Fig. 1. Schematic of the main composition of a typical heterodyne laser Doppler vibrometer

Fig. 2. Simulation results. (a) Absolute value of demodulated velocity obtained by normal method; (b) spectrogram of demodulated velocity obtained by normal method; (c) spectrogram of demodulated velocity obtained by DPM

Fig. 3. Verification experiment objects of derivative preprocessing method. (a) Measurement target; (b) measurement system

Fig. 4. Verification experiment results. (a) Absolute value of demodulated velocity obtained by normal method; (b) spectrogram of demodulated velocity obtained by normal method; (c) spectrogram of demodulated velocity obtained by DPM after partial replacement

Fig. 5. Power spectral density (PSD) of demodulated velocity of two methods. (a) PSD of demodulated velocity of normal method; (b) PSD of demodulated velocity of DPM after partial replacement