Research on outlier detection in marine magnetic data based on Hampel Filtering
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摘要: 海洋磁测数据易受导航误差、仪器故障及人工记录错误等因素干扰，导致异常值频现。这些异常值不仅扭曲磁异常形态，还会破坏磁条带的连续性，严重影响数据质量及后续解释的可靠性。因此，异常值的检测与去除是海洋磁测数据处理中的关键环节。然而，传统方法难以有效区分不同类型的异常值，尤其是上下文异常值，且人工检测既耗时又易产生误判，效率较低。针对这一问题，本研究提出了一种基于局部中位数加权策略的自适应Hampel滤波方法。该方法通过动态调整数据点权重，能够更精准地识别和去除海洋磁测数据中的异常值，尤其在数据分布异质性较大的区域表现优异。与自回归模型、孤立森林及自编码器等传统方法相比，加权Hampel滤波器不仅能够有效检测并去除全局异常值和上下文异常值，还能更好地保留数据的原始特征，显著提升了检测精度。在对中西太平洋麦哲伦海隆地区实测数据的验证中，加权Hampel滤波器的F1分数始终领先于其他方法，证明其在异常值检测中的优越性。该方法为提升海洋磁测数据质量及可解释性提供了重要技术支持，并为未来大规模数据的自动化处理奠定基础。Abstract: Marine magnetic data are susceptible to interference from factors such as navigation errors, instrument malfunctions, and transcript mistakes, leading to frequent outliers. These outliers not only distort the magnetic anomaly patterns but also disrupt the continuity of magnetic stripes, severely affecting data quality and the reliability of subsequent interpretations. Therefore, outlier detection and removal are crucial steps in marine magnetic data processing. However, traditional methods often fail to effectively distinguish between different types of outliers, especially contextual outliers. Additionally, manual detection is time-consuming, prone to errors, and inefficient. To address this issue, this study proposes a weighted Hampel filter based on a local median weighting strategy. This method dynamically adjusts the weights of data points to more accurately identify and remove outliers in marine magnetic data, especially performing well in regions with significant data heterogeneity. Compared to other methods such as autoregression, isolation forest, and autoencoder, weighted Hampel filter not only effectively detects and removes global and contextual outliers but also better preserves the original features of the data, significantly improving detection accuracy. In validation with real data from the Magellan Rise in the Central Pacific Ocean, weighted Hampel filter consistently achieved higher F1 scores than other methods, demonstrating its superiority in outlier detection. This method provides important technical support for improving the quality and interpretability of marine magnetic data and lays a foundation for the future automated processing of large-scale data.
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Key words:
- marine magnetics /
- marine magnetic data processing /
- outlier detection /
- hampel filter
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图 1 全局异常值（左）与上下文异常值（右）示例
Fig. 1 Examples of global outliers (left) and contextual outliers (right)
图 2 GH7801航次海洋磁测磁异常数据分布
a) 包含显而易见的全局异常值的原始磁异常数据，图2a中的矩形指示图2b中的放大范围；b）图2a中矩形区域的细节展示
Fig. 2 Distribution of marine magnetic anomaly data from the GH7801 survey
a) Original magnetic anomaly data containing obvious global outliers, with the rectangle in Figure 2a indicating the zoomed-in region shown in Figure 2b; b) Detailed view of the rectangular region in Figure 2a
图 3 a ）加权后的Hampel滤波器异常值识别结果及细节子图； b）未加权的Hampel滤波器异常值识别结果及细节子图
Fig. 3 a) Weighted Hampel filter outlier detection results and detailed subplot; b) Unweighted Hampel filter outlier detection results and detailed subplot
图 4 不同参数选择的影响。k代表滤波窗口，T代表阈值。红色矩形与蓝色矩形区域突出显示不同参数选择导致的异常值检测结果差异较明显的区域。
Fig. 4 The impact of different parameter choices. k represents the filter window, and T represents the threshold. The red and blue rectangular regions highlight areas where the differences in outlier detection results due to different parameter selections are particularly evident
图 5 自编码器示意图：编码层将输入数据X降维至Z，解码层将数据投影回原始维度得到X'
Fig. 5 Autoencoder schematic: the encoder layer reduces the input data X to a lower-dimensional representation Z, while the decoder layer projects the data back to the original dimension to obtain X'
图 6 孤立森林示意图：更短路径长度的数据点将被隔离识别出来
Fig. 6 Isolation Forest schematic: Data points with shorter path lengths are identified as outliers and isolated
图 7 a) OR-1异常值检测结果。为了使5种方法同时对比，将后4种方法对应的磁异常数值大小每次减小3000 nT，以此绘制到同一张图中进行比较；b) SY-1异常值检测结果。绘制方法同于图7a
Fig. 7 a) OR-1 outlier detection results. To enable a comparison of the five methods, the magnetic anomaly values of the remaining four methods are each reduced by 3000 nT and plotted on the same graph; b) SY-1 outlier detection results. The plotting method is the same as that in Figure 7a
表 1 5种算法分别应用于5条示例数据段的F1分数统计
Tab. 1 The F1 score statistics of five algorithms applied to five example data segments
方法名称 OR-1 OR-2 OR-3 SY-1 SY-2 Weighted Hampel filter 0.9091 0.9804 0.9310 0.9455 0.9375 Hampel filter 0.8387 0.9600 0.8800 0.8276 0.9032 Autoregression 0.7692 0.8335 0.6136 0.4816 0.4615 Autoencoder 0.6250 0.9615 0.7500 0.2963 0.1131 Isolation Forest 0.6250 0.9796 0.9474 0.4000 0.3077 
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