Investigation of ionospheric gradients for GAGAN application

Abstract

To cater to the needs of aviation applications, GPS Aided GEO Augmented Navigation (GAGAN) system is being implemented over the Indian region. The most prominent parameter affecting the navigation accuracy of GAGAN is ionospheric delay which is a function of TEC. In the equatorial and low latitude regions such as India, TEC is often quite high with large spatial gradients. Carrier phase data from the GAGAN network of Indian TEC Stations is used for estimating ionospheric gradients in multiple viewing directions. Rate of TEC (ROT) and Rate of TEC Index (ROTI) are calculated to identify the ionospheric gradients. Among the satellite signals arriving in multiple directions, the signals which suffer from severe ionospheric gradients are identified and avoided for improving GAGAN positional accuracy. The outcome of this paper will be helpful for improving GAGAN system performance.

Investigation of the Effect of Ionospheric Gradients on GPS Signals in the Context of Laas

“…The maximum ionosphere slope of 460. 4 [25]. But, at low latitudes, the decorrelation of ionosphere is comparatively large, this is evident from the data analysis.…”

“…For example, Figure 16 shows the MIEVs obtained for nC 4 combinations at an epoch (9.35 Hrs LT) on 9th March 2012 for which the MIEV is 184.4 m due to 'all-in-view' satellites. At this epoch, it is observed that the number of total visible satellites are '11' (SV PRN 1, 3, 6, 11, 14, 16, 20, 21, 30, 31 and 32) at this epoch.…”

“…The vertical delay estimation due to the models at the user's Ionospheric Pierce Point (IPP) will be in error if any of the satellite signals get affected due to ionospheric irregularity. Especially, the ionosphere above the Indian subcontinent, which is located near the equatorial region, is highly volatile and varies both temporally and spatially [2][3][4]. In general the rate of change of Total Electron Content (TEC) over short distance (∼100 km) is very small [5].…”

Investigation of the relationship between the spatial gradient of total electron content (TEC) between two nearby stations and the occurrence of ionospheric irregularities

“…The spatial gradient of TEC utilized in this study was computed using Eq. (1) (Lee et al, 2007;Ravi Chandra et al, 2009;Cesaroni et al, 2015).…”

“…Recently, Seba et al (2018) investigated the relationship between equatorial ionization anomaly and nighttime ESF over the East Africa longitudinal sector using data from ground-based Global Positioning System (GPS) stations and a horizontal meridional neutral wind model. To identify signals which suffer severely from the ionospheric gradient, Ravi Chandra et al (2009) andRungraengwajiake et al (2015) used rate of change of TEC (ROT) and rate of change of TEC index (ROTI). From the definition, however, ROTI mixes both the spatial and temporal gradients of TEC variations.…”