Auroral alert version 1.0: two-step automatic detection of sudden aurora intensification from all-sky JPEG images

IF 1.8 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY
M. Yamauchi, U. Brändström
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引用次数: 0

Abstract

Abstract. A sudden and significant intensification of the auroral arc with expanding motion (we call it “local-arc breaking” hereafter) is an important event in many aspects but easy to miss for real-time watching due to its short rise time. To ease this problem, a real-time alert system for local-arc breaking was developed for the Kiruna all-sky camera (ASC) using ASC images in the JPEG format. The identification of the local-arc breaking is made in two steps using the “expert system” in both steps: (1) explicit criteria for classification of each pixel and simple calculations afterward are applied to each ASC image to obtain a simple set of numbers, or the “ASC auroral index”, representing the occupancy of aurora pixels and characteristic intensity of the brightest aurora in the image; (2) using this ASC auroral index, the level of auroral activity is estimated, aiming for Level 6 as clear local-arc breaking and Level 4 as a precursor for it (reserving Levels 1–3 for less active aurora and Level 5 for less intense sudden intensification). The first step is further divided into two stages. Stage (1a) uses simple criteria for R (red), G (green), and B (blue) values in the RGB color code and the H (hue) value calculated from these RGB values, each pixel of a JPEG image is classified into three aurora categories (from brightest to faintest, “strong aurora”, “green arc”, and “visible diffuse (aurora)”) and three non-aurora light source categories (“cloud”, “artificial light”, and “Moon”). Here, strong aurora means that the ordinary green color by atomic oxygen's 558 nm emission is either nearly saturated or mixed with red color at around 670 nm emitted, by molecular nitrogen. In stage (1b), the percentage of the occupying area (pixel coverage) for each category and the characteristic intensity of the strong aurora pixels are calculated. The obtained ASC auroral index is posted in both an ASCII format and plots in real time (https://www.irf.se/alis/allsky/nowcast/, last access: 11 April 2023). When Level 6 (local-arc breaking) is detected, an automatic alert email is sent out to the registered addresses immediately. The alert system started on 5 November 2021, and the results (both Level 6 detection and Level 4 detection) were compared to the manual (eye) identification of the auroral activity in the ASC during the rest of the aurora season of the Kiruna ASC (i.e., all images during a total of 5 months until April 2022 were examined and occasionally double-checked in the sky). Unless the Moon or the cloud blocks the brightened region, a nearly one-to-one correspondence between Level 6 and eye-identified local-arc breaking in the ASC images is achieved with an uncertainty of under 10 min.
极光警报1.0版:从所有天空JPEG图像中两步自动检测突然的极光增强
摘要极光弧的突然显著增强和扩张运动(我们在下文中称之为“局部断弧”)在许多方面都是一个重要事件,但由于上升时间短,很容易错过实时观测。为了缓解这个问题,为Kiruna全天空相机(ASC)开发了一个用于局部电弧断裂的实时警报系统,该系统使用JPEG格式的ASC图像。局部断弧的识别分两步进行,两步都使用“专家系统”:(1)对每个像素进行明确的分类标准,然后对每个ASC图像进行简单的计算,以获得一组简单的数字,或“ASC极光指数”,表示极光像素的占有率和图像中最亮极光的特征强度;(2) 使用ASC极光指数,估计了极光活动的水平,目标是6级为明确的局部电弧断裂,4级为其前兆(为活动较少的极光保留1-3级,为强度较小的突然增强保留5级)。第一步进一步分为两个阶段。阶段(1a)使用RGB颜色代码中的R(红色)、G(绿色)和B(蓝色)值以及根据这些RGB值计算的H(色调)值的简单标准,JPEG图像的每个像素被分类为三个极光类别(从最亮到最暗,“强极光”、“绿弧”和“可见漫射(极光)”)和三个非极光光源类别(“云”、“人造光”和“月亮”)。在这里,强烈的极光意味着普通的绿色由原子氧的558 nm发射在670左右几乎饱和或与红色混合 nm发射。在阶段(1b)中,计算每个类别的占用面积(像素覆盖率)的百分比和强极光像素的特征强度。获得的ASC极光索引以ASCII格式发布,并实时绘制(https://www.irf.se/alis/allsky/nowcast/,最后访问时间:2023年4月11日)。当检测到6级(本地断弧)时,会立即向注册地址发送自动警报电子邮件。警报系统于2021年11月5日启动,并将结果(6级检测和4级检测)与基鲁纳ASC极光季节剩余时间ASC极光活动的手动(眼睛)识别进行了比较(即,对截至2022年4月的5个月内的所有图像进行了检查,偶尔还会在天空中进行双重检查)。除非月亮或云层挡住了变亮的区域,否则ASC图像中6级和眼睛识别的局部电弧断裂之间几乎一一对应,不确定性低于10 最小。
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来源期刊
Geoscientific Instrumentation Methods and Data Systems
Geoscientific Instrumentation Methods and Data Systems GEOSCIENCES, MULTIDISCIPLINARYMETEOROLOGY-METEOROLOGY & ATMOSPHERIC SCIENCES
CiteScore
3.70
自引率
0.00%
发文量
23
审稿时长
37 weeks
期刊介绍: Geoscientific Instrumentation, Methods and Data Systems (GI) is an open-access interdisciplinary electronic journal for swift publication of original articles and short communications in the area of geoscientific instruments. It covers three main areas: (i) atmospheric and geospace sciences, (ii) earth science, and (iii) ocean science. A unique feature of the journal is the emphasis on synergy between science and technology that facilitates advances in GI. These advances include but are not limited to the following: concepts, design, and description of instrumentation and data systems; retrieval techniques of scientific products from measurements; calibration and data quality assessment; uncertainty in measurements; newly developed and planned research platforms and community instrumentation capabilities; major national and international field campaigns and observational research programs; new observational strategies to address societal needs in areas such as monitoring climate change and preventing natural disasters; networking of instruments for enhancing high temporal and spatial resolution of observations. GI has an innovative two-stage publication process involving the scientific discussion forum Geoscientific Instrumentation, Methods and Data Systems Discussions (GID), which has been designed to do the following: foster scientific discussion; maximize the effectiveness and transparency of scientific quality assurance; enable rapid publication; make scientific publications freely accessible.
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