Wu Huan, Wang Liang, Zhao Zhiyong, Guo Nan, Shu Chester, Lu Chao
Opt Express. 2018 Mar 5;26(5):5126-5139. doi: 10.1364/OE.26.005126.
We have experimentally analyzed and compared the performance of Brillouin optical time-domain analyzer (BOTDA) sensors assisted by non-local means (NLM) and wavelet denoising (WD) techniques in terms of measurement accuracy and experimental spatial resolution, respectively. Degradation of the measurement accuracy and experimental spatial resolution after denoising by NLM and WD are observed, which originate from the fact that higher signal-to-noise ratio (SNR) improvement is achieved at the expense of sacrificing the details of BOTDA data, and smaller data sampling point number (SPN) gives rise to insufficient redundant information for denoising. The two parameters degrade to different extents depending on the amount of SNR improvement and SPN adopted in data acquisition. Compared with WD, NLM relies more on the features of the raw data, which makes its performance highly dependent on the level of neighbouring data similarity. Also, for the first time we propose and demonstrate a BOTDA assisted by advanced Block-Matching and 3D filtering (BM3D) denoising technique, which minimizes the degradation of the two parameters even under higher SNR improvement and smaller SPN. BM3D takes the advantage of NLM and WD and utilizes the spatial-domain non-local principle to enhance the denoising in the transform domain, thus it shows the least degradation of measurement accuracy/experimental spatial resolution after denoising. Thus the BOTDA assisted by BM3D maintains the best measurement accuracy/experimental spatial resolution compared with those by NLM and WD. We also show that BM3D has the advantage of temperature independent performance, unlike NLM where the accuracy is affected by the temperature value. We believe BM3D would be an excellent denoising technique for state-of-the-art BOTDA sensors. In addition, this work is also valuable for practical applications of image denoising techniques in BOTDA sensors with respect to the appropriate choice of image denoising techniques, design of SNR improvement and the adoption of SPN to maintain optimal measurement accuracy/experimental spatial resolution/data acquisition speed.
我们分别从测量精度和实验空间分辨率方面，对采用非局部均值（NLM）和小波去噪（WD）技术辅助的布里渊光时域分析仪（BOTDA）传感器的性能进行了实验分析和比较。观察到经NLM和WD去噪后测量精度和实验空间分辨率出现了下降，这源于以牺牲BOTDA数据细节为代价实现了更高的信噪比（SNR）提升，以及较小的数据采样点数（SPN）导致去噪所需的冗余信息不足。这两个参数的下降程度取决于数据采集中采用的SNR提升量和SPN。与WD相比，NLM更依赖原始数据的特征，这使得其性能高度依赖相邻数据的相似程度。此外，我们首次提出并演示了一种采用先进的块匹配和三维滤波（BM3D）去噪技术辅助的BOTDA，即使在更高的SNR提升和更小的SPN情况下，该技术也能将这两个参数的下降降至最低。BM3D利用了NLM和WD的优势，并利用空间域非局部原理增强变换域中的去噪效果，因此在去噪后测量精度/实验空间分辨率的下降最小。因此，与NLM和WD辅助的BOTDA相比，BM3D辅助的BOTDA保持了最佳的测量精度/实验空间分辨率。我们还表明，BM3D具有与温度无关的性能优势，而NLM的精度会受温度值影响。我们认为BM3D将是用于先进BOTDA传感器的一种出色的去噪技术。此外，这项工作对于图像去噪技术在BOTDA传感器中的实际应用在图像去噪技术的恰当选择、SNR提升设计以及采用SPN以维持最佳测量精度/实验空间分辨率/数据采集速度方面也具有重要价值。
