As signals emitted by global navigation satellite systems (GNSS) propagate toward users on or near the surface of the Earth, they experience delay due to the presence of charged particles in the ionosphere. Currently, ionospheric delay is the largest source of GNSS positioning error. To guarantee the safety of airline navigation based upon GNSS signals, satellite-based augmentation systems have been developed to ensure the accuracy, integrity, availability, and continuity of user position estimates derived from GNSS measurements.

In the United States, the Wide Area Augmentation System (WAAS) of the Federal Aviation Administration (FAA) measures the ionospheric slant delay of signals propagating from Global Positioning System (GPS) satellites to multiple, dual-frequency receivers distributed across North America in a network of 38 reference stations. To allow the user to correct for the error due to ionospheric delay, WAAS derives from these measurements a vertical delay estimate at each ionospheric grid point (IGP) on a specified grid; this delay is designated the ionospheric grid delay (IGD) at that IGP. In addition, WAAS derives the grid ionospheric vertical error (GIVE) at each IGP from inflated and augmented values of the formal estimation error. GIVEs protect the user from the effects of delay estimation error resulting from ionospheric irregularity, both sampled and undersampled. The Ionospheric Slant TEC Analysis using GNSS-based Estimation (IonoSTAGE) software package is a Matlab platform for performing analysis and visualization of ionospheric slant total electron content (TEC) using measurements of GNSS. IonoSTAGE requires Matlab version 7.7 or later for execution.

IonoSTAGE provides three fundamental capabilities: (1) estimation of ionospheric slant TEC along arbitrary ray paths, based upon fits of historical GNSS data; (2) calculation of the WAAS ionospheric threat model; and (3) calculation of the IGDs and the GIVEs that are broadcast by WAAS for a given set of observational data. In addition, IonoSTAGE contains various scripts that serve as tools for analyzing the behavior of ionospheric TEC and for optimizing WAAS performance. IonoSTAGE computations have been used by the FAA to validate the ionospheric threat model for WAAS’s initial operating capability and for three successive upgrades.

This work was done by Lawrence C. Sparks, Anthony J. Mannucci, and Attila Komjathy of Caltech for NASA’s Jet Propulsion Laboratory.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:

Innovative Technology Assets Management
Mail Stop 321-123
4800 Oak Grove Drive
Pasadena, CA 91109-8099
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Refer to NPO-43504.

This Brief includes a Technical Support Package (TSP).
Ionospheric Slant TEC Analysis Using GNSS-Based Estimation (IonoSTAGE)

(reference NPO-43504) is currently available for download from the TSP library.

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This article first appeared in the August, 2014 issue of NASA Tech Briefs Magazine.

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