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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
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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
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作者根据能量叠加原理和“喇叭噪声当量车”模型,得出了估算由喇叭鸣号引起的交通噪声等效声级增量的计算公式,提出了一种实地测量和计算的简便方法。 相似文献
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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
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Depth dependence of noise resulting from ship traffic and wind 总被引：1，自引：0，他引：1
Under conditions of distantly generated noise, the noise level is found to decrease with depth in the mid-northeastern Pacific. These data show a decrease in noise level greater than 25 dB between critical depth and the ocean bottom. A result of this decrease is that locally wind-generated noise can be detected on near-bottom receivers for wind speeds less than 10 kn. It is shown that the noise level generated form local sources such as wind and nearby shipping is almost independent of receiver depth. The differences in spectra shape between the distant shipping noise and wind-generated noise and the low noise levels detected near the ocean bottom allow the measurement in the frequency band at 200-500 Hz of local wind noise level for wind speeds less than 10 kn 相似文献
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A buoy for measuring wind speed and the ambient noise sound pressure level from 10 to 1500 Hz with 1-Hz resolution is described. The measurement buoy was deployed in a remote fjord in southeastern Alaska from October to December, 1989. The results from the data collected show that, for a wind speed of 5 kn, the measured ambient noise level at 900 Hz lies well below the Knudsen curve for open-ocean, wind-generated noise. As the wind speed increases from 5 to 10 kn, the measured ambient noise level approaches the Knudsen curve, increasing at 4 dB/kn compared to 1 dB/kn for the Knudsen curve. Above 10 kn, the measured ambient noise level matches the Knudsen curve 相似文献
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多通道带乘性噪声系统观测噪声的最优估计 总被引：1，自引：0，他引：1
研究在多通道观测时观测噪声的最优估计问题。就多通道的乘性噪声为对角阵且动态噪声一步相关并与观测噪声在同时刻和过去相邻时刻也相关的复杂情况下给出了在线性最小方差意义下的观测噪声最优滤波估计算法和固定区间平滑估计算法。针对这些算法进行了仿真研究 ,仿真结果表明了算法的有效性。 相似文献
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通过物理模型实验给出了沙坝海岸丁坝附近交叉波浪场形成的裂流沿裂流槽水深平均速度剖面中心线的垂向分布,研究了各个测量断面上横向速度、纵向速度以及速度矢量沿水深的分布特征。研究分析了沿岸方向驻波节腹点和裂流槽相对位置的影响以及规则波和不规则波结果的差异,得到了裂流速度时均值和时变值的结果。结果表明,纵向速度在不同的时间段上的平均值基本是相同的,但横向速度不是这样,其在不同时间段上的平均值在大小和正负号上都可能存在较大差别,这导致整个速度矢量在不同时间段上也表现出不同的三维分布特征。但这些不同的分布也存在着共同点,即沿水深速度矢量大部分存在着向丁坝方向偏转,这反映了丁坝存在的影响。特别是,纵向速度沿水深分布都可以采用统一的幂函数表达。 相似文献
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研究带乘性噪声广义系统的观测噪声最优估计问题。在假设系统正则的情况下,针对乘性噪声为一般随机矩阵即各观测通道乘性噪声同时刻相关的情况,通过受限等价变换和状态扩维的方法,给出了线性最小方差意义下的观测噪声最优滤波算法和最优平滑估计算法。数字仿真结果表明了算法的有效性。 相似文献
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研究特征系统实现算法在模态识别过程中的噪声处理问题。特征系统实现算法为目前土木工程领域应用较为广泛的一种模态识别法。在处理实测数据时,特征系统实现算法将实测数据分解为结构真实信号和噪声信号,从而将噪声消除。分块Hankel矩阵的维数对信噪分离过程影响很大。提出当分块Hankel矩阵的分块行与分块列数接近时,真实和噪声信号可以最好的分离。通过在实测信号里添加噪声(产生噪声-噪声信号),将实测信号和噪声-噪声信号识别的结果进行比较,提出了1种验证识别模态参数是否为结构真实模态的检验方法。本文应用导管架平台实例来验证提出方法的适用性。结果表明,当分块Hankel矩阵的分块行与分块列数接近时,真实和噪声信号能够有效地分离,此时添加的噪声主要影响噪声信号部分。由实测信号和噪声-噪声信号识别的模态参数非常吻合。 相似文献
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In December 1987, on the occasion of the first demonstration flight of the shuttle-borne Tethered Satellite System (T.S.S.), NASA will deploy in orbit a 20-km vertical conducting wire (electrodynamic tether) and will test, among other things, the wire's ability to function as generator of de electric power, through thenu times B mechanism of interaction, as well as its capability to operate as a serf-powered radiator of ultra-low frequency/ extremely low frequency waves (ULF/ELF), through such mechanisms as the Alfvén Wings. The wire's ability to generate dc electric power up to the 100 kW level has been investigated by several authors and it is now considered to be a reasonable expectation. Concerning the wire's ability to radiate ULF/ELF waves, rigorous analytical evidence still has to be worked out. The expectation at this time is that this vertical radiator may be able to inject from above into the earth-ionosphere transmission line about 10 W at night and10^{-1} by day. Thus in the "hot spot" on the earth's surface, directly underneath (in a magneto-conjugate sense) the orbiting system, signal-to-noise ratios of practical interest may be achievable against natural micropulsation noise. The tether's ability to excite from above long-range propagation modes in the earth-ionosphere transmission line has still to be verified analytically. It is expected that by 1987-1989, comprehensively analytical and experimental evidence will be available to the ULF/ELF community, so that conclusions may be drawn as to the feasibility of strategic communications using orbiting wires. The advantage of the spaceborne placement for the ULF/ELF radiator, compared with the traditional ground-based placement, may be the avoidance of the potential environmental threat posed by the conventional siting. 相似文献
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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
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The measurement of the signal to noise ratio in continuous seismic profiling systems is carried out by means of a small general purpose digital computer equipped with an analog to digital converter. The computer is programmed to compute and compare the power spectrum of a sample of noise to the power spectrum of a sample of noise plus an echo. Power spectra of some twenty to fifty shots are averaged to yield reliable estimates of the signal to noise ratio as a function of frequency. The observed spectra agree well with spectra calculated from signals measured near to an air-gun. This measurement of signal to noise ratio as a function of frequency provides unambiguous information for the adjustment of the necessary band-pass filter thus improving the operation of a continuous seismic profiler. 相似文献
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一种新型便携式旋桨流速仪 总被引：1，自引：0，他引：1
介绍了一种新型BH-1型便携式旋桨流速仪,主要由自主研制的流速传感器、手持式主机及微机数据回放处理软件三部分组成.其传感器采用独特的导流筒和导流罩结构设计,增加了系统的抗干扰能力,有效提高了测量准确性.应用单片机技术实现了数据的实时检测与处理,多路存储以及瞬时测量流量功能.通过静态试验标定,表明该流速仪测量范围(0.04～4)m/s,非线性误差为0.874%.该流速仪结构新颖、使用轻巧方便、稳定可靠,已广泛应用于国家海洋局对陆源入海排污口排污监测和海洋环境管理工作中. 相似文献
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带乘性噪声系统由于其广泛的适用性,一直成为研究的热点。针对带乘性噪声系统状态最优估计的自适应算法进行研究,探讨在噪声服从平稳正态分布情况下,对未知动态噪声方差阵与观测噪声方差阵的辨识问题。在证明带乘性噪声系统新息在稳态时和线性系统新息有着相似稳定特性的前提下,通过对线性系统辨识方法的改进,完成对带乘性噪声系统噪声方差阵的辨识,并利用新息特性对该方法进行进一步改进,以提高辨识精度;最后通过仿真验证该方法的有效性。 相似文献