*Guanyi Ma[1]
,Takashi Maruyama [1]
Communications Research Laboratory[1]
In order to monitor the progress in ionospheric storms with maps
of ionospheric total electron content (TEC) in real time, a global
positioning system (GPS) network over Japan is being established
by Ionosphere and Radio Propagation group of Communications Research
Laboratory (CRL). As a part of the project, an algorithm is being
developed to get absolute TEC maps with GPS network. This study
is a simulation of potential of monitoring ionospheric storm
by deriving TEC from GPS observations. A period of Apr. 19-28,
2001 was selected, during which an ionospheric storm occurred.
The GPS data was from GPS Earth Observation Network (GEONET)
of Geographical Survey Institute, Japan. The absolute TEC is
estimated by removing satellite and receiver biases with least
squares fitting technique. The evaluation of the GPS-derived
TEC, and the behavior of the storm over Japan will be discussed,
by comparison with ionosonde foF2 observations.
In order to monitor ionospheric weather, especially the progress in ionospheric storms with maps of ionospheric total electron content (TEC) in real time, a global positioning system (GPS) network over Japan is being established by Ionosphere and Radio Propagation group of Communications Research Laboratory (CRL). As a part of the project, an algorithm is being developed to produce absolute ionospheric vertical TEC maps with GPS network. This study is a simulation of potential of monitoring ionospheric storm by deriving TEC from combined GPS pseudo-ranges and phases observations. A period of Apr. 19 to 28, 2001 was selected, during which an ionospheric storm occurred. The GPS data was downloaded from GPS Earth Observation Network (GEONET) of Geographical Survey Institute, Japan. Nearly 200 TOPCON receivers are used in the study, which give precise code (P code) psudoranges (P1 and P2) at both frequencies. The differenced pseudoranges, P2-P1, and the differenced carrier phases, L1-L2, are used to obtain "slant" path TECS between the GPS receiver and satellite. TECS contains biases intrinsic to receiver and satellite. In order to estimate absolute vertical TEC from TECS, the ionosphere is assumed to be a shell with a height of 400 km, then the ionosphere over Japan is partitioned into 32 meshes. For those slant path TECSs which go through the same mesh, their vertical components (that is, TECs) are assumed to be the same. The absolute TEC a different meshes for one day is derived with least squares fitting technique, and the biases of satellites and receivers are estimated at the same time. With the procedure described above, the ionospheric storm occurred on Apr. 23 is successfully detected. By comparison with ionosonde foF2 observations, the evaluation of the GPS-derived TEC, and the behavior of the storm over Japan will be discussed.