Research On Spectral Radiation Properties Of Limb Atmospheric Background

With development and progress of science and technology, atmospheric remote sensing technology becomes more mature. Limb viewing mode proposed by researchers is a novel atmospheric remote sensing method with advantage of high spatial coverage and high vertical resolution. Different atmospheric condition, viewing geometry, and spectral range will result different spectral radiation properties of limb atmospheric background. Research on spectral radiation properties of limb atmospheric background is not only quite important for atmospheric profiles and trace gas retrieval, environment remote sensing and monitoring, and target detection and tracking, but also provides important reference data for performance and design parameters in developing limb sensors.In recent years, more spaceborne limb sensors have been developed, and establishing atmospheric radiative transfer models for limb viewing mode has become a hot issue and forefront in atmospheric science. However, the current limb atmospheric radiative transfer models have several disadvantages, such as narrow spectrum, slow computation speed, and only can calculate limb atmospheric scattering radiation. Therefore, in order to solve above problems and achieve the purpose of wide spectrum and fast computation speed for limb atmospheric radiative transfer, in this dissertation, research on calculation models of key parameters in limb atmospheric radiative transfer, fast limb atmospheric transmittance and fast limb atmospheric radiance has been carried on based on the basic theory of atmospheric radiative transfer. And eventually, a Fast Limb Atmospheric TRANsmission(FLATRAN) model has been established, with a wide spectral range from ultraviolet to far infrared(0.2~20 μm) band and can perform fast calculation for limb atmospheric scattering radiation and limb atmospheric thermal radiation. In addition, a systemic and comprehensive sensitivity analysis of limb atmospheric radiation has been investigated by the FLATRAN model. The main researches in this dissertation are as follows:(1) A Layered Tracing Iterative(LTI) algorithm has been proposedA LTI algorithm has been proposed based on layered spherical atmosphere model to calculate limb absorber amount. The advantage of the LTI algorithm is that the effect of the curvature of the earth and atmospheric refraction is considered, and limb absorber amount is calculated with high accuracy for the sub-layered process in the calculation. Furthermore, observer zenith angles at each atmospheric layer boundary are obtained during the limb absorber amount calculation process.(2) Calculation method of limb angle parameters in the geodetic coordinate system has been proposedTo our knowledge, this dissertation is the first report of modeling research on limb atmospheric radiative transfer in the geodetic coordinate system. Calculation method of limb angle parameters in the geodetic coordinate system has been proposed based on longitude, latitude and altitude of tangent point and observer, and date and UTC time, which makes FLATRAN model can execute limb atmospheric radiative transfer calculation both in the regular geometric model and the geodetic coordinate system.(3) A Fast limb atmospheric transmittance algorithm has been proposedThe current limb atmospheric radiative transfer models all use Line-by-Line(LBL) algorithm to calculate limb atmospheric transmittance, however, they are very time consuming. Atmospheric molecular BM database in 0.2~20 μm band has been established based on the latest released molecular spectroscopy database of HITRAN2008. And a fast limb atmospheric transmittance algorithm has been proposed based on the BM algorithm. Compared with the results from the LBL algorithm, the relative difference between them is less than 1.99%, while the algorithm is about 6 times faster.(4) A Hemisphere Radiation Adding algorithm has been proposedThe current limb atmospheric radiative transfer models are computational inefficiency, and only can calculate limb atmospheric scattering radiation. A HRA algorithm has been proposed to solve limb atmospheric radiative transfer equation based on layered spherical atmosphere model, composite analysis of limb atmospheric radiance, and geometric characteristic of limb viewing. The advantage of the HRA algorithm is that results from two limb viewing mode at an arbitrary tangent height can be obtained with only one calculation process. Furthermore, flux approximation method is employed to calculate limb atmospheric multiple scattering radiation. Experiment results reveal that computation speed of the FLATRAN model is about 12, 105, and 936 times faster than the CDIPI model, SASKTRAN model, and SIRO model, respectively. In addition, the FLATRAN model is able to calculate limb atmospheric scattering radiation and limb atmospheric thermal radiation.(5) Calculation software of spectral radiation properties of limb atmospheric background has been developedThe current limb atmospheric radiative transfer computation softwares are developed based on the Fortran language, and some related function libraries needed to be installed and parameter settings are complicated. A calculation software of V1.0 version of spectral radiation properties of limb atmospheric background has been developed with the VC++ platform, which has a simple and convenient interface, and is intuitive and friendly to the users. According to the parameters of atmospheric mode, underlying surface, aerosol mode, cloud mode, limb geometry and spectral range set by the user, image of limb spectral radiation characteristics, average transmittance, limb integrated radiance and time-consuming per wavelength are calculated and outputted by the software. The results of data and images can be saved.In conclusion, the FLATRAN model proposed in this dissertation has great advantages in calculation spectral range, computation speed and calculation limb atmospheric radiation type, achieving the goal of modeling of wide spectrum and fast computation speed for limb atmospheric radiative transfer, which establishes a solid theoretical foundation for limb atmospheric radiative transfer theory and applications of limb remote sensing.