Modelling Uncertainty Caused by Internal Waves on the Accuracy of MBES

A 3D ray tracing model has been developed to estimate the effects of internal waves upon the accuracy of multibeam echosounders (MBES). A case study examines the variability in these effects as a function of survey line direction and also considers the case of improving 2D ray tracing models with wave parameters derived from MBES water column imagery. Results indicate that, under certain circumstances, the effects of internal waves can prove to be a significant source of uncertainty that detracts from the ability to efficiently map the seafloor with wide swath angles

Modeling the Effect of Oceanic Internal Waves on the Accuracy of Multibeam Echosounders

When ray bending corrections are applied to multibeam echosounder (MBES) data, it is assumed that the varying layers of sound speed lie along horizontally stratified planes. In many areas internal waves occur at the interface where the water’s density changes abruptly (a pycnocline), this density gradient is often associated with a strong gradient in sound speed (a velocline). The internal wave introduces uncertainty into the echo soundings through two mechanisms: (1) tilting of the velocline, and (2) vertical oscillation of the velocline’s depth. A model has been constructed in order to examine how these effects degrade the accuracy of MBES measurements. The model numerically simulates the 3D ray paths of MBES soundings for a synthetic flat seafloor, as though the soundings have been collected through a user-defined internal wave. Along with sound speed information, the ray paths are used to estimate travel times which are then utilized as inputs for a conventional 2D ray trace. The discrepancy between the 3D and 2D ray traced solutions serve as an estimate of uncertainty. The same software can be extended to model the expected anomalies associated with tidal fronts and other phenomena that result in significant tilting or oscillation of the velocline. A case study was undertaken using observed internal wave parameters on the Scotian Shelf. The case study examines how survey design parameters such as line spacing, direction of survey lines, and water column sampling density can influence the uncertainty introduced by internal waves. In particular, an examination is undertaken in which 2D ray tracing models are augmented with MBES water column imaging of the velocline. The investigation shows that internal waves have the potential to cause vertical uncertainties exceeding IHO standards and that the uncertainty can potentially be mitigated through appropriate survey design. Results from the case study also indicate that acoustic tracking of the velocline has the potential to counteract the effects of internal waves through augmentation of 2D ray tracing models. This technique is promising, however, much more research and field testing is required to ascertain the practicality, reliability and repeatability of such an approach

Community detection with spiking neural networks for neuromorphic hardware

We present results related to the performance of an algorithm for community detection which incorporates event-driven computation. We define a mapping which takes a graph G to a system of spiking neurons. Using a fully connected spiking neuron system, with both inhibitory and excitatory synaptic connections, the firing patterns of neurons within the same community can be distinguished from firing patterns of neurons in different communities. On a random graph with 128 vertices and known community structure we show that by using binary decoding and a Hamming-distance based metric, individual communities can be identified from spike train similarities. Using bipolar decoding and finite rate thresholding, we verify that inhibitory connections prevent the spread of spiking patterns.Comment: Conference paper presented at ORNL Neuromorphic Workshop 2017, 7 pages, 6 figure

Modelling Uncertainty Caused by Interval Waves on the Accuracy of MBES

A 3D ray tracing model has been developed to estimate the effects of internal waves upon the accuracy of multibeam echosounders (MBES). A case study examines the variability in these effects as a function of survey line direction and also considers the case of improving 2D ray tracing models with wave parameters derived from MBES water column imagery. Results indicate that, under certain circumstances, the effects of internal waves can prove to be a significant source of uncertainty that detracts from the ability to efficiently map the seafloor with wide swath angles.Se ha desarrollado un modelo de seguimiento de rayos en 3D para estimar los efectos de las olas internas en la exactitud de los sondadores acústicos multihaz (MBES). El estudio de un caso examina la variabilidad en estos efectos como función de la dirección de las líneas de sondas y considera también el caso consistente en mejorar el seguimiento de rayos en 2D con parámetros de olas derivados del tratamiento de imágenes de la columna de agua con MBES. Los resultados indican que, en algunas circunstancias, los efectos de las olas internas pueden resultar ser una fuente significativa de incertidumbre que le resta valor a la capacidad de representar eficazmente el fondo del mar con ángulos de corte anchos.Un modèle de traçage à rayons tridimensionnels a été développé en vue d’évaluer les effets des ondes internes sur l’exactitude des échosondeurs multifaisceaux (MBES). Une étude de cas examine la variabilité sur ces effets comme fonction de la direction des lignes de sondes et traite également de l’amélioration des modèles de traçage à rayons bidimensionnels avec des paramètres d’ondes tirés de l’imagerie MBES des colonnes d’eau. Les résultats indiquent que, dans certaines circonstances, les effets des ondes internes peuvent s’avérer une importante source d’incertitudes qui porte atteinte à la capacité de cartographier de manière efficace le fond marin avec de larges angles de couverture

HAWAII LONGLINE VESSEL ECONOMICS

Public Economics,

Applications of Persistent Homology in Nuclear Collisions

We introduce a novel set of observables associated to the rapidly developing field of persistent homology for the quantitative characterization of nuclear collisions and their evolution. Persistent homology allows for the identification of topological and homological characteristics of distributions in multi-dimensional spaces. We demonstrate here how to apply the toolset of persistent homology to the extraction of novel clustering signatures and the identification of long-range flow correlations in the particle production process of nuclear collisions

Beam Steering Thermal Emitters

Thermal sources, such as an incandescent light bulb or heated stove top, are understood to be incoherent sources of radiation. This property ensures a desk lamp’s light does not create fringe patterns when passed through double slits. Their inability to form interference patterns has made beam steering for thermal sources impractical. This thesis, addresses the use of surface propagating electromagnetic waves called surface plasmon polaritons (SPPs) to emit coherent radiation from a thermal source at near field. Through a corrugated surface, SPPs were scattered away from the surface to form a condensed beam. Through modeling of SPP interference at near field, a micron-level device was characterized and fabricated to exhibit beam steering properties at a specified wavelength of 8 μm. Laboratory testing with a Fourier transform spectrometer allowed comparison of the model with laboratory data. Laboratory testing showed that the signal-to-noise ratio was too low to prove beam steering had been achieved. This may have been due to mistakes in the fabrication process or the proximity of the focusing plane to the thermal source.Ope