A Robust and High-Speed Automated Detection Model for Lightning Whistler
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摘要: 张衡一号卫星在轨6年积累了海量观测数据, 检测其中的闪电哨声波事件(Lightning Whistler, LW)对于分析空间物理环境规律具有重要意义. 但现有基于时频图像的方法推理速度过慢, 完成任务需约40年. 为此, 研究首次从音频事件检测的角度提出高速的闪电哨声波检测模型WhisNet, 将检测的时间成本从40年压缩至54天. 方法为以4s滑动窗截取波形, 提取梅尔频谱特征, 利用轻量级卷积循环神经网络(CRNN)提取音频事件特征, 输出层预测LW事件起始时间和持续时长. 基于2020年4月1日至10日的感应磁力仪(SCM)数据实验显示, WhisNet检测性能与传统方法相当, 但计算量和参数量减少99%, 速度提升98%. 进一步在2020年5月SCM数据上的应用结果与WCLG(全球闪电气候学和时间序列, WWLLN Global Lightning Climatology and time series )全球闪电密度趋势高度一致, 验证了WhisNet在大规模卫星数据处理中的准确性与适用性. 研究结果为挖掘其他海量地球空间事件提供了重要参考.Abstract: The Zhangheng Satellite has accumulated a vast amount of observational data over its six years in orbit. Detecting all Lightning Whistler Wave (LW) events from this dataset is crucial for comprehensively analyzing the variation patterns of the space physical environment. However, using the current mainstream LW detection technology, which is based on time-frequency spectrograms, it would take approximately 40 years to complete this task. To address the slow inference speed and meet practical engineering demands, this study proposes, for the first time, a high-speed detection model for lightning whistler waves from the perspective of audio event detection—WhisNet. This model reduces the time cost from 40 years to just 54 days. First, waveform data is segmented using a 4-second sliding window; then, Mel-spectrogram audio features are extracted. Next, a lightweight Convolutional Recurrent Neural Network (CRNN) is constructed to further extract the audio event features of LW. Finally, two fully connected networks are created at the output layer to predict the start time and duration of each LW event. To evaluate the model’s performance and computational speed, experiments were conducted on data from the SCM (Search Coil Magnetometer) between April 1 and April 10, 2020. The results show that the performance of the WhisNet model is comparable to that of time-frequency image-based methods, but with a 99% reduction in computational and parameter costs and a 98% increase in computational speed. The model was further applied to SCM data from May 2020, and the detection results were statistically analyzed and visually compared to the average lightning density trend from the WWLLN Global Lightning Climatology and timeseries (WGLC) for May 2020. The high consistency between the two further confirms the applicability and accuracy of the WhisNet model in processing large-scale satellite data. This method offers significant reference value for thoroughly exploring other large-scale geospace events.
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图 6 不同模型检测哨声波的效果. (a)原始波形与时频图, (b) WhisNet, (c) Mask RCNN, (d) Mask Scoring RCNN, (e) YOLOv5-Upgraded, (f) Yolov8s, (g) Yolov8m, (h) Yolov8l
Figure 6. Performance of different models in detecting whistlers. (a) Original image, (b) WhisNet, (c) Mask R-CNN, (d) Mask scoring R-CNN, (e) YOLOv5-Upgraded, (f) Yolov8s, (g) Yolov8m, (h) Yolov8l
图 8 模型实际应用情况. (a) WGLC在2020年5月份的平均闪电密度, (b) WhisNet模型自动检测张衡卫星LW的密度估计, (c) Kriging插值法
Figure 8. Practical Application. (a) Average lightning density in May 2020 recorded by WGLC, (b) density estimation of lightning whistlers from the Zhangheng Satellite LW detected automatically by WhisNet, (c) Kriging interpolation method
图 9 各模块输出的特征. (a)音频处理模块, (b)轻量化卷积模块, (c)循环神经网络模块, (d)输出模块. 图中数字表示相应特征图的维度
Figure 9. Feature maps output by each module. (a) Audio processing module, (b) lightweight convolutional module, (c) recurrent neural network module, (d) output module. The numbers shown indicate the corresponding dimensions of the feature maps
表 1 模型超参数
Table 1. Hyperparameters of the model
超参数 值 损失函数 Binary CrossEntropy Loss 优化器 Adam 学习率 0.001 批大小 128 训练轮次 50 表 2 模型性能评估
Table 2. Performance evaluation of the model
Model Precision/(%) Recall/(%) F1/(%) FLOPS/GByte Params /MByte Cost time/h WhisNet 93.3 89.4 91.3 0.17 0.09 18.15 Mask RCNN 85.1 95.2 89.8 144 44.32 842.16 Mask Scoring RCNN 85.2 96.3 90.2 181 62.75 935.61 YOLOv5 Upgraded 91.6 90.0 90.8 31.7 13.78 579.86 Yolov8 s 91.3 90.1 90.6 28.6 11.2 574.43 Yolov8 m 92.5 89.9 91.2 78.9 25.9 591.82 Yolov8 l 94.0 88.8 91.3 165.2 43.7 622.61 注 表中加粗的数字表示该指标下的最佳结果. 表 3 生成单个特征所需时间
Table 3. Time to generate a single feature
特征名称 Time/s Size/KByte Mel频谱 0.003 25 时频图 1.7 165 -
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