Ionosphere Monitoring by Ground and Space based GNSS techniques

Abstract

GNSS based ionosphere sounding techniques are well established since the availability of GPS signals in the early nineties. Regional and global TEC maps allow studying horizontal structures and propagation effects of ionospheric perturbations. Accurate TEC maps essentially contribute to mitigate navigation and positioning errors (e.g. WAAS, EGNOS). The GNSS based exploration of the vertical electron density distribution began with the establishment of the GPS radio occultation experiment GPSMET onboard the Microlab-1 satellite mission. Follow-up missions such as CHAMP or SAC–C up to the most recent multi-satellite Formosat-3 mission contribute to further developments of the challenging measurement and retrieval techniques. The talk reviews some specific observations obtained by ground based GNSS monitoring in DLR, and focuses on the use of space based radio occultation measurements in the limb sounding mode and navigation measurements using a zenith viewing GPS antenna. Reported are ground based observation results obtained since more than a full solar cycle over Europe and both high-latitude ionospheres. These observations contribute to explore the physics of ionospheric perturbations caused by changes of the solar irradiation, by particle precipitation, or by amplifying plasma transport processes due to perturbation-induced neutral winds and electric fields. The additional availability of space based GNSS measurements opens new possibilities in studying the physics of perturbation processes. Reported are sample studies as well as statistical results obtained by using GPS measurements onboard CHAMP since 2001 including more than 200,000 electron density profiles from GPS radio occultation measurements. Presented are promising results of a first comparative study of the electron density profiles retrieved from CHAMP and from Formosat -3 data products. A three-dimensional imaging of the electron density distribution near the CHAMP orbit plane between CHAMP and GPS orbit height is performed by using link-related TEC data derived from dual frequency navigation measurements (zenith antenna) onboard CHAMP. These measurements indicate some aspects of the interaction of the solar wind with the global Earth’s atmosphere, thus providing a good opportunity for studying space weather phenomena. The Formosat-3/COSMIC satellite mission provides a great potential for reconstructing the global 3D – ionosphere on a routine basis.