Research On Nanjing Wind Field Characteristics And Pollution Process Based On Coherent Wind Lidar

Coherent lidar has the advantages of high spatial-temporal resolution and high measurement accuracy,which is widely used to detect the atmospheric wind field.In addition to obtaining the information of atmospheric wind field,coherent lidar can also obtain the information of aerosol at the same time.Based on a 1.55 μm all fiber coherent wind lidar system,this paper introduces its detection principle,system composition and data inversion method.The signal processing of coherent lidar is optimized,which is mainly to extract power spectrum and denoise it.The traditional fast Fourier transform and the fast zero-padded Fourier transform are compared,and the results show that the fast zero-padded Fourier transform can improve the frequency spectrum accuracy.In terms of denoising,the use of multi-pulse superposition and the subtracted final distance gate denoising effectively improves the signal-to-noise ratio.The results of the observation of coherent lidar at 65 m and 121 m are compared with the wind cup anemometer and wind vane.The observation results of coherent lidar at 65 m and 121 m are compared with the wind cup anemometer and wind vane.It is found that the average deviation of wind speed is 0.02 m/s,and the average deviation of wind direction is 0.22°.The fitted straight lines are all near y=x,and the correlation coefficient is greater than 0.99,indicating that the radar has good detection performance.The data of wind field in Nanjing are obtained and analyzed,including seasonal and diurnal variations.The results show that easterly wind prevails in summer,northeast wind prevails in autumn and winter,and southeast wind prevails in spring.The average wind speed in spring is the largest,followed by summer.5:00to 7:00 in the morning is the lowest time of wind speed in the whole day,and the maximum wind speed generally appears between 15:00 and 19:00.With the change of seasons,the time of maximum wind speed gradually changes from 15:00 to 19:00.Applying the coherent lidar data to the characteristic analysis of polluted weather,the analysis results show that the horizontal wind speed of haze days is less than that of foggy days,and the smaller the wind speed,the better the formation of haze.Compared with haze,the backscattering ability of fog is greater than that of haze.An example of polluted weather and sandstorm weather is analyzed.Observational data shows that wind speed and wind direction have an important impact on the transportation and dissipation of pollutants,and coherent lidar has a very good application effect in the pollution process.