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