Recent Publications

Weekly Highlighted Publication

Self-contained local broadband seismogeodetic early warning system: Detection and location

Impact:
We have described the elements of our seismogeodetic earthquake and tsunami early warning system, where the detection and location algorithms initiate higher-order products such as earthquake magnitude scaling, and centroid moment tensor and finite fault slip solutions. These higher-order products can then be used as input to local tsunami prediction and modeling algorithms. The seismogeodetic method allows for a self-contained earthquake early warning system that utilizes the best qualities of seismic and geodetic approaches to earthquake and local tsunami early warning.

Search Recent Publications

  • Abstract Summary:

    Conventional and adaptive plane-wave beamforming with simultaneous recordings by large-aperture horizontal and vertical line arrays during the 2009 Philippine Sea Engineering Test (PhilSea09) reveal the rate of occurrence and the two-dimensional arrival structure of seismic phases that couple into the deep ocean. A ship-deployed, controlled acoustic source was used to evaluate performance of the horizontal array for a range of beamformer...

  • Shimura T., Ochi H., Song HC.  2013.  Experimental demonstration of multiuser communication in deep water using time reversal. Journal of the Acoustical Society of America. 134:3223-3229.
    Abstract Summary:

    Multiuser communication is demonstrated using experimental data (450-550 Hz) collected in deep water, south of Japan. The multiple users are spatially distributed either in depth or range while a 114 -m long, 20-element vertical array (i.e., base station) is deployed to around the sound channel axis (similar to 1000 m). First, signals received separately from ranges of 150 km and 180 km at various depths are combined asynchronously to...

  • Abstract Summary:

    Although Basin and Range-style extension affected large areas of western Mexico after the Late Eocene, most consider that extension in the Gulf of California region began as subduction waned and ended ca. 14-12.5 Ma. A general consensus also exists in considering Early and Middle Miocene volcanism of the Sierra Madre Occidental and Comond Group as subduction related, whereas volcanism after ca. 12.5 Ma is extension related. Here we present a...

  • Abstract Summary:

    A series of experiments conducted in the Philippine Sea during 2009-2011 investigated deep-water acoustic propagation and ambient noise in this oceanographically and geologically complex region: (i) the 2009 North Pacific Acoustic Laboratory (NPAL) Pilot Study/Engineering Test, (ii) the 2010-2011 NPAL Philippine Sea Experiment, and (iii) the Ocean Bottom Seismometer Augmentation of the 2010-2011 NPAL Philippine Sea Experiment. The...

  • Sirovic A., Wiggins SM, Oleson E.M.  2013.  Ocean noise in the tropical and subtropical Pacific Ocean. Journal of the Acoustical Society of America. 134:2681-2689.
    Abstract Summary:

    Ocean ambient noise is well studied in the North Pacific and North Atlantic but is poorly described for most of the worlds' oceans. Calibrated passive acoustic recordings were collected during 2009-2010 at seven locations in the central and western tropical and subtropical Pacific. Monthly and hourly mean power spectra (15-1000 Hz) were calculated in addition to their skewness, kurtosis, and percentile distributions. Overall, ambient noise at...

  • Abstract Summary:

    There is anecdotal evidence that under conditions of moderate to high wind speeds (8-15 m . s(-1)), clouds of bubbles entrained in the near-surface layer by breaking waves can create a benign underwater communications channel through the resonant absorption of forward-scattered sound, reducing reverberation times and the occurrence of high-intensity, Doppler-shifted arrivals. Current models for the effects of bubbles on surface-interacting...

  • Song HC.  2013.  Time reversal communication with a mobile source. Journal of the Acoustical Society of America. 134:2623-2626.
    Abstract Summary:

    Broadband underwater acoustic communication signals undergo either a compression or dilation in the presence of relative motion between a source and a receiver. Consequently, underwater acoustic communications with a mobile source/ receiver require Doppler compensation through resampling. However, resampling may not be necessary when a channel-estimate-based time reversal approach is applied with frequent channel updates. Using experimental...

  • Abstract Summary:

    Radio wave propagation on low-altitude paths over the ocean above 2 GHz  is significantly affected by negative refractivity gradients in the  atmospheric surface layer, which form what is often referred to as an  evaporation duct (ED). Refractivity from clutter (RFC) is an inversion  approach for the estimation of the refractivity profile from radar  clutter, and RFC-ED refers to its implementation for the case of  evaporation ducts. An...

  • Grare L, Lenain L., Melville W.K.  2013.  Wave-coherent airflow and critical layers over ocean waves. Journal of Physical Oceanography. 43:2156-2172.
    Abstract Summary:

    An analysis of coherent measurements of winds and waves from data  collected during the Office of Naval Research (ONR) High-Resolution  air-sea interaction (HiRes) program, from the Floating Instrument  Platform (R/P FLIP), off the coast of northern California in June 2010  is presented. A suite of wind and wave measuring systems was deployed to  resolve the modulation of the marine atmospheric boundary layer by  waves. Spectral analysis of...

  • Abstract Summary:

    Between 15 and 17 August 2010, a simple two-element vertical array was deployed off the continental slope of Southeast Alaska in 1200 m water depth. The array was attached to a vertical buoy line used to mark each end of a longline fishing set, at 300 m depth, close to the sound-speed minimum of the deep-water profile. The buoy line also served as a depredation decoy, attracting seven sperm whales to the area. One animal was tagged with both...

  • Abstract Summary:

    The discrete whitecap method (DWM) to model the sea spray aerosol (SSA) production flux explicitly requires a whitecap timescale, which up to now has only considered a whitecap decay timescale, (decay). A reevaluation of the DWM suggests that the whitecap timescale should account for the total whitecap lifetime ((wcap)), which consists of both the formation timescale ((form)) and the decay timescale (timescale definitions are given in the...

  • Abstract Summary:

    Measurements of ambient noise have been used to infer information about the ocean acoustic environment. In recent years the correlation of ambient noise has been shown to give estimates of the travel time of acoustic paths between the sensors recording the noise. A number of issues affect the results of the noise correlation. This paper presents the results of noise correlation of the two horizontally separated arrays of sensors in the 2010...

  • Abstract Summary:

    Passive acoustic monitoring of marine mammal calls is an increasingly important method for assessing population numbers, distribution, and behavior. A common mistake in the analysis of marine mammal acoustic data is formulating conclusions about these animals without first understanding how environmental properties such as bathymetry, sediment properties, water column sound speed, and ocean acoustic noise influence the detection and character...

  • Abstract Summary:

    As the field of ocean acidification has grown, researchers have increasingly turned to laboratory experiments to understand the impacts of increased CO2 on marine organisms. However, other changes such as ocean warming and deoxygenation are occurring concurrently with the increasing CO2 concentrations, complicating the understanding of the impacts of anthropogenic changes on organisms. This experimental aquarium design allows for independent...

  • Song HC, Hodgkiss WS.  2013.  Efficient use of bandwidth for underwater acoustic communication. Journal of the Acoustical Society of America. 134:905-908.
    Abstract Summary:

    In a recent shallow water experiment, acoustic communication transmissions were carried out over the 10 to 32 kHz band in similar to 100m deep water over a 3 km range. A natural question is how best to utilize that bandwidth. In one multiband approach discussed previously, the band was divided into four smaller subbands that were processed independently using time reversal decision-feedback equalizers (TR-DFEs). This letter presents a...

  • Abstract Summary:

    Dinoflagellate bioluminescence serves as a wholecell reporter of mechanical stress, which activates a signaling pathway that appears to involve the opening of voltage-sensitive ion channels and release of calcium from intracellular stores. However, little else is known about the initial signaling events that facilitate the transduction of mechanical stimuli. In the present study using the red tide dinoflagellate Lingulodinium polyedrum (...

  • Abstract Summary:

    Acoustic attenuation in seawater usually has little effect on the spatial statistics of ambient noise in the ocean. This expectation does not hold, however, at higher frequencies, above 10 kHz, and extreme depths, in excess of 6 km, an operating regime that is within the capabilities of the most recently developed acoustic instrument platforms. To quantify the effects of attenuation, theoretical models for the vertical directionality and the...

  • Xaver F., Gerstoft P, Matz G., Mecklenbrauker C..  2013.  Analytic sequential Weiss-Weinstein bounds. Signal Processing, IEEE Transactions on. PP:1-1.
    Abstract Summary:

    In this paper, we explore a sequential Bayesian bound for state-space models focusing on hybrid continuous and discrete random states. We provide an analytic recursion for the sequential Weiss-Weinstein (SWW) bound for linear state-space models with solutions for Gaussian, uniform, and exponential distributions as derived, as well as for a combination of these. We compare the SWW bound for discretized states with the corresponding bound for...

  • Bromirski PD, Stephen RA, Gerstoft P.  2013.  Are deep-ocean-generated surface-wave microseisms observed on land? Journal of Geophysical Research: Solid Earth. 118:3610-3629.
    Abstract Summary:

    Recent studies attribute land double-frequency (DF) microseism observations to deep water generation. Here we show that near-coastal generation is generally the dominant source region. This determination is based on observations at land and ocean seismic stations, buoys, gravity-wave hindcasts, and on beamforming results from continental seismic arrays. Interactions between opposing ocean wave components generate a pressure excitation pulse...

  • Tan B.A, Gerstoft P, Yardim C, Hodgkiss WS.  2013.  Broadband synthetic aperture geoacoustic inversion. Journal of the Acoustical Society of America. 134:312-322.
    Abstract Summary:

    A typical geoacoustic inversion procedure involves powerful source transmissions received on a large-aperture receiver array. A more practical approach is to use a single moving source and/or receiver in a low signal to noise ratio (SNR) setting. This paper uses single-receiver, broadband, frequency coherent matched-field inversion and exploits coherently repeated transmissions to improve estimation of the geoacoustic parameters. The long...

  • Carriere O, Hermand J.P.  2013.  Feature-oriented acoustic tomography for coastal ocean observatories. Ieee Journal of Oceanic Engineering. 38:534-546.
    Abstract Summary:

    The deployment of coastal observatories motivates the development of acoustic inversion schemes able to characterize rapidly time-varying range-dependent environments. This paper develops feature models as parameterization schemes for the range-dependent temperature field, when the latter is mainly influenced by an identified oceanic feature, here thermal fronts. The feasibility of feature-oriented acoustic tomography (FOAT) is demonstrated...

  • Abstract Summary:

    A parameterization is presented for turbulence dissipation due to internal tides generated at and impinging upon topography steep enough to be supercritical with respect to the tide. The parameterization requires knowledge of the topography, stratification, and the remote forcingeither barotropic or baroclinic. Internal modes that are arrested at the crest of the topography are assumed to dissipate, and faster modes assumed to propagate away...

  • Dunlop RA, Cato DH, Noad MJ, Stokes D.M.  2013.  Source levels of social sounds in migrating humpback whales (Megaptera novaeangliae). Journal of the Acoustical Society of America. 134:706-714.
    Abstract Summary:

    The source level of an animal sound is important in communication, since it affects the distance over which the sound is audible. Several measurements of source levels of whale sounds have been reported, but the accuracy of many is limited because the distance to the source and the acoustic transmission loss were estimated rather than measured. This paper presents measurements of source levels of social sounds (surface-generated and vocal...

  • Abstract Summary:

     We developed a model for partitioning the spectral absorption coefficient of suspended marine particles, a(p)(), into phytoplankton, a(ph)(), and nonalgal, a(d)(), components based on the stacked-constraints approach. The key aspect of our model is the use of a set of inequality constraints that account for large variability in the a(ph)() and a(d)() coefficients within the world's oceans. The bounds of inequality constraints were determined...

  • Baumann-Pickering S, McDonald MA, Simonis AE, Berga ASolsona, Merkens KPB, Oleson EM, Roch MA, Wiggins SM, Rankin S, Yack TM et al..  2013.  Species-specific beaked whale echolocation signals. The Journal of the Acoustical Society of America. 134:2293-2301.
    Abstract Summary:

    Beaked whale echolocation signals are mostly frequency-modulated (FM) upsweep pulses and appear to be species specific. Evolutionary processes of niche separation may have driven differentiation of beaked whale signals used for spatial orientation and foraging. FM pulses of eight species of beaked whales were identified, as well as five distinct pulse types of unknown species, but presumed to be from beaked whales. Current evidence suggests...

  • Yardim C, Gerstoft P, Hodgkiss WS.  2013.  Particle smoothers in sequential geoacoustic inversion. The Journal of the Acoustical Society of America. 134:971-981.
    Abstract Summary:

    Sequential Bayesian methods such as particle filters have been used to track a moving source in an unknown and space/time-evolving ocean environment. These methods treat both the source and the ocean parameters as non-stationary unknown random variables and track them via the multivariate posterior probability density function. Particle filters are numerical methods that can operate on nonlinear systems with non-Gaussian probability density...

  • Deane GB.  2013.  Determining the bubble cap film thickness of bursting bubbles from their acoustic emissions. The Journal of the Acoustical Society of America. 133:EL69-EL75.
    Abstract Summary:

    A study of the sound generated by 2.5 mm radius bubbles bursting on the surface of fresh water is presented. The sound pulses are found to be sensitive to the time interval between the bubble reaching the water surface and bursting. Bubbles that burst within a few 10's of milliseconds behave like a Helmholtz resonator and radiate a swept chirp pulse. Bubbles that persist for 100's of milliseconds or more exhibit more complex acoustic behavior...

  • Abstract Summary:

    Seismic interferometry processing is applied to an active seismic survey collected on ocean bottom seismometers (OBS) deployed at 900-m water depth over a carbonate/hydrates mound in the Gulf of Mexico. Common midpoint processing and stacking of the extracted Green's function gives the subsurface PP reflectivity, with a horizontal resolution of half the receiver spacing. The obtained seismic section is comparable to classical upgoing/...

  • Abstract Summary:

    Measurements of radiocarbon (C-14) in carbon dioxide (CO2), methane (CH4) and carbon monoxide (CO) from glacial ice are potentially useful for absolute dating of ice cores, studies of the past atmospheric CH4 budget and for reconstructing the past cosmic ray flux and solar activity. Interpretation of C-14 signals in ice is complicated by the fact that the two major C-14 components-trapped atmospheric and in situ cosmogenic-are present in a...

  • Abstract Summary:

    The behavioural response study (BRS) is an experimental design used by field biologists to determine the function and/or behavioural effects of conspecific, heterospecific or anthropogenic stimuli. When carrying out these studies in marine mammals it is difficult to make basic observations and achieve sufficient samples sizes because of the high cost and logistical difficulties. Rarely are other factors such as social context or the physical...

  • Lani SW, Sabra KG, Hodgkiss WS, Kuperman WA, Roux P.  2013.  Coherent processing of shipping noise for ocean monitoring. Journal of the Acoustical Society of America. 133:EL108-EL113.
    Abstract Summary:

    Ambient noise was recorded on two vertical line arrays (VLAs) separated by 450m and deployed in shallow water (depth similar to 150 m) off San Diego, CA continuously for 6 days. Recordings were dominated by non-stationary and non-uniform broadband shipping noise (250 Hz to 1.5 kHz). Stable coherent noise wavefronts were extracted from ambient noise correlations between the VLAs during all 6 days by mitigating the effect of discrete shipping...

  • Abstract Summary:

    The effect of soluble surfactant on the persistence of salt-water bubbles and their ability to produce aerosol particles upon bursting was investigated. Ensembles of individual, millimetric bubbles were produced in NaCl solutions of varying surfactant concentration. Aerosol production efficiency-a fundamental property of single bubbles defined as the number of particles produced per bubble film cap area-decreased by 79% to 98% following the...

  • Abstract Summary:

    Photonic structures in the skin of pelagic fishes and squids evolved specifically for hiding in the complex light field of the open ocean. To understand the principles under which these structures operate, a detailed characterization of their optical properties is required. An optical scatterometer has been developed to measure one important property, the bidirectional reflectance distribution function (BRDF). The instrument was used to...

  • Cho SE, Song HC, Hodgkiss WS.  2013.  Multiuser acoustic communications with mobile users. Journal of the Acoustical Society of America. 133:880-890.
    Abstract Summary:

    A multiuser receiver is developed that is capable of separating receptions from independent, mobile users whose transmissions overlap in both time and frequency. With respect to any one user's Doppler corrected signal, the other communication signals appear as multiple-access interference distributed across the Doppler dimension. A previously developed receiver composed of an adaptive time-reversal processor embedded within a successive...

  • Abstract Summary:

    Intense phytoplankton blooms were observed along the Patagonian shelf-break with satellite ocean color data, but few in situ optical observations were made in that region. We examine the variability of phytoplankton absorption and particulate scattering coefficients during such blooms on the basis of field data. The chlorophyll-a concentration, [Chla], ranged from 0.1 to 22.3 mg m(-3) in surface waters. The size fractionation of [Chla] showed...

  • Abstract Summary:

    Spectrophotometric pH measurements stand to benefit greatly from the consistency and speed made possible through automation. Here we describe a simple, fast, and precise automated spectrophotometric pH measurement system for seawater samples. The system requires 4 min per analysis, consumes 60 mL seawater from a sample bottle, and requires little operator interaction to obtain repeatability comparable with the best results published with...

  • Sabra KG, Fried S, Kuperman WA, Prior M.  2013.  On the coherent components of low-frequency ambient noise in the Indian Ocean. Journal of the Acoustical Society of America. 133:EL20-EL25.
    Abstract Summary:

    This letter demonstrates that the dominant coherent component of low-frequency (1 Hz < f < 20 Hz) ambient noise propagating between hydrophone pairs of the same hydroacoustic station, deployed in the deep sound channel of the Indian Ocean, is directional and mainly originates from Antarctica. However, the amplitude of the peak coherent noise arrivals, obtained using a 4-month-long averaging interval, was relatively low given the small...

  • Barclay DR, Buckingham MJ.  2013.  Depth dependence of wind-driven, broadband ambient noise in the Philippine Sea. Journal of the Acoustical Society of America. 133:62-71.
    Abstract Summary:

    In 2009, as part of PhilSea09, the instrument platform known as Deep Sound was deployed in the Philippine Sea, descending under gravity to a depth of 6000 m, where it released a drop weight, allowing buoyancy to return it to the surface. On the descent and ascent, at a speed of 0.6 m/s, Deep Sound continuously recorded broadband ambient noise on two vertically aligned hydrophones separated by 0.5 m. For frequencies between 1 and 10 kHz,...

  • Abstract Summary:

    Turbulent mixing rates are inferred from measurements spanning 25°–37°N in the Pacific Ocean. The observations were made as part of the Internal Waves Across the Pacific experiment, designed to investigate the long-range fate of the low-mode internal tide propagating north from Hawaii. Previous and companion results argue that, near a critical latitude of 29°N, the internal tide loses energy to high-mode near-inertial motions through...

  • Abstract Summary:

    We review the physics of near-inertial waves (NIWs) in the ocean and the observations, theory, and models that have provided our present knowledge. NIWs appear nearly everywhere in the ocean as a spectral peak at and just above the local inertial period f, and the longest vertical wavelengths can propagate at least hundreds of kilometers toward the equator from their source regions; shorter vertical wavelengths do not travel as far and do not...

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