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Ionospheric Delay Measurements Using GPS Satellite Signals,

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The ionospheric group delay associated with GPS satellite signals is usually compensated by use of a wavelength squared formula. Using this relationship the typical GPS receiver minimizes the ionospheric effects by tracking both the L1 and L2 signals and correcting the navigation solution with the two frequency measurements independent of the ionosphere or carrier frequency. Normally, these compensations are performed in the navigation software and the ionospheric group delay values are not specifically characterized or accessible to the user. This level of functionality is sufficient if the operator desires only navigation data. However, the ionospheric delay may be useful for other purposes and could be provided to the user if the receiver and navigation software were appropriately designed. A receiver employing distinct tracking loops for Range and TEC dynamic estimation can directly supply the navigation function with ionosphere corrected ranges and interested observers with the ionospheric delay parameters directly from the L-band tracking process. Further, this receiver can track the time varying nature of the ionosphere and provide continuously corrected ranges to the navigation function in times of highly distressed disturbances. A GPS receiver manufactured by Texas Instruments for the Space Systems Division of the Air Force Systems Command has this capability. The receiver is capable of tracking L1 and L2 simultaneously on six satellites and, as a byproduct of its design, outputs L1 excess delay and delay rate directly. This receiver has been used to obtain L1 excess delay data spanning several months during 1989 through measurements from L1 and L2 on GPS satellites.

Subject Categories:

  • Atmospheric Physics
  • Radiofrequency Wave Propagation

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