Ionospheric time delay variations in the equatorial anomaly region during low solar activity using GPS

Abstract

Ionosphere can be a greatest variable source of error in precise time transfer using GPS<b> </b>satellites. The proposed navigation concept requires that a user measures the time-delay that satellite emitted signals experience in traversing the distance between satellite and user. The difference between the apparent range and the true range, or the free space velocity and the true velocity, is the quantity of interest. This quantity is directly proportional to the total electron content along the path of propagating signal. Thus, if the total electron content is known or is measured, a perfect correction to ranging could be performed. The equatorial anomaly region, Bhopal (geographic latitude. 23.2ºN, longitude 77.6°E), India with dual frequency from the GSV4004A GPS Ionospheric Scintillation and TEC Monitor (GISTM) receiver have demonstrated a high degree of accuracy in measuring the ionospheric group delay. The diurnal and seasonal variations of ionospheric time delay have been studied during the solar minimum period January to December 2005. It was found that diurnal variation of ionospheric time delay is maximum in the month of April and minimum in the month of December. The study reveals that during low solar activity, equinox season shows the maximum delay while summer gives the moderate and winter shows the minimum delay. The ionospheric time delay was also studied during magnetic storm conditions for the same period and the occurrence of daily maximum ionospheric time delay as a function of day during this period