超短基线系统定位精度改进方法

超短基线是一种常用的水声定位技术,与其它基线相比,超短基线定位系统基线基阵尺寸小,易于安装。由于在远距离误差发散快,超短基线作用距离不远,其远距离定位精度也不高。为了满足深海作业需要,提高超短基线远距离的定位精度,提出改进超短基线定位精度的两种方法,一种方法是通过改进基阵阵形,从而加大基阵孔径提高定位精度;另一种是通过使用宽带信号测向,采用相关峰内插时延估计的方法。经计算机仿真,通过两种方法改进后的超短基线系统定位精度都得到不同程度的提高。     

超短基线定位系统的误差分析

本文对超短基线定位系统的误差进行了分析,建立了定位的随机误差和测量值误差之间的关系,指出了提高定位精度的某些方法和措施.     

超短基线定位的海上应用及精度评估

超短基线定位系统可以为水下调查设备提供精确的定位信息,是当今海洋探测工作必不可少的装备。超短基线定位系统的定位结果包含了多种来源的误差影响,对超短基线定位数据进行有效的处理是保证水下精确定位的前提。本文通过对超短基线基阵进行校准,并对其定位精度进行精度评估,对海上应用采集到的数据进行处理分析,对原始数据中出现的跳点进行剔除、滤波处理,得到较可靠的水下定位结果。     

一种适于浅水定位的超短基线装置与定位方法

针对浅水水域水声信号多途效应导致信道衰落,真实时延信号获取难度大的问题,研制了一种适用于浅水定位的超短基线装置,并提出一种附有约束条件的互相关时延估计方法。采用脉冲挑选和时延差相位修正方法对目标轨迹进行精确跟踪定位,某湖试实验结果表明,该方法的定位轨迹光滑稳定,野点少, 定位精度高。     

两种水下定位方式的误差对比与分析

利用在富钴结壳海山实测的2条海底摄像测线资料,通过超短基线水下定位数据和LAYBACK方式定位校正结果的分析与对比,结果表明,通过超短基线定位系统的同步测量,可实现对海底摄像拖体的高精度水下定位,而通过LAYBACK校正方式得到的拖体定位数据误差变化范围很大。LAYBACK校正误差受航速和拖缆长度变化的影响程度较小,而受母船航向变化的影响程度要大得多,因此,当利用LAYBACK方法进行水下定位校正的时候,尤其需要注意船向变化对定位精度的影响。     

用海洋GPS进行水下运动载体的三维定位

用单个装载超短基线的海洋GPS进行水下运动载体的三维定位,和三个智能型浮标进行水下运动载体的三维定位相比,定位精度相当,隐蔽性更好,造价更低,更具实用价值。本文对单个装载超短基线的海洋GPS进行水下运动载体三维定位的原理和精度进行了较为详细的讨论,并得到了一些有益的结论,以供同行参考。     

超短基线声学定位原理及其应用

声学定位系统（Acoustic Positioning System)的技术研究和应用开发在现代海洋科学调查中起着重要作用。以挪威Simrad公司的HPR410P超短基线定位系统为例，从几方面讨论了超短基线（Ultrashort Baseline)声学定位系统的原理、应用范围、定位误差来源及其相应的修正方法；通过最大程度地减少误差来提高系统的定位精度，从而获取高质量的海洋科研调查资料。     

超短基线定位原理及校正方法研究

通过探讨超短基线和GPS技术相结合的三维立体定位原理,分析超短基线定位误差来源,如安装偏差、声速误差、船姿态变化引起的偏差等,利用以最小二乘法为理论基础的动态校正法对超短基线定位误差进行了修正,将校正前后的定位数据标准偏差和剩余偏差处理后对比发现,这种方法可以极大地提高水下目标定位的精度,减少定位的误差,这也在实际应用...     

基于最小二乘法的超短基线水声定位系统校准方法

超短基线水声定位系统是海洋工程及水下无人系统中应用较广泛的精密仪器设备,为了提高对水下目标的定位精度,在使用前需对其进行校准。描述了一种基于最小二乘法迭代修正的超短基线水声定位系统校准方法,该方法以最小二乘法为基本原理,通过多次迭代修正的方式,修正基阵与GPS天线之间的平移偏差以及基阵与罗经之间的旋转偏差,从而提高系统的测量精度,最终通过湖上试验验证了该方法的有效性。     

用于AUV定位的等效声速剖面改进算法研究

以自主式水下机器人为载体,搭载多种测量设备的深海工程作业的方式,目前已经得到了广泛的应用。而基于AUV完成各类水下任务的前提是能否精确的进行定位,传统的声学定位方法因过于依赖声速剖面而导致定位精度不高且造成实际操作过程复杂化,在各种声线改进的方法中,等效声速剖面法的计算过程较为简单,且对实际声速剖面的依赖程度较低,然而最大的问题是相对面积误差的求解过于复杂。结合AUV自身特点,提出了超短基线与等效声速剖面法相结合的水下AUV定位方法,并改进了等效声速剖面法。实验结果表明,改进后的方法计算精度得到提高且相对面积误差的求解更加简单,另外也改进了原始方法误差随水深及掠射角变化而增加的问题,具有良好的工程应用价值。     

Combined Geoacoustic Inversion of Propagation and Reverberation Data

Sonar performance predictions in shallow water are strongly dependent on good knowledge of the geoacoustic and scattering properties of the seabed. One technique to extract information about the bottom is to use a towed source and a towed horizontal array. This towed system has been shown to be applicable for characterizing the bottom properties locally by inversion of the acoustic signals received directly on the towed array at short ranges. The same towed system has also been applied to extract bottom properties from long-range reverberation data providing effective bottom properties over a large area. However, independent geoacoustic inversion of the short-range propagation and long-range reverberation data can introduce low sensitivity and uncertainty in the extracted bottom properties. An attempt to resolve this low sensitivity and ambiguity is made by a simultaneous geoacoustic inversion of short-range propagation and long-range reverberation data with the intention of constraining the possible solutions of the bottom properties.      

Deep-water acoustic coherence at long ranges: theoreticalprediction and effects on large-array signal processing

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     

Temporal domain processing for a synthetic aperture array

A method for the synthesis of an aperture with improved bearing resolution and signal gain is described. The proposed method temporally synthesizes data from an overlap correlator, which is obtained by aperture domain averaging of phase differences. Previous studies, such as extended towed array measurements (ETAM), had a restriction in that the overlapped hydrophones between successive measurements of a towed array were required to have identical positions in space. In this paper, however, it is shown that the phase correction factors can be estimated without restriction on the positions of the overlapped hydrophones. This implies that the proposed method is able to utilize more snapshots to extend the towed array. Simulation results showed that the proposed method resulted in higher estimation accuracy than ETAM. In addition, the effects of coherency and other systematic errors on the proposed method were examined     

Numerical study on attenuation of bubble pulse through tuning the air-gun array with the particle swarm optimization method

A numerical method for improving the quality of the far-field signal generated by a marine seismic air-gun array is presented, in which particle swarm optimization is used in conjunction with the theory of the oscillating spherical bubble to tune the array. Two sets of objective functions, including the primary-to-bubble ratio and the variance of the normalized amplitude spectrum, are built to screen the array. With this method, attempts are made to improve the far-field signals generated by four typical arrays, including the planar array, spatial array, irregular array and delayed array. It is concluded that the far-field signal can be largely improved just through the simple adjustment of the chamber volume, the firing depth, the horizontal location or the firing time of each individual gun in the array. We believe that this method will be useful in the air-gun array design and helpful to find a desirable array from a population of air-gun array distributions for a brief time.     

Geoacoustic inversion results from the ASIAEX East China Sea experiment

This work presents the results of geoacoustic inversions carried out using data from the Asian Seas International Acoustics Experiment East China Sea. Broadband data from small explosive sources were used for the inversions. Compressional wave speeds in the sediment and basement layers were estimated using a nonlinear, long-range, tomographic inversion technique based on group speed dispersion. This tomographic technique is a hybrid approach that combines a genetic algorithm for global parameter search with a Levenberg-Marquardt method for fine-scale parameter tuning. The results were compared with data from gravity and piston cores and a geophysical survey conducted at the experimental location using a watergun and towed hydrophone array.     

基于四阶累积量的被动测向声纳高分辨力算法研究

利用高阶累积量的阵列扩展和抑制高斯噪声特性,提出1种基于四阶累积量的逆波束形成算法,并通过滑动平均进一步改善了算法。仿真结果和实验数据表明:逆波束形成算法较常规波束形成方法在空间方位分辨力和噪声抑制能力上明显提高,可以更有效地应用于被动测向声纳中。     

深海潜标布阵方式对海面声源定位精度的影响

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。     

Using matched-field processing to estimate shallow-water bottomproperties from shot data taken in the Mediterranean Sea

It is extremely difficult to determine shallow ocean bottom properties (such as sediment layer thicknesses, densities, and sound speeds). However, when acoustic propagation is affected by such environmental parameters, it becomes possible to use acoustic energy as a probe to estimate them. Matched-field processing (MFP) which relies on both field amplitude and phase can be used as a basis for the inversion of experimental data to estimate bottom properties. Recent inversion efforts applied to a data set collected in October 1993 in the Mediterranean Sea north of Elba produce major improvements in MFP power, i.e., in matching the measured field by means of a model using environmental parameters as inputs, even using the high-resolution minimum variance (MV) processor that is notoriously sensitive and usually results in very low values. The inversion method applied to this data set estimates water depth, sediment thickness, density, and a linear sound-speed profile for the first layer, density and a linear sound-speed profile for a second layer, constant sound speed for the underlying half space, array depth, and source range and depth. When the inversion technique allows for the array deformations in range as additional parameters (to be estimated within fractions of a wavelength, e.g., 0.1 m), the MFP MV peak value for the Med data at 100 Hz can increase from 0.48 (using improved estimates of environmental parameters and assuming a vertical line array) to 0.68 (using improved estimates of environmental parameters PLUS improved phone coordinates). The ideal maximum value would be 1.00 (which is achieved for the less sensitive Linear processor). However, many questions remain concerning the reliability of these inversion results and of inversion methods in general     

SAMI: a low-frequency prototype for mapping and imaging of theseabed by means of synthetic aperture

The objective of the Synthetic Aperture Mapping and Imaging (SAMI) project was to develop and to test at sea a wide-band synthetic aperture sonar prototype, capable of providing high-resolution seafloor images together with bathymetry maps. This system used the motion of a physically small array in order to synthesize a longer array, providing images with an across-track resolution independent of both range and transmit frequency. Such systems are clearly very relevant to the high-precision long-range (low-frequency) imaging of the sea bottom. The project has led to the construction of a prototype tested at sea on several well-known areas for comparison with existing images and maps. These areas included several types of sea bottom, depths, and geological structures. The results obtained in real time, on-board ship, have shown the relevance of the proposed wide-band techniques. The many profiles produced have provided high-resolution images and maps of various seafloors. Interpretation by geologists showed that the system was capable of providing the same or finer detail than a deep-sea short-range, high-frequency system and maintained a higher resolution over a wider swath. The sea data processed have shown that the system provided maps with a cubic meter voxel. The resolution cell is constant over the whole range (50 to 2500 m) thanks to the dynamic focusing of the synthetic aperture. Postprocessing of a part of the data stored during the experiments has been carried out in the laboratory. This work has shown that techniques such as autofocusing can give an increase in resolution (i.e., gain in contrast and resolution of about 3 dB). The results displayed in the paper show the relevance of the techniques developed to the provision of a complete high-performance imaging tool for the oceanographic community