Mapping the low-latitude lonosphere with GPS. (Innovation).

Since the late 1980s various research groups have been investigating the behavior of the ionosphere using GPS data. These investigations are based on the total electron content (TEC) measurements derived from dual-frequency GPS observations taking advantage of the dispersive nature of the ionospheric medium. Currently, there is a large number of GPS receivers in continuous operation worldwide. Even though numerous, these stations are unevenly distributed, being situated mostly in the Northern Hemisphere. The relatively smaller number of GPS receivers in the Southern Hemisphere, and consequently the reduced number of available TEC measurements, results in less accurate ionospheric modeling for this region.

In this month's column, an international team of researchers describes how they are using GPS data from the Rede Brasileira de Monitoramento Continuo do Sistema GPS (RBMC, the Brazilian Network for Continuous Monitoring of GPS) and other stations to assess the behavior of the ionosphere above South America and neighboring regions.

Mariangel Fedrizzi is a Ph.D. student at the Instituto Nacional de Pesquisas Espaciais (INPE), Sao Jose dos Campos, Brazil, where she received her Master's degree in space geophysics in 1999. Currently, she is a visiting graduate student at the University of New Brunswick (UNB) in Fredericton, Canada, under the supervision of Dr. Richard Langley. She has worked on ionospheric studies using GPS data since 1997. Eurico de Paula is the chief of INPE's Aeronomy Division. He received his Ph.D. at INPE in 1986. His areas of interest are GPS amplitude scintillations, using VHF coherent radar to study ionospheric irregularities, and analyzing TEC behavior during geomagnetic storms over South America. Ivan Kantor is chief of INPE's Antarctic Development Project. He received his Ph.D. at Rice University in 1972. He is currently studying storm-induced TEC behavior. Richard Langley is a professor in the Department of Geodesy and Geomatics Engineering at UNB, where he has been teaching and supervising student research sin ce 1981. He has a B.Sc. in applied physics from the University of Waterloo and a Ph.D. in experimental space science from York University, Toronto. Marcelo Santos is an associate professor in the Department of Geodesy and Geomatics Engineering at UNB. He holds an M.Sc.E. in geophysics from the National Observatory in Rio de Janeiro, and a Ph.D. in geodesy from UNB. His research is in the fields of geodesy and navigation. Attila Komjathy is currently a technical staff member at the NASA Jet Propulsion Laboratory specializing in atmospheric and ionospheric remote sensing techniques using GPS. He received his Ph.D. from the Department of Geodesy and Geomatics Engineering at UNB in 1997 with a dissertation on ionospheric total electron content mapping using GPS.

Despite significant recent progress in studies of the behavior of the ionosphere, there are still many questions to be investigated in order to achieve a better understanding of the energy coupling processes between the Sun and the Earth. Various observing techniques, such as transionospheric radio signals, ionosonde measurements and incoherent scattering radars, have been used to study ionospheric behavior during both magnetically quiet and disturbed periods. However, previous ionospheric studies were based mainly on measurements obtained either from a single station or a local network of instruments. On a global scale, isolated orbiting satellites carrying ionospheric sensors also were not able to monitor ionospheric behavior due to the lack of instantaneous worldwide coverage.

The understanding of the coupling processes between the magnetosphere and the ionosphere-thermosphere requires a global monitoring …