【作者】 徐贤胜； 郭鹏；

【Author】 Xu Xiansheng~1 Guo Peng~2 (1.Shanghai Institute of Applied Mathematics and Mechanics,Shanghai University,200030,China; 2.Shanghai Astronomical Observatory,Chinese Academy of Sciences,200030,China)

【机构】 上海大学上海市应用数学和力学研究所； 中国科学院上海天文台；

【摘要】 在大气多路径条件下,讨论了两种无线电信号的反演方法:几何光学方法(Geometric-Optical,GO)和后传播方法(Back-Propagation,BP)。当大气存在多路径效应时,用几何光学方法反演大气参数会引入误差,而后传播方法将无线电信号由多路径区域反推至单路径区域,因此能克服多路径效应。为了比较不同反演方法,采用多相位屏模型,数值模拟了存在大气多路径条件下无线电信号在大气中的传播过程。假设信号在理想条件下(仅受大气多路径的影响),分别用几何光学和后传播方法反演大气参数廓线,结果验证了后传播方法能消除大气多路径的影响,获得较好的反演结果。分别用几何光学和后传播方法对2007年第60天至180天4个月约15000个CHAMP掩星观测数据进行反演,将其折射率反演结果与ECMWF分析场资料比较,统计结果表明:在低对流层(5 km以下),几何光学方法反演折射率的相对误差的平均偏差的最大值:在南半球(30°S～90°S)为-0.605%,热带(30°S～30°N)为-1.705%,北半球(30°N～90°N)为-0.510%;后传播方法在南半球为-0.440%,热带为-0.965%,北半球为-0.293%。将反演结果与NCEP资料进行比较时,也能得到类似的结论。更多还原

【Abstract】 Two methods for determination of refraction angle profiles from radio occultation in multipath areas are discussed: geometric optics inversion method and back-propagation inversion method.The geometric optics inversion method does not work in multipath areas while in back-propagation inversion method electromagnetic field can be back-propagatd from multipath areas to a single-ray area for overcoming effects of multipath propagation.The atmospheric propagation of GPS signals under multipath conditions and their detection are simulated by using multiple-phase-screen model.Under the assumption of idea signal,atmospheric variables can be retrieved from geometric optics and by back-propagation inversion method which validate that the back-propagation inversion method can solve the problem of calculating bending angle profiles within multipath regions.About 15000 CHAMP radio occultations from March to July in 2007 are retrieved from geometric optics and by back-propagation inversion method,statistical comparison of CHAMP radio occultations with analysis data of the European Centre for Medium-Range Weather Forecast(ECMWF)(below 5 km) shows:the maximum of mean deviation of fractional difference in refractivity for geometric optics inversion method is:-0.605%in southern hemisphere(30°S~90°S),-1.705%in tropics(30°S~30°N),-0.510%in northern hemisphere(30°N~90°N);for back-propagation inversion method:-0.440%in southern hemisphere,-0.965%in tropics,-0.293%in northern hemisphere. Similar conclusions can be drew comparing CHAMP radio occultations with NCEP data.更多还原