共查询到20条相似文献，搜索用时 15 毫秒
1.
This correspondence provides expressions for the Cramer-Rao lower bounds for the estimates of azimuth and elevation made with an arbitrary three-dimensional array of sensors. These results are formulated for a plane wave Gaussian signal in uncorrelated Gaussian noise. In addition, sufficient conditions on the array geometry are given which ensure that the azimuth and elevation angle estimates are uncoupled 相似文献
2.
It is desired to track the location of an underwater acoustic source with range difference measurements from a stationary passive array. Many times, the array has only one or two sensors, and the multipath and intersensor range difference measurements are insufficient to localize and track a source moving along an arbitrary path [1]. Here, we propose to track sources with one- or two-sensur stationary passive arrays by making the simplifying assumption that the source's path can be described by a small set of so-called track parameters. Range difference information can then be used to estimate the track parameter set rather than the source location as a function of time. In this paper, we choose the track parameters to specify a straight-line constant-velocity constant-depth path. Cramer-Rao bounds are presented for estimating these track parameters from the time history of multipath and intersensor range difference measurements. It is shown that this track parameter set cannot be accurately estimated from the time history of a single multipath range difference without side information (an independent velocity estimate, for instance), although multipath and intersensor range difference measurements from a two-sensor array are generally sufficient to estimate the track parameter set. Computationally efficient techniques are presented which estimate track parameters from range difference measurements taken from one- and two-sensor arrays. Monte-Carlo simulations are presented which show that these techniques have sample mean-square error approximately equal to the Cramer-Rao bound when a single multipath range difference and an independent velocity estimate are available. The sample mean-square error is shown to be in the range of two to ten times the corresponding Cramer-Rao bounds when these techniques are applied to two-sensor range difference data. 相似文献
3.
The author addresses the spatial coherence of high-frequency acoustic signals that have been forward scattered from the sea surface. The Fresnel-corrected Kirchhoff approximation is applied to derive closed-form expressions for the spatial coherence. These expressions are used to study the influence of geometrical and environmental factors on the coherence. An application of the theory involving the rejection of the surface image of a source by a vertical adaptive line array is presented. The author concludes that the environment has a strong impact on the array processing of surface-scattered fields through its influence on both vertical and horizontal spatial coherence 相似文献
4.
Pierre Cervenka Ute Christina Herzfeld Christian De Moustier 《Marine Geophysical Researches》1994,16(6):407-425
When isobath maps of the seafloor are constructed with a bathymetric sidescan sonar system the position of each sounding is derived from estimates of range and elevation. The location of each pixel forming the acoustic backscatter image is calculated from the same estimates. The accuracy of the resulting maps depends on the acoustic array geometry, on the performances of the acoustic signal processing, and on knowledge of other parameters including: the platform's navigation, the sonar transducer's attitude, and the sound rays' trajectory between the sonar and the seafloor. The relative importance of these factors in the estimation of target location is assesed. The effects of the platform motions (e.g. roll, pitch, yaw, sway, surge and heave) and of the uncertainties in the elevation angle measurements are analyzed in detail. The variances associated with the representation (orientation and depth) of a plane, rectangular patch of the seafloor are evaluated, depending on the geometry of the patch. The inverse problem is addressed. Its solution gives the lateral dimensions of the spatial filter that must be applied to the bathymetric data to obtain specified accuracies of the slopes and depths. The uncertainty in the estimate of elevation angle, mostly due to the acoustic noise, is found to bring the main error contribution in across-track slope estimates. It can also be critical for along-track slope estimates, overshadowing error contributions due to the platform's attitude. Numerical examples are presented.On leave at the Naval Research Laboratory, Code 7420, Washington D.C. 20375-5350, U.S.A. 相似文献
5.
《Oceanic Engineering, IEEE Journal of》2008,33(2):224-231
6.
For distributed sensor technologies whose costs are understood (or which may be estimated in some reasonable manner), we derive a simple analytic means by which to estimate the most cost-effective sensor detection range. Specifically, we consider design of sensor nodes whose purpose is to exploit a set of coherent acoustic array technologies to detect a target with a specified radiated signature in an environment characterized by the sonar equation. We define a simplified calculus of distributed search that exploits simple target motion as a means to enhance spatial coverage for a sparse field of uniformly distributed sensor nodes. We examine this strategy in the context of both area (two-dimensional) and volume (three-dimensional) surveillance coverage under both cylindrical and spherical spreading models. In all situations, cost-effective design guidance is given based on maintaining spatial detection coverage 相似文献
7.
Le Gac J.-C. Asch M. Stephan Y. Demoulin X. 《Oceanic Engineering, IEEE Journal of》2003,28(3):479-493
The inversion of broad-band low-frequency acoustic signals received on sparse arrays can lead to robust and efficient estimations of sea-bed properties. This paper describes a shallow-water geoacoustic inversion scheme based on the use of a model-based matched-impulse response on a single hydrophone. Results from the INTIMATE'96 experiment on the Portuguese shelf break are reviewed. In order to minimize the effects of strong time variability due to internal tides, only the time-stable waterborne bottom-surface reflected arrivals are exploited. A quasi-linear inversion algorithm is first applied to refine the geometry of the experiment. Then, inversion of bottom parameters is performed with an objective function that only makes use of the bottom-surface reflected arrivals' amplitudes. The experimental results show that broad-band transmissions (300-800 Hz) received on a single hydrophone, combined with the use of a simple eigenray code, are sufficient to correctly resolve geometrical parameters and bottom features. The analysis of the reflection coefficients both on simulated and real data helps to understand the validity of the inverted parameters and to derive the basis of an equivalent medium concept for geoacoustic inversion based on a "through-the-sensor" approach. 相似文献
8.
Acoustic vector-sensor correlations in ambient noise 总被引：3，自引：0，他引：3
Most array-processing methods require knowledge of the correlation structure of the noise. While such information may sometimes be obtained from measurements made when no sources are present, this may not always be possible. Furthermore, measurements made in-situ can hardly be used to analyze system performance before deployment. The development of models of the correlation structure under various environmental assumptions is therefore very important. In this paper, we obtain integral and closed form expressions for the auto- and cross-correlations between the components of an acoustic vector sensor (AVS) for a wideband-noise field, under the following assumptions concerning its spatial distribution: 1) azimuthal independence; 2) azimuthal independence and elevational symmetry; and 3) spherical isotropy. We also derive expressions for the cross-covariances between all components of two spatially displaced AVSs in a narrowband-noise field under the same assumptions. These results can be used to determine the noise-covariance matrix of an array of acoustic vector sensors in ambient noise. We apply them to a uniform linear AVS array to asses its beamforming capabilities and localization accuracy, via the Cramer-Rao bound, in isotropic and anisotropic noise 相似文献
9.
Propagation of shallow water waves in an open parabolic channel using the WKB perturbation technique
A singular perturbation analysis based on the WKB technique to study the hydrodynamic performance of periodic ocean waves that are incident on an open parabolic channel of constant depth is proposed. We derive a linear model to predict the propagation of the long ocean waves into the channel. In this manner, the spatial distribution for the surface elevation of the ocean waves inside the channel as a function of two dimensionless parameters, namely, a kinematical parameter, κ and a geometrical parameter ε, is governed by a second-order ordinary differential equation. The kinematical parameter κ denotes the ratio of the potential head, due to gravity, to the kinetic head of the ocean waves along the longitudinal axis of the parabolic channel. Meanwhile, ε is a dimensionless geometrical parameter that represents a characteristic ratio of the parabolic channel. Using matching conditions, simple expressions for the reflection and transmission coefficients are obtained. 相似文献
10.
《Oceanic Engineering, IEEE Journal of》1996,21(1):24-36
The treatment of acoustic energy forward scattered from the sea surface, which is modeled as a random communications scatter channel, is the basis for developing an expression for the time-dependent coherence function across a vertical receiving array. The derivation of this model uses linear filter theory applied to the Fresnel-corrected Kirchhoff approximation in obtaining an equation for the covariance function for the forward-scattered problem. The resulting formulation is used to study the dependence of the covariance on experimental and environmental factors. The modeled coherence functions are then formed for various geometrical and environmental parameters and compared to experimental data 相似文献
11.
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
12.
13.
Kopp L. Cano D. Dubois E. Wang L. Smith B. Coates R.F.W. 《Oceanic Engineering, IEEE Journal of》2000,25(3):282-295
From a designer viewpoint, a parametric array should not appear different from any other type of acoustic transducer and should be described by a limited set of design equations together with their range of validity. In this paper, these design equations are stated and discussed. They are used to optimize the acoustic parameters of an underwater communication system using parametric transduction and to evaluate its performance in terms of signal-to-noise ratio and data-rate limits as a function of transmission range. It turns out that, for a maximum data transmission rate at a given range, there is a set of optimum design parameters which is a function of the array size only. This means that, once given an operational range, the primary frequency, the electrical power, the maximum acoustic source level, and the directionality of the transducer can be deduced directly from the array diameter 相似文献
14.
针对深远海条件下海面声源目标定位精度与海底潜标布阵方式相关性问题,建立了基于到达时间差(TDOA)体制的被动定位模型,根据设计工况讨论了海底潜标布阵原则,利用蒙特卡洛数值模拟方法分析了声源位于阵内、阵外以及阵元失效3种情况下定位精度分布情况。仿真结果表明：当4个潜标呈矩形分布时,仅东、西两侧较小区域未覆盖,覆盖范围内平均定位精度约为34.1 m。随着阵元数增加,在中心区域附近定位精度显著提高,阵型外侧定位精度由内向外逐渐下降。当目标位于对角线方向靠近顶角附近时,模型交汇解算性能较差,定位精度大于500 m。当1#潜标失效时,测量海域西北角方向定位精度较差,但精度优于25 m的区域要比5#潜标失效情况大。7#潜标失效时,定位精度与各阵元均正常的情况接近。研究结果为海面声源测量系统设计、阵型选择、精度评估等海洋工程应用提供理论依据。 相似文献
15.
Orbital motion of azimuth waves imposes differential Doppler shifts on wave imagery as seen by a SAR. This paper shows that these Doppler shifts are a function only of the wave and sensor geometry, and are not a function of SAR parameters. The azimuth wave reflectivity so modulated is equivalent to a redistributed scatterer density which can be used as an input with the SAR modulation transfer function for general distributed scenes to derive the azimuth wave image. The static scatterer density is calculated for a variety of sea states. Wave accelerations are not of first-order importance. Scatterer fade (decorrelation) is of central importance, as it impacts the SAR transfer function that is effective in wave imaging. 相似文献
16.
The role of sub seabed topographically controlled fluid migration is assessed to improve our understanding of distributions of acoustic chimneys at the Nyegga pockmark field on the mid-Norwegian continental margin. 3D seismic data interpretations resulted in topographic gradients of seismic time surfaces and RMS amplitude maps. Topographical gradient maps and flow tracing allowed identifying migration pathways and trapping locations for free gas within the shallow sub seabed. The occurrence of acoustic chimneys, pockmarks and mounds correlate with identified fluid migration pathways and gas trapping locations. An important factor that controls the trapping locations and the lateral distribution of seeps on the seabed at Nyegga is the variation through time of the depth of the base of the gas hydrate stability zone (BGHSZ). Fluids can derive from gas hydrate systems that are suspected of being a biogenic source and/or Tertiary domes that are considered to show leakage of thermogenic fluids to the shallow geosphere. 相似文献
17.
《Oceanic Engineering, IEEE Journal of》2008,33(2):215-223
18.
A submerged acoustic source radiates narrowband Gaussian noise. Its signal propagates to a remote, large aperture vertical array over a multipath channel whose characteristics may or may not be fully known. The primary concern of this study is the accuracy of source depth estimates obtainable from the array output. Cramer-Rao bounds for the depth estimate are calculated. When the velocity profile is known exactly, the value of the bound is quite insensitive to the precise form of the velocity profile. A bound calculated from a constant velocity profile yields an excellent approximation for many situations likely to be encountered in practice. Introduction of an unknown parameter into the velocity profile has little effect on the Cramer-Rao bound for depth. However, a maximum likelihood estimator of depth working with an inaccurate value of the unknown parameter performs poorly. To obtain satisfactory performance, one must estimate the unknown parameters along with the source depth. Simulations demonstrate the success of this approach 相似文献
19.
The source localization and tracking capability of the freely drifting Swallow float volumetric array is demonstrated with the matched-field processing (MFP) technique using the 14-Hz CW data collected during a 1989 float experiment conducted in the northeast Pacific. Initial MFP of the experimental data revealed difficulties in estimating the source depth and range while the source azimuth estimate was quite successful. The main cause of the MFP performance degradation was incomplete knowledge of the environment. An environment adaptation technique using a global optimization algorithm was developed to alleviate the environmental mismatch problem, allowing the ocean-acoustic environment to be adapted to the acoustic data in a matched-field sense. Using the adapted environment, the 14-Hz source was successfully localized and tracked in azimuth and range within a region of interest using the MFP technique at a later time interval. Two types of environmental parameters were considered, i.e., sound speed and modal wave number. While both approaches yield similar results, the modal wave number adaptation implementation is more computationally efficient 相似文献
20.
《Oceanic Engineering, IEEE Journal of》2006,31(2):299-307
A common problem in sonar system prediction is that the ocean environment is not well known. Utilizing probabilistic based results from geoacoustic inversions we characterize parameters relevant to sonar performance. This paper describes the estimation of transmission loss and its statistical properties based on posterior parameter probabilities obtained from inversion of ocean acoustic array data. This problem is solved by first finding an ensemble of relevant environmental model parameters and the associated posterior probability using a likelihood based inversion of the acoustic array data. In a second step, each realization of these model parameters is weighted with their posterior probability to map into the transmission loss domain. This approach is illustrated using vertical-array data from a recent benchmark data set and from data acquired during the Asian Seas International Acoustics Experiment (ASIAEX) 2001 in the East China Sea. The environmental parameters are first estimated using a probabilistic-based geoacoustic inversion technique. Based on the posterior probability that each of these environmental models fits the ocean acoustic array data, each model is mapped into transmission loss. This enables us to compute a full probability distribution for the transmission loss at selected frequencies, ranges, and depths, which potentially could be used for sonar performance prediction. 相似文献