Proceedings Article | 8 June 2023
KEYWORDS: Simulations, Windows, Doppler effect, Fourier transforms, Signal to noise ratio, Spectral resolution, Particles, Velocity measurements, Laser frequency, Interference (communication)
Coherent Doppler laser velocimetry is an accurate non-intrusive velocimetry method. In this regard, the commonly used methods embrace the fast Fourier transform (FFT) and Weleh spectrum estimations. However, all these methods are limited by the frequency resolution that tightly relies on the sampling points during FFT. This paper introduces a spectrum estimation algorithm using FFT spectral estimation combined with continuous FT spectral thinning, which greatly improves the spectrum resolution and the speed measurement accuracy in the inversion process. Firstly, Hanning window was added to suppress the spectral leakage, and then the rough estimation of Doppler shift was obtained by FFT. Then the spectrum near the Doppler peak obtained by FFT is continuously refined by FT spectrum, and the spectral resolution is increased from 7629Hz to 100Hz. Finally, according to the refined spectrum, the centroid estimation method is used to obtain the Doppler frequency shift, and then the motion velocity is obtained. The velocity accuracy can reach more than 0.0006m /s. The average absolute error of velocity was increased by 51.3%, 65.8%, 77.3% and 83.2% respectively by comparison with Welch spectrum estimation at different speeds of 10m/s, 60m/s, 100m/s and 150m/s. The stability of measurement results increased by 22.2%, 62.6%, 66.9% and 68.2%, respectively. By setting up experiments to obtain the inversion comparison of 10m/s, 30m/s and 60m/s data, the average error of Welch spectral estimation velocity was increased by 39.9%, 24.8% and 67.2%, respectively, and the stability of measurement results was increased by 61.3%, 69.8% and 23.1%, respectively.
