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With the maturity of synthetic aperture radar (SAR) technology, the problem of imbalanced data has gradually emerged. This problem makes it difficult for the automatic target recognition (ATR) model to properly learn the classification boundaries of majority and minority category target samples. In this article, we propose an ATR model with new architecture, called the cost-sensitive awareness-based automatic target recognition (CA-ATR) model, which provides an effective way of solving the problem of imbalanced data. Aimed at the two issues caused by imbalanced data on ATR models, the proposed method solves the problems from both the data and algorithm levels. At the data level, CA-ATR avoids adverse correlations among the target samples through different oversampling methods. By making the ATR model cost-sensitive, the proposed method also avoids the empirical risk preference of the ATR model for majority category target samples at the algorithm-level. At the same time, CA-ATR can autonomously learn different cost-sensitive awareness from different imbalanced data sets. The awareness enables the ATR model to more accurately learn the classification boundaries between target samples that belong in different categories. Several experimental results show the superiority of the proposed approach based on the Moving and Stationary Target Acquisition and Recognition (MSTAR) data set. Compared with other imbalanced learning methods, the proposed method is able to solve different types of imbalanced data problems.

Noncontact gesture recognition is gradually being applied to emerging applications, such as smart cars and smart phones. Negative latency gesture recognition (recognition before a gesture is finished) is desirable due to the instantaneous feedback. However, it is difficult for existing methods to achieve a high precision and negative latency gesture recognition. A fragment can provide too few features to directly identify all gestures well. By observing a large number of existing gesture sets and people’s daily operating habits, we found that some high frequency used gestures are similar. To the best of our knowledge, it is the first time to redivide the gestures into two subsets according to their movement physical states. We divided the gestures with different shapes or motion states into a parent-class subset, and further divided each pair of parent-class gestures to obtain a child-class subset. In order to achieve a better tradeoff between the high-precision and negative latency, an approach of motion pattern and behavior intention (MPBI) is proposed. Taking full advantage of the characteristics of each subset, MPBI includes two models. First, pattern model coarsely classify the parent-class gestures by a convolutional network, and then intention model further classifies child-class gestures according to their opposite motion direction. MPBI is evaluated on a 340-GHz terahertz radar. With the advantage of its accurate ranging, intention model can recognize child-class gestures directly without training. MPBI is evaluated on 12 gestures and achieves a recognition accuracy of 94.13%, which only needs a 0.033-s gesture fragment as an input sample.

The rapid development of generative adversarial nets (GANs) has led to an increasing number of applications for the synthetic aperture radar (SAR) automatic target recognition (A-TR) with a small sample set in the past few years. However, the generated samples by the GAN s sometimes even lead to a decrease in the performance of the ATR model. In this paper, we propose a filtering approach to address this harm of generated samples. The proposed filtering approach is based on a stable generation model. The stable generation model can continuously and stably generate different batches of target samples. Then, multiple SVMs trained by different SAR target sample sets provide pseudo-labels to the other SVMs to improve the accuracy of the filtering results. Therefore, the proposed approach improves the recognition ability of the A-TR model dynamically while continuously filtering generated target samples. Several experimental results show the superiority of the proposed filtering approach based on the Moving and Stationary Target Acquisition and Recognition (MSTAR) data set. When the number of training samples is 14.5% of the original training set, the recognition rate of the ATR model still reaches 91.27% with the help of the proposed approach.

Deep convolutional neural networks (DCNNs) have been widely used for SAR image target recognition. However, the huge demands of DCNNs for computing, storage, and energy resources limit their use on edge computing devices. In this article, we propose a method based on image quality evaluation (IQE) criterion to prune deep neural networks. We use IQE criterion to identify unimportant filters, and then remove them, to obtain a lightweight network while maintaining the performance of the neural network as much as possible. Besides, we verified the effectiveness of our method on the MSTAR dataset with cheap edge computing devices.

This paper proposes a set of simple but effective features using a terahertz radar, specifically for device-free gesture recognition based on high resolution range profiles. Three types with seven features are extracted, including the tracking features, directional features, and behavioural features. The proposed method is evaluated on a dataset based on 0.34 THz radar, which contains 10 kinds of 5 pairs of frequently-used gestures. These features are demonstrated to be effective to encode the morphological differences among various gestures and be sensitive to the moving direction in a short period of time. The results show that the proposed method achieves 95.5% accuracy on frame-level gesture recognition.

As a mission-critical sensor, SAR has been applied in environmental monitoring and battlefield surveillance; moreover, SAR target recognition is one of the most important applications of SAR technology. However, in practical applications, the number of samples available for training is relatively small, so the SAR target recognition can be regarded as a small sample recognition problem. One of the main directions to solve the small sample recognition problem is to realize the data augmentation. Therefore, a SAR image data augmentation method via Generative Adversarial Nets (GAN) is proposed in this paper. The method uses Wasserstein GAN with a gradient penalty (WGAN-GP) to generate new samples based on existing SAR data, which can augment the sample number in training dataset. Meanwhile, the sample selection filters are designed to extract the generated samples with high quality and specific azimuth, which can avoid the randomness of the data augmentation, and improve the quality of the newly generated training samples. The experiments based on MSTAR data show that, for three-class recognition problem, when the training sample is only 108, the proposed method can improve the recognition rate from 79% to 91.6%; and for ten-class recognition problem, when the training sample is only 360, the proposed method can improve the recognition rate from 57.48% to 79.59%. Compared with the traditional data linear generation method, the proposed method shows significant improvement on the quantity and quality of the training samples, and can effectively solve the problem of the small sample recognition.