共查询到20条相似文献，搜索用时 15 毫秒
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Feng Lu Milios E. Stergiopoulos S. Dhanantwari A. 《Oceanic Engineering, IEEE Journal of》2003,28(3):552-563
In real-time towed-array systems, performance degradation of array gain occurs when a line array that is not straight is assumed straight in the beamforming process. In this paper, a new method is proposed for array shape estimation. The novelty of this method is that it accounts for the variations in the tow ship's speed, which are typical during course alterations. The procedure consists of two steps. First, we solve for the tow-point induced motion in the time domain based on the constraints from the tow-point compass-sensor readings and from a discretized Paidoussis equation. At each time instance, the shape estimate is solved from a linear system of equations. We also show that this solution is equivalent to a previous frequency-domain solution while the new approach is much simpler. In the second step, we use the tail compass-sensor data to adjust the overall array shape. By noting that variations in the ship speed lead to a distortion in the normalized time axis, we first register the predicted tail displacement with the tail sensor readings along the time axis. Then, distortions in the estimated array shape over its length can be compensated accordingly. We also model a slow-changing bias between sensor zeros and remove systematic sensor errors. The effectiveness of the new algorithm is demonstrated with simulations and real sea-trial data. 相似文献
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在多波束回声声纳系统中，高分辨处理算法例如MUSIC、ESPRIT，被广泛应用于海底地形的测绘。在应用高分辨算法时，一条均匀线阵是必要条件。然而，由于系统覆盖范围/分辨率的需求以及安装空间的限制，在多波束系统中经常会采用特殊形状的接收阵列，这使得高分辨算法无法直接应用。同时回波信号的短时平稳特性使得难以估计出协方差矩阵，这也增加了高分辨算法在多波束系统中的应用难度。本文首先介绍一种基于多角度子阵波束形成的ESPRIT算法，该算法能降低高分辨算法对信噪比、样本点数和计算能力的要求。仿真表明此算法能提供更好的分辨力。接着提出一种将基于多角度子阵波束形成的ESPRIT算法与虚拟阵列变换相结合的高分辨底检测算法，并针对高分辨底检测算法在U型阵上的应用进行了探讨。计算机仿真和试验数据处理结果验证了文章所提高分辨底检测算法的有效性。 相似文献
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An HF radar called the Coastal Ocean Dynamics Applications Radar (CODAR) is presently being used in several forms to measure ocean surface parameters. The original version was developed by the National Oceanic and Atmospheric Administration (NOAA) and utilizes a four-element receive array. The array consists of four equally spaced elements arranged on a circle with a radius of 0.2151 wavelengths (at 25.4 MHz). It was designed to measure ocean currents using a direction-finding technique based on an extension to a simple two-element interferometer. The problem of determining the bearing of a radiating source can be readily shown to be equivalent to that incurred in spectral estimation. In an attempt to improve upon the processing of existing data, modern nonlinear spectral estimation techniques are applied in a beam-forming bearing estimation procedure and compared against several direction-finding algorithms. Enhancement of bearing estimators via analysis of the eigenstructure of a spatial correlation matrix is included. Antenna response patterns are calculated and used to investigate properties of direction-finding algorithms. Simulated data are used for a comparison of direction finding and beam forming. The asymmetrical bias of each method is investigated to determine its effect on the error in estimating the angle of arrival of a radar target. 相似文献
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Aperture extension is achieved in this novel ESPRIT-based two-dimensional angle estimation scheme using a uniform rectangular array of vector hydrophones spaced much farther apart than a half-wavelength. A vector hydrophone comprises two or three spatially co-located, orthogonally oriented identical velocity hydrophones (each of which measures one Cartesian component of the underwater acoustical particle velocity vector-field) plus an optional pressure hydrophone. Each incident source's directions-of-arrival are determined from the source's acoustical particle velocity components, which are extracted by decoupling the data covariance matrix's signal-subspace eigenvectors using the lower dimensional eigenvectors obtainable by ESPRIT. These direction-cosine estimates are unambiguous but have high variance; they are used as coarse references to disambiguate the cyclic phase ambiguities in ESPRIT's eigenvalues when the intervector-hydrophone spacing exceeds a half-wavelength. In one simulation scenario, the estimation standard deviation decreases with increasing intervector-hydrophone spacing up to 12 wavelengths, effecting a 97% reduction in the estimation standard deviation relative to the half-wavelength case. This proposed scheme and the attendant vector-hydrophone array outperform a uniform half-wavelength spaced pressure-hydrophone array with the same aperture and slightly greater number of component hydrophones by an order of magnitude in estimation standard deviation. Other simulations demonstrate how this proposed method improves underwater acoustic communications link performance. The virtual array interpolation technique would allow this proposed algorithm to be used with irregular array geometries 相似文献
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Towed array beamforming algorithms require accurate array shape information in order to perform properly. Very often, these algorithms assume the array is linear. Unfortunately, the mechanical forces on the array due to ship motion and sea dynamics can change the shape of the array, which degrades the performance of the beamforming algorithm. A data-driven approach to estimating the relative shape of a nominally linear array is presented. The algorithm is robust in that it optimally combines information contained in a wide band of frequencies and source bearings. At the heart of the algorithm is a maximum-likelihood (ML) estimation scheme. The Cramer-Rao lower bound is derived and compared to the performance of the ML estimator. The utility of the algorithm is verified using both simulated and actual towed array data experiments 相似文献
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The effects of both small perturbations and large deformations to the array's shape on both conventional and adaptive beamformers are shown for two frequencies: the spatial Nyquist frequency (or design frequency) of the array and a frequency about three times greater. Large shape deformations lead to a decrease in the conventional beamformer's output power for a beam steered in the direction of the signal source, together with an increase in the sidelobe levels (or secondary maxima), while small perturbations in the array shape have little effect. Signal suppression is observed to be far greater for the adaptive beamformer because it is very sensitive to system errors. The imposition of a weight norm constraint on the adaptive beamformer reduces the signal suppression only for small shape perturbations array shape estimation techniques are needed to reduce signal suppression for large shape deformations. The adverse effects of a nonlinear array shape on both conventional and adaptive beamforming are shown to be substantially reduced by applying techniques that estimate the coordinates of the hydrophones prior to beamforming 相似文献
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The problem of beam formation from a towed line array whose shape has been distorted is considered. Emphasis is placed on the beam broadening and range estimation effects of array shape perturbations and how the resulting losses can be regained if the actual element positions are known. Specific illustrations are provided for various levels of shape distortion. For example, a 15-m bow in a 232.5-m-long array broadens the beamwidth by a factor of 3 at 50 Hz. As another example, a 6-m bow in an 800-m-long array leads to a 20-pereent range underestimation at 10 km for a 100-500-Hz broadband source. 相似文献
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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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An important area of towed underwater acoustic research is the determination of the 3D positions of all hydrophones in the array. Although there are a number of methods available that provide position information at a small number of locations along the array, an interpolation scheme is needed that will permit the estimation of the position of all hydrophones so that further processing of acoustic data may proceed. An interpolation technique based on a twisted quartic spline approximation to a space curve is presented. This technique provides the advantages of numerical stability, necessary smoothness, and satisfaction of physical boundary conditions. Most importantly, it permits the estimation of the positions of all hydrophones in an array 相似文献
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The problem of towed array shape estimation is reformulated and shown to be mathematically equivalent to the problem of state estimation with abruptly changing bias of the plant noise process. An algorithm belonging to the family of adaptive multimodel partitioning algorithms is subsequently applied to this problem, and its performance is comparatively evaluated with that of nonadaptive algorithms previously proposed through simulation experiments 相似文献
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《Oceanic Engineering, IEEE Journal of》2008,33(2):215-223
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随着人类社会对海洋认识和探索的深入,对水下监测和探测设备提出了更高的要求,探测阵列模型和阵列信号处理算法决定了监测和探测设备的复杂度。 针对特定水下多目标定位平台的复杂环境,建立了一种任意空间阵列数学模型,介绍了四阶累积量算法,分析了阵列信号处理中四阶累积量的阵列扩展特性。 基于四阶累积量的 MUSIC 算法的空间谱分析,建立了任意阵列形状的欠自由度多目标方位估计的理论基础。 计算机仿真结果表明了算法的正确性和有效性。 相似文献
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Hodgkiss W.S. Ensberg D.E. Murray J.J. D'Spain G.L. Booth N.O. Schey P.W. 《Oceanic Engineering, IEEE Journal of》1996,21(4):393-401
Accurate knowledge of array shape is essential for carrying out full wavefield (matched-field) processing. Direct approaches to array element localization (AEL) include both nonacoustic (tilt-heading sensors) and acoustic (high-frequency, transponder-based navigation) methods. The low-frequency signature emitted from a distant source also can be used in an inversion approach to determine array shape. The focus of this paper is on a comparison of the array shape results from these three different methods using data from a 120-m aperture vertical array deployed during SWellEx-3 (Shallow Water evaluation cell Experiment 3). Located 2 m above the shallowest array element was a self-recording package equipped with depth, tilt, and direction-of-tilt sensors, thereby permitting AEL to be performed non-acoustically. Direct AEL also was performed acoustically by making use of transponder pings (in the vicinity of 12 kHz) received by high-frequency hydrophones spaced every 7.5 m along the vertical array. In addition to these direct approaches, AEL was carried out using an inversion technique where matched-field processing was performed on a multitone (50-200 Hz), acoustic source at various ranges and azimuths from the array. As shown, the time-evolving array shape estimates generated by all three AEL methods provide a consistent picture of array motion throughout the 6-h period analyzed 相似文献
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海浪方向谱的现场观测与分析 总被引：3，自引：0，他引：3
方向谱是海浪的基本性质之一。本文在国内首次采用测波仪阵列法在渤海采油平台上成功地观测到海浪方向谱，给出了当地随波浪成长而变化的方向谱表达式。观测前采用数模和模型试验方法，对阵列的布置型式、测波仪间距和平台等对观测结果的影响，以及现有各种方向谱分析方法的精度等进行了对比分析，为提高观测精度，保证方向谱分析的质量提供了依据。 相似文献
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The spectral structure of oceanic incoherent Doppler sonar data is analyzed with Fourier and two finite-parameter modeling methods (Spectral Moment Estimation (SME) and AutoRegressive (AR)). Fourier spectral analysis, applied to long-range segments of echo return data, validates a theoretical point scattering model. It is demonstrated that Fourier spectral techniques, applied to data from incoherent sonar systems, cannot be used to probe oceanic spectral and velocity fields on the scales that frequently are important in oceanographic applications. The finite-parameter methods model the spectral structure on closely spaced range intervals. The SME method calculates the first moment of the Doppler spectrum at each range interval and the AR method provides spectral estimates at these same intervals. Trade-offs in estimating scatterer radial velocity using the various algorithms are considered. It is shown that a frequency-integrated AR technique has velocity estimation performance comparable to the SME method. In addition, the AR technique reveals that several regions of data possess asymmetric spectral structure. The implications of this spectral structure for oceanic velocity estimates are discussed. 相似文献
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In traditional spectral analysis the use of windows is required because the assumption is made that the data outside the sample are zero. A data window is simply equal to unity inside, and zero outside the sample. This is equivalent to the truncation of the autocovariance function beyond some lag after which zeros are added. In Fast Fourier Transform spectral estimation a spectral window with smaller or greater negative side lobes is used. Any use of windows results in a smearing or spectral leakage that limits the spectral resolution. Maximum entropy spectral estimation (MEM) is equivalent to an extrapolation of the autocovariance function being consistent with some model assumptions. The result of the extrapolation is an increased spectral resolution in the frequency domain. In applications of MEM no kind of windows are used. MEM is applied to describe wind wave scalar spectra. The technique can also be used in the plane to estimate directional spectra. Our results show that MEM is a powerful tool for estimation of scalar spectra and simulation of the sea surface. There are also theoretical reasons for assuming that MEM are superior to traditional methods when only short samples are available. Our preliminary results verify this assumption. We propose a data acquisition system based on MEM, and also show that the response of linear systems can be calculated and simulated by MEM. 相似文献
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A new technique for two-dimensional (2-D) spectral estimation of a stationary random field (SRF) is investigated in this paper. This is based on the extension of the Radon transform theory to stationary random fields (SRF's), proposed by Jain and Ansari [19]. Using the Radon transform, the 2-D estimation problem is reduced to a set of one-dimensional (1-D) independent problems, which could then be solved using 1-D linear prediction (LP) or by any other high-resolution estimation procedure. This is unlike previous methods which obtain the 2-D power spectral density OPSD) estimate by using 1-D high-resolution techniques in the spirit of a separable estimator [2]. Examples are provided to illustrate the performance of the new technique. Various features of this approach are highlighted. 相似文献
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海浪通常以风浪和涌浪混合的形式存在,如何进行分离风浪和涌浪一直是海浪理论研究和海洋工程应用中的重要问题。本文利用模型试验和实测资料,对目前提出的一种二维谱风涌浪分离方法（2D法）和三种一维谱风涌浪分离方法（PM法、WH法、JP法）进行了检验,分析发现：2D法给出的结果整体而言最为可靠,与2D法相比,PM法明显高估了风浪成分,WH法低风速时高估了风浪,高风速时跟2D法比较接近,而JP法在整体上高估了风浪成分。通过调整分割频率的比例系数,改进了PM法,改进后的PM法给出的分离结果与2D法最为一致。 相似文献