Quality Evaluation of IGS GIMs Based on the Statistical Characteristics of VTEC/RMS Eigenvalues: A Macro Perspective

Abstract

With the expanded application scope of the International GNSS Service (IGS) global ionospheric maps (GIMs), it is of great theoretical significance and practical value to evaluate the quality of IGS ionospheric products. A new methodology is proposed to mosaic ionospheric grid maps, and GIMs-based solutions for global ionosphere vertical total electron content (VTEC)/Root Mean Square (RMS) eigenvalues are put forward for subsequent quality assessment. Moreover, based on the proposed method and the strategy, it is the first time that the quality of IGS GIMs from a macro perspective is assessed using the extracted daily global maxima of ionosphere VTEC/RMS (1998–2016). The results show that there are some abnormal maxima values in the GIMs data between 1998 and 2004, while products from 2005 to 2016 are of relatively better quality and are suitable for use as follow-up experimental data. In addition, we analyze the statistical characteristics of spatial and temporal distribution of GIMs-based VTEC/RMS eigenvalues and the correlation between eigenvalues and solar activity, in order to verify the conformity between ionosphere physics characteristic and eigenvalues statistical properties which is for further data quality assessment of GIMs. By analyzing the spatial distribution of VTEC/RMS maxima and minima, we found that VTEC maxima are located on both sides of the geomagnetic equator and there is a “dual-hump” phenomenon in the distribution, and VTEC minima are concentrated in the high latitudes, while RMS minima are distributed throughout the globe but RMS maxima in the low latitudes. Meanwhile, in terms of time distribution, VTEC maxima distribute mainly in the local time from 13:00 to 17:00, while VTEC minima are mainly at nighttime; for RMS, the maxima are mostly distributed in the daytime, while the minima are of a slightly higher distribution proportion at night than in the daytime. At the same time, it was found that the eigenvalues, except RMS minima, are strongly correlated with solar activity but there are lags of 2 to 3 days. Consequently, the above statistical characteristics of GIMs-based VTEC/RMS eigenvalues are in conformity with ionospheric physics. It verifies the availability and reliability of GIMs from a macroscopic perspective and provides a favorable support for the further application and promotion of GIMs.