Ionosphere/Plasmasphere Imaging Based on GPS Navigation Measurements from CHAMP and SAC-C

Abstract

Ground based GPS measurements are well proved as a powerful tool to monitor the vertical Total Electron Content (TEC) of the ionosphere. The installation of GPS receivers on board of LEO (Low Earth Orbiting) satellites such as CHAMP and SAC-C offers new opportunities of ionospheric remote sensing. Beside the GPS radio occultation measurements both satellites CHAMP and SAC-C are using a dedicated zenith looking antenna to track permanently several GPS satellites for precise orbit determination. These 0.1 Hz sampled navigation measurements provide valuable information on the ionization state of the upper ionosphere and plasmasphere up to GPS altitude on global scale. After preprocessing and calibration, link related TEC measurements are derived from the GPS navigation observations. The three dimensional electron density distribution is reconstructed by assimilating these TEC measurements into the Parameterized Ionospheric Model (PIM) which includes also the Gallagher model of the plasmasphere. Due to the orbit properties of CHAMP and SAC-C there are periods when both satellites circle the earth at nearly the same orbit plane but at different altitudes. We will focus on these constellations which are of special interest for the combined assimilation of TEC measurements from both satellites. In this talk reconstruction results are presented for selected assimilation examples by means of two dimensional slices along the respective CHAMP/SAC-C orbit plane. The assimilation technique will be described briefly. Validation results using electron density measurements from the Langmuir Probe on board CHAMP will be presented.