| Explosion vessels as the specified equipments for the study of explosive effect have been widely applied in industry, national defense and scientific research. This paper attempts to explore the feasibility of a system based on laser Doppler technique which has been established to realize remote dynamic measurement of high velocity deformation parameters of explosion vessel. It aims at developing a stable and reliable non-contact instrument with high precision for the measuring of explosion on site. Its performance criteria are: the measurement range of deformation velocity is from -10m/s to +20m/s (+ indicates expanding direction of vessel; - indicates shrinking direction of vessel), and measuring distance reaches 4.5m, and that of deformation is±20mm.Doppler signal's SNR is very low in remote measurement of explosion vessel, a moving solid object with high velocity. To enhance signal intensity, restrain noise and extract weak Doppler signal is the key to realizing remote measurement with high precision. Both optical structure optimizing and digital signal processing used to solve the arduous problem above will be discussed in this paper.First of all, optimization design of the heterodyne longitudinal laser Doppler optical structure for enhancing signal intensity and improving SNR is the premise of remote measurement with high precision. The main points are as follows.(1) In accordance with the analysis of Gaussian theory, scattering light energy can become more effective when a scattering object lies in the location of measuring beam waist. As done above, Doppler broadening can be cut down and scattering light collected by big aperture lens.(2) On the basis of statistical characteristic of laser speckle principle, the intensity of Doppler signal is in direct proportion to photosensitive area of receiver and in verse proportion to diameter of focusing light spot. A photoelectric receiver S7516 with 9mm diameter of photosensitive area has been selected, and the diameter of focusing spot projected on the surface of explosion vessel should be less than 1mm.(3) Principle of polarized interference has been adopted to distribute light intensity between object beam and reference beam for less loss of light energy. Polarized splitter and wave plate have been employed to ensure scattering light back from vessel surface projecting on photoelectric receiver with minimum energy loss.Furthermore, Doppler signal is extracted from weak signal with modern digital signal processing, which is the effective way to obtain time-frequency distribution of Doppler signal. The major points are mentioned below:(1) According to analysis of noise source and principle of Chebyshev optimal approximation, a band-pass and notch filter has been established, and its dynamic range is 40dB. The band-pass frequency range of filter is from 1MHz to 97MHz, and its notch frequency is 65MHz. Noise beyond useful frequency range can be filtered, and interference from acousto-optic modulator restrained.(2) On the basis of statistical characteristic of signal against noise, the combination of correlate detection and short-time Fourier transform has been used to obtain time-frequency distribution of Doppler signal.(3) According to phase information of Fourier transform, phase diversity method has been employed to correct the frequency of maximum spectrum in the result of Doppler signal's Fourier transform. The method above can eliminate Picket-fence effect of Fourier transform algorithm, and improve identification accuracy to Doppler signal.(4) Wavelet transform has been used to decompose Doppler shift signal in the course of explosion. According to the spread characteristic of singular point's Modulus Maximum from big scale to small scale, the frequency singular point caused by Doppler signal's drop-off can be identified. The accuracy of time-frequency distribution can be improved by curve fitting further.In addition, a weak signal amplifying circuit has been designed by a clamp amplifier AD8036 and a software has been programmed on LabVIEW platform. Moreover, the main causes of the instrument's deviation have been analyzed. In accordance with the data of comparison experiments with a reference vibrator, the relative uncertainty of measurement is 0.39%.The test results in Tianjin Institute of Measurement Technology prove that the relative error of the instrument is less than 1% in measuring displacement. Seven explosion experiments were conducted on the Xinjiang military base, and the instrument measured high velocity deformation parameters of steel cylinder accurately and achieved good results.
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