Crockettrodgers2505

Three 1000-km long, high resolution conductivity, temperature, depth sections in the North Pacific Ocean obtained by the ship towed vehicle SeaSoar are analyzed to quantify 2005 March/April upper-ocean sound-speed structure and determine the effects on low to mid-frequency transmission loss (TL) through numerical simulation. The observations reveal a variable mixed layer acoustic duct (MLAD) with a mean sonic layer depth of 91-m, and an even higher variability, 80-m-average-thickness transition layer connecting the mixed layer (ML) with the main thermocline. The sound-speed structure is hypothesized to be associated with thermohaline processes such as air-sea fluxes, eddies, submesoscale, fronts, internal waves, turbulence, and spice, but the analysis does not isolate these factors. Upper-ocean variability is quantified using observables of layer depth, ML gradient, and sound speed to compute low order moments, probability density functions, horizontal wavenumber spectra, and empirical orthogonal function decomposition. buy UPF 1069 Coupled mode acoustic propagation simulations at 400 and 1000 Hz were carried out using the sound-speed observations from the upper 400-m appended to climatology, which reveal propagation physics associated with diffraction, random media effects, and deterministic feature scattering. Statistics of TL reveal important energy transfers between the MLAD and the deep sound channel.A rupture induced underwater sound source (RIUSS) is being developed as an alternative to other impulsive sound sources commonly utilized in underwater acoustics experiments and surveys. The device is comprised of a graphite rupture disk mounted over an evacuated chamber. After the disk breaks, an inrush of water creates a high amplitude acoustic pulse. A field test was conducted to measure the acoustic output as a function of depth for a given source configuration, and high speed underwater video was simultaneously captured with an acoustic recording system to correlate the features of the acoustic output to the ensuing bubble activity.The impact of an extraneous formant on intelligibility is affected by the extent (depth) of variation in its formant-frequency contour. Two experiments explored whether this impact also depends on masker spectro-temporal coherence, using a method ensuring that interference occurred only through informational masking. Targets were monaural three-formant analogues (F1+F2+F3) of natural sentences presented alone or accompanied by a contralateral competitor for F2 (F2C) that listeners must reject to optimize recognition. The standard F2C was created using the inverted F2 frequency contour and constant amplitude. Variants were derived by dividing F2C into abutting segments (100-200 ms, 10-ms rise/fall). Segments were presented either in the correct order (coherent) or in random order (incoherent), introducing abrupt discontinuities into the F2C frequency contour. F2C depth was also manipulated (0%, 50%, or 100%) prior to segmentation, and the frequency contour of each segment either remained time-varying or was set to constant at the geometric mean frequency of that segment. The extent to which F2C lowered keyword scores depended on segment type (frequency-varying vs constant) and depth, but not segment order. This outcome indicates that the impact on intelligibility depends critically on the overall amount of frequency variation in the competitor, but not its spectro-temporal coherence.Brass wind instruments with long sections of cylindrical pipe, such as trumpets and trombones, sound "brassy" when played at a fortissimo level due to the generation of a shock front in the instrument. It has been suggested that these shock fronts may increase the spread of COVID-19 by propelling respiratory particles containing the SARS-CoV-2 virus several meters due to particle entrainment in the low pressure area behind the shocks. To determine the likelihood of this occurring, fluorescent particles, ranging in size from 10-50 μm, were dropped into the shock regions produced by a trombone, a trumpet, and a shock tube. Preliminary results indicate that propagation of small airborne particles by the shock fronts radiating from brass wind instruments is unlikely.Timbre dissimilarity of orchestral sounds is well-known to be multidimensional, with attack time and spectral centroid representing its two most robust acoustical correlates. The centroid dimension is traditionally considered as reflecting timbral brightness. However, the question of whether multiple continuous acoustical and/or categorical cues influence brightness perception has not been addressed comprehensively. A triangulation approach was used to examine the dimensionality of timbral brightness, its robustness across different psychoacoustical contexts, and relation to perception of the sounds' source-cause. Listeners compared 14 acoustic instrument sounds in three distinct tasks that collected general dissimilarity, brightness dissimilarity, and direct multi-stimulus brightness ratings. Results confirmed that brightness is a robust unitary auditory dimension, with direct ratings recovering the centroid dimension of general dissimilarity. When a two-dimensional space of brightness dissimilarity was considered, its second dimension correlated with the attack-time dimension of general dissimilarity, which was interpreted as reflecting a potential infiltration of the latter into brightness dissimilarity. Dissimilarity data were further modeled using partial least-squares regression with audio descriptors as predictors. Adding predictors derived from instrument family and the type of resonator and excitation did not improve the model fit, indicating that brightness perception is underpinned primarily by acoustical rather than source-cause cues.The relations describing the reflection of three-dimensional acoustic ray paths impinging on a non-flat surface are derived and used to approximate the propagation of infrasonic signals over irregular terrain in the geometric limit. The influence of non-flat ground is strongest for those paths that reflect off the surface multiple times, such as those in the tropospheric waveguide; however, notable differences in source and receiver elevations for stratospheric and thermospheric paths can produce notable differences in travel times and arrival amplitudes. The interaction of ray paths with topographical features is investigated using a simple hill to demonstrate the impact of topography on propagation within an azimuthal plane, as well as cases in which the ground surface interaction deflects the path out of the azimuthal plane. Finally, broadband waveform predictions are compared with observations for an event in the western U.S., and a statistical analysis of scattering losses due to interaction with topography in the limit of geometric acoustics is used to improve the agreement between predicted and observed infrasonic signals.