Quality assessment of CNES real-time ionospheric products

Real-time single-frequency precise point positioning (RT-SF-PPP) has become a desired positioning approach because it can achieve high positioning accuracy with a low-cost global navigation satellite system (GNSS) chipset or receiver. For single-frequency precise point positioning (SF-PPP) applications, the ionospheric delay is a dominant error source, and thus the quality of applied ionospheric products is critical to the performance of SF-PPP. To meet the demands of the RT-SF-PPP users, the international GNSS service (IGS) is planning to provide open-access real-time ionospheric products. By now, the Centre National d'Etudes Spatiales (CNES) is the only IGS analysis center (AC) to broadcast real-time ionospheric vertical total electron content (VTEC) message through its real-time service (RTS). The quality of the CNES real-time ionospheric products is drawing increasing attention from the GNSS community. We evaluate the quality of CNES real-time VTEC message both in the ionospheric correction domain and positioning domain. First, 374 consecutive days of CNES VTEC products are collected and compared with the IGS final global ionospheric map (GIM) products. Second, slant total electron content (STEC) computed with CNES VTEC message is fully assessed with respect to STEC derived from dual-frequency GNSS measurements. Finally, RT-SF-PPP is conducted for assessing the quality of CNES real-time ionospheric products in the positioning domain. The degree and order of the spherical harmonic expansions broadcasted in the CNES VTEC messages changed from 6 to 12 in the time span of collected data, the effects of higher degree and order parameters are investigated at the same time in the experiments above.