面向电离层反演的参数平滑迭代层析方法

层析是电离层三维结构反演的重要技术.增加约束可缓解层析模型的病态问题.然而, 迭代层析中, 大量无射线穿过的网格易对施加的约束产生与真实意图相违背的约束结果(称负面约束).针对该问题, 提出了一种参数平滑的迭代层析方法(iterative tomography method via parameters smoothing, ITPS).每次迭代中, 先用Chapman函数及最小二乘法拟合及改正每一垂直剖面, 获取关于Chapman函数参数的二维图像, 然后用移动窗口法平滑各参数图像并以此改正各网格的电子密度.实验表明: ITPS方法可一定程度上减少负面约束并抑制层像的扰动.相对于MART和CMART算法, ITPS方法在垂直剖面、F2层临界频率(f_oF₂)、F2层峰值高度(h_mF₂)、斜电子总含量(Slant Total Electron Content, STEC)及h_mF₂以上电子密度等方面均具有更佳的表现.相对于精度较高的CMART算法, ITPS方法在f_oF₂与h_mF₂的平均优化率分别为7.49%及6.60%, STEC的平均优化率为5.19%, h_mF₂以上电子密度的平均优化率为11.41%.

Iterative tomography method for ionosphere inversion via parameters smoothing

Tomography is an important technology for three-dimensional ionosphere inversion. The well-known problem of ill-posed in ionosphere tomography is usually addressed by introducing additional constraints into tomographic models. However, in the method of iterative tomography, the existence of the massive unpassed grids facilitates the method to produce an unexpected result for the added constraints (named negative constraint hereafter). This paper is to develop a new ionosphere tomography method, named iterative tomography method via parameters smoothing (ITPS), to lower down the negative constraint. In ITPS method, each vertical profile of the ionosphere is fitted and corrected by a Chapman function via a least square fitting method. After that, an image for each parameter of the Chapman is generated. The image is smoothed by a moving window method and then used to correct the electron density of each voxel. Real experiments showed that ITPS method reduces the negative effect of the constraints and the fluctuations of the tomographic image. When compared with the MART and CMART algorithms, ITPS shows a better performance on the vertical profiles, the peak frequency of F2 layer (foF2), the peak height of F2 layer (hmF2), slant total electron content (STEC) and the electron density above hmF2. The average improvement of the ITPS over the CMART algorithm, the better one, are 7.49%, 6.60%, 5.19% and 11.41%, respectively, on the aspects of foF2, hmF2, STEC and the electron density above hmF2.