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Ann. Geophys., 21, 2083-2093, 2003
www.ann-geophys.net/21/2083/2003/
© European Geosciences Union 2003
Derivation of TEC and estimation of instrumental biases from GEONET in Japan
G. Ma and T. Maruyama
Applied Research and Standards Division, Communications Research Laboratory, 4-2-1 Nukui-kitamachi, Koganei-Shi, Tokyo 184-8795, Japan
Abstract. This paper presents a
method to derive the ionospheric total electron content (TEC) and to estimate
the biases of GPS satellites and dual frequency receivers using the GPS Earth
Observation Network (GEONET) in Japan. Based on the consideration that the TEC
is uniform in a small area, the method divides the ionosphere over Japan into
32 meshes. The size of each mesh is 2° by 2° in latitude and longitude,
respectively. By assuming that the TEC is identical at any point within a given
mesh and the biases do not vary within a day, the method arranges unknown TECs
and biases with dual GPS data from about 209 receivers in a day unit into a set
of equations. Then the TECs and the biases of satellites and receivers were
determined by using the least-squares fitting technique. The performance of the
method is examined by applying it to geomagnetically quiet days in various
seasons, and then comparing the GPS-derived TEC with ionospheric critical
frequencies (foF2). It is found that the biases of GPS satellites and
most receivers are very stable. The diurnal and seasonal variation in TEC and foF2
shows a high degree of conformity. The method using a highly dense receiver
network like GEONET is not always applicable in other areas. Thus, the paper
also proposes a simpler and faster method to estimate a single receiver’s
bias by using the satellite biases determined from GEONET. The accuracy of the
simple method is examined by comparing the receiver biases determined by the
two methods. Larger deviation from GEONET derived bias tends to be found in the
receivers at lower (<30° N) latitudes due to the effects of equatorial
anomaly.
Key words. Ionosphere (mid-latitude
ionosphere; instruments and techniques) – Radio science (radio-wave
propagation)
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