The Global Ionospheric Monitoring and Forecasting System (GIMSYS) computer program generates global maps of the total electron content (TEC) (electron density integrated over all altitude) of the ionosphere, maps of ionospheric irregularities, and related data byproducts. The maps are generated primarily from signal-propagation measurements taken by more than 100 continuously operating two-frequency Global Positioning System (GPS) receivers in a world-wide network. GIMSYS interpolates the measurements temporally and spatially generating a global TEC map every 15 minutes. When updating the map with new measurements, GIMSYS uses a Kalman filter and stochastic estimation to obtain an optimal combination of the measurements with constraints derived from ionospheric physics and empirical ionospheric models. By applying time-series analysis to recent TEC maps, GIMSYS can also generate forecast TEC maps that are reasonably accurate for 2 to 4 hours. The numerous actual and potential users of the data products of GIMSYS include military, industrial, and academic organizations concerned with radio communication, navigation, mapping, scientific observations, and effects of ionospheric storms on power-distribution systems.

This program was written by Ulf J. Lindqwister; Charles D. Edwards, Jr.; Ron Muellerschoen; Xiaoqing Pi; Anthony J. Mannucci; Lawrence Sparks; Thomas Runge; Byron A. Iijima; Mark Reyes; and Brian Wilson of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at under the Software category.

This software is available for commercial licensing. Please contact Don Hart of the California Institute of Technology at (818) 393-3425. Refer to NPO-20460.