Comparison of ionospheric total electron content from the Navy Navigation Satellite System and the GPS

Abstract

Abstract. About 25,000 total electron content (TEC) values obtained in 2 years from Navy Navigation Satellite System (NNSS) differential Doppler were compared with the corresponding TECs obtained from the Global Positioning System (GPS). The method by which the comparison is effected is also described. The resulting statistics are very effective in showing a good agreement between the two techniques. The GPS TEC results are statistically larger than NNSS TEC, namely, 3 _+ 1 TEC units; the lower quartile of the differences is always greater than zero. IntroductionAn effective tool for calculating total electron content (TEC) is the differential Doppler method. At present, this is practically the only method provided by satellite navigation systems.Basically, this method relies on measuring the differential phase between two coherent carriers transmitted by satellite and scaled to the same nominal frequency. This facility is provided by all satellite navigation systems as a tool for correcting the delays introduced by the ionosphere. In a first-order approximation, a signal of given carrier frequency f undergoes a phase delay resulting from the contribution of two terms: One, due to the nondispersive terms (geometrical distance and troposphere), is proportional to f; the second, the dispersive one, is inversely proportional to f, depending on the electrons contained in a unitary column along the path (TEC). This T tropospheric contribution to the electromagnetic path; TEC total electron content (electrons m-2).A suitable combination of two phases observed at different frequencies, arranged in such a way as to eliminate the nondispersive terms, provides a direct evaluation of the TEC as described bywhere d is the measured differential phase (differential Doppler), /3 is a term resulting from the phase ambiguity, and C a is a constant, depending on the way in which the signals have been combined. Here as follows, phases will be expressed in equivalent TEC units (TEC unit -1016 m-2), so that Ca is 1.It must be emphasized that (1) and, consequently, (2) hold for time spans during which the phases of the two carriers have been observed with continuity without fading (maximum probability of cycle slips) or signal loss: At each occurrence of these events, a new /3 must generally be used. Detection and resolution of such events, in order to arrive at a single value of/3 for the whole satellite pass, are carried out during the preprocessing of the data, and here as follows, it is assumed that this problem has been solved. The only remaining problem in evaluating TEC is the determination of the phase ambiguity/3.Practically all the techniques used to solve this problem assume the possibility of comparing measurements of TEC taken along different paths with a certain common ionospheric quantity. This quantity is the vertical ionospheric content V. The model used in this work, in order to fulfill this requirement, is a simple one, as it assumes that the ionosphere is limited to a slab of infinitesimal width located at a 1071

Time-dependent prediction degredation assessment of neural-networks-based TEC forecasting models

“…On the other hand, this could be due to the fact that both TEC and foF2 exhibit stronger variability during the equinoxes (Kouris et al, 1999). It is also known that the foF2 and TEC variabilities differ, to some extent at least due to the fact that the topside ionosphere and influences from the plasmasphere above the F2-region are important contributors to the TEC (Ciraolo and Spalla, 1997). If this is taken into account, then the error increase seems reasonable.…”

“…The use of neural networks to predict values of ionospheric peak electron density or foF2 is now well established (Xenos, 2002). However, the variability of TEC is not governed by exactly the same factors as foF2, since important contributors to the TEC are also the topside ionosphere and influences from the plasmasphere above the F2-region (Ciraolo and Spalla, 1997).…”

Observations of quiet-time moderate midlatitude L-band scintillation in association with plasma bubbles

“…In order to investigate the presence of electron density gradients leading to the occurrence of scintillation, the Slant TEC (STEC) values recorded by the receiver at every minute interval are used to estimate the Rate of TEC (ROT), i.e., temporal change in STEC. The latitude and longitude of the ionospheric pierce point (IPP) for the different ray paths have been calculated assuming a thin single shell ionospheric model at an altitude of 350 km (Ciraolo and Spalla 1997).…”

Morphological and spectral characteristics of L-band and VHF scintillations and their impact on trans-ionospheric communications

“…In the conversion of vertical TEC, the ionosphere and the protonosphere were assumed as spatially uniform thin shells, and the height of the centroid of ionization of mass distribution was taken as the Ionospheric Pierce Point (IPP). In the present study, the TEC variations during the presence of scintillations at the GPS-L1 frequency of 1.575 GHz, the IPP height is taken as 350 km (Davies and Hartmann, 1997;Goodwin et al, 1992;Ciraolo and Spalla, 1997) and the mapping function, assuming the ionosphere as a homogenous thin shell, is used in the conversion of slant TEC to vertical TEC. The bias of the receiver is determined by observing the diurnal variation of TEC at Waltair, and fixing the minimum value by averaging the 3 to 4 hr of data around the day minimum, which is further validated using the bottom-side electron content derived from ionosonde data and topside electron content from the IRI model.…”