基于多波束声学遥感探测海底甲烷羽状流基本特征研究

The detection and study of the methane bubble plume caused by seabed gas seepage is of great significance to the evaluation of submarine gas hydrate reserves, carbon cycling and marine environment research. Nowdays the detection of undersea methane plumes is mainly based on shipboard single - beam and split -beam sonar system. For multi-beam sonar system, the resolution of acoustic image is higher, and the covering width is larger,so it has a good application prospect in the detection of submarine methane plume.Approximate inversion model of gas leakage location and quantity from scattering signal will be builded in this project by the study on sonar parameters of multibeam sonar system and acoustic characteristics of bubbles.The relationship between methane plume rise height and bubble size will be considered,which will be used to enhance the credibility and accuracy of the method by constraint of methane bubble size. The location and flux of seabed gas leak will be determined in the target area in order to provide theoretical and practical basis for the further use of detection to the submarine methane plumes by multibeam sonar system.

探测海底天气渗漏活动形成的甲烷气泡羽状流，对海底天然气水合物储量评价、碳循环以及海洋环境研究等具有重要的意义。目前对于海底甲烷羽状流的探测主要以船载单波束和分裂波束声纳系统为主。而多波束声纳系统的声学图像分辨率较高，覆盖宽度也较大，因此在海底甲烷羽状流探测中具有良好的应用前景。该项目从探测海底甲烷羽状流气体运移通量的目标出发，根据多波束声纳系统参数和水体中气泡的声学特性，建立利用多波束声纳系统获得的水体散射信号反演甲烷羽状流位置和气体运移通量的近似理论模型。分析甲烷羽状流上升高度和气泡大小的相关性，利用该相关性对甲烷气泡大小进行约束，提高该方法反演海底甲烷羽状流气体运移通量的可信度和准确度。对目标海域进行甲烷羽状流位置标定和气体运移通量测算，为进一步利用多波束声纳系统探测海底甲烷羽状流提供理论和实践依据。

结合相关项目，在我国某海域开展了针对海底冷泉泄漏活动的多波束测深及水体声学探测，并随船对多波束水体数据进行了噪音和混响分析以及原始数据的校正和补偿等处理。结果探测到大量海底气泡羽状流显示。通过和多波束系统获取的地形地貌资料对比发现，该区域羽状流与发源于泥火山和麻坑等特殊地貌的冷泉喷溢活动密切相关。探测到的最高羽状流自海底至顶部高约578米，其形态呈弯曲炊烟状。经其它手段探测结果验证，并与国内外类似研究对比，确认该巨型羽流为泥火山成因的冷泉气体渗漏的典型结果，这也是迄今为止在我国海域发现的最大规模的海底冷泉羽状流。 海底冷泉羽状流的水体探测与常规多波束测深在探测方法上具有较大差别，在成功利用多波束水体技术探测海底冷泉的基础上，结合相关项目，开展了针对海底冷泉泄漏活动的多波束测深及水体声学探测工作。在多波束工作方式、作业航速、作业频率、处理方法等方面，对该探测方法进行了系统总结。针对冷泉羽状流气体通量估算，建立了相关正演模型，获得相关专利授权7项。