully protected and 10.1 % is partially protected, only 0.7 % of the highly persistent kelp which may be indicative of climate refugia are fully protected. Regionally, the amount of kelp fully protected inside MPAs decreases from Central Northern California (8.0 %) to Oregon (5.9 %), Northern California (1.7 %), and Washington (0 %). Five years after the 2014–2016 marine heatwaves, kelp forests did not recover in California (∼90 % loss for both regions), while Oregon and Washington remained near pre-heatwave values. The low amount of protection in Northern California is concerning and likely exacerbates the vulnerability of kelp and associated species to marine heatwaves. Meeting a target of protecting 10 % of existing kelp habitat will require a 2.5-fold increase in kelp representation in MPAs. Moreover, we propose protecting highly persistent kelp is a cost-effective approach to increase representation and efficacy of MPAs to support climate resilience of kelp forest ecosystems.
  • Article
    Langmuir turbulence controls on observed diurnal warm layer depths
    (American Geophysical Union, 2023-05-24) Wang, Xingchi ; Kukulka, Tobias ; Farrar, J. Thomas ; Plueddemann, Albert J. ; Zippel, Seth F.
    The turbulent ocean surface boundary layer (OSBL) shoals during daytime solar surface heating, developing a diurnal warm layer (DWL). The DWL significantly influences OSBL dynamics by trapping momentum and heat in a shallow near‐surface layer. Therefore, DWL depth is critical for understanding OSBL transport and ocean‐atmosphere coupling. A great challenge for determining DWL depth is considering wave‐driven Langmuir turbulence (LT), which increases vertical transport. This study investigates observations with moderate wind speeds (4–7 m/s at 10 m height) and swell waves for which breaking wave effects are less pronounced. By employing turbulence‐resolving large eddy simulation experiments that cover observed wind, wave, and heating conditions based on the wave‐averaged Craik‐Lebovich equation, we develop a DWL depth scaling unifying previous approaches. This scaling closely agrees with observed DWL depths from a year‐long mooring deployment in the subtropical North Atlantic, demonstrating the critical role of LT in determining DWL depth and OSBL dynamics.
  • Article
    Broadband backscattering from scyphozoan jellyfish
    (Acoustical Society of America, 2023-05-24) Kahn, Rachel E. ; Lavery, Andone C. ; Govindarajan, Annette F.
    As the ecological importance of gelatinous organisms becomes increasingly appreciated, so has the need for improved knowledge of their abundance and distribution. Acoustic backscattering measurements are routine for fisheries assessments but are not yet widely used to survey populations of gelatinous zooplankton. The use of acoustic backscattering techniques to understand the distribution and abundance of organisms requires an understanding of their target strength (TS). This study presents a framework for a sound scattering model for jellyfish based on the Distorted Wave Born Approximation that incorporates size, shape, and material properties of individual organisms. This model, with a full three-dimensional shape rendition, is applied to a common species of scyphomedusa (Chrysaora chesapeakei) and verified experimentally with broadband (52-90 and 93-161 kHz) laboratory TS measurements of live individuals. Cyclical changes in the organism's shape due to swimming kinematics were examined, as well as averages over swimming position and comparisons with scattering from simpler shapes. The model predicts overall backscattering levels and broad spectral behavior within <2 dB. Measured TS exhibits greater variability than is predicted by scaling the size of the organism in the scattering model, showing that density and sound speed vary among individuals.
  • Article
    Broadband properties of potential and kinetic energies in an oceanic waveguide
    (Acoustical Society of America, 2023-05-23) Flamant, Julien ; Bonnel, Julien
    The energetic properties of an acoustic field can be quantified through the potential (Ep) and kinetic (Ek) energies. This article derives broadband properties of Ep and Ek in an oceanic waveguide, with restriction to a far-field context under which the acoustic field can be described by a set of propagating trapped modes. Using a set of reasonable assumptions, it is analytically demonstrated that, when integrated over a wide enough frequency-band, Ep = Ek everywhere in the waveguide, except at four specific depths: z = 0 (sea surface), z = D (seafloor), z = zs (source depth), and z = D -zs (mirrored source depth). Several realistic simulations are also presented to show the relevance of the analytical derivation. It is notably illustrated that, when integrated over third-octave bands, Ep ≡ Ek within 1 dB everywhere in the far-field waveguide, except in the first few meters of the water column (on a dB scale, no significant difference is found between Ep and Ek for z = D, z = zs, and Z = D - Zs).
  • Article
    Acoustic travel-time variability observed on a 150-km radius tomographic array in the Canada Basin during 2016–2017
    (Acoustical Society of America, 2023-05-02) Worcester, Peter F. ; Dzieciuch, Matthew A. ; Vazquez, Heriberto J. ; Cornuelle, Bruce D. ; Colosi, John A. ; Krishfield, Richard A. ; Kemp, John N.
    The Arctic Ocean is undergoing dramatic changes in response to increasing atmospheric concentrations of greenhouse gases. The 2016–2017 Canada Basin Acoustic Propagation Experiment was conducted to assess the effects of the changes in the sea ice and ocean structure in the Beaufort Gyre on low-frequency underwater acoustic propagation and ambient sound. An ocean acoustic tomography array with a radius of 150 km that consisted of six acoustic transceivers and a long vertical receiving array measured the impulse responses of the ocean at a variety of ranges every four hours using broadband signals centered at about 250 Hz. The peak-to-peak low-frequency travel-time variability of the early, resolved ray arrivals that turn deep in the ocean was only a few tens of milliseconds, roughly an order of magnitude smaller than observed in previous tomographic experiments at similar ranges, reflecting the small spatial scale and relative sparseness of mesoscale eddies in the Canada Basin. The high-frequency travel-time fluctuations were approximately 2 ms root-mean-square, roughly comparable to the expected measurement uncertainty, reflecting the low internal-wave energy level. The travel-time spectra show increasing energy at lower frequencies and enhanced semidiurnal variability, presumably due to some combination of the semidiurnal tides and inertial variability.
  • Article
    Observations of the space/time scales of Beaufort sea acoustic duct variability and their impact on transmission loss via the mode interaction parameter
    (Acoustical Society of America, 2023-05-02) Kucukosmanoglu, Murat ; Colosi, John A. ; Worcester, Peter F. ; Dzieciuch, Matthew A. ; Sagen, Hanne ; Duda, Timothy F. ; Zhang, Weifeng Gordon ; Miller, Christopher W. ; Richards, Edward L.
    The Beaufort duct (BD) is a subsurface sound channel in the western Arctic Ocean formed by cold Pacific Winter Water (PWW) sandwiched between warmer Pacific Summer Water (PSW) and Atlantic Water (AW). Sound waves can be trapped in this duct and travel long distances without experiencing lossy surface/ice interactions. This study analyzes BD vertical and temporal variability using moored oceanographic measurements from two yearlong acoustic transmission experiments (2016–2017 and 2019–2020). The focus is on BD normal mode propagation through observed ocean features, such as eddies and spicy intrusions, where direct numerical simulations and the mode interaction parameter (MIP) are used to quantify ducted mode coupling strength. The observations show strong PSW sound speed variability, weak variability in the PWW, and moderate variability in the AW, with typical time scales from days to weeks. For several hundreds Hertz propagation, the BD modes are relatively stable, except for rare episodes of strong sound speed perturbations. The MIP identifies a resonance condition such that the likelihood of coupling is greatest when there is significant sound speed variability in the horizontal wave number band ⁠1/11 < kh < 1/5 km-1. MITgcm ocean model results are used to estimate sound speed fluctuations in this resonance regime.
  • Article
    Increased utilization of storm surge barriers: a research agenda on estuary impacts
    (American Geophysical Union, 2023-03-27) Orton, Philip ; Ralston, David ; Prooijen, Bram ; Secor, David ; Ganju, Neil ; Chen, Ziyu ; Fernald, Sarah ; Brooks, Bennett ; Marcell, Kristin
    Rising coastal flood risk and recent disasters are driving interest in the construction of gated storm surge barriers worldwide, with current studies recommending barriers for at least 11 estuaries in the United States alone. Surge barriers partially block estuary‐ocean exchange with infrastructure across an estuary or its inlet and include gated areas that are closed only during flood events. They can alter the stratification and salt intrusion, change sedimentary systems, and curtail animal migration and ecosystem connectivity, with impacts growing larger with increasing gate closures. Existing barriers are being used with increasing frequency due to sea level rise. New barrier proposals typically come with maximum closure frequency recommendations, yet the future adherence to them is uncertain. Given that the broader environmental effects and coupled‐human dynamics of surge barriers are not well‐understood, we present an interdisciplinary research agenda for this increasingly prevalent modification to our coastal zone.
  • Article
    Geometry of freezing impacts ice composition: implications for icy satellites
    (American Geophysical Union, 2023-03-14) Buffo, Jacob J. ; Meyer, Colin R. ; Chivers, Chase J. ; Walker, Catherine C. ; Huber, Christian ; Schmidt, Britney E.
    Non‐ice impurities within the ice shells of ocean worlds (e.g., Europa, Enceladus, Titan, Ganymede) are believed to play a fundamental role in their geophysics and habitability and may become a surface expression of subsurface ocean properties. Heterogeneous entrainment and distribution of impurities within planetary ice shells have been proposed as mechanisms that can drive ice shell overturns, generate diverse geological features, and facilitate ocean‐surface material transport critical for maintaining a habitable subsurface ocean. However, current models of ice shell composition suggest that impurity rejection at the ice‐ocean interface of thick contemporary ice shells will be exceptionally efficient, resulting in relatively pure, homogeneous ice. As such, additional mechanisms capable of facilitating enhanced and heterogeneous impurity entrainment are needed to reconcile the observed physicochemical diversity of planetary ice shells. Here we investigate the potential for hydrologic features within planetary ice shells (sills and basal fractures), and the unique freezing geometries they promote, to provide such a mechanism. By simulating the two‐dimensional thermal and physicochemical evolution of these hydrological features as they solidify, we demonstrate that bottom‐up solidification at sill floors and horizontal solidification at fracture walls generate distinct ice compositions and provide mechanisms for both enhanced and heterogeneous impurity entrainment. We compare our results with magmatic and metallurgic analogs that exhibit similar micro‐ and macroscale chemical zonation patterns during solidification. Our results suggest variations in ice‐ocean/brine interface geometry could play a fundamental role in introducing compositional heterogeneities into planetary ice shells and cryoconcentrating impurities in (re)frozen hydrologic features.
  • Article
    Sources of drag in estuarine meanders: momentum eedistribution, bottom atress wnhancement, and bend-scale form drag
    (American Meteorological Society, 2023-07-01) Bo, Tong ; Ralston, David K. ; Geyer, W. Rockwell
    Curvature can create secondary circulation and flow separation in tidal channels, and both have important consequences for the along-channel momentum budget. The North River is a sinuous estuary where drag is observed to be higher than expected, and a numerical model is used to investigate the influence of curvature-induced processes on the momentum distribution and drag. The hydrodynamic drag is greatly increased in channel bends compared to that for straight channel flows. Drag coefficients are calculated using several approaches to identify the different factors contributing to the drag increase. Flow separation creates low-pressure recirculation zones on the lee side of the bends and results in form drag. Form drag is the dominant source of the increase in total drag during flood tides and is less of a factor during ebb tides. During both floods and ebbs, curvature-induced secondary circulation transports higher-momentum fluid to the lower water column through vertical and lateral advection. Consequently, the streamwise velocity profile deviates from the classic log profile and vertical shear becomes more concentrated near the bed. This redistribution by the lateral circulation causes an overall increase in bottom friction and contributes to the increased drag. Additionally, spatial variations in the depth-averaged velocity field due to the curvature-induced flow are nonlinearly correlated with the bathymetric structure, leading to increased bottom friction. In addition to affecting the tidal flow, the redistributed momentum and altered bottom shear stress have clear implications for channel morphodynamics.
  • Article
    Kelpwatch: a new visualization and analysis tool to explore kelp canopy dynamics reveals variable response to and recovery from marine heatwaves
    (Public Library of Science, 2023-03-23) Bell, Tom W. ; Cavanaugh, Kyle C. ; Saccomanno, Vienna R. ; Cavanaugh, Katherine C. ; Houskeeper, Henry F. ; Eddy, Norah ; Schuetzenmeister, Falk ; Rindlaub, Nathaniel ; Gleason, Mary
    Giant kelp and bull kelp forests are increasingly at risk from marine heatwave events, herbivore outbreaks, and the loss or alterations in the behavior of key herbivore predators. The dynamic floating canopy of these kelps is well-suited to study via satellite imagery, which provides high temporal and spatial resolution data of floating kelp canopy across the western United States and Mexico. However, the size and complexity of the satellite image dataset has made ecological analysis difficult for scientists and managers. To increase accessibility of this rich dataset, we created Kelpwatch, a web-based visualization and analysis tool. This tool allows researchers and managers to quantify kelp forest change in response to disturbances, assess historical trends, and allow for effective and actionable kelp forest management. Here, we demonstrate how Kelpwatch can be used to analyze long-term trends in kelp canopy across regions, quantify spatial variability in the response to and recovery from the 2014 to 2016 marine heatwave events, and provide a local analysis of kelp canopy status around the Monterey Peninsula, California. We found that 18.6% of regional sites displayed a significant trend in kelp canopy area over the past 38 years and that there was a latitudinal response to heatwave events for each kelp species. The recovery from heatwave events was more variable across space, with some local areas like Bahía Tortugas in Baja California Sur showing high recovery while kelp canopies around the Monterey Peninsula continued a slow decline and patchy recovery compared to the rest of the Central California region. Kelpwatch provides near real time spatial data and analysis support and makes complex earth observation data actionable for scientists and managers, which can help identify areas for research, monitoring, and management efforts.
  • Article
    Salt marsh response to inlet switch‐induced increases in tidal inundation
    (American Geophysical Union, 2022-12-22) Yellen, Brian ; Woodruff, Jonathan D. ; Baranes, Hannah E. ; Engelhart, Simon E. ; Geywer, W. Rockwell ; Randall, Noa ; Griswold, Frances R.
    There is widespread concern that rapidly rising sea levels may drown salt marshes by exceeding the rate at which these important ecosystems can build elevation. A significant fraction of marshes reside within backbarrier estuaries, yet little attention has been paid to how changes in inlet geometry influences estuarine tides and marshes. In 1898, a coastal storm eroded a new inlet through the barrier beach that fronts the North‐South Rivers Estuary in Massachusetts, USA. The new inlet shortened the North River by 5.6 km and lengthened the South River channel by the same amount. Modern measurements of tidal attenuation suggest that channel shortening abruptly increased mean high tide along the North River by at least 30 cm. Foraminifera communities within North River marsh sediments indicated an environmental change from infrequent to frequent inundation at the time of the 1898 switch in inlet location, which supports this hypothesis. Increased mineral sediment deposition after the inlet switch played a dominant role in allowing marshes along the North River channel to adjust to greater inundation. Following the inlet switch, sediment accreted in North River marshes at 2–5 times the rate of sea level rise (SLR). The North River channel widened by an average of 18% relative to pre‐1898 conditions to accommodate the increased tidal prism. The role of mineral sediment accretion in making this marsh resilient to an abrupt increase in inundation depth highlights the importance of maintaining adequate sediment supplies in coastal regions as SLR accelerates.
  • Article
    Improving wave‐based air‐sea momentum flux parameterization in mixed seas
    (American Geophysical Union, 2023-03-07) Sauvage, César ; Seo, Hyodae ; Clayson, Carol Anne ; Edson, James B.
    In winter, the Northwest Tropical Atlantic Ocean can be characterized by various wave age‐based interactions among ocean current, surface wind and surface waves, which are critical for accurately describing surface wind stress. In this work, coupled wave‐ocean‐atmosphere model simulations are conducted using two different wave roughness parameterizations within COARE3.5, including one that relies solely on wind speed and another that uses wave age and wave slope as inputs. Comparisons with the directly measured momentum fluxes during the ATOMIC/EUREC4A experiments in winter 2020 show that, for sea states dominated by short wind waves under moderate to strong winds, the wave‐based formulation (WBF) increases the surface roughness length in average by 25% compared to the wind‐speed‐based approach. For sea states dominated by remotely generated swells under moderate to strong wind intensity, the WBF predicts significantly lower roughness length and surface stress (≈15%), resulting in increased near‐surface wind speed above the constant flux layer (≈5%). Further investigation of the mixed sea states in the model and data indicates that the impact of swell on wind stress is over‐emphasized in the COARE3.5 WBF, especially under moderate wind regimes. Various approaches are explored to alleviate this deficiency by either introducing directional alignment between wind and waves or using the mean wave period instead of the wave period corresponding to the spectral peak to compute the wave age. The findings of this study are likely to be site‐dependent, and mostly concern specific regimes of wind and waves where the original parameterization was deficient.
  • Article
    Faster-than-real-time hybrid automotive underwater glider simulation for ocean mapping
    (The Korean Society of Marine Environment and Safety, 2022-05-28) Choi, Woen-Sug ; Bingham, Brian ; Camilli, Richard
    The introduction of autonomous underwater gliders (AUGs) specifically addresses the reduction of operational costs that were previously prohibited with conventional autonomous underwater vehicles (AUVs) using a "scaling-down" design philosophy by utilizing the characteristics of autonomous drifters to far extend operation duration and coverage. Long-duration, wide-area missions raise the cost and complexity of in-water testing for novel approaches to autonomous mission planning. As a result, a simulator that supports the rapid design, development, and testing of autonomy solutions across a wide range using software-in-the-loop simulation at faster-than-real-time speeds becomes critical. This paper describes a faster-than-real-time AUG simulator that can support high-resolution bathymetry for a wide variety of ocean environments, including ocean currents, various sensors, and vehicle dynamics. On top of the de facto standard ROS-Gazebo framework and open-sourced underwater vehicle simulation packages, features specific to AUGs for ocean mapping are developed. For vehicle dynamics, the next-generation hybrid autonomous underwater gliders (Hybrid-AUGs) operate with both the buoyancy engine and the thrusters to improve navigation for bathymetry mappings, e.g., line trajectory, are is implemented since because it can also describe conventional AUGs without the thrusters. The simulation results are validated with experiments while operating at 120 times faster than the real-time.
  • Article
    CubeSats show persistence of bull kelp refugia amidst a regional collapse in California
    (Elsevier, 2023-03-11) Cavanaugh, Katherine C. ; Cavanaugh, Kyle C. ; Pawlak, Camille C. ; Bell, Tom W. ; Saccomanno, Vienna R.
    Bull kelp populations in northern California declined drastically in response to the 2014–2016 marine heatwave, sea star wasting disease, and subsequently large increases in herbivorous purple urchin populations. Despite the regional kelp forest collapse, there were small, remnant populations where bull kelp was able to survive. Moderate resolution satellites (i.e., Landsat) have been important for creating long-term, large-scale time series of bull kelp forests, however, these have been shown to underestimate or entirely exclude refugia due to their low densities and proximity to the coastline. While measurements from Unoccupied Aerial Vehicles (UAV) are spatially detailed, they are temporally limited and difficult to collect over regional scales. The development of CubeSat constellations has enabled a workaround for these tradeoffs, with global imagery available near-daily at meter-scale.We developed a method for mapping bull kelp canopy across the different sensor cohorts in the PlanetScope constellation. This required correcting surface reflectance measurements to account for differences in the spectral response functions among the sensors and leveraging the temporal frequency of PlanetScope data to increase the automation of classifying kelp canopy in imagery with increased noise. Using the PlanetScope derived kelp canopy extents, we identified locations where bull kelp refugia have persisted in northern California. We found that bull kelp refugia occupied about 2% of the total available habitat in the region and about 9.4% of the average canopy area observed prior to 2014. These areas may be critical to the success of kelp forest re-establishment in northern California, which increases their importance for ongoing monitoring, conservation, and restoration efforts.•Developed the first bull kelp canopy time series from high resolution CubeSat data.•CubeSats can effectively detect kelp canopy at low population abundance and density.•Refugia persisted during historically low kelp abundance in northern California.
  • Article
    Toward a new era of coral reef monitoring
    (American Chemical Society, 2023-03-17) Apprill, Amy ; Girdhar, Yogesh ; Mooney, T. Aran ; Hansel, Colleen M. ; Long, Matthew H. ; Liu, Yaqin ; Zhang, W. Gordon ; Kapit, Jason ; Hughen, Konrad ; Coogan, Jeff ; Greene, Austin
    Coral reefs host some of the highest concentrations of biodiversity and economic value in the oceans, yet these ecosystems are under threat due to climate change and other human impacts. Reef monitoring is routinely used to help prioritize reefs for conservation and evaluate the success of intervention efforts. Reef status and health are most frequently characterized using diver-based surveys, but the inherent limitations of these methods mean there is a growing need for advanced, standardized, and automated reef techniques that capture the complex nature of the ecosystem. Here we draw on experiences from our own interdisciplinary research programs to describe advances in in situ diver-based and autonomous reef monitoring. We present our vision for integrating interdisciplinary measurements for select “case-study” reefs worldwide and for learning patterns within the biological, physical, and chemical reef components and their interactions. Ultimately, these efforts could support the development of a scalable and standardized suite of sensors that capture and relay key data to assist in categorizing reef health. This framework has the potential to provide stakeholders with the information necessary to assess reef health during an unprecedented time of reef change as well as restoration and intervention activities.
  • Article
    Semi-supervised visual tracking of marine animals using autonomous underwater vehicles
    (Springer, 2023-03-01) Cai, Levi ; McGuire, Nathan E. ; Hanlon, Roger ; T Aran Mooney ; Girdhar, Yogesh
    In-situ visual observations of marine organisms is crucial to developing behavioural understandings and their relations to their surrounding ecosystem. Typically, these observations are collected via divers, tags, and remotely-operated or human-piloted vehicles. Recently, however, autonomous underwater vehicles equipped with cameras and embedded computers with GPU capabilities are being developed for a variety of applications, and in particular, can be used to supplement these existing data collection mechanisms where human operation or tags are more difficult. Existing approaches have focused on using fully-supervised tracking methods, but labelled data for many underwater species are severely lacking. Semi-supervised trackers may offer alternative tracking solutions because they require less data than fully-supervised counterparts. However, because there are not existing realistic underwater tracking datasets, the performance of semi-supervised tracking algorithms in the marine domain is not well understood. To better evaluate their performance and utility, in this paper we provide (1) a novel dataset specific to marine animals located at, (2) an evaluation of state-of-the-art semi-supervised algorithms in the context of underwater animal tracking, and (3) an evaluation of real-world performance through demonstrations using a semi-supervised algorithm on-board an autonomous underwater vehicle to track marine animals in the wild.