基于RF-PSO-LSTM模型的探地雷达煤岩界面智能识别方法

Intelligent identification method for coal-rock interface in ground penetrating radar based on RF-PSO-LSTM model

  • 摘要: 面向煤矿智能化开采中煤岩界面识别的需求,针对多噪声、实时与动态场景下专家解释在效率与一致性方面的局限,构建了一种融合随机森林(Random Forest,RF)、粒子群优化(Particle Swarm Optimization,PSO)与长短期记忆网络(Long Short-Term Memory,LSTM)的探地雷达(Ground Penetrating Radar,GPR)煤岩界面智能识别方法。以山西阳泉新景矿15219工作面的钻孔柱状图为参照,采用有限时域差分法建立砂岩−煤层−泥岩的3层倾斜界面正演模型,模拟结果为特征的分析和筛选提供了无噪声的基础数据。对每道信号中的1 024个采样点提取18项时频域特征,利用RF算法,以贡献度大于总值的60%为阈值筛选出8个关键特征:一阶差分、原始信号振幅、希尔伯特包络、小波系数均值、中心频率、信号均值、低频能量与频谱带宽,并采用Z-score标准化消除量纲影响。在此基础上,采用粒子群优化算法对LSTM及作为对比的RNN和SVM模型进行超参数自动寻优,获得LSTM模型的最优参数:单元数128,初始学习率3.3×10−3,Dropout率0.394。针对不同模型特性,其中LSTM与RNN的模型输入为样本数, 1 024时间步, 8特征的张量形式组织数据,以确保模型可以学习到电磁波在介质中传播的动力学特征与相位连续性,SVM则使用对应的二维特征矩阵。最终在15219工作面低位抽采巷实测的GPR数据上开展试验。结果显示:在相同测试集上RNN模型的定量评价指标要优于LSTM模型,针对这种“反差”情况,对LSTM模型的预测结果进行分析,其预测的煤层顶界面中,呈现出连续性中断、剧烈起伏等与原始标签不符的异常区域,恰好对应工区内地质勘探资料所揭示的陷落柱和巷道地面积水区等地质构造影响范围。分析其机理在于,LSTM独特的门控机制使其在学习时可以从信号的局部与整体特征、细节与结构的信息中提取到蕴藏的深层次信息,结果更贴近实际矿区的地质情况,具有突破依赖人工标签的能力。相比之下,RNN仅能拟合训练标签,SVM难以处理高维时序特征而识别结果零散。综合结果表明,LSTM模型在探地雷达的时序数据特征解析方面具有独特的优势,不仅能学习给定标签信息,胜任识别煤岩界面的任务,更能深入挖掘GPR数据中隐含的物理规律,更加全面地识别出人工解释时难以察觉的,由地质构造引起的微弱的信号差异。

     

    Abstract: To meet the demands for coal–rock interface identification in intelligent mining and to overcome the limitations of manual interpretation—such as inefficiency and inconsistency under noisy, real-time, and dynamic conditions—an intelligent recognition method based on ground-penetrating radar (GPR) is proposed, integrating Random Forest (RF), Particle Swarm Optimization (PSO), and Long Short-Term Memory (LSTM) networks. Using the borehole columnar section of the 15219 working face in Xinjing Mine, Yangquan, Shanxi as a reference, a three-layer forward model with an inclined interface (sandstone–coal–mudstone) is constructed by the finite-difference time-domain (FDTD) method. The simulation results provide noise-free reference data for feature analysis and selection. For each trace containing 1024 sample points, 18 time-and frequency-domain features are extracted. RF is then applied to rank feature importance, and 8 key features with cumulative contribution exceeding 60% are retained: first-order difference, raw-signal amplitude, Hilbert envelope, mean wavelet coefficient, central frequency, signal mean, low-frequency energy, and spectral bandwidth. All features are standardized via Z-score normalization to eliminate dimensional effects. Subsequently, PSO is employed to automatically optimize the hyperparameters of LSTM—as well as, for comparison, those of RNN and SVM. The optimal LSTM hyperparameters are determined as follows: 128 units, an initial learning rate of 3.3×10−3, and a dropout rate of 0.394. Considering the structural characteristics of each model, the input data for both LSTM and RNN are organized into a tensor format of number of samples, 1 024 time steps, 8 features, enabling the models to capture dynamic characteristics and phase continuity in electromagnetic wave propagation through the medium. In contrast, SVM is trained using a corresponding two-dimensional feature matrix. Finally, validation is performed using measured GPR data collected from the lower extraction roadway of the 15219 working face. Results indicate that, on the same test set, the RNN model quantitatively outperforms the LSTM model. To investigate this discrepancy, the prediction results of the LSTM model are further analyzed. In the LSTM-predicted roof interface of the coal seam, discontinuous segments, sharp undulations, and other anomalies inconsistent with the original labels are observed. These anomalies correspond precisely to the influence zones of geological structures—such as collapse columns and watered floor sections—identified in the mining area’s geological survey data. The underlying mechanism is attributed to LSTM’s unique gating architecture, which enables deep extraction of information from both local and global characteristics, as well as from detailed and structural signal features. Consequently, LSTM predictions more accurately reflect the actual geological conditions and demonstrate the ability to transcend reliance on manual labels. In comparison, the RNN model tends to overfit the training labels, while SVM struggles with high-dimensional time-series features, resulting in fragmented recognition outputs. Overall, the findings confirm that the LSTM model offers unique advantages in analyzing the time-series characteristics of GPR data. It not only learns from manual labels to perform coal–rock interface recognition, but also uncovers latent physical patterns within the GPR signals, thereby enabling more comprehensive detection of subtle signal variations caused by geological structures—variations often missed by manual interpretation.

     

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