Dr. Manuel Hernandez-Pajares and Dr. Miguel Juan from the Polytechnical University of Catalonia in Barcelona, Spain, have received a one-year Senior Scientist Fellowship from the Spanish government to work with Dr. Dieter Bilitza at NSSDC on incorporating Global Positioning System (GPS) data into the International Reference Ionosphere (IRI). Drs. Hernandez and Juan will share the one-year award and will each come for a half-year time period.
Dr. Manuel Hernandez-Pajares, right with Dieter Bilitza, visited NSSDC to work with IRI and GPS data.
Drs. Hernandez and Juan are experts in extracting ionospheric information from the signals received by the now more than 200 GPS receivers that are part of the International GPS (IGS) network. Their new methods and application to ionospheric storm studies are described in several recent papers in the Geophysical Research Letters and Radio Science.
The ionospheric electron content along the signal path from GPS transmitter to ground receiver can be deduced from the code and phase delay of the GPS dual frequency signals. Some of the code signals are affected by encryption for civilian users (GPS is a system initially designed for military purposes), but for ionospheric purposes this problem can be overcome with certain techniques.
Using tomography and signals received from different elevation angles (that can be also negative for Low Earth Orbiting GPS receivers like the GPS/Meteorology [MET]), a world map of the electron content can be constructed. This map is, of course, affected by the availability and distribution of the IGS ground stations. IRI can be of help in several phases of the map creation process: defining the different layer heights, assisting the tomographic process, providing a background model for defining the sampling box sizes, and interpolating between grid points.
GPS data in turn can help to update IRI to provide a more realistic specification of the ionospheric electron density profile. Such improved predictions will be of great importance for space-weather-related applications of IRI.
Dr. Hernandez-Pajares started his visit at Goddard Space Flight Center on November 4, 1997, and will be joined by Dr. Juan in mid-January 1998 for a brief overlap period.
Erin D. Gardner, email@example.com, (301) 286-0163
Raytheon STX, Code 633, NASA Goddard Space Flight Center
Greenbelt, MD 20771, U.S.A.