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Eliminating negative VTEC in global ionosphere maps using inequality-constrained least squares
- Source :
- Advances in Space Research
- Publication Year :
- 2013
-
Abstract
- Currently, ground-based Global Navigation Satellite System (GNSS) stations of the International GNSS Service (IGS) are distributed unevenly around the world. Most of them are located on the mainland, while only a small part of them are scattered on some islands in the oceans. As a consequence, many unreasonable zero values (in fact negative values) appear in Vertical Total Electron Content (VTEC) of European Space Agency (ESA) and Center for Orbit Determination in Europe (CODE) IONEX products, especially in 2008 and 2009 when the solar activities were rather quiet. To improve this situation, we directly implement non-negative physical constraints of ionosphere for global ionosphere maps (GIM) with spherical harmonic functions. Mathematically, we propose an inequality-constrained least squares method by imposing non-negative inequality constraints in the areas where negative VTEC values may occur to reconstruct GIM models. We then apply the new method to process the IGS data in 2008. The results have shown that the new algorithm efficiently eliminates the unwanted behavior of negative VTEC values, which could otherwise often be seen in the current CODE and ESA GIM products in both middle and high latitude areas of the Southern Hemisphere (45°S∼90°S) and the Northern Hemisphere (50°N∼90°N). About 64% of GPS receivers’ DCBs have been significantly improved. Finally, we compare the GIM results between with and without the inequality constraints, which has clearly shown that the GIM result with inequality constraints is significantly better than that without the inequality constraints. The inequality-constrained GIM result is also highly consistent with the final IGS products in terms of root mean squared (RMS) and mean VTEC.
- Subjects :
- Atmospheric Science
Total electron content
business.industry
Northern Hemisphere
Aerospace Engineering
Spherical harmonics
Astronomy and Astrophysics
Satellite system
Geodesy
Geophysics
Space and Planetary Science
GNSS applications
Global Positioning System
General Earth and Planetary Sciences
Ionosphere
Orbit determination
business
Remote sensing
Mathematics
Subjects
Details
- Database :
- OpenAIRE
- Journal :
- Advances in Space Research
- Accession number :
- edsair.doi.dedup.....631f861d511d23b05982f9b1d43f3715