ABSTRACT
A denoising method applied to atmospheric coherent length lidar is proposed. Wavelet decomposition (WD) and the adaptive median filter (ADMF) are combined in this method. In this research, the effectiveness of the WD-ADMF has been verified through simulation and measurement. The results show that this filter algorithm, when applied to lidar data, improves the average peak signal-to-noise ratio (PSNR) and centroid error while maintaining data integrity such that the measurement of coherence length or the inference of C n2 from coherence length more closely matches simulated truth and measured data.
ABSTRACT
A two-stage Fabry-Perot etalon (FPE)-based high-spectral-resolution (HSR) Mie Doppler lidar technology is proposed that is capable of simultaneously detecting tropospheric wind and aerosol optical properties with high precision. The lidar structure is designed, and the measurement principle is analyzed. A two-channel integrated FPE forming a two-stage FPE ensures the relative stability of the spectra. The HSR first-stage etalon can effectively suppress the contamination of Rayleigh signal. The transmission and reflection spectra of the second-stage etalon can form a double edge (DE) to measure wind speed. Two multimode polarization-insensitive optical circulators are used to achieve high-efficiency utilization for backscattering signals. The parameters of the two-stage FPE are optimized. According to the selected system parameters, the detection performance of the proposed lidar is simulated. Simulation results show that with 150 m range resolution and 1 min total accumulation time for the paired line-of-sight (LOS) measurement, within ±25 m/s LOS wind speed range, the nighttime and daytime LOS wind speed errors are below 0.48 m/s and 2.5 m/s, respectively, for a clear day, and below 0.58 m/s and 5.5 m/s, respectively, for a hazy day from 0.1 km to 8 km altitude; the backscatter ratio relative errors are below 2.7% up to 8 km for a clear day, and below 4.6% up to 5 km for a hazy day. Compared with the traditional dual-FPE-based DE Mie Doppler lidar, the wind speed accuracies are improved by 2.02-3.58 times for a clear day and 2.14-4.31 times for a hazy day.
ABSTRACT
A novel ultraviolet trifrequency high-spectral-resolution lidar (HSRL) based on a triple Fabry-Perot etalon (FPE) and polarization discrimination technique is proposed, to the best of our knowledge, for measuring atmospheric wind, temperature, and aerosol optical properties simultaneously from the troposphere to low stratosphere. The measurement principle of wind speed, temperature, and aerosol is analyzed, and the structure of the proposed HSRL is designed. The parameters of the triple FPE are optimized. The multiparameter inversion method based on the nonlinear iterative approach and cubic spline interpolation method is also discussed, and the specific iteration steps are given. Finally, the detection performance of the proposed HSRL is simulated. The simulation results show that for 0.3 WSr-1 m-2 nm-1 at 355 nm sky brightness, by using a 350 mJ pulse energy, a 50 Hz repetition frequency laser, and a 0.45 m aperture telescope, the measurement errors of temperature, aerosol backscattering ratio and vertical wind speed are below 2.1 K, 2.5×10-3, and 2.2 m/s in nighttime and below 3.2 K, 3.4×10-3, and 2.6 m/s in daytime from 0.2 to 35 km with a temporal resolution of 5 min for temperature and aerosol, 1 min for vertical wind, and a vertical resolution of 30 m at 0.2-10 km, 100 m at 10-20 km, 200 m at 20-35 km; the measurement error of two other orthogonal line-of-sight wind speeds with a fixed zenith angle of 30° is below 2.9 m/s in nighttime and 3.9 m/s in daytime in the range of ±50 m/s from 0.2 to 35 km with a temporal resolution of 1 min and a vertical resolution of 26 m at 0.2-8.6 km, 87 m at 8.6-17.3 km, and 173 m at 17.3-35 km. Compared with the traditional double-edge wind-detection technique with the same complete instrumental parameters including those of the FPEs and FPE-based high-spectral-resolution temperature-detection technique with the optimal parameter values of FPEs for the same laser power and telescope aperture, the wind accuracy of the proposed technique improved by 1.5 times at night and by 1.5-1.9 times during the day, and the temperature accuracy of the proposed technique improved by 2.2-2.6 times at night and by 1.7-2.6 times during the day.
ABSTRACT
Similar in principle to recent implementations of a lidar system at 355 nm [Opt. Lett. 25, 1231 (2000), Appl. Opt. 44, 6023 (2005)], an incoherent-detection Mie Doppler wind lidar at 1064 nm was developed and deployed in 2005 [Opt. Rev. 12, 409 (2005)] for wind measurements in the low troposphere, taking advantage of aerosol scattering for signal enhancement. We present a number of improvements made to the original 1064 nm system to increase its robustness for long-period operation. These include a multimode fiber for receiving the reference signal, a mode scrambler to allow uniform illumination over the Fabry-Perot interferometer, and a fast scannable Fabry-Perot interferometer for calibration and for the determination of outgoing laser frequency during the wind observation. With these improvements in stability, the standard deviation of peak transmission and FWHM of the Fabry-Perot interferometer was determined to be 0.49% and 0.36%, respectively. The lidar wind measurements were validated within a dynamic range of +/-40 m/s. Comparison experiments with both wind profiler radar and Vaisala wiresonde show good agreement with expected observation error. An example of 24 h continuous observations of wind field and aerosol backscatter coefficients in the boundary layer with 1 min and 30 m temporal and spatial resolution and 3 m/s tolerated wind velocity error is presented and fully demonstrates the stability and robustness of this lidar.
