Biomedical subjects

G L D'Spain

Publications and source records attributed to G L D'Spain.

3 recordsLinked to original sources

PubMed2006

Observations of biological choruses in the Southern California Bight: A chorus at midfrequencies.

This paper describes the characteristics of an underwater biological chorus recorded in the midfrequency band (1-10 kHz) in the Southern California Bight. The recordings were made in July, 2002 by a large-vertical-aperture, 131-element, 2D billboard array. The chorus, observed predominantly on two consecutive nights during the 8-day experiment, is composed of two bands of energy centered around 1.5 kHz and between 4 and 5 kHz. It causes a complete reversal in the vertical directional characteristics of the mid-frequency ambient sound field between day and nighttime periods; whereas the vertical structure during the day shows a notch in the horizontal direction with levels more than 10 dB below those at higher angles, the nighttime levels in the horizontal can exceed those at other vertical angles by more than 10 dB. These nighttime sounds also are strongly anisotropic in azimuth; they appear to come mainly from a popular Southern California fishing spot where the water depths exceed 75 m. Vertical beam-to-beam coherence squared estimates suggest the chorus source region exists on spatial scales greater than the multipath interference wavelengths of this environment. Individual sounds comprising the chorus, although difficult to separate from the background din, have a fluttering, rasping character.

Animals↗

PubMed2001

Long range source localization from single hydrophone spectrograms.

A source near the deep sound channel axis excites mode groups (or paths) that involve both deep sound channel and boundary interacting propagation. Dispersion from a broadband source as measured on a single hydrophone can be used to estimate source range. Furthermore, modal group speeds have a functional transition when passing through purely refractive to boundary reflecting phase speed regions which, under certain conditions, provides additional arrival structure to aid in source localization. This additional arrival structure is in the form of a focal region in a spectrogram. Indeed, different data sets from the Acoustic Thermometry of the Ocean Climate (ATOC) Program [ATOC Consortium, Science 281, 1327-1332 (1998)] show that localization can be accomplished using this focal region and/or the overall dispersion properties as originally suggested fifty years ago [M. Ewing and J. L. Worzel, Geo. Soc. Am., Memoir 27 (1948)].

Journal Article↗

PubMed2000

Matched-field processing, geoacoustic inversion, and source signature recovery of blue whale vocalizations.

Matched-field processing (MFP) and global inversion techniques have been applied to vocalizations from four whales recorded on a 48-element tilted vertical array off the Channel Islands in 1996. Global inversions from selected whale calls using as few as eight elements extracted information about the surrounding ocean bottom composition, array shape, and the animal's position. These inversion results were then used to conduct straightforward MFP on other calls. The sediment sound-speed inversion estimates are consistent with those derived from sediment samples collected in the area. In general, most animals swam from the east to west, but one animal remained within approximately 500 m of its original position over 45 min. All whales vocalized between 10 and 40 m depth. Three acoustic sequences are discussed in detail: the first illustrating a match between an acoustic track and visual sighting, the second tracking two whales to ranges out to 8 km, and the final sequence demonstrating high-resolution dive profiles from an animal that changed its course to avoid the research platform FLIP (floating instrument platform). This last whale displayed an unusual diversity of signals that include three strong frequency-modulated (FM) downsweeps which contain possible signs of an internal resonance. The arrival of this same whale coincided with a sudden change in oceanographic conditions.

Acoustics↗