基于深度卷积网络的海洋涡旋检测模型

传统的利用遥感数据检测涡旋的方法通常是基于物理参数、几何特征、手工特征或专家知识。本文重点研究了基于深度学习技术从海表面高度图中识别海洋涡旋的方法。针对海洋卫星拍摄的海洋表面高度图中的涡旋检测问题,提出了一种基于卷积神经网络的多涡旋检测模型,该模型能够准确提取涡旋的特征信息,拟合语义信息与海面高度之间的关系。同时,在用于涡旋检测的最新公开数据集SCSE⁃Eddy上进行模型训练,以评估基于人工智能的涡旋检测方法性能,该数据集涵盖了15年来位于中国南海及其东部部分海域的每日卫星遥感海表面高度数据。实验结果表明,与现有的方法相比,本文模型取得了更好的检测结果,能够更好地区分相距较近的涡旋。

深度学习的SAR图像海洋涡旋自动检测及其特征提取

本文针对SAR卫星遥感图像海洋涡旋自动检测问题,提出一种基于YOLOX高性能目标检测的海洋涡旋检测模型YOLOX-EDDY,该模型能够精准检测到亚中尺度海洋涡旋。根据SAR图像海洋涡旋的螺旋线形态,本文提出了涡旋中心位置、涡旋尺度和涡旋边缘位置等特征参数自动提取方法,实现了从海洋涡旋自动检测到涡旋特征信息提取的自动化处理。利用国家卫星海洋应用中心和中国资源卫星应用中心提供的高分三号卫星海洋涡旋SAR图像,构建SAR图像涡旋样本库,进行涡旋自动检测模型训练与验证、涡旋特征参数提取实验。实验表明,本文提出方法具有较强的泛化能力,能够实现海洋涡旋精准检测和涡旋特征参数提取。

涡旋特征和轨迹演化的可视化研究

海洋动态过程本身固有的复杂性使得自动的特征挖掘或传统的依赖人工的分析方法变得特别困难,因此改进了涡旋轨迹跟踪算法。据此实现的涡旋可视分析系统提供了多元海洋数据探索、涡旋时空特征和演化规律的多个联动视图和交互方式,方便用户灵活地进行不同维度或时空上的涡旋特征的可视分析和探索。文章以中国东南海涡旋轨迹的时空演化分析为例,验证了该可视分析系统的有效性。

基于微纳结构的光子轨道角动量复用及检测进展

1992年Allen等认识到光子可以携带轨道角动量(OAM),其表现为波前的螺旋相位分布。由于其独特的光场分布以及其拓扑荷理论上可取任意整数等特性, OAM光束在超分辨成像、高密度数据编码等领域具有重要作用。对微纳尺度下OAM光束与物质相互作用新机制的研究,有望为现代光子器件以及多维光与物质相互作用等领域提供新的思路和方法。介绍了本课题组利用OAM光束在纳米结构上实现多维信息复用以及OAM光束拓扑荷的探测技术,并对纳米尺度OAM光束的应用进行了展望。

Theoretical and Experimental Analysis of Vortex Origin

Several investigations refer to the issue of creation and identification of vortices in flows with different regime and presence of obstacles. Reasons have to do with the crucial role that vortices play in nature and industrial processes （sediment transport, mixing, radiation, noise, etc.）. Despite the contributions, further work is needed in order to perform more analysis of the mathematical arguments used to explain this phenomenon. In this idea order, the paper presents some advances in mathematical analysis and experimental results. In the first section, we do a description of the fluid motion from a fractional view through a sequence of three steps： Darcy＇s law, Navier-Stokes equations and Reynolds equations. Next, a representation of the temporal change of kinetic energy is found, which allows the possibility of the two signs. We obtain a description of the process of vortex creation. A length that represents the transition between flow and vortex intensity is found; then a succession of lengths is established that allows scaling from micro to macro. In the second section, experimental results are present; we consider vortex creation and its detection upstream of a bed form similar to that found in rivers, installed in an open channel, equipped with a water circulation system. For vortex detection, a methodology based on the particle image velocimetry PIV technique is proposed. So, we fulfill two objectives： vortex identification and its passage frequencies behind the bed form installed in the channel. Such procedure allows a computer process time reduction in vortices identification task.

Automatic detection of oceanic mesoscale eddies in the South China Sea

This study focuses on the spatial and temporal distribution characteristics of mesoscale eddies in the South China Sea(SCS). An automatic eddy detection method,based on the geometry of velocity vectors,was adopted to obtain an eddy dataset from 21 years of satellite altimeter data. Analysis revealed that the number of anticyclonic eddies was nearly equal to cyclonic eddies; in the SCS,cyclonic eddies are generally stronger than anticyclonic eddies and anticyclonic eddies are larger and longer-lived than cyclonic eddies. Anticyclonic eddies tend to survive longer in the spring and summer,while cyclonic eddies have longer lifetimes in the autumn and winter. The characteristics and seasonal variations of eddies in the SCS are strongly related to variations in general ocean circulation,in the homogeneity of surface wind stress,and in the unevenness of bottom topography in the SCS. The spatial and temporal variation of mesoscale eddies in the SCS could,therefore,be an important index for understanding local hydrodynamics and regional climate change.

Eddy Current Test for Detection of Foreign Material using Rotating Probe

There are several elements that affect on the integrity of steam generator tubes. One of the elements is loose parts located on outside of the tubes. It causes erosion which is possible to lead fatal defect like crack on the outside surface of the tubes. In this study, artificial loose parts on Inconel 690 tube are demonstrated and eddy current testing data of the region is acquired using rotating probe. Ferromagnetic and nonmagnetic foreign materials were used to demonstrate artificial loose parts. Eddy current channel of 100 KHz frequency shows definite signals of those foreign materials but stainless steel was not clearly detected. This result can be explained based on the electrical conductivity of the materials and it can be confirmed with lissajous window and C-scan. In addition, no indication was detected when the distance of the gap between the foreign materials and the tube is increased to more than 3 mm under this test condition. Based on these experimental inspections, we were able to find suitable methods for analyzing the signals obtained under various conditions that could occur when conducting steam generator eddy current test in NPP.

Automatic detection of oceanic eddies in reanalyzed SST images and its application in the East China Sea

Oceanic eddies may cause local sea surface temperature （SST）, height, and salinity anomalies in remote sensing （RS） images. Remote sensed SST imagery has proven to be an effective technique in oceanic eddy detection, because of its high temporal and spatial resolution. Various techniques have been used to identify eddies from SST images. However, mainly owing to the strong morphological variation of oceanic eddies, there is arguably no uniquely correct eddy detection method. A scheme of algorithm based on quasi-contour tracing and clustering of eddy detection from SST dataset is presented. The method does not impose fixed restrictions or limitations during the course of ＂suspected＂ eddy detection, and any eddy-like structures can be detected as ＂suspected＂ eddies. Then, ＂true＂ eddies can be identified based on the combination of intensity and spatial/temporal scale criteria. This approach has been applied to detect eddies in the East China Sea by using Operational SST ＆ Sea Ice Analysis （OSTIA） dataset. Experiments proved that oceanic eddies ranging in diameter from tens to hundreds of kilometers can be detected. Through investigation of the 2007-2011 OSTIA daily SST dataset from the Kuroshio region in the East China Sea, we found that the most active regions for oceanic eddies are those along the Kuroshio path, northeast of Taiwan Island, the Yangtze Estuary and the Ryukyu Islands. About 86% of the cyclonic eddies and 87% of the anticyclonic eddies have the size of 50-100 km in diameter. Only 25% of the anticyclonic eddy and 26% of the cyclonic eddy have the strength more than 0.4℃ in the sea surface layer.

A mesoscale eddy detection method of specific intensity and scale from SSH image in the South China Sea and the Northwest Pacific

Mesoscale eddies exist almost everywhere in the ocean and play important roles in the ocean circulation of the world. These eddies may cause sound spread singular regions and bring great influences to the upwater ship and underwater aircraft. Due to the lack of hydrographic survey datasets, study of mesoscale eddies has been greatly restricted. Fortunately, satellite altimeter provided an effective way to study mesoscale eddies. An automatic detection algorithm is introduced to detect mesoscale eddies of specific intensity and spatial/temporal scale based on satellite sea surface height(SSH) data and the algorithm is applied in a strong eddy activity region: the South China Sea and the Northwest Pacific. The algorithm includes four steps. The first step is preprocessing of the SSH image, which includes elimination of error SSH data and interpolation. The second step is to detect suspected mesoscale eddies from preprocessed SSH images by dynamic threshold adjustment and morphological method, and the suspected mesoscale eddy detection includes two procedures: suspected mesoscale eddy core region detection and suspected mesoscale eddy brim extraction. The third step is to pick out mesoscale eddies satisfied with specified criteria from suspected mesoscale eddies. The criteria include three items, that is, intensity criterion, spatial scale, criterion and temporal scale criterion. The last step is algorithm performance analysis and verification. The algorithm has the capability of adaptive parameter adjustment, and can extract mesoscale eddies of interested intensity and spatial/temporal scale. The paper can provide a basis for analyzing space-time characteristics of mesoscale eddy in the South China Sea and the Northwest Pacific.