The Global Positioning System (GPS) radio occultation (RO) technique has been used to receive multi-channel GPS carrier phase signals from low Earth orbiting (LEO) satellites and demonstrate active limb sounding of the Earth's ionosphere. Applying Abel inversion through compensated total electron content (TEC) values, the GPS RO observations can obtain ionospheric electron density (n(e)) profiles and then scale F2-layer characteristics including foF2 and hmF2, especially, hmF2 that cannot be directly deduced from ionosonde observations. From the GPS/MET and FS3/COSMIC missions, we call collect on average two hundred and eighteen hundred vertical n(e) profiles, respectively, within one day. The retrieved foF2 and hmF2 results have been used to produce numerical maps representing complex properties on a world-wide scale. This paper presents a physically appealing representation of foF2 and hmF2 medians based on GPS RO data. The derived numerical maps have also been examined by ground-based ionosonde data.
