Research On Construction Of Forward Model And Inversion Algorithm For OH Radicals In Middle And Upper Atmosphere Based On SCIATRAN

In recent years,mankind has emitted more and more polluting gases into the atmosphere,and these emissions have greatly changed the concentration profile of atmospheric trace gases,leading to a series of global climate change problems.OH radicals are one of the most important oxidants in the atmosphere and play a central role in the atmospheric photochemical reaction of the earth.The upper and middle atmosphere is not only the main working area of the spacecraft,but also an important response to changes of global climate and even surface environment.Therefore,it is of great significance to research the OH radicals in the upper and middle atmosphere for understanding the change regulation of global climate and environment,improving the knowledge of momentum and energy transportation,and ensuring the safety of spacecraft flight.At present,Anhui Institute of Optics and Fine Mechanics,Chinese Academy of Sciences,is conducting a pre-study of the very high-resolution spectrometer for OH radicals in the upper and middle atmosphere.This paper conducts relevant research to provide theoretical basis and data support for the instrument.OH radicals are excited by the solar energy to produce fluorescence energy near 309 nm,and the concentration information of OH radicals can be obtained by establishing the relationship between the fluorescence signal and the concentration.The detector is composed of two SHS(Spatial Heterodyne Spectroscopy)for limb detection,whose scanning directions are orthogonal to each other.That is,a cross track scanning is added on the traditional along track scanning.Therefore the forward and inversion model for the way of traditional scanning,i.e.single SHS,is constructed first.In the study,it is found that the SCIATRAN radiation transmission model used in the calculation cannot meet the requirements of conducting the forward modeling,and the model is improved based on the radiation transmission theory: OH emission energy calculations are added in the source function of radiation transmission based on the construction of the OH emission spectrum database;The OH concentration spatiotemporal database conducted by the product of the MLS(Microwave Limb Sounder)sensor from 2005 to 2009 is used as an input parameter for radiation transmission.The improved SCIATRAN and the combination of optical interference theory are used to simulate the global limb detection of SHS.The results of simulation keep the same trend in altitude with observation from another sensors.There is a peak of energy near the altitude of 40 km,and the value decreases quickly while the altitude increase linearly.The simulation images of a single position are selected,whose uncertainty and sensitivity to the geometric conditions are also analyzed.Since there is no on-orbit observation data of sensor at present,the inversion model is constructed by using the global simulation results as the observed values.The combination of the OH concentration data under different time-space conditions and the radiation transmission model is used to obtain the radiance threshold to identify the polar mesosphere cloud.Then the background energy in limb scattering radiation obtained by the sensor is calculated to extract the OH fluorescence emission energy.The sensitivity to OH concentration is increased by using OH energy as inversion data,which has a good effect during the inversion.SCIATRAN and LSUV algorithm are used to invert OH concentration profiles.The error factors in the inversion process are discussed,and the quantitative effects of those factors on the inversion results are quantitatively calculated.The results show that the error of inversion of OH concentration in the middle layer is between 15% and 20%,and the error at the bottom of the stratosphere increases rapidly with the height decrease,reaching the level of 500%,so the in inversion data can not be trust,which is consistent with the inversion results of other OH radical detectors in the world.Based on the forward and inversion model of single SHS,the instrument structure and detection mode of double orthogonal SHS spectrometer are discussed.It is proved that the three-dimensional detection for the target atmosphere can be realized by multi-time and multi-angle detection of double orthogonal SHS,and the global observation result of the spectrometer is given.According to the spatiotemporal variation of OH concentration and the theory of three-dimensional tomography,a look-up table based on six-dimensional parameters(latitude,longitude,time date,OH concentration,solar zenith angle and relative azimuth angle)is constructed,and it is used in three-dimensional dimension inversion.This inversion method is more efficient than the iterative inversion,and the error of the inversion result in bottom atmosphere is improved obviously,which is only in the level of 10%.In this paper,the forward and inversion models are constructed for the mesosphere atmospheric OH radical detectors,and the error factors in the satellite observation process are quantitatively analyzed.These can provide the scheme for the optimization of the sensor's parameters and data support for the application of SHS.During the normal operation of the sensor,it can also provide technical support for the processing and application of remote sensing data,which plays an important role in the optimization,correction,detection,application and development of the sensor.