In laser Doppler velocimeter (LDV), calculation precision of Doppler shift is affected by noise contained in Doppler signal. In order to restrain the noise interference and improve the precision of signal processing, wavelet packet threshold denoising methods are proposed. Based on the analysis of Doppler signal, appropriate threshold function and decomposition layer number are selected. Heursure, sqtwolog, rigrsure, and minimaxi rules are adopted to get the thresholds. Processing results indicate that signal-to-noise ratio (SNR) and root mean square error (RMSE) of simulated signals with original SNR of 0 dB, 5 dB, and 10 dB in both low- and high-frequency ranges are significantly improved by wavelet packet threshold denoising. A double-beam and double-scattering LDV system is built in our laboratory. For measured signals obtained from the experimental system, the minimum relative error of denoised signal is only 0.079% (using minimaxi rule). The denoised waveforms of simulated and experimental signals are much more smooth and clear than that of original signals. Generally speaking, denoising effects of minimaxi and saqtwolog rules are better than those of heursure and rigrsure rules. As shown in the processing and analysis of simulated and experimental signals, denoising methods based on wavelet packet threshold have ability to depress the noise in laser Doppler signal and improve the precision of signal processing. Owing to its effectiveness and practicability, wavelet packet threshold denoising is a practical method for LDV signal processing.

中文翻译：

---

基于小波包阈值法的激光多普勒信号降噪

在激光多普勒测速仪（LDV）中，多普勒频移的计算精度受多普勒信号中包含的噪声影响。为了抑制噪声干扰并提高信号处理的精度，提出了小波包阈值去噪方法。基于对多普勒信号的分析，选择适当的阈值函数和分解层数。采用Heursure，sqtwolog，rigrsure和minimaxi规则来获取阈值。处理结果表明，在低频和高频范围内，原始SNR分别为0 dB，5 dB和10 dB的模拟信号的信噪比（SNR）和均方根误差（RMSE）显着提高了小波包阈值去噪。我们的实验室内置了双光束和双散射LDV系统。对于从实验系统获得的测量信号，去噪信号的最小相对误差仅为0.079％（使用minimaxi规则）。模拟和实验信号的去噪波形比原始信号的平滑和清晰得多。一般而言，极小极大值和saqtwolog规则的去噪效果要优于启发式和严格规则的去噪效果。如对模拟信号和实验信号的处理和分析所示，基于小波包阈值的去噪方法具有抑制激光多普勒信号中的噪声并提高信号处理精度的能力。由于其有效性和实用性，小波包阈值去噪是LDV信号处理的一种实用方法。模拟和实验信号的去噪波形比原始信号的平滑和清晰得多。一般而言，极小极大值和saqtwolog规则的去噪效果要优于启发式和严格规则的去噪效果。如对模拟信号和实验信号的处理和分析所示，基于小波包阈值的去噪方法具有抑制激光多普勒信号中的噪声并提高信号处理精度的能力。由于其有效性和实用性，小波包阈值去噪是LDV信号处理的一种实用方法。模拟和实验信号的去噪波形比原始信号的平滑和清晰得多。一般而言，极小极大值和saqtwolog规则的去噪效果要优于启发式和严格规则的去噪效果。如对模拟信号和实验信号的处理和分析所示，基于小波包阈值的去噪方法具有抑制激光多普勒信号中的噪声并提高信号处理精度的能力。由于其有效性和实用性，小波包阈值去噪是LDV信号处理的一种实用方法。如对模拟信号和实验信号的处理和分析所示，基于小波包阈值的去噪方法具有抑制激光多普勒信号中的噪声并提高信号处理精度的能力。由于其有效性和实用性，小波包阈值去噪是LDV信号处理的一种实用方法。如对模拟信号和实验信号的处理和分析所示，基于小波包阈值的去噪方法具有抑制激光多普勒信号中的噪声并提高信号处理精度的能力。由于其有效性和实用性，小波包阈值去噪是LDV信号处理的一种实用方法。