The effect of the protonosphere on the estimation of GPS total electron content: Validation using model simulations

Abstract

Abstract. Simulated observations of total electron cornera (TEC) along ray paths from Global Positiomng System (GPS) satellites have been used to validate the estimation of TEC using GPS measuremeres. The Sheffield Umversity plasmasphere ionosphere model (SUPIM) has been used to create electron densities that were integrated along ray paths from actual configurations of the GPS constellation. The resultant slant electron contents were then used as inputs to validate the self-calibration of pseudo-range errors (SCORE) process for the deternfination of TEC from GPS observations. It is shown that if the plasma resides only in the ionosphere below 1100 km, then the SCORE procedure determines the TEC to a high degree of accuracy. When the contribution of the electrons in the protonosphere above 1100 km is included, the analysis results in TEC estimates that are high by some 2 TEC umts (TECU) for conditions appropriate to European nfidlatimdes at solar nfimmum However, if a restriction is placed in the analysis on use of observations equatorward of the station, then allowance can be made for the effect of the proionosphere. It is shown that with appropriate selection of the boundary for the observations, TEC can be estimated by SCORE to better than 1 TECU for the conditions of the simulation. Sample results are included from actual experimemal observations using GPS to demonstrate the effect of compensation for the protonosphenc plasma.

Accuracy analysis of the GPS instrumental bias estimated from observations in middle and low latitudes

“…4. Other research has found that the distribution of the plasmaspheric electron content along the meridional line has a significant effect on TEC and GPS instrumental bias estimation, and the accuracy of the instrumental bias can be improved by properly considering the distribution of the plasmaspheric electron content (Lunt et al, 1999;Mazzella et al, 2002Mazzella et al, , 2007Mazzella et al, , 2009Anghel et al, 2009;Carrano et al, 2009). Based on this improvement the distribution of the plasmaspheric electron content was estimated using GPS measurements (Mazzella et al, 2002(Mazzella et al, , 2007Anghel et al, 2009;Carrano et al, 2009).…”

“…4 gradually increases and the accuracy becomes worse with latitude decreasing. Certainly, the influence of the distribution of the plasmasphere along the meridional line in the lower latitude on the estimation of the instrumental bias should also be noted (Lunt et al, 1999;Mazzella et al, 2007). Although this brings about the complication for the interpretation of these results, further study to distinguish their influences can increase undoubtedly the accuracy of the ionospheric and plasmaspheric TEC from GPS observations.…”

“…The instrumental biases (including satellite and receiver) and vertical TEC in Eq. (5) can be determined using the selfcalibration of pseudo-range errors (SCORE) process (Lunt et al, 1999). The basic concept in the SCORE process is that when the IPP-derived line between two satellites and a receiver arrive at the same moment at a same point, that is, when a so-called conjunction occurs, the vertical TECs at the two IPP derived using Eq.…”

“…This assumption undoubtedly introduces error during the derivation process of vertical ionospheric TEC from GPS data. Another basic ionospheric condition assumes the ionospheric variation stable in the sun-fixed coordinate system, or the ionosphere should exhibit smooth temporal and spatial variation (Sardon et al, 1994;Sardon and Zarraoa, 1997;Ciraolo et al, 2007;Ma and Maruyama, 2003;Lunt et al, 1999). This assumption is satisfied in most situations, but in some special ionospheric conditions or in some special ionospheric regions, the error of this ionospheric assumption is larger.…”

“…It is found that the standard deviation of instrumental biases during active geomagnetic days is obviously larger than that during the quiet days, and this deviation can degrade the accuracy of ionospheric TEC derived from GPS observations. The significant effect of the asymmetrical distribution of the plasmaspheric electron content on the GPS instrumental bias estimation has been studied, and it is found that the accuracy of ionospheric TEC increases if considering the plasmaspheric electron content meridional distribution during bias estimation (Lunt et al, 1999;Mazzella et al, 2002). Besides the latitude-related distribution of the plasmasphere, the ionospheric electron content also exhibits an obvious asymmetrical distribution along the meridional line related to the Equatorial Ionospheric Anomaly (EIA) that strongly controls the variation of the low latitude ionosphere.…”