共查询到20条相似文献，搜索用时 93 毫秒
1.
Based on the general concept of the inverse acoustic radiation problem, the temporal scanning of a stationary acoustic field along a closed contour is used to simplify the measurement approach for obtaining information on source directionality. The mathematical formulation is derived from a model of the two-dimensional acoustic field. The formulation of the inverse problem is also investigated to establish a methodology for improving the angular resolution of the array processing. The fundamental relationship between the sound sources and the circular passive synthetic array is explored, utilizing existing mathematical methods, in order to develop the processing algorithm. Other subjects of practical interest, such as directional ambiguity, effect of Doppler frequency, interference noise, and processing gain are discussed. It is concluded that the results can be used to establish guidelines for engineering design and deployment of this type of synthetic array, and to further exploit the new array signal processing technique 相似文献
2.
3.
This paper presents and applies a new acoustic imaging approach to quantitatively determine geophysical parameters of complex inhomogeneous sediment layers. The concept is called an Acoustic Sub-seabed Interrogator or ASI and it is based on optimising the criteria of temporal and spatial resolution and of coherence by utilizing broadband, narrow beam calibrated sources and fixed receivers on a stationary platform.The ASI concept was experimentally tested over a complex pseudo-glacial till built at a scale of 20:1. Compressional velocity, attenuation losses and thickness values were easily attained using the ASI's coherent spatial scanning approach and through a discrete application of the Hilbert transform in the post processing of data. The simulations provided indepth insight into the model's physical and spatial variations and by statistical distribution emphasized the depositional processes involved in creating the layer. It is believed that the fundamental internal information elucidated by the ASI for the pseudo-till structure and illustrated in the resultant acoustic core cannot be attained using current marine geophysical and geotechnical techniques. 相似文献
4.
近海水产养殖为人类提供优质的动物蛋白，对海洋经济高质量发展具有重要意义。卫星遥感技术已被广泛用于海岸带水产养殖的监测，但目前相关的研究聚焦基于单一传感器卫星数据并使用单一信息提取算法而忽略与不同卫星传感器以及处理方法之间的比较。本研究以北莉岛东北部为研究区，基于多光谱Sentinel 2A卫星和高分一号B（GF 1B）卫星数据，分别使用自适应阈值法、支持向量机监督分类法以及多尺度分割面向对象分类法，开展海岸带人工水产养殖区的识别。研究表明，更高空间分辨率的GF 1B卫星对人工水产养殖水网密集区的提取正确率远优于Sentinel 2A卫星；基于高空间分辨率GF 1B卫星，多尺度分割面向对象分类法的正确率最高，为94.65%，优于支持向量机监督分类法的94.45%和自适应阈值法的84.62%；自适应阈值法更适用于中等空间分辨率卫星数据的水产养殖信息提取，其提取的水产养殖水面的面积与目视解译提取的面积差异小于4%。针对单个养殖池使用情况的业务化监测需使用高空间分辨率卫星数据，而大范围水产养殖面积的变化分析则可应用中等空间分辨率卫星数据。 相似文献
5.
This paper deals with the basic modeling problem in underwater acoustics that is the characterization of the channel between a transmitter and a receiver. The problem is analyzed here using an array of sensors that receive PSK signals emitted by several sources. Data come from an experiment realized by a physical system situated in the Mediterranean Sea. In order to identify the multipath channel, we need to access the propagation time delay and the angle of arrival of each propagation ray. However, many of these acoustic ray paths are too close to be separated by classic processing methods (matched filter, beamforming, etc.); new methods with better resolution must be applied in order to analyze the experimental signals and to determine their arrival time on the array of sensors. After a presentation of this problem, we will first discuss high-resolution methods that are usually applied in the localization problem; we will then focus on wavelet packet analysis which provides good results by improving the temporal resolution of acoustic signals 相似文献
6.
The finite-time behavior of a quadratically constrained version of the minimum-variance, distortionless-response line-array beamformer is examined. An entity known as the weight ratio is defined and it is demonstrated that there are simple expressions that relate the weight ratio to the field scenario which explicitly take into account the finite-time misadjustment phenomenon. It is further demonstrated that holding the weight ratio to a value of about 0.5 produces an adaptive beamformer with a beneficial combination of robustness to nonideal situations (e.g., sensor misalignment, pointing errors, correlated interferers, misadjustment effects, etc.) while retaining the ability to adapt quickly in highly dynamic fields 相似文献
7.
This is the first part of a publication that describes the generation of adaptive grids (this part), and simulations with vector-ocean-model (VOM) in unstructured grids resulting from the adaptation (part II). A static vertical adaptive grid in z-coordinates allows improving the approximation of topography and vertical resolution at slopes. Adaptive grids use elements from a set of grid sizes by multiplying a basic smallest cell size with powers of two, as in cell division. Grids with locally isotropic vertical resolution at surface, seabed, and slopes can be generated whereby resolution decreases towards the ocean interior. The adaptation to topography yields unstructured grids that are organised in a one-dimensional vector by column-wise storage of cells, discarding land cells. The vector storage suggested the model’s name. Grids are generated by an iterative procedure that relies on rules, i.e. criteria and directives to control the grid structure in favour of a good representation of physics and smooth numerical operations. The directives govern vertical resolution at sea surface and seabed, and at slopes. For the latter vertical resolution is extended in the horizontal. In the ocean interior horizontal distances between changes in grid size can be controlled for the sake of smooth numerics. The use of a z-grid that avoids transformation errors, the depth-independence of vertical resolution, and the lateral extension of vertical resolution at slopes towards the ocean interior are the most significant differences of adaptive grids in comparison to vertical coordinate transformations. Unstructured grids do not rely on a smoothing of topography and can be used within any of the horizontal Arakawa-grids. For the same topography directives allow creating various grids as demonstrated for a shelf-ocean topography. The number of cells per column in two unstructured grids generated for the North Atlantic may locally well exceed typical layer numbers in conventional model matrices. But the domain average is similar to layer numbers of today’s ocean models. Thus, with the same investment of cells per domain a higher resolution in slope regions can be achieved by unstructured grids as compared to conventional z-grids. 相似文献
8.
A two-dimensional numerical wave flume based on SA-MPLS method 总被引：1，自引：0，他引：1
A spatially adaptive(SA) two-dimensional(2-D) numerical wave flume is presented based on the quadtree mesh system,in which a new multiple particle level set(MPLS) method is proposed to solve the problem of interface tracking,in which common intersection may be traversed by multiple interfaces.By using the adaptive mesh technique and the MPLS method,mesh resolution is updated automatically with time according to flow characteristics in the modeling process with higher resolution around the free surface and the solid boundary and lower resolution in less important area.The model has good performance in saving computer memory and CPU time and is validated by computational examples of small amplitude wave,second-order Stokes wave and cnoidal wave.Computational results also indicate that standing wave and wave overtopping are also reasonably simulated by the model. 相似文献
9.
A model-based approach is developed to solve an adaptive ocean-acoustic signal-processing problem. Model-based signal processing is a well-defined methodology enabling the inclusion of propagation models, measurement models, and noise models into sophisticated processing algorithms. Here, we investigate the design of a so-called model-based identifier (MBID) for a general nonlinear state-space structure and apply it to a shallow water ocean-acoustic problem characterized by the normal-mode model. In this problem, we assume that the structure of the model is known and we show how this parameter-adaptive processor can be configured to jointly estimate both the modal functions and the horizontal wave numbers directly from the measured pressure-field and sound speed. We first design the model-based identifier using a model developed from a shallow-water ocean experiment and then apply it to a corresponding set of experimental data demonstrating the feasibility of this approach. It is also shown that one of the benefits of this adaptive approach is a solution to the so-called “mismatch” problem in matched-field processing (MFP) 相似文献
10.
Abstract. Adaptive strategies on the ecosystem level are demonstrated using the properties of systems (community biomass, trophic level energy transfer). Development of stabilizing storages versus rapid turnover and energy transfer through the grazing food chain versus detritus food chain are shown to be adaptive processes leading towards an optimal performance of the system. A model of incorporation and processing of information in ecosystems is proposed which contains the essential features of evolution. The persistence of "interspecific altruism" is discussed. 相似文献
11.
《Oceanic Engineering, IEEE Journal of》1979,4(2):52-59
Estimation of ship rotational motions induced by ocean waves plays a central role in many navigation and fire control applications. Inertial-type instruments are available which give good measurements of the attitude, but some form of signal processing is necessary to obtain angular rates or predict attitudes. Using optimal moving-average (or transversal) filters, we can obtain very good estimates of attitude rates as well as predictions of these values. Filter parameters can be changed adaptively to maintain good performance as the ship changes heading or velocity. The problem of designing these optimal filters is examined in detail and numerical results are given for a particular set of conditions. Two implementations of the adaptive filter are discussed. One is based on a recursive estimation of the process autocorrelations with the filter coefficients being recomputed at periodic intervals or whenever nonstationary conditions are detected. The second implementation is based on Widrow's LMS algorithm. Both alternatives for the adaptive filter implementation are quite reasonable in terms of their computational requirements. The steady-state performance analysis can be considered to be a lower bound on the errors incurred by an adaptive filter. 相似文献
12.
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
13.
14.
A. V. Rakitin V. S. Kostsov Yu. M. Timofeev 《Izvestiya Atmospheric and Oceanic Physics》2012,48(9):909-917
The problem of reconstructing the temperature distribution along optical paths from satellite measurements of the Earth’s limb radiation in the CO2 15-μm absorption band with a high spectral resolution is formulated and analyzed on the basis of numerical experiments performed in accordance with the MIPAS experiment. It is shown that the two-dimensional temperature field can be obtained through the processing of radiation measurements on paths with different target heights provided that spectral channels with essentially different optical thicknesses are used. The error in the stratospheric temperature determination varies from 1.8 to 5.6 K and depends on the target height of the optical path and the distance from the target point. The best horizontal resolution is 73–100 km, and it is achieved for optical paths with a target height of about 18–20 km. 相似文献
15.
Various approaches to the beamforming of data from large aperture vertical line arrays are investigated. Attention is focused on the conventional beamforming problem where the angular power spectrum is estimated, in this case by the adaptive minimum variance processor. The data to be processed are 200 Hz CW transmissions collected at sea by a 900 m vertical line array with 120 equally spaced sensors. Correlated multipath arrivals result in signal cancellation for the adaptive processor, and spatial smoothing techniques must be used prior to beamforming. The processing of subapertures is proposed. Full aperture and subaperture processing techniques are used on the 200 Hz data. Multipath arrivals are found to illuminate only parts of the array, thus indicating that the wavefield can be highly inhomogeneous with depth 相似文献
16.
17.
18.
Motoyoshi Ikeda 《Journal of Oceanography》1979,35(2):100-109
Characteristics of stationary Rossby-waves are investigated by use of equations expressing conservation of potential vorticity for a quasi-geostrophic two-layer flow of an incompressible inviscid fluid on a beta-plane. A two-dimensional problem is discussed; the basic flow is directing eastward without horizontal shear, and the stationary Rossby-waves are produced by a two-dimensional bump extending in the north-south direction which is located on a sloping bottom with a constant north-south gradient.When the slope is steep, stream-lines are scarcely displaced being influenced by the bump. When the bottom has no north-south inclination, however, there is a case where group velocity of Rossby-waves produced by the bump directs westward and the stream-lines meander sinusoidally at the west of the bump. This phenomenon is called upstream influence. These two special cases have a possibility to explain two different mean paths for the Kuroshio namely, the path along the continental slope and the path with a stationary meander at the west of the Izu-Ogasawara Ridge. 相似文献
19.
In an attempt to investigate the technical feasibility of a CW Doppler sonar, we have examined a method of measuring low velocities with a high-velocity resolution, or frequency resolution, by use of a simple circuit configuration employing digital signal processing technique. The following discussion presents the results of the investigation. In the measuring method described, the fast Fourier transform (FFT) of undersampled data is calculated and the Doppler shift is obtained by searching for a peak frequency of the power spectrum. To achieve the intended frequency resolution of 1 Hz by FFT operation, measurement of data for a minimum measuring period of 1 s is essential. If the sampling frequency is set to 50 kHz, the number of samples obtained during the minimum measuring period of I s would amount to 50000. This is not practical in light of the time required for the FFT operation. To overcome this problem, our new measuring method employs a decimation technique for reducing the number of samples down to 1024 while maintaining a frequency resolution of about 1 Hz. This paper describes how the processing time can be drastically reduced to about 1/300th compared to the conventional technique by a combination of complex exponential functions, filtering and decimation, and thereby indicates the possibility of real-time CW Doppler data processing 相似文献
20.
Acoustic signal parameter estimation is important for diverse marine geodesy surveys and several other applications. However, the received signal from a far-field target characterized by planar wavefront propagation is frequently affected by strong nearby interfering signals. Their presence deteriorates the performance of direction-of-arrival (DOA) estimation for far-field target. In order to enhance the reception of signal from far-field target, the near-field/far-field (NFFF) beamformer is proposed. Such a beamformer optimizes beam pattern for far-field detection by maximizing beamformer output in the direction of the far-field target with the imposed condition to eliminate interfering signals generated in near-field locations. As the interference suppression only occurs at the position of near-field interference, a possible blind zone for far-field detection in conventional methods is not created. The NFFF beamformer is applicable for coherent signals and the scenario with multi interferences. For stationary situation where interferers locations are fixed, the NFFF beamformer computations do not require time updates with associated computational load. Furthermore the proposed method can be extended to several new situations such as acoustic monitoring performed from a stationary platform subjected to water currents, waves, winds and other variables, all of them generating nearby interferences and also to different array configurations including 2D and 3D arrays. 相似文献