Scattering Matrix Polarimetry Technique And Its Application To Aerosol Particles

Aerosol particles affect weather,climate,radiative transfer and the heat balance of Earth-atmosphere system through the direct scattering and absorption of both incoming visible solar radiation and outgoing terrestrial IR radiation,and it also reduces visibility and affects human health.The scattering characteristics of aerosol particles have always been a research hot issue.The study and detection of aerosol scattering characteristics can have a positive effect on weather forecasting,climate prediction,environmental monitoring,and remote sensing applications.Researchers have developed many theoretical methods to calculate the scattering characteristics of aerosol particles.However,these algorithms all have their own limitations for non-spherical particles.Since the 1960s,experimental methods for measuring the light scattering characteristics of particles by using a nephelometer have been in the ascendant.However,the existing nephelometers generally have the disadvantages that only a few of the scattering matrix elements can be measured,or the validation accuracy is low,or the sample aerosol particles needed to be pre-processed,resulting in a deviation between measured scattering characteristics and the actual particle scattering characteristics.This paper attempts to improve the deficiencies of these instruments,mainly studies and discusses how to take advantage of polarimetry technique to measure scattering matrix of aerosol particles and the application of this technology to develop a polarized scanning nephelometer.The main contributions and innovations are summarized as follows:(1)The advantages and disadvantages of the scattering measurement technology at home and abroad are analyzed and compared,and the advantages of directly measuring the ensemble scattering properties of the aerosol particles by scanning polarimetry technique are demonstrated.(2)The design of the subsystem structure and the total system structure are completed.The optimum angles for the Stokes parameter polarimeter are proposed based on the condition number method.This configuration significantly reduces the sensitivity of indirect measurements to errors in direct measurements without using high-grade optical components or high-grade electronic components.The design and analysis of the sample cell with especially low stray light are completed.A new form of light trap with multiple hollow cones is proposed,which overcomes the disadvantage of existing light trap that the light entrance is small.(3)A high accuracy nephelometer to measure the scattering matrix of atmosphere particles is designed and implemented,which can in situ non-destructive measure the full matrix elements of ensemble-averaged scattering matrix of aerosol particles.Calibration tests were performed on key parameters of each part.Then,nitrogen gas was used to qualitatively analyze the stray light suppression level of the polarized scanning nephelometer.The accuracy of the scattering matrix of the polarized scanning nephelometer were quantitatively verified with homogeneous polydisperse spherical particles.The results show that the average relative errors of the scattering matrix element of DEHS droplets between measurements and the Mie scattering theory are within 0.01,the average absolute relative errors are within 0.025,which has reached the international advanced level.