A study of ionospheric effects on IRNSS/NavIC positioning at equatorial latitudes

Abstract

The Indian Regional Navigation Satellite System (IRNSS/NavIC) is fully operational and broadcasting radio signals at L5 (1176.45 MHz) and S-band (2492.028 MHz). When these signals pass through the ionosphere, carrier phase delay, which depends on Total Electron Content (TEC), causes error in positioning. Corrections are applied in the augmented navigation system to minimize the position error due to TEC; however, 100% removal of error is practically impossible. Thus, a study has been carried out to understand the role of ionospheric determinants, such as TEC and scintillation S4, on the accuracy of augmented navigation over low latitude region using a dual-frequency NAVigation with Indian Constellation (NavIC) receiver installed at BITS-Pilani K.K. Birla Goa Campus (Geog. Lat. 15.39°N, Geog. Long. 73.87°E). Data collected using the Indian Space Research Organization (ISROs) NavIC receiver (make DataPattern) during the low solar period between March 2019 to December 2019 is utilized for this study. The important findings of the study are as follows: (a) Mean position error was in the range of 2–4 m. (b) Diurnal variation of the position error indicated a maximum at afternoon hours, coinciding with the time of maximum TEC over the EIA crest region. (c) Mean position error in afternoon hours indicated a linear relation with mean TEC, in a scatter-plot analysis. (d) Statistically, the position error during the scintillation nights was found to be similar to non-scintillation nights, indicating that the post-sunset equatorial density depletions during low solar do not significantly impact navigation accuracy. Absolute position error during the active phase of a moderate geomagnetic storm of 14 May 2019 was found to be significantly higher compared to a quiet period, which also depends on the mode of operation of the augmented navigation system. It was found that a hybrid NavIC (Dual) + GPS (SBAS) augmented navigation was more accurate than NavIC with dual- ionospheric corrections or NavIC with grid corrections, alone. Besides, the dynamic behavior of the ionosphere, i.e., diurnal, monthly, and seasonal variations of ionospheric TEC, have also been studied using the iono-delay values derived from the NavIC receiver.