Estimation and Assessment of Ionospheric Slant Total Electron Content (STEC) Using Dual-frequency NavIC Satellite System

Many atmospheric errors affect the positional accuracy of a satellite-basednavigation device, such as troposphere, ionosphere, multipath, and so on, butthe ionosphere is the most significant contributor to positional error. Sincethe ionosphere’s dynamics are highly complex, especially in low latitudeand equatorial regions, a dual-frequency approach for calculating slant totalelectron content (STEC) for ionospheric delay estimation performs betterin these conditions. However, the STEC is ambiguous and it cannot beused directly for ionospheric delay prediction, accurate positioning purposes,or ionospheric study. As a result, STEC estimation and pre-processing arerequired steps prior to any positioning application. There is very little litera-ture available for STEC pre-processing in the NavIC system, necessitating anin-depth discussion. This paper focuses on how to extract navigational data from a raw binary file obtained from the Indian NavIC satellites, estimate andpre-process STEC, and build a database for STEC. It has been found that anhourly averaged STEC data is suitable for ionospheric studies and monthlymean value can be used for ionospheric behavioral research. Furthermore, theSTEC is affected by diurnal solar activity, thus, the seven-month data analysisthat includes summer and winter months has been used to study ionosphereaction during the summer and winter months. It has been observed that STECvalues are higher during the summer months than the winter months; someseasonal characteristics are also been found.