Ionospheric TEC observations from TOPEX satellite

Summary form only given. Variability of total electron content (TEC) in the equatorial anomaly region of the ionosphere can be studied extensively using the results of measurements taken by the NASA/CNES satellite, TOPEX/Poseidon, which provides global ocean coverage (0 to 360 degrees longitude, -66 to +66 degrees latitude). The NASA radar altimeter (NRA) is the first spaceborne dual-frequency altimeter capable of accurately measuring vertical ionospheric TEC below 1340 km. TOPEX TEC observations have already been used to support results from an ionospheric measurement campaign that was conducted in equatorial anomaly regions of South America by Phillips Laboratory in Spring, 1994. The best agreement in TEC values is seen during intervals of longitudinal proximity of the satellites´ paths. Vertical measurements from TOPEX are obtained at a rate of one per second at 5.3 and 13.6 GHz. Along the same surface tracks every 10 days during which global ocean coverage is accomplished. TOPEX data records from 9/92 to 9/95 have been processed and reduced to one CDROM disc using one degree averaging over 110 km. Along track for evaluation of TEC measurements. Various plotting programs have been developed to represent the data for observation of TEC values and the occurrence of the equatorial anomaly. To facilitate further TEC studies, interface software has been prepared to provide easy access to specific dates, local times and longitudes with identification of anomaly formation and structure. The TOPEX over-ocean data can be used as a supplement to land based measurements in applications to ionospheric research at low and middle latitudes. This study focuses on comparisons between TOPEX vertical TEC data and GPS equivalent vertical TEC measurements taken near the East and West coastal regions of South America. Also the Phillips Laboratory Global Parameterized Ionospheric Model (PIM) is utilized in an effort to estimate slant to vertical conversion errors.