4-D Simulations of Ionospheric Tomography

Bruce M. Howe

Abstract:	Data from the Global Positioning System (GPS) can be used to map the global distribution of electron den- sity in the earth’s ionosphere. Improved estimates of the ionosphere can, in turn, be used to improve lpo- sition estimates. Using a four-dimensional model of ionosphere perturbations, simulations are made of a tomography system based on data from GPS and a low earth-orbiting satellite (LEO). The spatial struc- ture is parameterized in terms of empirical orthogo- nal functions in the vertical and spherical harmonics in the horizontal. The horizontal covariance structure is specified by variance and correlation length scales as functions of latitude and longitude. Time depen- dence is modeled as a first-order Markov process with a 6-hour time scale and random forcing. A sun-fixed coordinate system is used so that ionospheric features are more steady in time. A Kalman filter is used to ob- jectively assimilate the simulated data into the sim.ple time-dependent model; in addition to solving for the three-dimensional ionosphere at each time step, the procedure solves for instrument clock biases. The sim- ulations show that the first three vertical modes (can be well resolved.
Published in:	Proceedings of the 1997 National Technical Meeting of The Institute of Navigation January 14 - 16, 1997 Loews Santa Monica Hotel Santa Monica, CA
Pages:	269 - 278
Cite this article:	Howe, Bruce M., "4-D Simulations of Ionospheric Tomography," Proceedings of the 1997 National Technical Meeting of The Institute of Navigation, Santa Monica, CA, January 1997, pp. 269-278.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In