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1.
In this study an attempt has been made to extract sediment geoacoustic properties using ambient noise measured from a vertical hydrophone array. Time series noise data recorded from three shallow water sites (Chennai, Cuddalore and Cochin) along the Indian continental shelf were used for the analysis. The compressional sound speed of sediment for all the sites was estimated from the vertical directionality of ambient noise. Using the value of the compressional sound speed remaining wave properties and material properties were deduced from the Grain-Shearing (G-S) theory of wave propagation in saturated granular media. The type of sediment extracted from the G-S theory correlates well with the results obtained from sieve and particle size analysis of grab samples, collected from all the sites. The study clearly shows the application of ambient noise in extracting environmental information in shallow water, and further applying it to improve sonar performance modeling. 相似文献
2.
关于海洋噪声谱级的理论,测量和分析以及相应噪声源的机理探讨已经有大量的工作;例如Knudson[6];EcKarf[2];Weng[10]和Piyyof[7]的工作.文〔1〕采用分层介质中的传播算子,推广了EcKarf的工作,建立了一般情况下由源特性及传播算子所表达的噪声场表示.目前关于传播条件--在浅海中特别是海底的反射特性--对环境噪声场特性的影响还较少有具体的结果. 相似文献
3.
The present study demonstrates the use of ambient noise for estimating the ocean depth in shallow waters of the Indian continental shelf. Ocean depth is estimated using a technique known as passive fathometer processing, which involves the correlation of surface-generated ambient noise with its reflection from the seabed. Ambient noise data collected using a vertical array from four locations (off Cochin, off Cuddalore, off Kakinada, and off Goa) along the Indian continental shelf were used for the study. The noise data recorded during windy conditions within the frequency band of 200–5000 Hz were used for analysis. Both conventional and adaptive beamforming techniques were applied for the passive estimation of the ocean depth. The estimated water column depth using the ambient noise measurement shows good agreement with the known depth from all the four locations. The advantages and limitations of the adaptive processing technique have also been discussed. The study clearly demonstrates the application of the surface-generated ambient noise in seabed image processing. 相似文献
4.
Solutions were computed for the vertical ambient sea noise field directionality at five sites in the Western North Atlantic Ocean using data from a 26-hydrophone element array with a 358.4-foot aperture at a center depth of 1,000 feet. Results show that the low-frequency noise below 100 Hz is concentrated near the horizontal (50 to 93 percent of the noise power between /spl plusmn/15/spl deg/ of horizontal) and is apparently dependent on bottom loss and shipping density. The results in the band 200 to 380 Hz are a combination of sea state and shipping noise dependent. A noise field solution technique was developed involving noise cross spectral matrix inversions. This technique overcomes some of the drawbacks of previous techniques such as least mean square estimation and successive approximations. 相似文献
5.
A novel array was designed and tested in the eastern Pacific Ocean for the measurement of the vertical directionality of ambient noise. The results of the test, conducted in 1983, illustrate the existence of a 5-dB "noise notch" for arrival angles associated only with submerged acoustic sources. A measurement system based on improvements to the design and processing is described. 相似文献
6.
《Oceanic Engineering, IEEE Journal of》2005,30(2):267-274
A theoretical model for the vertical directionality and depth dependence of high frequency (8 to 50 kHz) ambient noise in the deep ocean is developed. The anisotropic noise field at a variety of depths and frequencies is evaluated and displayed. It was found that at high frequencies and deep depths, a bottom-mounted hydrophone receives the maximum noise energy from overhead rather than from the horizontal. This leads to the consideration of an oblate hydrophone receiving response pattern for underwater tracking ranges that would provide a constant signal-to-noise ratio (SNR) for an acoustic source located anywhere in a circular area centered above the hydrophone. Two of the desirable characteristics of this type of pattern are the increase in receiving range of a bottom-mounted sensor and the decrease of the dynamic range of signals that a signal processor must handle. 相似文献
7.
8.
A digital array of 120 acoustic channels 900 m in length has been constructed to study low-frequency (20-200 Hz) ambient noise in the ocean. The array may be deployed vertically or horizontally from the research platform FLIP and the array elements are localized with a high-frequency acoustic transponder network. The authors describe the instrumentation, telemetry, and navigation systems of the array during a vertical deployment in the northeast Pacific. Preliminary ambient noise spectra are presented for various array depths and local wind speeds. Ambient noise in the frequency band above 100 Hz or below 25 Hz increases with local wind speed. However, in the frequency band 25-100 Hz, ambient noise is independent of wind speed and may be dominated by shipping sources 相似文献
9.
The vertical directionality of ambient noise due to surface agitation for frequencies between 2 and 5 kHz propagated to a subsurface receiver has a characteristic shape, knowledge of which may enhance shallow-water operations. In general, the noise level is highest at upward-looking angles and attenuated at downward-looking angles depending on the nature of the bottom. In environments with a negative profile gradient, the noise level is also greatly reduced in a low-angle shadow zone or "notch" at angles around horizontal. This paper reviews the character of vertical noise directionality by examining two measured data sets and considering the underlying physical mechanisms that drive the form of the distribution. A discussion of the implications of vertical noise directionality for design and operation of receiving sonar systems is presented. In particular, the effect of mainlobe beamwidth and sidelobe suppression are considered along with the directionality of the noise field. Finally, an overview of the derivation of a vertical noise model based on the integrated mode method of propagation prediction is followed by model reproduction of measurements. 相似文献
10.
An ambient noise model for the Northeast Pacific Ocean Basin is presented. This model possesses the capability of synthesizing the noise field, with resolution in the vertical and horizontal finer than 1/spl deg/. Simulation results utilizing the synthesized field are shown to be in excellent agreement with measured horizontal directionality, vertical directionality, and depth dependence data for frequencies from 12.5 to 250 Hz. An important difference between this model and other models is the consideration of the SOFAR channel component, which is the dominant noise at these low frequencies. It is shown that only when this component of the noise is included can the simulation results be expected to agree with measured data. 相似文献
11.
Sabra K.G. Roux P. Thode A.M. D'Spain G.L. Hodgkiss W.S. Kuperman W.A. 《Oceanic Engineering, IEEE Journal of》2005,30(2):338-347
Estimates of the travel times between the elements of a bottom hydrophone array can be extracted from the time-averaged ambient noise cross-correlation function (NCF). This is confirmed using 11-min-long data blocks of ambient noise recordings that were collected in May 1995 near the southern California coast at an average depth of 21 m in the 150-700 Hz frequency range. Coherent horizontal wavefronts emerging from the time derivative of the NCF are obtained across the array's aperture and are related to the direct arrival time of the time-domain Green's function (TDGF). These coherent wavefronts are used for array element self-localization (AESL) and array element self-synchronization (AESS). The estimated array element locations are used to beamform on a towed source. 相似文献
12.
Carey W.M. Evans R.B. Davis J.A. Botseas G. 《Oceanic Engineering, IEEE Journal of》1990,15(4):324-334
The structure of beam noise measured at the output of a vertical array in a range dependent ocean basin was investigated using the modified wide-angle parabolic equation (PE). Noise sources were distributed throughout the basin, and the field due to each noise source at an array located in the midbasin was calculated. The response of the array to the superposition of the noise sources was found by beamforming. An efficient and direct approach that superimposes the noise sources on the PE field as the field is marched toward the array was developed. Downslope calculations of the midbasin vertical directionality were made between 50 and 400 Hz with this technique. Use of a geoacoustic model shows that the bottom behaves as a low-pass filter 相似文献
13.
The shipping noise properties in the deep ocean are studied. Shipping noise exhibits the strong dual-horned directionality features in the flat-seabed ocean, and its directional density can be modeled by a Von Mises distribution. With the explicit expression for the directional density function, the spatial coherence functions of shipping noise are also derived, and the relative features are studied. The research result shows that the properties of shipping noise are different from the ambient noise of other sources, and it can be used for the sonar array design. The model is well matched with the experimental result, and it can be extended to the situations when the ambient noise exhibits the dual-horned structure. 相似文献
14.
尚尔昌 《海洋学报(英文版)》1982,1(1):47-57
The effects of boundary reflection loss, scattering loss caused by the rough surface and the radiative directivity of the surface sources (parameter m) on the ambient noise field in shallow-water homogeneous layer have been discussed theoretically. It has been found that the parameter m has the stronger controlling role on the behavior of the ambient noise field than others. 相似文献
15.
Ambient noise measurements were made at seven different locations during the first four months of 1977. The measurement systems included: two types of towed arrays, a bottomed array, and systems with sensors distributed throughout the water column. The noise in the frequency regime dominated by shipping was found to be extremely high with a spectrum level of 92 dB//1 /spl mu/Pa at 50 Hz. These high levels were attributed to the high-density shipping. Horizontal directionality of the noise varied from site to site, ranging from highly directional to nearly nondirectional. The character of the directionality was highly dependent on the site position relative to shipping lanes. The noise showed very little dependence on depth. 相似文献
16.
The correlation of ambient noise with wind speed, and the depth dependence of ambient noise are both investigated, where the ocean noise data were recorded by a vertical line array in the northern South China Sea. It is shown that the correlation coefficients increase with increasing hydrophone depth during typhoon periods when the frequency ≥ 250 Hz, which opposes the generally accepted knowledge that the correlation coefficients of noise level and wind speed decrease with increasing depth during non-typhoon periods. Particularly at frequencies of 250 Hz, 315 Hz and 400 Hz, the correlation coefficients increase by more than 0.05 at depths ranging from 155 m to 875 m. At the three frequencies, the average noise levels also increase with increasing depth during typhoon periods. It is suggested that these differences are attributed to the wind-generated noise in shallow waters and the effect of "downslope enhancement" to sound propagation. During typhoon periods, the surf breaking and surf beat upon the shores and reefs are strengthened, and the source levels are increased. The wind-generated noise in shallow waters interacts with the downslope sea floor, with the noise-depth distribution changed by a "downslope enhancement" effect promoting noise propagation. 相似文献
17.
Simultaneous measurements of low-frequency sound generated by an explosive source and backscattered from the seafloor in the eastern Mediterranean were made with two receiver configurations: a towed horizontal array and a vertical array. Images of the scattering features on the beam-time data of the horizontal array were useful in the interpretation of the scattering process and in estimating areas of scatterers received by the vertical array, and permitted scattering strengths to be estimated for both configurations. Images of the vertical array data provided information about the vertical arrival angles at the array from specific scatterers. At long range, the sound from the scattering features was received at grazing angles less than13deg . The scattering strengths for three features varied from - 47 to - 25 dB. The mean frequency dependence over the band 125 to 700 Hz varied from 0 to 2.5 dB/octave with greater variations occurring within smaller bands. 相似文献
18.
Gorodetskaya E.Yu. Malekhanov A.I. Sazontov A.G. Vdovicheva N.K. 《Oceanic Engineering, IEEE Journal of》1999,24(2):156-171
This paper presents results of combined consideration of sound coherence and array signal processing in long-range deep-water environments. Theoretical evaluation of the acoustic signal mutual coherence function (MCF) of space for a given sound-speed profile and particular scattering mechanism is provided. The predictions of the MCF are employed as input data to investigate the coherence-induced effects on the horizontal and vertical array gains associated with linear and quadratic beamformers with emphasis on the optimal ones. A method of the radiation transport equation is developed to calculate the MCF of the multimode signal under the assumption that internal waves or surface wind waves are the main source of long-range acoustic fluctuations in a deep-water channel. Basic formulations of the array weight vectors and small signal deflection are then exploited to examine optimal linear and quadratic processors in comparison with plane-wave beamformers. For vertical arrays, particular attention is paid also to evaluation of the ambient modal noise factor. The numerical simulations are carried out for range-independent environments from the Northwest Pacific for a sound frequency of 250 Hz and distances up to 1000 km. It was shown distinctly that both signal coherence degradation and modal noise affect large-array gain, and these effects are substantially dependent on the processing technique used. Rough surface sound scattering was determined to cause the most significant effects 相似文献
19.
A seismic reflection profiling system consisting of a 264 m long, deep-towed, 15-element, end-fire, vertical array and a 40 cubic inch airgun was successfully used to profile a sediment pond in the trough of the inactive segment of the Kane Fracture Zone close to it's intersection with the Mid-Atlantic Ridge at 24° N. The increased signal to noise ratio achieved with the array demonstrates that it is a useful tool for detailed seismic profiling in areas of rough topography in the deep ocean.Woods Hole Oceanographic Institution Contribution No. 5443. 相似文献