Grayson H. Rayborn

Dissociative photoionization cross sections of O2 from threshold to 120 Å

The photoionization cross sections for producing the O2+ parent ion and the O+ fragment ion from neutral O2 are presented from 650 to 120 A. A new technique was used that eliminated the serious problem of identifying the true abundance of the O+ ions. These ions are generally formed with considerable kinetic energy and because most mass spectrometers discriminate against energetic ions true O+ abundances are difficult to obtain. In the present work the relative cross sections for producing O2+ are obtained and normalized against the total cross sections in a spectral region where dissociative ionization is not possible. The fragmentation cross sections for O+ were then obtained by subtraction of the O2+ cross section from the total photoionization cross section.

Detection of Oscillatory and Impulsive Transients Using Higher Order Correlations and Spectra

Higher‐order cross and ordinary correlation detectors are applied to four deterministic transients contaminated by uncorrelated Gaussian noise only. Histograms and moments are used to examine the properties of the signals and their effect on detector performance. Receiver operating characteristic (ROC) curve analysis and limiting signal‐to‐noise ratios for ‘‘good’’ detection provide comparative measures for different detectors. Probability density functions of detection ordinate values of signal‐present and noise‐only correlations are used to explain ROC curve behavior. Using a known source, the cross‐correlation detector performs better than the higher‐order correlation detectors for each transient studied. However, for an unknown narrow pulse source signal, the bicorrelation and tricorrelation detectors outperform the cross‐correlation detector. In contrast, the bicorrelation detector performs very poorly for low‐frequency narrow‐band signals with a small third moment embedded in uncorrelated Gaussian n...

Approximating the finite square well with an infinite well: Energies and eigenfunctions

Polynomial expansions are used to approximate the equations of the eigenvalues of the Schrodinger equation for a finite square potential well. The technique results in discrete, approximate eigenvalues which, it is shown, are identical to the corresponding eigenvalues of a wider, infinite well. The width of this infinite well is easy to calculate; indeed, the increase in width over that of the finite well is simply the original width divided by the well strength. The eigenfunctions of this wider, infinite well, which to first order has the same width for the ground state and all excited states, are also good approximations to the exact eigenfunctions of the finite well. These approximate eigenfunctions and eigenvalues are compared to accurate numeric calculations and to other approximations from the literature.

Measurements of ambient noise and sperm whale vocalizations in the northern Gulf of Mexico using near bottom hydrophones

The Littoral Acoustic Demonstration Center (LADC) consisting of the University of Southern Mississippi (USM), the University of New Orleans (UNO), and the Naval Research Laboratory at Stennis Space Center (NRL-SSC), with guidance and technical assistance from the Naval Oceanographic Office (NAVOCEANO), was formed to do ambient noise and marine mammal acoustic measurement and analysis. Three Environmental Acoustic Recording System (EARS) buoys, designed and produced by NAVOCEANO, were deployed by LADC in the northern Gulf of Mexico (GoM) in the summer of 2001. These bottom-moored omni-directional hydrophone recording systems were modified by NAVOCEANO to sample almost 12 kHz, so that the vocalizations of sperm whales could be recorded. The Sperm Whale Acoustic Monitoring Program (SWAMP) was conducted during that summer by the Minerals Management Service and its collaborators. The EARS buoys recorded during the entire 36 days of SWAMP from 17 July through 21 August of 2001. The EARS buoy hydrophones, 50m above the bottom, were placed on a downslope line, ending at the largest concentration of sperm whale sightings in the northern GoM, in 600m, 800m, and 1000m water depths. The moorings were instrumented with self-recording environmental sensors to obtain time series data of temperature, conductivity, and pressure at specified depths spanning the water column. Four cruises were made to deploy and recover the buoys and to collect a suite of environmental measurements, including CTD and XBT casts and a chirp sonar survey for bottom properties to support propagation modeling. In between the first and second cruises, Tropical Storm Barry moved through the area and changes in the oceanographic properties were observed. Each EARS buoy recorded a bandwidth of 5859 Hz for 36 days. These data clearly reveals sperm whale vocalizations, passing ships, and seismic airguns. Marine mammal vocalizations and airgun signatures have been isolated and are being analyzed. Spectral levels for ten minute averages of ambient noise on four different days show moderate shipping levels except during the passage of the tropical storm. A plateau in the noise spectrum from 200 to 1000Hz on one day is due to the presence of sperm whales. Spectrograms show sperm whale clicks and creaks and the seismic airgun signal is very clear.

Spectrogram analysis of low to mid frequency marine mammal clicks

Previous investigators have proposed explanations for some sperm whale click structure and pointed out that the separation of individual pulses within the click might be used to determine approximately the size of the sperm whales. Recently, Mohl et al. [J. Acoust. Soc. Am. 114, 1124–1154 (2003)] have shown that echo‐location click structure is highly dependent on the received angle. In data measured by the Littoral Acoustic Demonstration Center using bottom‐moored hydrophones in the northern Gulf of Mexico in the summers of 2001 and 2002, rich click structures were observed in the spectrograms of many click trains, some of which exhibit strikingly consistent spectral nulls across the train. Although this structure in the spectra could be due to propagation effects, investigations to date suggest this possibility is highly unlikely, as discussed in the next abstract. Therefore it is at least plausible that the structure could be used to identify individual animals. This is known to be a difficult problem ...

Automated detection of sperm whale sounds as a function of abrupt changes in sound intensity

An algorithm designed to detect abrupt changes in sound intensity was developed and used to identify and count sperm whale vocalizations and to measure boat noise. The algorithm is a Matlab routine that counts the number of occurrences for which the change in intensity level exceeds a threshold. The algorithm also permits the setting of a ‘‘dead time’’ interval to prevent the counting of multiple pulses within a single sperm whale click. This algorithm was used to analyze digitally sampled recordings of ambient noise obtained from the Gulf of Mexico using near bottom mounted EARS buoys deployed as part of the Littoral Acoustic Demonstration Center experiment. Because the background in these data varied slowly, the result of the application of the algorithm was automated detection of sperm whale clicks and creaks with results that agreed well with those obtained by trained human listeners. [Research supported by ONR.]

Iterative and function-continuation Fourier deconvolution methods for enhancing mass spectrometer resolution

Mass spectrometer data in the form of ion current versus mass-to-charge ratio often include overlapping mass peaks, especially in low- and medium-resolution instruments. Numerical deconvolution of such data effectively enhances the resolution by decreasing the overlap of mass peaks. In this paper two approaches to deconvolution are presented: a function-domain iterative technique and a Fourier transform method which uses transform-domain function-continuation. Both techniques include data smoothing to reduce the sensitivity of the deconvolution to noise. The efficacy of these methods is demonstrated through application to representative mass spectrometer data and the deconvolved results are discussed and compared to data obtained from a spectrometer with sufficient resolution to achieve separation of the mass peaks studied. A case for which the deconvolution is seriously affected by Gibbs oscillations is analyzed.

Correction of instrumental distortion by analytical deconvolution of data

A general, analytical theorem developed by van de Hulst for inverting the convolution integral is reviewed and illustrated both with synthetic data and with experimental data from time‐of‐flight measurements. If the undesired influence of an instrument used in an experimental measurement can be represented by the convolution integral, the original undistorted or ’’true’’ distribution may sometimes be recovered in post‐processing the data by means of deconvolution. Analytic deconvolution is achieved by using the coefficients from a power series representation of the distorted output distribution and a set of ’’solving polynomials’’ which may be readily derived from the response function of the instrument. The distortion due to the excitation pulse duration in time‐of‐flight molecular beam data has been removed by application of the theorem. Some possible advantages of this analytical method over conventional deconvolution techniques are discussed.

Localization to verify the identification of individual sperm whales using click properties.

Previous research to identify individual sperm and beaked whales from the properties of their echolocation and coda clicks using cluster analysis has been reported. Although reasonably consistent and robust results showing distinct classes (each corresponding to an individual) have been obtained with both self‐organizing maps and K‐means, no independent verification of these identifications has previously been available. However, data from a July 2007 experiment in the Gulf of Mexico should provide enough geometry information to verify some identifications. The Littoral Acoustic Demonstration Center deployed six environmental acoustic recording system buoys, measuring to 96 kHz for 9 days, to record sperm and beaked whale clicks in the northern Gulf of Mexico. Three buoys were in close proximity to enable multisensor detections of single clicks for possible localization, tracking, or bearing estimation sufficient to confirm the identification of individuals from cluster analysis. Displays of cluster class...

Source characterization study 2007: The three‐dimensional primary field of a seismic airgun array.

During September 2007 the Littoral Acoustic Demonstration Center collected acoustic and related data from three moored arrays and ship‐deployed hydrophones spanning the full water column to measure the 3‐D acoustic field of a seismic airgun array. A seismic source vessel shot a series of lines to give detailed angle and range information concerning the field of the primary arrival. The data were collected in the western Gulf of Mexico between the East Break and Alamos Canyon regions. Peak pressures, sound exposure levels, total energy spectra, one‐third octave band, and source directivity analyses are measures used to characterize the field. Three‐dimensional maps of these quantities are generated to show dependence on emission and azimuthal angles and range. Three‐dimensional visualizations are being developed using a visualization cave and software for 2‐D cave emulation. [Research supported by the Joint Industry Programme through the International Association of Oil and Gas Producers.]