Evaluation of COMPASS ionospheric grid

AbstractAs an important component of the augmentation service, the ionospheric grid contributes to improving single-frequency positioning accuracy. The ionospheric delay corrections are broadcast as vertical delay estimates at specified ionospheric grid points (IGPs) for most satellite-based augmentation system, where the IGPs are predefined with a resolution of 5° and 5° in latitude and longitude. Different from the general strategy, the COMPASS IGPs are predefined with a resolution of 2.5° and 5° in latitude and longitude. The need for this special IGPs distribution is investigated with experiments using real data. The performance of the COMPASS ionospheric grid is analyzed in terms of accuracy and availability. Comparing the performance of the special IGPs distribution with that of 5° × 5° IGPs, the results show that the ionospheric correction improves by 0.2 m and the 3D positioning accuracy improves by 1 m in middle-low latitude regions. The RMS of the COMPASS grid ionospheric correction accuracy is better than 0.5 m in most regions of the China mainland, and the availability is better than 95 % except in the northeast, northwest and outside China. In addition, we investigated the performance of the method that combined the inverse distance weighted and spherical harmonics grid modeling algorithm. Simulations show that the new method clearly improves grid availability. The mean availability in the mainland is better than 99 %.