The number of humpback whales frequenting Glacier Bay has been decreasing in recent years while the number of whales in the Fredrick Sound and Stevens Passage area has been increasing. A study was made to determine the acoustic characteristics of both areas and measure the influence of man-made noise sources on ambient levels. ‘Transmission loss (TL) in selected regions of both areas was measured and ambient noise spectra obtained. The TL characteristics for a shallow source and receiver were observed to have a 20 log (range) dependence below 1 kHz in both areas. In Glacier Bay a shallow surface duct was observed which changed the TL to approximately 10 log (range) dependence above 1 kHz. Low ambient noise levels were observed in the absence of boat and ship traffic. Thus the sound from louder vessels dominated the ambient out to a range of up to six miles in some measurements. A significant low-frequency noise contribution, believed to be due to glacier motion, was observed at some locations in Glacier Bay. [Work supported by NOAA, NMFS and National Park Service.]

Correspondence analysis has been applied to 34 spectral curves of volume reverberation to cluster the spectra into groups. The clustering is compared with an earlier grouping of the spectra based on the crossstandard-deviation matrix with essentially similar results. However, the correspondence analysis technique has a number of clear-cut advantages: (1) the clustering is quickly displayed in a two-dimensional plot; (2) eigenvectors computed in the analysis are spectral curves which are characteristic of extremum environments in the data set (we call them volume reverberation environments and discuss their possible indentification with preponderant fish species); (3) those frequencies which most directly serve as indicators of a particular cluster of spectra are identified; and (4) the examination of the relationship of environmental parameters and the factor scores computed in the analysis provide a basis for extrapolation of the spectra to their appearance in unmeasured conditions. The volume reverberation spectra (known as column strengths) are chosen as a particular example of the application of correspondence analysis; we believe it is broadly applicable to the problem of identifying and classifying spectra in many disciplines. As an aid to the reader in understanding the technique, we have summarized the governing equations of correspondence analysis and given a geometrical interpretation relating the original spectra, eigenvectors, and factor scores.Subject Classification: 60.20' 30.40.

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Volume-reverberation observations were made at 34 stations on Cruise 105 .of R/V CHAIN during its passage from Newfoundland to the Azores, and thence to Portugal and Ireland. The acoustic returns at each station were analyzed in 16 1/3-octave bands extending from 1 kHz to 31.5 kHz to yield column strength spectra. Techniques to maximize the accuracy of these spectra are described. Representative spectra are plotted. Using a measure we have called the cross-standard deviation, we found evidence that the spectra for nearby stations were similar and thus could be classed in geographically-based groups called pelagic regions. This is reasonable since much volume reverberation is sound scattered from animals which in turn are distributed in pelagic faunal regions. We present a matrix showing the similarity of each pair of stations; a small number indicates similarity, while a large number indicates difference in the two spectra. We have identified many of these regions on the basis of physical-oceanographic features such as the polar front. These features are used in defining boundaries for the regions. Subject Classification: 30.40. the front south of our stations had been shown to be a faunal boundary. 0 Since a pattern existed, we felt justified in extending our analysis technique to the remainder of the cruise to look for further patterns and the boundaries they suggested. Acoustic column-strength spectra were determined from broad-band measurements of the deep scattering layers at 34 stations and were computed in 1/3-octave bands from 1 to 31.5 kHz. A few of these stations lay near or within regions which had already been delimited by Backus et al., o but most were in regions where their sampling was being carried out for the first time. The paper is divided as follows: I. Data gathering and processing describes the experimental methods followed in both collecting the data at sea and processing them ashore. Techniques followed at both stages to maximize spectral accuracy are discussed. H. Spectral results is a summary of the prominent spectral features found at many stations. HI. A measure of the similarity of spectra describes the measure we propose to quantify the similarity of spectra. It is called the cross-standard deviation and has been computed for each pair of stations. Low values of the cross-standard deviation are hypothesized to correspond to stations lying in a common pelagic region. IV. Spectral pelagic regions--their description and justification considers the full matrix of cross-standard deviations and various submatrices in order to define different pelagic regions for the portions of the North Atlantic covered by the cruise. l•hysical-oceanographic arguments are adduced where appropriate to reinforce the decisions defining regions.V. Boundaries is an attempt to set some geographic limits to these regions beyond that given by the spectral information. Physical-oceanographic information such as the defining 200-m isotherm for the polar front is used to draw boundaries suggested by the acoustic dat...

A point scatterer model is used to formulate expressions for the expected number of level and zero crossings of backscattered volume reverberation signals. It is shown that zero crossing measurements on narrow-band transmitted signals can yield quantitative estimates of scatterer population density in oceanic deep scattering layers. Level crossing data can be used to estimate scattering strengths. For wide-band transmitted signals, level crossing information can provide a relationship between scatterer Q and resonant frequency. Some features of using crossing data are (a) level and zero crossing systems are relatively simple to implement; (b) scattering strength measurements are independent of transmitted signal waveshape; and (c) since zero crossings are unaffected by the general time dependent decrease in reverberation level, zero crossing measurement systems do not require time-varying gain compensation. An experiment east of Bermuda compares scattering strength determination through level crossings to more conventional measurements. Also, the experiment gives scatterer density as a function of depth through a scattering layer. Peak densities of between 10−3 and 2 × 10−3 scatterers/m3 are found.