多波束声呐水柱影像在中底层水域目标探测中的应用

Multibeam sonar plays an irreplaceable role in oceanic economy, marine science, hydrographic security. Its data include not only water depth, backscatter image but also water column image (WCI). WCI carries total information from the transducer to seafloor, and provides several significant advantages to the hydrographer in quality control. WCI can be used to to survey internal wave, find gas plumes, and detect fish school. It can also be used to improve the accuracy of water depth, precisely calculate the height of small object, clearly reveal all the protruding features. All of these cannot be accomplished by multibeam bathymetric or backscattered data. Therefore, WCI improves the survey efficiency, ensure the reliability of soundings, enlarges the scope of application,and utmost develops potential abilities of multibeam sonar. However, because of too many factors, such as complex of oceanic environment, transmit side lobes, receiver side lobes, noise patterns, incomplete occlusion, pulse bandwidth, beam width, electronic noises, WCI is faint and include too many systematic errors and noises. Therefore, it is a challenge for WCI processing and actual application. Now it is hot and hard problem in the field of multieam sonar application. Based on WCI, this project will research the methods of reducing systematic errors, analyze the influences of various device parameters and oceanic environments at first. We will also use WCI to precisely locate a wreck or other hazard and determine the least depth to navigation. Internal wave has an important impact for hydrographic survey. Then we will also utilize WCI to detect internal wave during multibeam survey, and concurrent reduce the influence of internal wave to multibeam bathymetry. The research results will enlarge and improve the application of multibeam sonar, and enhance technical level of hydrographic security.

多波束水柱影像携带了波束从换能器到海底的完整信息，利用其可探测从海面至海底的声照射目标，如探测海洋内波、发现活动的热液喷口、准确确定海底突起目标高度，而常规应用一般仅提取海底信息，可能遗漏特殊目标或造成突起地形失真。由于水柱影像模糊、系统误差较多，水柱影像的处理、识别和应用现已是国际上多波束应用研究热点之一，国内尚未公开报导这方面研究。基于多波束水柱影像，本项目围绕中底层水域目标的探测及应用，研究水柱成像系统误差带来的假目标剔除，研究设备参数、海洋环境和目标条件等因素对探测目标的影响，以海底突起目标、内波为研究对象，分析其探测、识别和应用。项目将拓展多波束应用领域，提供一种高效率大面积探测中低层水域固体及非固体目标的新手段，削弱内波对多波束测深的影响，提升海道测量有关的港口或浅水航道障碍物探测的技术水平。

多波束水柱影像携带了波束从换能器到海底的完整信息，利用其可探测从海面至海底的声照射目标，如探测海洋内波、发现新的热液喷口、准确确定海底突起目标高度，而常规检测算法一般仅提取海底信息，可能遗漏特殊目标或造成突起地形失真。由于水柱影像模糊、系统误差较多，它的处理、识别和应用现已是国际上多波束应用研究热点之一。.本项目对多波束水柱目标物探测、海底反向散射强度误差改正及其分类、多波束测深精细化处理等方面深入研究。在多波束水柱及海底回波强度成像处理方面，分析了多波束水柱成像和优化方法，影像镜面回波异常改正和非目标信息弱化剔除等算法，并对目标边缘进行跟踪检测、目标轮廓提取以及三维重建；研究多波束反向散射强度误差改正方法，有效提高了后期底质分类的准确度；利用实验室消声水池对多波束声源级、频率和波束角指向性进行检测方法的研究，为多波束水柱和海底回波图像的归一化提供了依据。在多波束水柱图像应用方面，利用水柱图像探测内波，对内波参数进行反演，研究其对多波束测深的影响及其改正方法。在多波束测深精细处理方面，研究了不同声速剖面插值方法的适用性，提出了等效声速梯度迭代计算方法，解决了地形起伏时采用单一等效声速剖面造成的精度损失问题；提出了基于随船GNSS大地高的水位改正与动态吃水改正技术等。.项目对中底层水域多波束目标探测时采集的水柱、海底回波强度和水深数据处理与应用方面进行深入研究，各种数据源互为补充，提供了多波束水柱目标探测的技术方案，提高了水下目标物识别率、多波束海底底质分类和多波束测深精度。项目取得了一些原创性成果，在海道测量、航道疏浚、海事搜救和海岛礁测量等方面有较大应用价值。