低仰角射线对电离层CT成像的影响分析

Influence of Rays at Low Elevation Angles on the Ionospheric CT Imaging

电离层层析成像(Computerized Tomography,CT)是一个有限视角问题,水平射线的缺失造成CT结果垂直分辨率的严重下降.很多人直观地认为低仰角射线可以弥补水平射线的缺失,然而本文的理论分析和数值模拟研究结果表明,低仰角射线对CT结果的影响十分微小,其无法弥补水平射线缺失所带来的垂直分辨率的下降.模拟结果显示,增加低仰角射线前后CT反演结果几乎没有变化;而去掉680条低仰角射线和高仰角射线后,CT反演结果差别巨大;去掉680条低仰角射线的CT结果与模型吻合很好;去掉680条高仰角射线的CT反演结果失真严重,几乎无法恢复模型的扰动特征.

The ionospheric CT imaging is a limited angle tomography problem.The lack of horizontal rays severely degrades the vertical resolution of the ionospheric CT reconstruction results. Many people intuitively thought that the adverse effects due to the lack of horizontal rays can be compensated by including rays at low elevation angles.However,it is shown by both theoretical analysis and numerical simulation that the influence of rays at low elevation angles on the CT results is too small to mitigate the degradation in vertical resolution due to the lack of horizontal rays. The numerical simulations show that electron density images reconstructed are almost no changes whether consider rays at low elevation angles or not.But,when disregards 680 rays at low elevation angles and 680 rays at high elevation angles at same time,the change is very large.The CT imaging result consists with the model after taking out 680 rays at low elevation angles.But The CT imaging result changes largely comparing with the model and the small-scale structures cannot be discriminated when taking out 680 rays at high elevation angles.