Fast Method for Automatic Extraction of Zhang Heng Satellite Lightning Sferics Wave Scattering Coefficients
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摘要: 闪电哨声波(Lightning Whistler,LW)的散射系数是探索空间环境信息的关键物理量。目前,主要依赖人工方式提取每条LW的散射系数。张衡卫星日产数据高达20G,人工方法已经无法适应海量数据的需求。本文将探索自动提取LW散射系数的方法:首先,以0.8秒的滑动窗提取张衡卫星感应磁力仪载荷(SCM)的详查数据, 并将其转换成时频图和音频文件;其次,针对其时频图,创建YOLOV5神经网络来自动定位单个LW并输出其时频位置信息,按照该时频位置信息截取相应的音频得到含有LW的音频数据并用零填充成0.8秒的音频片段;最后,提取音频数据的梅尔频率倒谱系数(MFCCs),创建基于多头注意力机制改进的GRU神经网络,将MFCCs特征输入到该网络,自动输出散射系数。在2020年2月的数据集上开展实验得到的结果是:其平均绝对误差和平均绝对百分比误差为0.453和0.176,相较于GRU模型和冯小康提出的基于Unet神经网络的LW的散射系数自动提取算法,平均绝对误差分别减少了1.908和1.079,平均绝对百分比误差分别减少了0.7和0.148,每张图的平均处理时间为0.074秒,本文提出的方法可较为准确和快速提取LW的散射系数。
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关键词:
- 张衡卫星 /
- GRU神经网络 /
- YOLOV5神经网络 /
- 闪电哨声波 /
- 散射系数
Abstract: The scattering coefficient of Lightning Whistler (LW) is a key physical quantity for exploring space environment information. Currently, the scattering coefficient of each LW is mainly extracted manually. However, with the daily production of 20G data from the Zhangheng satellite, manual methods are no longer able to meet the demand for massive data. This paper explores an automatic method for extracting the scattering coefficient of LW: First, detailed data of the Zhangheng satellite’s induction magnetometer payload (SCM) is extracted using a sliding window of 0.8 seconds, and it is converted into a time-frequency graph and an audio file. Second, a YOLOV5 neural network is created to automatically locate a single LW and output its time-frequency position information based on its time-frequency graph. The corresponding audio containing the LW is then intercepted according to this time-frequency position information and zero-padded into an audio segment of 0.8 seconds. Finally, the Mel-frequency cepstral coefficients (MFCCs) of the audio data are extracted, and a GRU neural network improved based on multi-head attention mechanism is created. The MFCCs feature is input into the network, which automatically outputs the scattering coefficient. Experimental results on the dataset in February 2020 showed that the average absolute error and average absolute percentage error were 0.453 and 0.176, respectively. Compared with the GRU model and the Unet neural network-based LW scattering coefficient automatic extraction algorithm proposed by Feng Xiaokang, the average absolute error was reduced by 1.908 and 1.079, respectively, and the average absolute percentage error was reduced by 0.7 and 0.148, respectively. The average processing time per image was 0.074 seconds. The method proposed in this paper can extract the scattering coefficient of LW more accurately and quickly. -
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