Bistatic synthetic aperture imaging of proud and buried targets from an AUV

The use of autonomous underwater vehicles (AUVs) for the detection of buried mines is an area of current interest to the Mine CounterMeasures (MCM) community. AUVs offer the advantages of lower cost, stealth, reduced operator risk, and potentially improved coverage rates over more traditional mine hunters. However, AUVs also come with their own set of difficulties, including significant error in navigation and low communication rates with the mother platform and each other. In the case of bistatic detection scenarios, AUVs will therefore have difficulty knowing where exactly in space they are and the trigger time of sources on other platforms, be they ships or other AUVs. However, the potential improvement in detection and coverage rates offered by bistatic sonar concepts makes resolution of these issues a high priority. In this paper, the problems of inaccurate navigation and source timing information are addressed for the Generic Oceanographic Array Technology data set. In this experiment, conducted off Marciana Marina during June 1998, a MIT AUV with a SACLANTCEN acoustic array and acquisition system was used together with a TOPAS parametric sonar to explore issues of buried target detection using AUVs. In this paper, solutions to the navigation and timing problems are proposed which enable the effective use of bistatic synthetic aperture sonar (SAS) concepts for the detection of buried objects in the mid-frequency regime of 2-20 kHz.     

Object detection and tracking method of AUV based on acoustic vision

This paper describes a new framework for object detection and tracking of AUV including underwater acoustic data interpolation, underwater acoustic images segmentation and underwater objects tracking. This framework is applied to the design of vision-based method for AUV based on the forward looking sonar sensor. First, the real-time data flow (underwater acoustic images) is pre-processed to form the whole underwater acoustic image, and the relevant position information of objects is extracted and determined. An improved method of double threshold segmentation is proposed to resolve the problem that the threshold cannot be adjusted adaptively in the traditional method. Second, a representation of region information is created in light of the Gaussian particle filter. The weighted integration strategy combining the area and invariant moment is proposed to perfect the weight of particles and to enhance the tracking robustness. Results obtained on the real acoustic vision platform of AUV during sea trials are displayed and discussed. They show that the proposed method can detect and track the moving objects underwater online, and it is effective and robust.     

深海拖曳系统定位技术及其应用与展望

阐述了海洋地球物理导航和水下声学导航等水下定位的技术方法,着重探讨了水声定位在深拖系统定位中的应用。分别简述了3种传统的声学定位系统的优缺点,并详尽介绍了超短基线定位系统,分别举例说明市场上典型产品的性能及应用情况,指出了在水下拖体导航中有待解决的关键技术问题及其发展方向,重点介绍了当前水下拖体定位技术发展的新方向,认为组合式声学导航和融合导航将成为未来的研究热点。     

Seafloor acoustic remote sensing with multibeam echo-sounders and bathymetric sidescan sonar systems

This paper examines the potential for remote classification of seafloor terrains using a combination of quantitative acoustic backscatter measurements and high resolution bathymetry derived from two classes of sonar systems currently used by the marine research community: multibeam echo-sounders and bathymetric sidescans sonar systems. The high-resolution bathymetry is important, not only to determine the topography of the area surveyed, but to provide accurate bottom slope corrections needed to convert the arrival angles of the seafloor echoes received by the sonars into true angles of incidence. An angular dependence of seafloor acoustic backscatter can then be derived for each region surveyed, making it possible to construct maps of acoustic backscattering strength in geographic coordinates over the areas of interest. Such maps, when combined with the high-resolution bathymetric maps normally compiled from the data output by the above sonar systems, could be very effective tools to quantify bottom types on a regional basis, and to develop automatic seafloor classification routines.     

基于声呐图像的深海采矿车组合定位导航算法

实现高精度的定位导航是深海采矿车完成海底工作任务的基础条件。在采矿车行进过程中,声呐设备生成的图像信息能够反映海底场景的变化,从而体现采矿车本身的运动,由此建立了一种声呐图像里程计,并将其与轮式里程计和USBL测量数据相结合提出了一种深海采矿车组合定位导航算法。首先对多波束前视声呐图像进行预处理,然后使用Canny算法进行特征检测并对特征点云进行配准,再结合声呐成像原理构建了声呐图像里程计运动模型,最后通过轮式里程计运动模型推导预测方程、声呐图像里程计运动模型和USBL测量数据推导更新方程,利用EKF（extended Kalman filter）算法实现基于多传感器融合的定位与姿态估计。海试数据验证了该组合定位算法能实现轮式里程计、声呐里程计和超短基线在速度、位置、艏向角估计、定位速率的精度互补,具有一定的有效性和精确性,该算法为深海采矿车的定位与导航算法研发提供了参考。     

一种深海拖曳系统稳健可靠的组合定位方法

为了解决深海拖曳系统定位异常、不连续以及误差积累的问题,提出了一种联合惯性导航系统(INS)和超短基线定位系统(USBL)的组合定位方法,利用在航声线跟踪实现USBL的高精度定位,顾及INS和USBL系统的互补性,并结合Kalman滤波构建了INS+USBL的组合定位模型。将该组合定位模型应用于"向阳红01"船深海拖曳系统在南海的定位实验并与USBL的定位结果比对,实验表明,组合定位方法有效地解决了深拖系统定位异常且不连续问题。INS+USBL组合定位方法可以满足深海拖曳系统的稳健可靠定位,对于深远海定位具有重要意义。     

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。     

Enhanced Kalman Filter Algorithm Using the Invariance Principle

Target tracking in multistatic active sonar systems is often limited in shallow-water environments due to the high level of bottom reverberation that produces false detections. Past research has shown that these false alarms may be mitigated when complete knowledge of the environment is available for discrimination, but these methods are not robust to environmental uncertainty. Recent work has demonstrated the existence of a waveguide invariant for active sonar geometries. Since this parameter is independent of specifics of the environment, it may be used when the environment is poorly known. In this paper, the invariance extended Kalman filter (IEKF) is proposed as a new tracking algorithm that incorporates dynamic frequency information in the state vector and uses the invariance relation to improve tracker discrimination. IEKF performance is quantified with both simulated and experimental sonar data and results show that the IEKF tracks the target better than the conventional extended Kalman filter (CEKF) in the presence of false detections.      

Bayesian Sonar Detection Performance Prediction With Source Position Uncertainty Using SWellEx-96 Vertical Array Data

Predicting sonar detection performance is important for the development of sonar systems. The classical sonar equation cannot accurately predict sonar detection performance because it does not incorporate the effect of ocean environmental and source position uncertainty. We propose an analytical receiver operating characteristic (ROC) expression that characterizes the performance of the optimal Bayesian detector in the presence of ocean environmental and source position uncertainty. The approach is based on a statistical model of the environment and a physical model of acoustic propagation, which translates ocean environmental and source position uncertainty to signal wavefront uncertainty. The analytical ROC expression developed in this paper is verified for source position uncertainty due to source motion using both simulated data and real data collected during the Shallow Water Evaluation Cell Experiment (SWellEx-96). The results showed that the primary effect of source position uncertainty on optimal sonar detection performance is captured by the rank that corresponds to the significant eigenvalues of the signal matrix, an ensemble of replica signal wavefronts (normalized acoustic pressure vector) at the receiving array. The results also showed that the proposed ROC expression provides a realistic detection performance prediction for the Bayesian detector for source position uncertainty using real data. The proposed approach to sonar detection performance prediction is much simpler and faster than those using conventional Monte Carlo approaches.     

基于倒置声学基阵的INSUSBL组合导航算法研究

文中关注水下潜航器导航定位时,电磁波传播途径中能量衰减、惯导系统长航时积累误差以及提高水下潜航器定位精度等问题。基于倒置的超短基线声学基阵,分析声波往返传播时间(RTT)、平面波近似方法和USBL导航解算方法及其坐标转换过程,结合INS误差方程,建立INS/USBL松组合模型。为进一步提高系统精度、动态性能和抗干扰性,考察USBL的原始斜距、斜距差以及声学基阵的空间分布信息,提出基于USBL原始输出信息的INS/USBL紧耦合组合导航方法。通过MATLAB仿真对导航算法进行验证,结果表明两种算法能充分抑制纯惯导误差随时间积累问题,且有效地估计出姿态、速度和位置误差角;其中紧耦合方法状态估计误差最小,导航参数精度相对松组合提高30%以上,对于提高水下载体导航定位精度、海洋探测具有重大意义。     

Autonomous underwater vehicle homing/docking via electromagneticguidance

Central to the successful operation of an autonomous undersea vehicle (AUV) is the capability to return to a dock, such that consistent recovery of the AUV is practical. Vehicle orientation becomes increasingly important in the final stages of the docking, as large changes in orientation near the dock are impractical and often not possible. A number of homing technologies have been proposed and tested, with acoustic homing the most prevalent. If AUV orientation is required as well as bearing and distance to the dock, an acoustic homing system will require high update rates, and extensive signal conditioning. An Electromagnetic Homing (EM) system is one alternative that can provide accurate measurement of the AUV position and orientation to the dock during homing. This system offers inherent advantages in defining the AUV orientation, when compared to high frequency acoustic systems. The design and testing of an EM homing system are given, with particular attention to one can be adapted to a wide class of AUVs. A number of homing, docking, and latching trials were successfully performed with the design. Homing data include dead reckoning computation and acoustic tracking of the homing track, and video documentation of homing into the dock     

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...     

Experimental Evaluation of Tracking Algorithms Used for the Determination of Fish Behavioral Statistics

The fine-scale swimming behavior of fish can now be studied because of the development of sophisticated measurement devices such as multibeam sonar and stereo video systems. However, even with these sensors, improved methods are still required to generate quality estimates of swimming speeds and turn rates. Biologists have commonly relied on pointwise differentiation of noisy position measurements while engineers have focused on Bayesian algorithms to track underwater vehicles. A comparative evaluation of the performance of these tracking algorithms for the analysis of fine-scale behavior of fish was performed using a data set of 100 fish tracks recorded simultaneously with a multibeam sonar and a stereo video camera system. The segmenting track identifier, a non-Bayesian curve fitting and segmenting tracker, is shown to be most effective for tracking the unpredictable and complex horizontal motion of fish while a Kalman smoother using a constant-velocity model is shown to be most effective for tracking the more predictable and piecewise linear vertical motion of fish. Both are shown to be more effective than pointwise differentiation. Criteria for selecting an appropriate algorithm for a given motion study are provided     

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。     

多波束声呐图像条带中央和边缘残差处理方法

多波束声呐图像是进行海底底质分类的主要数据源之一,由于受海洋噪声、声波散射和混响、仪器设备等因素影响,其经各项常规改正后仍存在明显残差,突出表现在中央波束区和条带重叠区,难以形成高质量的声呐图像。文中分析了多波束声呐图像残差的成因及影响,提出了一种基于多条带最小二乘拟合的多波束声呐图像残差处理方法。首先,得到相邻声脉冲(ping)信号中央区域、重叠区域以及整体趋势的拟合函数;然后,通过拟合函数计算得到中央和重叠区域的残差改正系数;最后,通过改正系数进行残差改正。实验分析表明,该方法在保留原始细节的基础上,有效削弱了残差对声呐图像的影响,对多波束声呐图像处理具有参考和应用价值。     

主动声纳探测效能评估的HMG法

海洋水声环境时空变化显著,评估其对主动声纳探测效能的影响具有重要的理论意义和应用价值。提出HMG方法用以评估水声环境效应对主动声纳探测的影响。采用UMPE(The university of miami parabolic equation)、CANARY、JACKSON模型模拟特定海洋环境下的传播损失、环境噪声、混响分布,将模拟结果融入主动声纳检测概率模型,计算检测概率。评估结果发现近场检测概率较高,远场可检测的区域与声能汇聚区一致。     

Underwater vehicle obstacle avoidance and path planning using amulti-beam forward looking sonar

This paper describes a new framework for segmentation of sonar images, tracking of underwater objects and motion estimation. This framework is applied to the design of an obstacle avoidance and path planning system for underwater vehicles based on a multi-beam forward looking sonar sensor. The real-time data flow (acoustic images) at the input of the system is first segmented and relevant features are extracted. We also take advantage of the real-time data stream to track the obstacles in following frames to obtain their dynamic characteristics. This allows us to optimize the preprocessing phases in segmenting only the relevant part of the images. Once the static (size and shape) as well as dynamic characteristics (velocity, acceleration,…) of the obstacles have been computed, we create a representation of the vehicle's workspace based on these features. This representation uses constructive solid geometry (CSG) to create a convex set of obstacles defining the workspace. The tracking takes also into account obstacles which are no longer in the field of view of the sonar in the path planning phase. A well-proven nonlinear search (sequential quadratic programming) is then employed, where obstacles are expressed as constraints in the search space. This approach is less affected by local minima than classical methods using potential fields. The proposed system is not only capable of obstacle avoidance but also of path planning in complex environments which include fast moving obstacles. Results obtained on real sonar data are shown and discussed. Possible applications to sonar servoing and real-time motion estimation are also discussed     

声相关海流剖面仪测速研究

声相关海流剖面仪(ACCP)适合深海测速,能够测得相对海底的绝对速度。文章在前人工作基础上,以声纳方程为基础,构造海底混响回波仿真模型,并对基于K irchhoff近似和利用微扰法的R ay le igh-R ice近似相结合的散射模型赋予新的物理意义,并将其应用到声相关测速仿真研究过程中,使仿真更加接近于海洋的实际环境。文章利用H ilbert变换进行包络检波来减小测速误差,并且根据接收信噪比得到了不同航速时能够达到最大底跟踪的距离,这与参考文献给出的结果是一致的。     

Sonar tracking of multiple targets using joint probabilistic data association

The problem of associating data with targets in a cluttered multi-target environment is discussed and applied to passive sonar tracking. The probabilistic data association (PDA) method, which is based on computing the posterior probability of each candidate measurement found in a validation gate, assumes that only one real target is present and all other measurements are Poisson-distributed clutter. In this paper, a new theoretical result is presented: the joint probabilistic data association (JPDA) algorithm, in which joint posterior association probabilities are computed for multiple targets (or multiple discrete interfering sources) in Poisson clutter. The algorithm is applied to a passive sonar tracking problem with multiple sensors and targets, in which a target is not fully observable from a single sensor. Targets are modeled with four geographic states, two or more acoustic states, and realistic (i.e., low) probabilities of detection at each sample time. A simulation result is presented for two heavily interfering targets illustrating the dramatic tracking improvements obtained by estimating the targets' states using joint association probabilities.     

Image projection and composition with a front-scan sonar system: methods and experimental results

This paper describes a complete set of methods for arranging acoustic images of the sea floor by projecting and interpolating data gathered with a novel front-scan sonar system, developed in the context of the EC-COSMOS project. Traditional sonar imaging systems for sea-floor analysis generate acoustic images during the motion of a ship; on the contrary, the front-scan sonar system not only provides information unreachable by traditional devices (blind region), but also does not need the ship motion to compose a whole image of the sea floor. Two different projection methods have been devised: a simpler analytical solution and a more precise ray-tracing approach. The development of an analytical solution is possible under the classical assumptions about a flat sea floor and a constant sound velocity profile; when these hypotheses are not realistic or a more precise image is required, a numerical solution obtained by a ray-tracing approach can be applied, which is based on some ad hoc solutions worked out for the front-scan sonar system. To move from the projection results to an image defined over a dense matrix of pixels, an interpolation stage is needed. To this end, an algorithm based on the generation of virtual-beam signals (only where necessary) has been tested and compared with more-traditional techniques. The potentials of the proposed projection and interpolation methods have been evaluated and some comparisons have been made, using real data gathered with the COSMOS sonar prototype during trials at sea.