A study of the spatial density distribution in the topside ionosphere and plasmasphere using the FedSat GPS receiver

The spatial electron density distribution observations using the Global Positioning System (GPS) receiver onboard, the Australian research micro satellite FedSat, are being used to investigate more detailed information about the topside ionospheric and plasmaspheric density distribution than can be obtained using ground based receivers. This is because with ground based receivers, the topside ionosphere and the plasmasphere contribute only a small fraction to the total electron content and so the measurements are dominated by the higher ionospheric structure at the F2 peak. Being in a polar Low-Earth Orbit (LEO), and with a GPS Total Electron Content (TEC) sampling rate of 10 s, FedSat is capable of covering a large area of interest within short period of data sampling period which is very important to obtain realistic electron density profiles of the topside ionosphere and plasmasphere. The GPS data from FedSat can be divided into two types: GPS below-the-horizon data that is recorded when FedSat detects GPS signals that have traversed the ionosphere below FedSat's orbiting height, GPS above-the-horizon data that is recorded when FedSat receives signals that have crossed the ionosphere above its orbiting height. FedSat's GPS below-the-horizon data can be used to supplement ground based GPS data to provide tomographic reconstruction with better resolution. FedSat's GPS above-the-horizon data can be used by itself to obtain the electron density distribution of the topside ionosphere and plasmasphere using tomographic reconstruction technique. For this paper we have used only above-the-horizon data to obtain the topside ionospheric electron density distribution during both geomagnetically quiet and severe storm-time conditions. (c) 2006 COSPAR. Published by Elsevier Ltd. All rights reserved.