Multi-Ground Remote Sensing Equipments Detection And Study On Key Issues In Low Visibility Weathers

Low visibility weathers can disrupt traffic and harm human health.Study on the low visibility weathers had great economic and social significance.In this paper,the fogs,dust storms and hazes,which were long time detected by ground remote sensing equipments,were studied based on multi-source detection data.By analyzing the structural characteristics of each meteorological element,the concept models and formation mechanisms of fog and haze were summarized,and the key issues in theory and application of Millimeter Wave Radar(MMWR)detecting dust particles were studied.In order to get the temporal-spatial variation characteristics and the vertical structure of fog and haze,the wind profile radar,microwave radiometer,atmospheric transmission meter and the automatic observation facilities were used to continuous detection of fog and haze from January 2015 to December2017 at Xi'an Xianyang International Airport,which is the eighth largest airport in China.Firstly,through comparing the temperature and relative humidity datas detected by microwave radiometer with the sounding datas of Jing He meteorological station,the correlations between the two instruments'data were larger than 0.8 and the difference values were in reasonable ranges.The wind's consistence and quality had been increased by controlling the data quality.With long term detection data of 37 fogs and 3 hazes with the visibilities between 1k and 1.5km,the findings were listed as follows.The fog at Xianyang Airport was mainly radiation fog.The height of the stable boundary layer was between 500m and 600m,however,the max height of the mixed layer was about 1200m.The fogs at Xianyang Airport usually appeared between21:00 and 10:00 within the stable boundary layer.The fogs after precipitations usually took place in September and October,and the fogs before precipitations basically occurred in November,December and January.However,the hazes with the visibility between 1 km and 1.5 km,usually appeared between 10:00and 18:00 within the mixed layer.During fog and haze weathers,the horizontal wind speed<3m/s,with weak downdraft.During the fogs after precipitations,the height of inversion layer was about 200m;during the fogs before precipitations,the height of inversion layer was larger than 500m.However,during the haze with the visibility between 1km and 1.5km,the height of inversion layer was less than 100m.When the altitude increased from ground to 1000m,the temperature difference in fogs was is less than 1.5?,while the average difference of haze was 4.91?;hence,the atmospheric structure of fog was more stable than that of haze.During the fog weather,the average relative humidity was larger than 80%;however,during the haze weather(the visibility between 1 km and 1.5 km),the average relative humidity was about 40%.When the thickens of inversion layer and the relative humidity at low altitudes increases at the same time,the haze will trn to fog;moreover,when the industrial activities lead to the increase of airborne particles,the height of inversion layer decease and the relative humidity decrease at the same time,the fog will turn to haze.In order to conduct real-time quantitative monitoring of dust storm,Ka-band MMWR was utilized for the consecutive detection of dust storms over the Taklimakan Desert,which was the first time in China.The dust spectrum distributions and dust mass concentrations were retrieved by multi-source data detected by the MMWR,the Laser Particle Size Analyzer(LPSA)and the Grimm180 particle detector.Firstly,the power spectrums were averaged to improve the signal-to-noise ratio.Secondly,in the MMWR meteorological equation,the dielectric constant and complex refractive index of dust particles were analyzed in theory.Whatmove,the characteristics of dust spectrum and reflectivity factors were calculated and analyzed by using the power spectrum data.From April 1 to June 30 2018,there were 3 dust storms with unstable thermal structure,which all occurred from 13:00 to 17:00 and the horizon winds were larger than 8m/s;and there were 38 blowing sands,which mainly appeared from 10:00—22:00 and the winds were between 6m/s and 8m/s.During sand dust and blow sand,the relative humidity was between 15%and30%.During dust storms and blow sands,there were more cloud nodules due to the suspension of dust particles in the air.In these periods,the average cloud occurrence time(more than 15 minutes per hour),the average thickness(more than 1.5km),the maximum average reflectivity factors(about 5d BZ)and the corresponding average liquid water contents(about10^-0.5gm³)were all larger than other period of the day.The probability density distribution of dust conformed to the lognormal distribution and the range of reflectivity factors was between-25 d BZ and 20 d BZ.Furthermore,during the blowing sand stage,the effective height of dust spectrum distribution was normally lower than 300m with the peak power of power spectrums less than 0.2mw and the values of dust mass concentration were less than 10¹?g.m^-3 at the height of 200m.However,during the blowing sand stage,the effective height of dust spectrum distribution was normally lower than 600m,and the peak power of power spectrum less than 1mw;furthermore,when the height was 200m,the values of dust mass concentration were mainly less than 10²?g.m^-3.During the dust stormperiod,the effective height of the dust spectrum distribution was between 1000m and 2000m,with the peak power of power spectrum about 10mw;however,when the height was 100m,the values of dust mass concentration are between 1220?g·m^-3 and 42146?g·m^-3 and the average mass concentration is 9287?g·m^-3;whereas,the values of dust mass concentration are between 2?g·m^-3 and 820?g·m^-3when the height is 1200m and the average mass concentration is 24?g·m^-3.The relationship between the reflectivity factor Z and the dust mass concentration M can be defined as Z=651.6M^0.796.Compared with the observational data from Grimm180 particle detector,the data of the retrieved dust mass concentration was basically accurate and this retrieved method was proved to be feasible.Thus,the MMWR can be used as a new device for quantitative monitoring of dust storms.