Schewe Marvin, Rembe Christian
Institute of Electrical Information Technology, Clausthal University of Technology, Leibnizstr. 28, D-38678 Clausthal-Zellerfeld, Germany.
Sensors (Basel). 2021 Feb 2;21(3):998. doi: 10.3390/s21030998.
The intensity of the reflected measuring beam is greatly reduced for laser-Doppler vibrometer (LDV) measurements on rough surfaces since a considerable part of the light is scattered and cannot reach the photodetector (laser speckle effect). The low intensity of the reflected laser beam leads to a so-called signal dropout, which manifests as noise peaks in the demodulated velocity signal. In such cases, no light reaches the detector at a specific time and, therefore, no signal can be detected. Consequently, the overall quality of the signal decreases significantly. In the literature, first attempts and a practical implementation to reduce this effect by signal diversity can be found. In this article, a practical implementation with four measuring heads of a Multipoint Vibrometer (MPV) and an evaluation and optimization of an algorithm from the literature is presented. The limitations of the algorithm, which combines velocity signals, are shown by evaluating our measurements. We present a modified algorithm, which generates a combined detector signal from the raw signals of the individual channels, reducing the mean noise level in our measurement by more than 10 dB. By comparing the results of our new algorithm with the algorithms of the state-of-the-art, we can show an improvement of the noise reduction with our approach.
对于在粗糙表面上进行激光多普勒振动计（LDV）测量而言，反射测量光束的强度会大幅降低，因为相当一部分光会发生散射，无法到达光电探测器（激光散斑效应）。反射激光束的低强度会导致所谓的信号丢失，这在解调后的速度信号中表现为噪声峰值。在这种情况下，在特定时刻没有光到达探测器，因此无法检测到信号。结果，信号的整体质量会显著下降。在文献中，可以找到通过信号分集来减少这种影响的首次尝试和实际应用。本文介绍了一种使用多点振动计（MPV）的四个测量头的实际应用，以及对文献中一种算法的评估和优化。通过评估我们的测量结果，展示了结合速度信号的算法的局限性。我们提出了一种改进算法，该算法从各个通道的原始信号生成组合探测器信号，将我们测量中的平均噪声水平降低了超过10 dB。通过将我们新算法的结果与现有技术的算法进行比较，我们可以证明我们的方法在降噪方面有所改进。
