A research group led by Professor Ken Umeno and Graduate Student Satoru Yoneyama (currently employee at Flect Co., Ltd.) from the Graduate School of Informatics at Kyoto University has discovered an algorithm that enables real-time visualization of the ionosphere with high resolution of 0.25 degrees in longitude and latitude (three-dimensional ionospheric tomography). The research group has revealed the detailed three-dimensional structure of medium scale traveling ionospheric disturbances (MSTID) and other phenomena using this algorithm.
Umeno stated, "We have made it possible to perform calculations fast enough to keep up with temporal resolution even when using an ordinary PC. We expect this will enable us to elucidate the detailed mechanisms behind ionospheric disturbances immediately before major earthquakes, which our laboratory has presented several times." The research was published online in the Journal of Geophysical Research: Space Physics.
Provided by Kyoto University
Understanding the three-dimensional structure of the ionosphere, which spans from 50 kilometers to 1,000 kilometers above the Earth, is essential for the stable operation of positioning services such as GPS and for obtaining accurate information about space weather, which changes due to effects such as solar flares. However, conventional methods required large computational resources such as supercomputers to obtain high-resolution three-dimensional structures in real time.
By receiving dual-frequency radio waves sent from positioning satellites at receiving stations and measuring the propagation delay of the two frequencies, the total electron content (TEC) along the path between the satellite and receiving station can be obtained. The basic process of three-dimensional ionospheric tomography involves the following steps: dividing the three-dimensional space of the ionosphere into a mesh; establishing simultaneous equations where the integral (sum) of electron number density along the path for each mesh between multiple satellites and multiple receiving stations is equal to the TEC; and finding a solution for the electron number density of each mesh.
The research group added three innovations to conventional methods in solving these simultaneous equations. First, since data sparsity inevitably results in a sparse matrix, they employed the conjugate gradient method to solve the simultaneous equations of ionospheric tomography. Additionally, because temporal changes in electron number density are continuous, they used the electron number density solution at the current time as the initial state for obtaining the solution at the next time. Furthermore, by using low-resolution data as an approximation of high-resolution data and performing iterative calculations, they were able to obtain high-frequency three-dimensional structures of the ionosphere that achieve high-resolution and enable real-time calculations at overwhelmingly fast speeds compared with conventional methods.
The group investigated the three-dimensional structure of MSTID, a type of space weather phenomenon. The results showed that in Japan, for all cases of MSTID occurring during winter daytime, winter nighttime, and summer nighttime, the peak electron number density and the peak height exhibited a negative correlation, with the degree of negative correlation being highest during summer nights and lowest during winter daytime.
Utilizing this method is expected to contribute to extracting the basic characteristics of specific types of ionospheric disturbances such as the detailed fundamental structure of MSTID. It is also expected to aid in elucidating their origin, clarifying the mechanisms of ionospheric disturbances observed immediately before major earthquakes, distinguishing them from phenomena related to space weather-related ionospheric disturbances, and elucidating the physical mechanisms of various ionospheric phenomena.
Journal Information
Publication: Journal of Geophysical Research: Space Physics
Title: Fast Computerized Ionospheric Tomography Using GNSS-TEC in Densely Observed Regions
DOI: 10.1029/2024JA033404
This article has been translated by JST with permission from The Science News Ltd. (https://sci-news.co.jp/). Unauthorized reproduction of the article and photographs is prohibited.