Modeling And Simulating Of Spectral Radiance Property For Sky Background

While a spatial object is observed by a ground detection system,besides thescattered solar radiance by the object oneself and its own thermal radiance,the systemwill receive some undesirable radiance,which includes scattered radiance by theatmospheric molecules and aerosols and cloud particles,atmospheric thermal radiance,direct solar radiance and so on.The radiance mentioned above constitutes total skybackground radiance.The object-background radiance contrast is a key parameter fordistinguishing an object from the sky background,so the spectral radiance and its scenedistribution constitute the basic database for application to some detection system suchas sky monitoring,aerial target searching and tracking.In the thesis,spectral radianceand scene simulation method for sky background are explored and investigated;thisprovides an important reference to the detection system simulation.The main contents and results are as follows:1.Methods of establishing vertical extinction parameter profile database foratmospheric molecules and aerosols are analyzed.Some scattering phase functions areintroduced for atmospheric molecules and aerosol particles,and their expresses aregiven out under some different conditions.2.Detailed research about the stream approximation of computing downwardspectral radiance for the cloudless sky background is also carried out.A process settingup the Radiative Transfer Equation (RTE) is studied in detail based on the transporttheory.And a universal solution to the RTE is obtained.The discrete ordinate method(DISORT) and the modified Eddington approximate method are employed to treat theproblems of the multiple scattering for the multilayer atmosphere.And some calculationexamples are given out.The results show that the modified Eddington approximatemethod has sufficient precision at least for the examples considered,but shortercomputer time,as compared with the DISORT.3.Approximate methods for computing extinction parameters of the typical waterclouds and ice clouds are studied.Numerical results show that the calculated values based on the new method is consistent well with the values on Mie theory.A way tocalculate cloud affection to the sky background is investigate.4.Based on the energy conservation law and an assumption that the ground is aLambertian reflecting surface,a model is developed to calculate the additional skyradiance due to the ground reflection.According to the ray tracing principle,a newmethod was proposed to compute the effection of the reflection radiance between theearth's albedo surface and the atmosphere.The results show that sky radiance increasesrapidly with the increase of the ground albedo while a viewing zenith angle is close to90°,i.e.,there is a limb-brightening effect for sky radiance.5.Methods of numerical scene simulation for sky background are analyzed andstudied,and the radiative transfer theory and fractal geometry algorithms aresimultaneity employed to simulate cloud scene.A software was designed to computegeneral spectral radiance and simulate numerical scene for sky background,whichincludes a primary simulation program for cloudy sky also,and an interface programpackage with the object-background synthesis scene is developed.