Present Status and Future Prospects for Ionospheric Propagation Corrections for Precise Time Transfer Using GPS
PHILLIPS LAB HANSCOM AFB MA
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The ionosphere can be the greatest variable source of error in precise time transfer using GPS satellites. For single frequency GPS users the iono spheric correction algorithm can provide an approximate 50 r.m.s. correction to the time delay, but users who desire a more complete correction must make actual measurements of ionospheric time delay along the path to the GPS satellite. Fortunately, at least three commercial GPS receivers, specifically designed to measure and correct for ionospheric time delay, are now, or soon will be, available. Initial operation with two different types of GPS iono spheric receivers has demonstrated a high degree of accuracy in measuring the ionospheric group delay. Results of these measurements will be presented. For those who use a model to correct for ionospheric time delay, it is tempting to use daily values of solar 10.7 cm radio flux to correct a monthly average ionospheric time delay model for each days operation. The results of correlation of daily maximum ionospheric time delay against solar radio flux values show a poor correction will be obtained by this procedure. Prospects for improving ionospheric corrections during the declining phase of the present solar cycle will he discussed.
- Navigation and Guidance
- Radiofrequency Wave Propagation