A Sensitivity Study On The Retrieval Of Aerosol Vertical Profiles Using The Polarimetric Oxygen A-Band Spectra

Aerosol vertical profile affects the global radiation balance and climate change.The pressure dependence of oxygen absorption line parameters provides a natural vehicle for retrieving photon path length distributions and vertical information of aerosols and clouds.Therefore,retrieve of aerosol vertical profile using polarized oxygen A-band(755nm-775nm)measurement spectrum is of great significance.However,the retrieval methods of aerosol vertical profiles are mostly based on the forward model of atmospheric radiation.The influence of surface albedos,observation geometry and prior error on the retrieve of aerosol vertical profile information need to be considered.Hence it is necessary to conduct extensive sensitivity studies to assess the effects of these factors.In this paper,the factors affecting the sensitivity of retrieval of aerosol vertical profile information measured by oxygen A with polarization are analyzed.Firstly,the Oxygen A-band spectra with different spectral resolutions are simulated,and the degree of information freedom(DFS)of the parameter aerosol peak height in each experiment is calculated using the optimal estimation theory.The results show that more aerosol information can be obtained by improving the spectral resolution and that polarization measurement is better than radiance measurement.On the basis of the above research and analysis,the data of coarse-mode and fine-mode aerosol particles are simulated,and the influence of the prior error,observation geometry and surface albedos on the information content of aerosol vertical profiles retrieve and its dependence on spectral resolution are analyzed.The results show that with the increase of spectral resolution,more information about aerosol peak heights can be retrieved,and when the spectral resolution is raised to0.01 nm,DFS does not increase any more,and the amount of information about aerosol peak height can be inverted reaches the maximum.In the case of high spectral resolution,the difference aerosol peak height information of between fine-mode aerosol particles and coarse-mode aerosol particles is the most obvious.The improved spectral resolution is helpful to distinguish coarse-mode and fine-modal aerosols.More information about aerosol peak height can be obtained at the same time with higher priori error and larger solar zenith angle.More information about aerosol vertical profile can be retrieved at dark surface conditions than at bright surface conditions.At higher spectral resolution,the dependence of the information on the aerosol peak height on priori error,solar zenith angle and surface albedos is greatly reduced,especially for aerosols layer in the middle and upper troposphere.The results provide a reference for instrument design parameters and inversion algorithm development of atmospheric polarization measurement.