HR: 1400h
AN: SP32A-02
TI: A Study on the Fluctuation of the Terrestrial Ionosphere for the Radio Occultation Measurements of
Planetary Ionospheres
AU: * Noguchi, K
EM: nogu@bochan.ted.isas.ac.jp
AF: The Institute of Space and Astronautical Science, 3-1-1, Yoshinodai, Sagamihara, 229-8510
Japan
AU: Imamura, T
EM: ima@bochan.ted.isas.ac.jp
AF: The Institute of Space and Astronautical Science, 3-1-1, Yoshinodai, Sagamihara, 229-8510
Japan
AU: Oyama, K
EM: oyama@bochan.ted.isas.ac.jp
AF: The Institute of Space and Astronautical Science, 3-1-1, Yoshinodai, Sagamihara, 229-8510
Japan
AB:
We focus on the fluctuation of the terrestrial ionosphere, which is a serious error source when we try to obtain the
information on planetary ionospheres by the radio occultation measurement. We are preparing for the radio occultation
measurements of the Martian atmosphere and the lunar ionosphere by using the spacecrafts Nozomi and Selene, respectively. By
using the radio occultation method, we can measure the electron densities in planetary ionospheres. The phase of the radio
wave transmitted from the spacecraft to the Earth is perturbed when the radio wave passes through the planetary ionosphere.
The electron density profile can be derived from the phase perturbation. The information on the nightside ionosphere of Mars is based on the observations by the Mars 4 and 5 and the Viking
orbiter. The detection of the lunar ionosphere by radio occultation technique was reported in the Luna 22 mission. Since the
phase shift caused by the fluctuation of the terrestrial ionosphere is comparable with those by the Martian nightside
ionosphere and the lunar ionosphere, the detection of these ionospheres is difficult in general. The fluctuation of the
terrestrial Total Electron Content (TEC) along the ray path between the spacecraft and the receiving station will be
estimated from two coherent signals transmitted from several Global Positioning System (GPS) satellites. We can obtain the
TEC information over Japan from the GPS network of the Geographical Survey Institute (GSI) in Japan, GPS Earth Observation
Network (GEONET). The possibility of the detection of the Martian nightside ionosphere and the lunar ionosphere at each local time is
investigated for the summer and winter cases by using the TEC data obtained by the GPS network. The result indicates that the
Martian nightside ionosphere and the lunar ionosphere can be measured if we choose suitable conditions of the terrestrial
ionosphere for the measurement and monitor the fluctuation of the terrestrial ionosphere along the ray path of the radio
occultation by using the GPS network. There are several ways to estimate the TEC fluctuation of the terrestrial ionosphere by using the GPS network. In
general, it is difficult to find a GPS satellite-ground receiver pair whose ray path is close to the ray path of the radio
occultation measurement of the planetary atmosphere. Therefore, we develop a method to estimate the TEC fluctuation of the
terrestrial ionosphere along the ray path of the radio occultation by many GPS satellite-ground receiver pairs. The
DE: 2435 Ionospheric disturbances
DE: 2459 Planetary ionospheres (5435, 5729, 6026, 6027, 6028)
SC: SP
MN: WPGM Meeting 2000