Relationships between GPS-signal propagation errors and EISCAT observations

Abstract

Abstract. When travelling through the ionosphere the signals of space-based radio navigation systems such as the Global Positioning System (GPS) are subject to modifications in amplitude, phase and polarization. In particular, phase changes due to refraction lead to propagation errors of up to 50 m for single-frequency GPS users. If both the L1 and the L2 frequencies transmitted by the GPS satellites are measured, first-order range error contributions of the ionosphere can be determined and removed by difference methods. The ionospheric contribution is proportional to the total electron content (TEC) along the ray path between satellite and receiver. Using about ten European GPS receiving stations of the International GPS Service for Geodynamics (IGS), the TEC over Europe is estimated within the geographic ranges!20°4 440°E and 32.5°4 470°N in longitude and latitude, respectively. The derived TEC maps over Europe contribute to the study of horizontal coupling and transport processes during significant ionospheric events. Due to their comprehensive information about the high-latitude ionosphere, EISCAT observations may help to study the influence of ionospheric phenomena upon propagation errors in GPS navigation systems. Since there are still some accuracy limiting problems to be solved in TEC determination using GPS, data comparison of TEC with vertical electron density profiles derived from EISCAT observations is valuable to enhance the accuracy of propagation-error estimations. This is evident both for absolute TEC calibration as well as for the conversion of ray-path-related observations to vertical TEC. The combination of EISCAT data and GPS-derived TEC data enables a better understanding of large-scale ionospheric processes.

Unusual topside ionospheric density response to the November 2003 superstorm

“…The vertical dashed lines indicate the longitude sectors where tomographic imaging is performed. sight between the satellite and the receiver (slant TEC) is calibrated from instrumental biases [e.g., Mannucci et al, 1998;Yizengaw et al, 2004] and then mapped to the vertical using a single spherical shell layer approximation of the ionosphere at h sp = 400 km altitude [e.g., Jakowski et al, 1996].…”

Comparison of temporal fluctuations in the total electron content estimates from EISCAT and GPS along the same line of sight

“…GPS TEC estimates as from TEC maps were then compared with EIS-CAT TEC within an overlapping region. The EISCAT TEC was obtained by integration of CP3 electron density profiles from about 150 km to about 500 km height and then verticalised at ionospheric pierce points by means of a mapping function (Jakowski et al, 1996). The results indicated larger GPS TEC as compared with EISCAT TEC values, given the geometry considered, which suggested a plasmaspheric contribution not captured by the radar, yet present on GPS radio signals (Jakowski et al, 1996).…”

“…A different analysis showed a comparison between EIS-CAT TEC obtained by integration of electron density profiles and verticalised GPS TEC from nearly co-located stations, with equivalent ionospheric pierce points overlapping the area covered by EISCAT (Jakowski et al, 1996). In that case, EISCAT was operated in a scanning mode (CP3) and electron density profiles were measured at different latitudes between 62 and 78 • N during a 30 min north-south scan.…”

First estimates of the second‐order ionospheric effect on radio occultation observations

“…Given that a typical ionospheric RO event lasts ∼ 1000 s, then the cumulative multipath-induced STEC would be <0.5 TECU. Additionally, it should be mentioned that the multipath effect in carrier-phase GPS measurements is two orders of magnitude smaller than that of the pseudo-range measurements [e.g., Jakowski et al, 1996;Byun et al, 2002;Kuang et al, 2008]. Simulating the local multipath is not the scope of this contribution, and we refer the reader to Byun et al [2002] for a more detailed description on existing theoretical models on local multipath simulators from reflecting surfaces.…”