Ionospheric Remote Sensing with the Ionospheric Occultation Experiment (IOX): First Results

The Ionospheric Occultation Experiment (IOX) is a dual-frequency GPS receiver with a single Earth-limb viewing antenna. Ionospheric remote sensing is possible during occultation events in which the line of sight to a GPS satellite being tracked by IOX sets through the Earth's limb. IOX is one of four experiments to be flown as part of the United States Air Force Space Test Program's PICOSat mission, with launch anticipated in early September of 2001. PICOSat will be placed into a 68 degree inclination, 800 km altitude orbit, enabling IOX to make ionospheric measurements at all local times under near-solar maximum conditions over the course of its mission. The IOX instrument will be described together with initial observations obtained from this mission. Plans for data analysis and scientific studies will be discussed. These include (1) cross-validation of UV ionospheric remote sensing techniques through comparisons with data from sensors on TIMED and DMSP F16 (both of which are also expected to launch sometime late in 2001); (2) potential observations of equatorial scintillations using an occultation sensor; (3) evaluation of aspects of the occultation data relevant to space weather prediction or assimilation into ionospheric specification models; and (4) detailed analysis of ionospheric structures through enhanced ionospheric tomography. Enhanced ionospheric tomography evaluations are possible through a combination of IOX data with ground-based observations of a dual-frequency beacon that is one of the other three experiments on PICOSat. Ground-based receiver chains will provide information on horizontal structures which can be combined with occultation measurements of vertical structure to provide a more complete picture of the local ionosphere than is possible with beacon measurements alone, as has been done on previous missions.