Ionospheric Gradients Estimation and Analysis of S-Band Navigation Signals for NAVIC System

Navigation with Indian constellation (NAVIC) is the operational name given to the Indian Regional Navigation Satellite System developed by the Indian Space Research Organisation, India. The most influential factor is ionospheric gradients that can degrade the positional accuracy of the global navigation satellite system users especially in low-latitude regions. The main aim of this paper is to estimate the ionospheric gradient variations obtained from the NAVIC receiver located at Guntur, India (16.23° N, 80.44° E). Code and carrier phase measurements of S-band (2492.028 MHz) signals are used to derive ionospheric time delays and total electron content (TEC) values. In this paper, S-band signals of NAVIC are used for the first time to investigate ionospheric gradients over low-latitude region. The recursive least squares (RLS) algorithm is implemented as a single frequency ionospheric model for estimating the absolute TEC, and longitudinal (E–W) and latitudinal (N–S) ionospheric gradients. Ionospheric gradient analysis has been carried for three consecutive days during September equinox, December solstice in 2016, and for a geomagnetic disturbed event observed during May 2017. The annual statistical analysis in the periodic structure of spatial ionospheric gradients from NAVIC S-band signals during June 2016–May 2017 is also discussed. It is evident that RLS model can estimate ionospheric gradients for a single NAVIC station. The outcome of this work would be useful for understanding ionospheric irregularities climatology over low-latitude region.