To break the π-phase criterion in phase demodulation, POFNet is proposed to fuse the OPD and the phase signal to estimate the unwrapping errors and recover larger phase. The results showcase its superiority performance.
Paper
Large Dynamic Range and High Frequency Acoustic Signal Detection with SNR Enhancement
Hongkun Zheng, Lingmei Ma* , Zechao Liu, Caiyun Li, and 3 more authors
In 2024 Conference on Lasers and Electro-Optics (CLEO) , 2024
An OPD-based demodulation method for acoustic signal detection is proposed, breaking the limit of phase demodulation. Experiment results demonstrated superior performance at high frequency, and the SNR increases proportionally with the frequency of the signal.
Paper
Detection of Large Dynamic Range Acoustic Signal Using OPD-based Fiber-Optic Interferometric Demodulation with SNR Enhancement
Hongkun Zheng, Lingmei Ma* , Zechao Liu, Caiyun Li, and 4 more authors
The measurement of acoustic signals at high frequencies with a large dynamic range remains a challenge for phase-demodulation-based fiber acoustic sensing systems due to the phase wrapping phenomenon. Here, an optical path difference (OPD)-assisted demodulation method aiming at breaking the limitations of phase demodulation is reported. By interrogating an imbalanced Michelson interferometer (IMI) with a frequency-modulated pulse light, a time-resolved interference spectrum is obtained and used for OPD demodulation. Theoretical analysis reveals that the variation amplitude of demodulated OPD signal not only is linearly dependent on the amplitude of the acoustic signal applied to the IMI, but also experiences a gain that is directly proportional to the signal frequency. Consequently, compensation of this gain introduces a noise suppression that favors high-frequency signals, resulting in a higher signal-to-noise ratio (SNR) at high frequencies. The method’s capability for detecting both single-frequency and multi-frequency acoustic signals is demonstrated by simulations and experiments, and the results show that the upper-frequency limit of the proposed scheme is at least 40 times the limit of the phase demodulation method for an acoustic signal with an amplitude of 1.135 μϵ. The proposed method can be easily extended to distributed acoustic sensing systems and is of great potential to break the limitation of a restricted dynamic range encountered in traditional phase demodulation methods.
2023
Paper
Deep Hyperspherical Clustering for Skin Lesion Medical Image Segmentation
Zuowei Zhang, Songtao Ye , Zechao Liu, Hao Wang*, and 1 more author
IEEE Journal of Biomedical and Health Informatics, 2023
Diagnosis of skin lesions based on imaging techniques remains a challenging task because data (knowledge) uncertainty may reduce accuracy and lead to imprecise results. This paper investigates a new deep hyperspherical clustering (DHC) method for skin lesion medical image segmentation by combining deep convolutional neural networks and the theory of belief functions (TBF). The proposed DHC aims to eliminate the dependence on labeled data, improve segmentation performance, and characterize the imprecision caused by data (knowledge) uncertainty. First, the SLIC superpixel algorithm is employed to group the image into multiple meaningful superpixels, aiming to maximize the use of context without destroying the boundary information. Second, an autoencoder network is designed to transform the superpixels’ information into potential features. Third, a hypersphere loss is developed to train the autoencoder network. The loss is defined to map the input to a pair of hyperspheres so that the network can perceive tiny differences. Finally, the result is redistributed to characterize the imprecision caused by data (knowledge) uncertainty based on the TBF. The proposed DHC method can well characterize the imprecision between skin lesions and non-lesions, which is particularly important for the medical procedures. A series of experiments on four dermoscopic benchmark datasets demonstrate that the proposed DHC yields better segmentation performance, increasing the accuracy of the predictions while can perceive imprecise regions compared to other typical methods.
Paper
Phase correction based SNR enhancement for distributed acoustic sensing with strong environmental background interference
Caiyun Li , Zechao Liu, Yiyang Zhuang, Hongkun Zheng, and 5 more authors
Fiber-optic distributed acoustic sensing (DAS) systems based on phase-sensitive optical time domain reflectometry (Φ-OTDR) measure acoustic waves by demodulating the phase variations of the Rayleigh backscattering (RBS) signals in a sensing optical fiber. However, in harsh environments, strong environmental background interference, coupled with the interference fading of the RBS, would introduce severe distortions in DAS signal that cannot be corrected or even can be worsened by phase unwrapping, thus resulting in low signal to noise ratio (SNR) and even undetectable signal. In this work, a novel method based on trend prediction is proposed to correct the distortions induced by phase unwrapping error around the fading points. The method is further validated in processing the data acquired from a field test performed in ocean environments using a home-built DAS system. By locating and erasing the distortion points, and then detrending, the acoustic signal buried in strong environmental background interference is retrieved with an SNR improvement greater than 10 dB. The results show that the proposed phase correction method can effectively enhance DAS’s SNR for those challenging applications with strong background interference.
Paper
Mining and reasoning of data uncertainty-induced imprecision in deep image classification
Zuowei Zhang, Liangbo Ning , Zechao Liu, Qingyu Yang, and 1 more author
Existing deep image classification techniques strive to suppress data uncertainty for various reasons such as blur, occlusion, noise, and label error and advance to higher accuracy. However, they ignore data uncertainty-induced imprecision and thus do not work as intended. In this paper, we propose a deep open-source framework to mine and reason the imprecision of such training and test sets, which can present better performance and reduce the risk of misclassification. First, we design a label reassignment mechanism. It allows the network to reassign training labels and allow imperfect training samples with multiple labels. As a result, they are removed from the original classes and considered new imprecise samples to represent partial ignorance. Second, we propose a new imbalanced data enhancement architecture to learn a generalized representation of each (precise and imprecise) class. It helps the network fuse the auxiliary information from both precise and imprecise classes, which is beneficial to extract more distinctive class features from single-labeled samples and characterize uncertainty-induced imprecision in the test set by imprecise test samples. Afterward, methodological analyses and empirical evaluations are conducted. The proposed framework is demonstrated to present better performance on different typical networks (Resnet50, MobileNetV2, DenseNet121, EfficientNetB0, ShuffleNetV2, SENet, SqueezeNet, Xception) based on five publicly available datasets (Imagewoof-5, Flowers, Monkey, Butterfly, and Cifar-10). In addition, several targeted deep techniques for uncertain images or imprecise results are also employed as comparisons to prove the superiority of the proposed framework.
Paper
SNR Improvement for Distributed Acoustic Sensing with Strong Environmental Background Interference
Caiyun Li , Zechao Liu, Hongkun Zheng, Yiyang Zhuang, and 5 more authors
In 28th International Conference on Optical Fiber Sensors , 2023
A novel method is proposed to correct the distortions induced by phase unwrapping error. The method is further validated in processing the data acquired from a field test performed in ocean environments using a DAS system.
The classification of missing data is a challenging task, because the lack of pattern attributes may bring uncertainty to the classification results and most classification methods produce only one estimation, which may have a risk of misclassification. A new incomplete pattern belief classification (PBC) method with multiple estimations based on K-nearest neighbors (KNNs) is proposed to deal with missing data. PBC preliminarily classifies the incomplete pattern using its KNNs obtained by the known attributes. The pattern whose KNNs contain only one class information can be directly divided into this class. If not, the p (p≤c) estimations will be computed according to the different KNNs in different classes when p classes are included in the KNNs of the pattern and it will yield p pieces of classification results by the chosen classifier. Then, a weighted possibility distance method is used to further divide the p classification results with their KNNs’ classification information. The pattern with similar possibility distances in different classes will be reasonably classified into a proper meta-class under the framework of belief functions theory, which truly reflects the uncertainty of the pattern caused by missing values and effectively reduces the error rate. Experiments on both artificial and real data sets show that PBC is effective for dealing with missing data.