A Two-Stage Ship-Radiated Noise Recognition Method Based on Contrastive Pre-Training and Progressive Self-Distillation with Limited Labeled Data
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摘要: 针对有限标注数据条件下船舶辐射噪声识别性能下降的问题,提出一种对比预训练与渐进式自蒸馏的两阶段识别方法。在对比预训练阶段,针对船舶信号特性设计组合数据增强方法,在无标签样本上通过对比学习完成编码器的预训练,得到不依赖标签的判别性特征;在渐进式自蒸馏阶段,对预训练编码器的浅层进行冻结,在少量带标签样本上引入模型的历史预测构造软标签,与硬标签共同监督分类模型的训练,实现对样本中监督信息的充分挖掘。在VTUAD(Vessel Type Underwater Acoustic Data)公开数据集上的试验结果表明,相较于常规有监督识别方法,所提方法在五种标注规模下的识别准确率平均提升6.17%,F1值平均提升8.11%。在仅使用1%标注训练样本的极端条件下,识别准确率和F1值分别提升了7.51%、8.27%。在ShipsEar公开数据集上的迁移试验结果表明,在船舶类别构成发生变化且标注训练样本更少的条件下,所提方法仍优于常规有监督方法,具有较好的跨数据集迁移能力。Abstract:
Objective With the rapid development of marine transportation, ship-radiated noise recognition has become essential for maritime safety. However, existing deep learning methods rely on large-scale labeled training data. In underwater acoustic scenarios, ship-radiated noise data are difficult to collect because hydrophone deployment and sea trials are difficult to control. Under this condition, conventional supervised recognition methods tend to suffer from performance degradation. Although contrastive learning can exploit unlabeled data, generic augmentation strategies may destroy critical spectral structures. In addition, conventional fine-tuning fails to fully use the similarity structure among ships. To address these challenges, a two-stage recognition method based on contrastive pre-training and progressive self-distillation is proposed. This research aims to improve the utilization of unlabeled data and limited labeled data and enhance the accuracy of ship-radiated noise recognition. Methods The ship-radiated noise signals are processed by the Constant-Q Transform (CQT) to obtain CQT spectra, which are then used as the input. The proposed method is carried out through contrastive pre-training and progressive self-distillation. In the contrastive pre-training stage, each unlabeled sample is transformed into two augmented views by a combined data augmentation strategy. This strategy includes time-axis flipping, random signal truncation and additive noise injection. These augmentations reflect variations in observation order, observation windows, and background interference. Time-axis flipping preserves the frequency positions of spectral lines, while signal truncation retains part of the waveform and restores its length through zero padding. These operations introduce view diversity while seeking to preserve structures relevant to ship recognition. The augmented views generated from the same sample are treated as a positive pair, and the views generated from other samples in the same mini-batch are treated as negative samples. An encoder and a projection head are used to map the CQT spectra into an embedding space. The contrastive loss is used to increase the similarity of positive pairs and decrease the similarity between negative ones. After contrastive pre-training, the projection head is discarded, and the encoder parameters are retained for the following recognition stage. In the progressive self-distillation stage, the pre-trained encoder is connected with a classifier to form the recognition model. The shallow layers of the encoder are frozen to preserve general acoustic features, while the deeper layers and the classifier are updated using limited labeled samples. The training objective includes the cross-entropy loss and the soft-label distillation loss. The soft labels are generated from the historical predictions of the model itself, and the weight of the distillation loss increases linearly with the training epoch. This progressive weighting strategy reduces the influence of unreliable soft labels in the early training stage and gradually introduces similarity information contained in historical predictions. Results and Discussions The proposed two-stage method is evaluated on the VTUAD dataset under five labeled-data scales, including 100%, 10%, 5%, 2%, and 1% labeled samples ( Table 1 ). The supervised baseline achieves an accuracy of 94.28% and an F1-score of 91.90% when all labeled samples are used. However, its performance decreases as the labeling scale is reduced, and the accuracy and F1-score drop to 72.60% and 58.08%, respectively, when only 1% labeled training samples are used (Table 3 ). After contrastive pre-training, standard fine-tuning improves the recognition performance over the supervised baseline. By introducing progressive self-distillation, the proposed method further improves the recognition performance (Table 3 ). Compared with CRNN, VGG, CNN-Transformer, and ECAPA-TDNN, the proposed method achieves the best recognition performance in all five settings. In the 1% labeled-data case, it improves the accuracy by 11.33% and the F1-score by 15.08% compared with the second-best method (Table 4 ). The comparison of different self-distillation strategies shows that progressive self-distillation performs better, indicating that the progressive weighting strategy can reduce the influence of noisy soft labels at the early training stage and make better use of category similarity information (Table 6 ). The shallow-layer freezing experiment shows that freezing the first two layers of the encoder achieves the best balance between preserving pre-trained features and adapting to the recognition task (Fig. 8 ). Noise robustness is further evaluated by adding Gaussian white noise to the test recordings under the 1% labeled training data setting. At a signal-to-noise ratio of −5 dB, the proposed method achieves 62.18% accuracy and a 43.82% F1-score, compared with 45.00% and 37.68%, respectively, for the supervised baseline (Table 7 ). The confusion matrices and feature visualizations show that the proposed method improves the recognition performance and produces more compact intra-class distributions and clearer inter-class separation (Fig. 9 ,Fig. 10 ). A cross-dataset transfer experiment is further conducted on the ShipsEar dataset. In this experiment, the encoder pre-trained on VTUAD is adapted using labeled ShipsEar training samples. The 1% training subset contains only 40 samples. Across the five labeled-data scales, the proposed method improves accuracy and F1-score over the supervised baseline by averages of 5.27% and 5.51%, respectively. Although VTUAD and ShipsEar differ in data distribution, and ShipsEar contains fewer labeled training samples, the proposed method outperforms the supervised baseline across different labeled-data scales, demonstrating cross-dataset transferability (Table 8 ).Conclusions This paper addresses the performance degradation of ship-radiated noise recognition with limited labeled data by proposing a two-stage method based on contrastive pre-training and progressive self-distillation. The proposed method improves the utilization of unlabeled and limited labeled data in three aspects: (1) A two-stage recognition framework is constructed, in which contrastive pre-training is used to learn general acoustic representations from unlabeled ship-radiated noise samples, and self-distillation is used to optimize the recognition model with limited labeled samples; (2) A combined data augmentation strategy is designed for contrastive pre-training to introduce different views; (3) A progressive self-distillation mechanism is introduced in the recognition stage, where the historical predictions are used as soft labels and are gradually incorporated into training to supplement hard-label supervision. The method is evaluated on the VTUAD dataset, and the experimental results show that it achieves average improvements of 6.17% in accuracy and 8.11% in F1-score over the supervised baseline across five labeled-data scales. The transfer experiment on ShipsEar further demonstrates that the proposed method remains superior to the supervised baseline when the source and target datasets differ in data distribution and the target dataset contains fewer labeled training samples. -
表 1 VTUAD各子集划分
子集 标注规模 背景
(s)货船
(s)客船
(s)油轮
(s)拖船
(s)总样本时长
(s)对比预
训练集无标签 — — — — — 115,800 识别训
练集100% 7,302 7,302 7,302 7,302 7,302 36,510 10% 730 730 730 730 730 3,650 5% 365 365 365 365 365 1,825 2% 146 146 146 146 146 730 1% 73 73 73 73 73 365 验证集 — 1,362 1,257 74 165 902 3,760 测试集 — 679 627 35 94 445 1,880 表 2 ShipsEar各子集划分
子集 标注规模 A (s) B (s) C (s) D (s) E (s) 总样本时长(s) 识别训
练集100% 798 798 798 798 798 3,990 10% 80 80 80 80 80 400 5% 40 40 40 40 40 200 2% 16 16 16 16 16 80 1% 8 8 8 8 8 40 验证集 — 187 156 427 245 114 1,129 测试集 — 376 312 854 492 228 2,262 表 3 不同标注规模下与基线方法的识别效果对比
方法 标注
规模准确率(%) 精确率(%) 召回率(%) F1值(%) 有监督
方法100% 94.28 89.45 95.02 91.90 10% 85.52 73.86 86.97 78.00 5% 79.54 67.43 78.65 69.64 2% 75.59 60.99 70.70 62.57 1% 72.60 57.48 66.06 58.08 对比预训练与
标准微调方法100% 97.61 94.45 97.31 95.80 10% 90.11 83.02 86.00 83.69 5% 85.43 76.10 83.58 78.65 2% 82.18 67.61 76.85 69.96 1% 77.39 62.95 75.12 64.40 对比预训练与渐进式
自蒸馏方法100% 97.93 97.55 97.63 97.56 10% 91.38 83.12 90.12 86.02 5% 86.76 75.46 86.66 79.19 2% 82.18 68.36 79.56 71.60 1% 80.11 64.92 70.35 66.35 表 4 不同标注规模下不同方法的识别性能对比
方法 准确率(%) / F1值(%) 100% 10% 5% 2% 1% CRNN 93.62 / 90.61 80.43 / 64.28 77.34 / 58.07 67.77 / 51.31 63.14 / 31.98 VGG 95.69 / 93.97 85.69 / 80.41 83.56 / 72.58 76.86 / 59.44 39.26 / 17.76 CNN-Transformer 90.27 / 84.70 74.04 / 59.53 73.24 / 58.41 72.07 / 52.57 68.78 / 51.27 ECAPA-TDNN 96.17 / 94.28 88.99 / 80.76 83.24 / 72.43 79.84 / 66.34 58.99 / 42.48 本文方法 97.93 / 97.56 91.38 / 86.02 86.76 / 79.19 82.18 / 71.60 80.11 / 66.35 表 5 不同识别方法的参数量和平均单样本推理时间对比
方法 参数量 (M) 平均单样本推理时间 (ms) CRNN 0.39 1.02 ± 0.16 VGG 14.72 2.03 ± 0.67 CNN-Transformer 5.74 2.76 ± 0.74 ECAPA-TDNN 6.23 4.44 ± 0.07 本文方法 11.44 3.02 ± 0.82 表 6 不同自蒸馏方法的识别性能对比
方法 准确率(%) / F1值(%) 100% 10% 5% 2% 1% 固定权重自蒸馏 96.33 / 94.53 90.21 / 84.55 86.91 / 79.18 80.90 / 69.57 78.30 / 65.63 同类样本
一致性蒸馏95.96 / 94.34 89.57 / 82.91 85.43 / 75.79 82.34 / 71.38 76.91 / 62.99 渐进式自蒸馏 97.93 / 97.56 91.38 / 86.02 86.76 / 79.19 82.18 / 71.60 80.11 / 66.35 表 7 1%标注规模下不同噪声条件的识别性能对比
方法 准确率(%)/F1值(%) 不叠
加噪声10 dB 5 dB 0 dB –5 dB 有监督方法 72.60/
58.0871.65/
58.2564.15/
53.4156.65/
47.8945.00/
37.68对比预训练与
标准微调方法77.39/
64.4077.13/
63.8274.36/
61.5064.41/
53.6352.55/
43.29对比预训练与渐进式
自蒸馏方法80.11/
66.3579.79/
65.5079.41/
65.3572.39/
56.8362.18/
43.82表 8 ShipsEar数据集不同标注规模下的跨数据集迁移识别结果
方法 标注规模 准确率
(%)精确率
(%)召回率
(%)F1值
(%)有监督方法 100% 92.84 92.33 93.01 92.52 10% 67.06 72.56 75.80 69.69 5% 59.28 57.07 59.71 57.01 2% 45.98 46.34 51.94 46.09 1% 41.38 43.17 47.53 40.00 对比预训练与
标准微调方法100% 93.59 93.61 93.79 93.66 10% 72.63 71.63 75.30 72.94 5% 60.52 61.02 62.61 59.60 2% 48.63 48.30 53.01 48.70 1% 44.34 47.87 48.30 45.48 对比预训练与渐进式
自蒸馏方法100% 95.00 94.70 95.59 95.13 10% 75.51 73.95 78.27 75.58 5% 64.90 63.59 68.38 64.87 2% 50.75 48.88 53.56 50.07 1% 46.73 46.91 49.81 47.22 -
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