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使用 ORCA®-Quest 进行极光观测
2025 年 8 月 19 日发布
The University of Electro-Communications 下属 Department of Communication Engineering and Informatics 的 Hosokawa Laboratory 使用高灵敏度相机观测极光。极光观测需要高帧率来捕捉形态和动态，需要高灵敏度来检测暗极光，需要低噪声来流畅地分析获取的图像，并且需要大尺寸传感器来实现宽场成像。ORCA-Quest qCMOSⓇ 相机解决了这些问题。
我们采访了 Keisuke Hosokawa 教授，了解 ORCA-Quest 的引进原因、使用感受以及对未来研究的展望。
关于研究
您能介绍一下您的研究吗？
我们实验室在北欧和阿拉斯加的多个地点使用高灵敏度相机对极光进行成像，观测脉动周期为几秒到几十秒的脉动极光。
The Pulsating Aurora Project 于 2015 年启动。我们使用滨松光子学株式会社的 EM-CCD 相机 (ImagEMⓇ) 进行高速高灵敏度成像。通过将这种相机的地基极光成像与The European Incoherent Scatter (EISCAT) radar、2016 年 12 月发射的Arase 号 (ERG) 卫星，以及 2022 年启动的 the Pulsating Aurora rocket experiment（LAMP mission）的观测数据相结合开展研究。通过这种综合方法，我们致力于解析脉动极光的起源。
挪威 Skibotn Observatory
Prof. Keisuke Hosokawa
极光成像中的问题
进行极光成像时您遇到了哪些问题？
极光成像的主要问题是
- 检测暗极光所需的灵敏度
- 详细观测极光形态所需的空间分辨率
- 相机噪声对数据分析产生负面影响
首先，对于相机灵敏度问题，之前我使用滨松光子学株式会社制造的 EM-CCD 相机 (ImagEM)。EM-CCD 相机可以通过倍增入射电子，以极高的高灵敏度采集图像，因而非常适合高时间分辨率极光观测。但是，EM-CCD 相机的像素尺寸较大、像素数较低，限制了宽场观测的空间分辨率，导致难以详细观测极光形态。
如前所述，EM-CCD 相机的空间分辨率是一个限制因素。因此，我们正在寻找一种能够提供更高空间分辨率同时还能保持灵敏度的相机。当滨松光子学株式会社推出高灵敏度且高分辨率的 ORCA-Quest qCMOS 相机时，我们认为提高成像系统空间分辨率具备了可能性，因而倍感振奋。
对于相机噪声对数据分析产生负面影响的问题，我们需要使用噪声尽可能小的相机，因为拍摄图像中除极光之外的任何信号都会对后续的数据分析产生不利影响。EM-CCD 相机可以通过信号倍增来提高信噪比。然而，信号倍增会增加很大的噪声（称为过剩噪声），这会导致采集图像的背景发生波动，从而增加图像分析难度。
挪威 Skibotn Observatory 穹顶内的 ORCA-Quest 相机
引入 ORCA-Quest 的决定性因素
您选择 ORCA-Quest 的决定性因素是什么？
我们决定使用 ORCA-Quest 的最终决定性因素是其极高的分辨率。EM-CCD 相机的像素为 512 × 512，而 ORCA-Quest 的像素为 4096 × 2304，相比前者高出很多。此外，每个像素的尺寸为 4.6 μm × 4.6 μm，而 EM-CCD 相机的像素尺寸则为 16 μm × 16 μm，因此 ORCA-Quest 能够以比 EM-CCD 相机高得多的空间分辨率观测极光。虽然成像范围略有变化，使用 ORCA-Quest 拍摄的图像的空间分辨率仍然比 EM-CCD 相机高出大约 10 倍。
对于灵敏度问题，ORCA-Quest 略逊于具有大像素尺寸和电子倍增功能的 EM-CCD 相机，但由于读出噪声非常低，这款相机甚至可以检测到相当暗的极光现象。EM-CCD 相机虽然可以通过电子倍增来增强信号，但过剩噪声会对分析产生不良影响。相反，ORCA-Quest 相机因为不使用电子倍增，所以不会产生过剩噪声。此外，这款相机的读出噪声和暗电流噪声也非常低，因此数据分析也不受噪声影响，这一点也很有吸引力。
观测示例
帘幕状极光
扫描模式：超静音扫描
帧速率：20 帧/秒（2048 像素 × 1152 像素）
像素合并：2×2
数据来源：Keisuke Hosokawa 博士。所属机构：The University of Electro-Communications 下属 Department of Communication Engineering and Informatics 的 Hosokawa Laboratory
波浪状极光
扫描模式：超静音扫描
帧速率：20 帧/秒（1024 像素 × 576 像素）
像素合并：4 × 4
数据来源：Keisuke Hosokawa 博士。所属机构：The University of Electro-Communications 下属 Department of Communication Engineering and Informatics 的 Hosokawa Laboratory
观测数据管理
你们是否会不断地运行相机观测极光？ 你们如何管理 ORCA-Quest 采集的数据？
由于极光的发生无法预测，我们通常每晚都会拍摄图像。这就需要大型存储系统来保存图像数据，但存储容量仍然有限。我们还需要将观测数据通过互联网从观测站传输到日本。因此，我们希望尽量减少不必要的数据，例如没有捕捉到极光的图像。
为此，我们目前正在开发一个使用 AI 进行自动分类的程序。我们计划利用日间时段通过 AI 对夜间拍摄图像进行自动分类，仅保留包含极光的图像并删除不必要的数据。自动分类 AI (Tromsø AI) 的开发进展顺利，我们计划近期在实际观测站进行测试。这样，我们可以减少无用数据的数量，从而节省存储空间。
此外，在未来开发基于 AI 的观测时，我们的目标是不仅能自动检测极光的发生，还能实时自动提供极光类型和亮度等详细信息，同时还能优化相机图像采集的参数。例如，在出现快速移动的极光时，我们希望缩短相机曝光时间以达到高时间分辨率；而在出现非常微弱的极光时，我们希望延长曝光时间或使用像素合并来提高灵敏度。
研究展望
您未来有什么研究计划？
对于未来的研究展望，我主要考虑以下几点：
- 解析空间尺度小于 100 km 的中尺度极光的作用
- 使用 EISCAT_3D、Arase 卫星、ORCA-Quest 等装置产生的地基观测数据进行多维数据分析
- 使用多台 ORCA-Quest 相机构建多点光学观测网络
对于第 1 点，传统相机的空间分辨率不足，无法解析具有精细结构的中尺度极光的机理。通过引入具有更高空间分辨率的 ORCA-Quest 相机，并结合目前正在通过国际合作开发的 EISCAT_3D 雷达的观测结果，我们正在努力加速解析中尺度极光的机理。
对于第 2 点，除了前面提到的 ORCA-Quest 和 EISCAT_3D 之外，再结合利用 Arase 号卫星产生的数据，我们可以从地面和空间两个角度获取极光数据，从而能够对极光机理进行多维分析。
但是，要做到第 2 点，必须满足以下所有条件：
- Arase 号卫星必须经过相机和雷达的观测范围
- Arase 号经过时必须出现极光
- 极光出现时必须天气晴朗（无云）
由于我们无法控制极光出现的时间或天气，因此我们将会推动实现第 3 点：使用多台 ORCA-Quest 相机构建多点光学观测网络。这将使我们能够在 Arase 号轨迹范围内观测尽可能广阔的区域。通过将三台相机放置在不同的位置，并将观测数据像拼图一样进行组合，我们可以观测广阔的区域。我们已经购入相机，目前正在进行安装并等待 EISCAT_3D 雷达投入运行。
EISCAT_3D 雷达
Researcher profile
Prof. Keisuke Hosokawa
Department of Communication Engineering and Informatics, The University of Electro-Communications, Hosokawa Laboratory, Professor
Mar. 2003
Department of Earth and Planetary Sciences, Graduate School of Science, Kyoto University, Ph.D.
Apr. 2004
Assistant researcher, Department of Information and Communication Engineering, The University of Electro-Communications
Apr. 2007
Assistant Professor, Department of Information and Communication Engineering, The University of Electro-Communications
Jun. 2012
Associate Professor, Department of Information and Communication Engineering, The University of Electro-Communications
Apr. 2019
Professor, Department of Computer and Network Engineering, The University of Electro-Communications
Apr. 2024
Director, Center for Space Science and Radio Engineering, The University of Electro-Communications
*本页显示的内容基于 2024 年 9 月进行的采访。
相关产品
ORCA-Quest 2 是一款新的 qCMOS® 相机，也是 ORCA-Quest 的后续产品，具有多项深化进步，例如在极低噪声扫描模式下读出速度更快，紫外区域灵敏度更高。
其他案例研究
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