| 基于全天空图像的极光活动变化检测方法研究 |
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| 引用本文： | 王倩,胡红桥,胡泽骏,丘琪.基于全天空图像的极光活动变化检测方法研究[J].地球物理学报,2015,58(9):3038-3047. |
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| 作者姓名： | 王倩 胡红桥 胡泽骏 丘琪 |
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| 作者单位： | 1. 中国极地研究中心 国家海洋局极地科学重点实验室, 上海 200136;
2. 西安邮电大学 通信与信息工程学院, 西安 710121 |
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| 基金项目： | 国家自然科学基金项目(41274164,41504115),极地专项(CHINARE 2014-02-03)陕西省自然科学基础研究计划(2015JQ6223)资助. |
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| 摘 要： | 面对日积月累产生的海量极光数据,快速发现极光现象的发生及活动特征是研究极光的物理机制及相关动力学过程的首要问题,它为研究极光现象提供有效的自动化分析手段,从而能够提供充足而有效的事件用于统计学分析.因为太阳风是等离子体,它有着磁流体力学的特征,本文采用流体力学的连续性方程对极光运动进行建模,提取全天空极光图像序列的运动场,对极光活动进行表征,进而构造极光活动变化曲线,从而有效的检测出极光活动的变化.该方法的优势在于,基于运动场的表征方法能够有效反映极光活动的二维形态和运动特征,生成的极光活动变化曲线可以准确地指示极光发生、变化和消失的时间,为进一步研究极光的活动周期及相关物理变化奠定基础.
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| 关 键 词： | 极光活动 变化检测 全天空图像 |
| 收稿时间： | 2015-04-02 |
A method for detecting the change of auroral activities based on the All-sky image sequence |
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| WANG Qian,HU Hong-Qiao,HU Ze-Jun,QIU Qi.A method for detecting the change of auroral activities based on the All-sky image sequence[J].Chinese Journal of Geophysics,2015,58(9):3038-3047. |
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| Authors: | WANG Qian HU Hong-Qiao HU Ze-Jun QIU Qi |
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| Institution: | 1. SOA Key Laboratory for Polar Science, Polar Research Institute of China, Shanghai 200136, China;
2. School of Telecommunication and Information Engineering, Xi'an University of Posts & Telecommunications, Xi'an 710121, China |
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| Abstract: | Aurora is light emissions caused by the collision of ionized streams of charged particles with high altitude atmospheric atoms and molecules. The auroral behaviors are ascribed to various dynamic processes of the solar wind-magnetosphere interaction. Therefore, the systematic observation and research of auroral phenomena help us to study the way and extent in which the sun affect the earth, and have significances for learning about behaviors of space weather. So far, auroral research and comprehensive observation have been carried out by many countries all over the world. Faced with the annually increasing amount of auroral data and the demands for statistical studying auroral physical process, we need to quickly browse the auroral activities and exactly find similar auroral events as more as possible. Traditional method of browsing auroral activities is keogram. It is generated by extracting the pixel columns along the geomagnetic north-south in all-sky image (ASI) and arranging the columns chronologically, which represent temporal variations of the emission intensities along the magnetic meridian. Obviously, the keogram loses two-dimensional information about appearance and motion, which result in missing of several auroral events, such as aurora images including curl structure or luminance structure not appearing on the magnetic meridian. Having had keogram, we need a tool which can quantitatively measure the change of auroral appearance and motion.
Optical ground imaging is the earliest applied and most popular auroral observation tools, which can continually obtain two-dimensional auroral image sequences with satisfied temporal and spatial resolutions. In order to monitor the auroral activities, ASI images are used in this study. An effective representation method of ASI image sequence which can capture auroral two-dimensional appearance and motion is urgently needed. For this purpose, motion field is extracted in ASI image sequence. We model the auroral motion using the continuous equation, considering the fact that the solar winds have magnetic fluid nature. And thereby the motion field of ASI image sequence can be more precisely extracted. Based on the obtained motion field, relative motion in neighborhood is represented by the local vector difference (LVD) between center pixel and neighborhood one. Then the LVDs are projected to a two-dimension map defined on polar coordinates. Spatiotemporally statistics of the LVDs is used as the representation of auroral sequences. By computing the difference between two successive auroral sequences using metric square histogram distance, the change of auroral activities can be quantitatively measured. By sliding the window chronologically which includes two successive auroral sequences, the change curve can be obtained. The local peaks of the curve indicate the changes of auroral activities.
The proposed method is used on the ASI observations at 557.7 nm from December 2003 to January 2004 at yellow river station (YRS). The experimental results show that the change curve can exactly detect the changes of auroral activities, by comparing with keogram. In the interval from 12:00 to 15:00 (UT) on 2003-12-25, there are five distinct changes shown in keogram. On the corresponding change curve, the times at which five local peaks happen coincide with those of auroral change in keogram. In addition, the change curve can also detect the changes which are not display in keogram. At 05:05:33—05:07:53 UT on 2004-01-16, the arc with several curls happened. The keogram failed to display the special two-dimensional auroral structure, but the change curve demonstrates there is a distinct change at 05:07:53 UT. By rechecking the ASI images during this interval, we found that the curl structures was disappearing.
Because motion field provides the auroral information about two-dimensional appearance and motion, the proposed method can detect the change of auroral activities. And thereby the change curve makes it feasible to fast browse auroral activities and to further study auroral activity period. |
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| Keywords: | Auroral activities Change detection ASI image |
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