Near point monitoring of the ionosphere using dual frequency GPS data over the hydearabad region: A Kalman filter approach

Abstract

In order to determine the position and attitude in a wide range of applications Global Positioning System is used. One of the utmost interests regarding navigation and positioning areas is the near point monitoring of the ionosphere using dual frequency GPS data. To determine the location and regulate time on the earth's surface through GPS receivers radio signals are broadcasted by the global positioning system (GPS) satellites which enable the receivers. These GPS signals comprehend time and status of entire satellite constellations, ranging signals, navigation messages. GPS provides entire information about positioning thoroughly for twenty four hours a day which covers any part of the world. The main cause of errors for GPS signals is the ionosphere which contains anonymous distribution of electrons which introduces a frequency dependant path delay proportional to the total electron content (TEC) along the signal path. This delay in the atmosphere specifically in ionosphere is due to the existence of electrons. Ionospheric effects can be miniaturized for single frequency GPS receivers via modelling using empirical or physics-based ionospheric models. But due to the dispersive nature of ionosphere in the electromagnetic spectrum the effects are considered for dual frequency GPS receivers. Though the errors likes, clock, orbital, satellite and multipath effects which effect the GPS signals are declined depending on the particular application. In this work we are only concerned with the ionospheric errors in which the ionosphere is modelled by Kalman filter approach and the obtained results are validated using SOPAC web application. To increase the accuracy and reliability of navigation Kalman filters are widely used. Using thin shell approximation of the ionosphere as the basis, ionosphere in the LOS is modelled using Kalman filter. It also contains how ionosphere impacts the GPS signals and about ionospheric TEC observables. Near point monitoring of ionosphere is investigated based on the data of dual frequency GPS receiver of an IGS station, NGRI Hyderabad (lat: 17° 22' 31" N, long: 78° 28' 27" E) which is collected through the web.