An ionospheric disturbance index for SBAS based on gradient variation
【摘要】：A simply constructed index is generally wanted to give direct indication of ionospheric status for Space-based augmentation system(SBAS) users. To this end, we make extensive analysis of ionospheric grid model performance under typical ionospheric storms. It was found that ionospheric delay gradients, instead of delays itself, are the main contributors for larger model errors. This feature makes indexes, which are defined on delay temporal variations, not preferred candidates for ionospheric condition indicating. A new index based on mean ionospheric delay gradients is then proposed and its applicability is analyzed. Results shows its consistence with grid model error variations, and the readily found threshold. Further analysis points out indexes based on delay spatial gradients, instead of temporal variations, is the key to construct sensible indicator for ionosphere status for SBAS.