| Atmospheric water vapor refers to gaseous water in the atmosphere,which plays an important role in atmospheric chemistry and atmospheric physics processes.Water vapor not only plays a key auxiliary role in the formation of haze,but changes in its concentration also affect the frequency of precipitation.Carrying out stereoscopic detection of the atmospheric water vapor vertical distribution is very important for effectively understanding the causes of atmospheric pollution and regional meteorological changes.The measurement of atmospheric gases by spectroscopic methods is an important part of optical research.Multi-axis differential absorption spectroscopy(MAX-DOAS)is a spectral telemetry technology with a simple structure,high temporal and spatial resolution,and multi-component measurement,which has great potential for detecting the vertical distribution of atmospheric water vapor.However,MAX-DOAS measurement of water vapor has problems such as saturable absorption and poor accuracy of the profile retrieval algorithm,resulting in a lack of current research on water vapor inversion.Focusing on the demand for high-precision,high-time-resolution stereoscopic water vapor detection,based on the MAX-DOAS optical remote sensing technology,the telemetry method and technical application for atmospheric water vapor vertical distribution are carried out in this study.This paper mainly improves the existing system,optimizes the vertical water vapor distribution inversion method,and establishes an optical telemetry method for water vapor flux(WVF).In addition,the spatiotemporal distribution and transport characteristics of water vapor in the typical urban pollution periods and coastal and inland cities are also obtained.In order to improve the accuracy of water vapor three-dimensional distribution detection,the accurate inversion of vertical column density(VCD)under the water vapor saturation absorption problem and the sensitivity of water vapor profile inversion under various parameter constraints were studied.At the same time,the existing MAX-DOAS system is optimized.The optimal inversion band(434-452 nm)of water vapor in the blue band was determined by analyzing the spectral fitting parameters.The saturation effect was corrected by the coefficient correction method,and the accurate inversion of the water vapor column density was realized.A broadband high-resolution spectrometer covering the blue light band and a PID high-precision temperature control system were used to achieve stable and effective resolution of the water vapor absorption spectrum in the blue light band.At the same time,taking into account the need for detection of various atmospheric components,the system optical import unit was optimized and integrated with visible light image acquisition.The deduction of system background noise and thick cloud interference was realized,and the accuracy of water vapor inversion was improved.Based on the atmospheric radiative transfer model,the influence of multiple parameters(a priori profile,covariance matrix,number of iterations,etc.)on the water vapor profile inversion was studied.The prior profile of water vapor was determined as a sensitive parameter for profile inversion,and the prior profile was optimized through the measured data.In addition,through the algorithm sensitivity analysis,the optimal inversion parameters of water vapor profile such as covariance and iteration times were determined.The comparison of long-term observations of water vapor VCD and profiles with various data(models,soundings,towers,etc.)shows that the water vapor VCD and profile inversion algorithms were accurate and stable(water vapor VCD:R~2≥0.76;water vapor profile:R~2≥0.67).In order to quantitatively analyze the effect of upper-altitude water vapor transport on regional rainfall,the MAX-DOAS precipitable water(PW)and WVF telemetry research was carried out for the first time,and the WVF optical telemetry method was established.Based on the water vapor VCD observation data,the PW was obtained by coefficient conversion.The WVF was successfully obtained by coupling the highly time-resolved MAX-DOAS water vapor profile with the exponentially interpolated 3D wind field data.Continued observational comparison studies were carried out in Qingdao and Xi’an,and the comparison with ECMWF showed that the results of MAX-DOAS optical telemetry PW and WVF were accurate(PW:R~2≥ 0.85;WVF:R~2≥0.60).Aiming at the relationship between the three-dimensional distribution and transport of water vapor,haze pollution,and regional meteorology,the temporal and spatial distribution characteristics of water vapor during typical urban(Qingdao and Beijing)pollution periods,as well as the temporal and spatial distribution and transport characteristics of PW and WVF in coastal(Qingdao)and inland(Xi’an)cities were studied.The results show that the water vapor concentration and aerosol concentration were highly correlated during heavy pollution,and under unfavorable meteorological conditions(small wind speed,temperature inversion,and high humidity),water vapor promotes the formation of haze.The PW and WVF were high in summer and low in winter,and water vapor was transported from west to east.Before the precipitation,the WVF showed a high value at about 2 km above the two cities,and the southerly transport played a leading role.The results of this study solve the problem that it is difficult to accurately retrieve water vapor based on MAX-DOAS technology and promote the extension of MAX-DO AS optical telemetry technology to the meteorological field.The technical application study provides data support for further understanding the formation of atmospheric smog and technical support for an in-depth understanding of the water cycle. |
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