| With the development of science and technology,the technology of atmospheric remote sensing detection is becoming more and more mature.In view of the increasing demands and applications of remote sensing,a new method of atmospheric remote sensing is proposed by scientists,it is limb observing with the characteristics of high spatial coverage and high vertical resolution.Due to different atmospheric conditions,observation geometry and spectral range,the detected spectral radiation signals show different changes.Therefore,it is of great significance for retrieving the variation of atmospheric temperature,density and trace gas concentration with height.With the continuous development of the capability of limb viewing,the establishment of the atmospheric radiation transmission model has become a hot and frontier issue,which is suitable for limb viewing mode.Although different limb atmospheric radiation transmission models have been established at home and abroad at present,there are still various shortcomings,such as slow calculation speed,insufficient calculation precision,narrow calculation spectral range and no multiple scattering of atmosphere,etc.In order to solve the problems existing in the above models and achieve the purpose of fast and wide spectrum calculation of limb atmospheric radiation transmission,this paper establishes a new limb atmospheric radiation transmission model on the basis of the fitted atmospheric spectral line parameter database in CART and spherical atmospheric model.The main contents and innovations of this paper are as follows:(1)Using the measured data of MIPAS satellite and the special SCITRAN limb atmospheric radiation transmission mode,the accuracy of the limb atmospheric radiation in middle and upper layers calculated by MODTRAN has been evaluated.The results show that the limb atmospheric background radiation calculated by MODTRAN5 is consistent with the change trend measured by MIPAS and simulated by SCITRAN,and the calculation speed is faster and the spectral range is wider than SCIATRAN.At the same time,it has been found that MODTRAN4 has a large error in calculating the limb atmospheric radiation intensity in visible band,and the atmospheric transmittance of MODTRAN5 is wrong only under the geometric configuration of observing altitude,zenith angle and distance,so MODTRAN5 can be used to simulate the limb atmospheric background and transmittance.These results have very important reference value for engineering application of MODTRAN to calculate atmospheric background radiation in limb space.(2)Using SCIATRAN and MODTRAN5 atmospheric radiation transmission software,the atmospheric transmittance and background radiation of several wave bands concerned in engineering have been simulated,and the changes of atmospheric transmittance and background radiation with various spatial geometric parameters at the limb viewing mode are studied,and the changes of atmospheric transmittance and background radiation with spatial geometry have been obtained.(3)Based on the layered spherical atmospheric radiative transfer model and considering the atmospheric refraction,a limb atmospheric transmittance model which can simulate the absorption of atmospheric molecules at the limb viewing mode has been established by using our existing universal radiative transfer software CART.(4)According to the calculation model of cirrus reflectance established by us and the atmospheric parameter profile retrieved from MODIS satellite remote sensing,the spatial distribution of cirrus cloud reflectance has been calculated,the cirrus reflectance algorithm is verified.Using MODIS data in the past 20 years to make statistical analysis,the global spatio-temporal distribution characteristics and seasonal variation characteristics of cirrus reflectance are obtained,which provides basic data for cirrus atmospheric background radiation calculation. |
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