Lower ionospheric detection by using radio occultation signal to noise ratio data

With the advent of global positioning system (GPS), radio occultation (RO) technique has been used to investigate planetary atmosphere and begins to obtain the profiles of Earth's atmospheric parameters. In 2006, Taiwan launched six low Earth orbit (LEO) satellites as a RO constellation mission, known as FORMOSAT-3/COSMIC (F-3). The release data of F-3 per day is 1500~2500 set for neutral atmosphere and the coverage is from near surface to several tens more than 100 km in altitude. In the one third to half of the F-3 release data, the signal to noise ratio (SNR) profile has the perturbation near 100 km in altitude, which is the ionospheric E region and F region occuring altitude. In this study, the analysis method of the perturbation is developed,and the distribution of the perturbation is constructed with the global coverage of the RO data. Furthermore, the relation between the perturbation and lower ionosphere is also be studied by using ray tracing method based on geometrical optics.