摘要:

Acoustic echo sounders have recently come into their own as valuable remote sensors for determining atmospheric structures and winds. Kelton and Bricout [Bull. Am. Meteor. Soc.45, 571–580 (1964)] first demonstrated that the acoustic Doppler shifted signals from scattered sound were related to the ambient winds. Later, McAllister [J. Atmos. Terr. Phys.30, 1439–1440 (1968)] showed that a vertically pointing monostatic acoustic sounder could reveal, in intricate detail, the atmospheric boundary layer structure. An acoustic echo sounder and wind sensor system capable of simultaneously measuring temperature fluctuations in the lower atmosphere and the vertical profile of wind speed and direction has been in operation at the Naval Electronics Laboratory Center since 1973. It is the purpose of this paper to describe the capability of this acoustic echo and wind sensor system for determining atmospheric structure and winds.

ISSN:0001-4966    

DOI:10.1121/1.2003216

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

An extensive set of published measurements of the propagation of noise from jet aircraft on the ground across an airport for differing weather conditions is compared with predictions using modern propagation theory from values of ground impedance, assuming an acoustically homogeneous atmosphere. When the atmosphere is in fact reasonably homogeneous under neutral weather conditions, there is quantitative agreement between calculated and measured behavior. The intricate pattern of acoustic behavior, as a function of frequency and distance, produced by inhomogeneous atmospheric conditions (gradients of wind temperature turbulence) is explained qualitatively by the appropriate modes of propagation revealed by the theory. The role of surface and sky waves in particular is illustrated.

ISSN:0001-4966    

DOI:10.1121/1.2003267

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

The ability to heat and emit the ultrasounds necessary for echolocation is not present at birth in the pallid bat and does not appear until at least a week postnatally. Dramatic changes occur both in pulse structure and auditory tuning as the bat matures. Pallid bats begin to fly at four weeks of age, but continue to nurse until seven weeks old. This allows them time to coordinate the flight and echolocation skills necessary for survival. Bats learn to correlate outgoing pulse with returning echoes. Naive bats approaching an obstacle do not exhibit the expected increase in pulse repetition rate, which occurs after some experience. The normal development of echolocation skills as judged by obstacle avoidance can be correlated with sound emission. Deficits occur in bats raised in environments in which their echoes are distorted or attenuated.

ISSN:0001-4966    

DOI:10.1121/1.2003326

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

Single units with phasic “on” firing patterns were recorded from the colliculus of unanesthetized bats (Tadarida brasiliensis mexicana). Our intention was to identify a population of neurons whose response characteristics are suitable for measuring the time interval between an emitted pulse and echo and, therefore, would be of value for echo ranging. Three catagories of units are distinguished on the basis of the consistency of the initial spike latent periods elicited by repetitive signals. Most important are the “phasic constant latency responders” (PCLR) in which the dispersions of initial spike latencies were at most ± 250 μsec at any intensity and where the mean latency charged by at most 1.7 msec when the signal level was increased from 3–6 dB to 30–40 dB above threshold. The initial spike latencies in most PCLR's were erratic with tone bursts but became highly synchronous with frequency‐modulated (FM) signals resembling the natural chirps of this species. Each PCLR had a “hair trigger” threshold to FM signals where the firing probability rose from near 0.0 to 0.8–1.0 as the signal level was increased from threshold to 2–6 dB above threshold. In addition, each of these units exhibited an “independent recovery” pattern where the presentation of an initially loud pulse did not effect the response to a simulated echo following shortly thereafter. The response and recovery characteristics of the PCLR's were correlated with behavioral data reported in previous studies and it is shown that the PCLR's have the capability for measuring the time interval between a pulse and the returning echo. Moreover, by assuming that the bat can correct for inherent “errors” resulting from dissimilar pulse‐echo intensities the population of PCLR's can provide a measurement of target distance that becomes progressively more accurate as the bat homes in on its target. [Supported by NSF Grant P401855‐000.]

ISSN:0001-4966    

DOI:10.1121/1.2003381

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

Results of a study of a Beluga trained to discriminate between two complex planar targets, indicate that this animal's echolocation discrimination capability with and without blindfolds is superior to that of bottlenosed dolphins tested on similar targets. The standard target used was a three‐step pyramid constructed of three polyvinyl chloride sheets each 13 mm thick. The first step was 10×10 cm, the second step was 7×7 cm and the third step was 3×3 cm. The selection of the standard target was considered a correct response. The comparison targets (incorrect choice) differed from the standard target only in the size (surface area) of the third step. With a comparison of a third step of 2.9×2.9 cm versus the standard, 3.0×3. 0 cm, the animal's mean correct response was 80.8% correct. When presented with two standard or identical targets the mean response dropped to chance (55. 5%). The performance of the bottlenosed dolphins tested on similar targets dropped to chance on a comparison of 2.7×2.7 cm versus 3.0×3.0 cm. The pulses used by the Beluga during the echolocation discrimination task contain very little acoustic energy below 12 kHz with the peak energy occurring at 40, 80, and 120 kHz. The measurements of the frequency components in the echolocation signal above 110 kHz are only tentatively believed due to limitations in the frequency response characteristics of the hydrophones used. The ability to use both sensory channels (tests without blindfolds) appeared to enhance discrimination ability slightly. [Work supported by NUC.]

ISSN:0001-4966    

DOI:10.1121/1.2003442

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

Constant frequency (CF) and frequency‐modulated (FM) pulses were utilized to examine the response characteristics of collicular neurons. Tonic, toniclike and various types of phasic “on” responses were noted depending upon the type of stimulus used. For example, a tonic response patten elicited from a given neuron with CF stimulation could be changed to a phasic “on” pattern with FM stimulation. Similarly, thresholds and input—output functions were affected by the stimulus type. Superimposed upon the effects of stimulus type were the effects of stimulus duration. Many neurons were found to have firing patterns and response characteristics to long duration stimuli that differed greatly from those observed with shorter signals having durations less than 2.0 msec. Results suggest that most inferior collicular neurons are best suited for extracting information from signals having durations comparable to those emitted during the search and approach phases of goal‐directed flight and are poorly suited for responding to shorter signals having durations typical of those emitted during the terminal phase of echolocation. [Supported by NSF Grant P401855‐000.]

ISSN:0001-4966    

DOI:10.1121/1.2003488

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

City planning has been an established professional discripline for nearly 50 years in the United States. Evolved from architecture mad other physically related disciplines city planning has broadened to also include interest in social and environmental concerns. Zoning was the first land use planning technique to incorporate noise performance requirements. Today many other land use planning techniques consider noise, among other environmental factors. An inventory of these planning techniques and their relative success are discussed, drawing upon municipal, state and Federal experiences. Recommendations are made for future courses of action to encourage greater effectiveness.

ISSN:0001-4966    

DOI:10.1121/1.2003539

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

As part of a comprehensive reference book on environmental impacts in transportation corridors, a practically oriented guide to assessment of noise effects has been prepared for the California Department of Transportation. Among the major areas covered are (1) review of current knowledge of noise and vibration effects associated with highway and rail traffic; (2) provision of methods of estimating exposure levels associated with varying amounts of traffic; (3) relation of expected levels of exposure to anticipated social impacts; (4) explanation of a quantitative Noise Impact Index for evaluating alternative routes; and (5) discussion of measures to mitigate noise impacts. This paper summarizes the findings contained in the guide to noise impact assessment to bring it to the attention of transportation planners and others concerned with assessment of noise effects.

ISSN:0001-4966    

DOI:10.1121/1.2003594

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

Image methods have been successfully used in the analysis of the acoustic properties of enclosures for the purpose of architectural design. In this paper we disuss use of image techniques for simulating the impulse response between two points in a small room. The resulting response is then convolved with any desired input signal and the reverberated output used for signal processing or psychoacoustic studies. The entire process is carried out using a digital computer so that bide ranges of parameters ran be simulated with perfect control over experimental conditions.

ISSN:0001-4966    

DOI:10.1121/1.2003643

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP

摘要:

The application of noise‐control engineering during the design of a new international airport for a future population center presents unique challenges. This airport will be constructed on a site 25 km long and 12 km wide and is 22 km from any populated area. The airport facilities include two international terminals, two domestic terminals, a large mosque, a control tower, a royal facility, and many support buildings. This paper discusses the organization and procedures used to provide noise‐control engineering support to the engineering and architectural firms designing these various facilities. Included is the methodology used in determining the acoustical criteria, the sound isolation and speech privacy requirements for the various spaces. Sound isolation details and unit cost comparisons are presented.

ISSN:0001-4966    

DOI:10.1121/1.2003085

出版商:Acoustical Society of America    

年代:1976

数据来源: AIP