Accession Number : ADP009131

Title :   Ionospheric Corrections to Precise Time Transfer Using GPS,

Corporate Author : HAHNEMANN UNIV SCHOOL OF MEDICINE PHILADELPHIA PA

Personal Author(s) : Snow, Robert W. ; Osborne, Allen W., III ; Klobuchar, John A.

Report Date : 02 DEC 1993

Pagination or Media Count : 7

Abstract : The free electrons in the earth's ionosphere can retard the time of reception of GPS signals received at a ground station, compared to their time in free space, by many tens of nanoseconds, thus limiting the accuracy of time transfer by GPS. The amount of the ionospheric time delay is proportional to the total number of electrons encountered by the wave on its path from each GPS satellite to a receiver. This integrated number of electrons is called Total Electron Content, or TEC. Dual frequency GPS receivers designed by Alien Osborne Associates, Inc. (AOA) directly measure both the ionospheric differential group delay and the differential carrier phase advance for the two GPS frequencies and derive from this the TEC between the receiver and each GPS satellite in track. The group delay information is mainly used to provide an absolute calibration to the relative differential carrier phase, which is an extremely precise measure of relative TEC. The AOA Mini-Rogue ICS-4Z and the AOA TurboRogue ICS-400OZ receivers normally operate using the GPS P code, when available, and switch to cross-correlation signal processing when the GPS satellites are in the Anti-Spoofing (A-S) mode and the P code is encrypted. An AOA ICS-Z receiver has been operated continuously for over a year at Hanscom AFB, MA to determine the statistics of the variability of the TEC parameter using signals from up to four different directions simultaneously. The 4-channel ICS-4Z and the 8-channel ICS-400OZ, have proven capabilities to make precise, well calibrated, measurements of the ionosphere in several directions simultaneously.

Descriptors :   *CORRECTIONS, *DELAY, *RADIO SIGNALS, *TIME INTERVALS, ACCURACY, ARTIFICIAL SATELLITES, AUTOMATIC, CALIBRATION, CHANNELS, CROSS CORRELATION, FREE ELECTRONS, GROUND STATIONS, MEASUREMENT, OPERATION, PARAMETERS, PATHS, PHASE, RECEIVERS, RECEPTION, SIGNAL PROCESSING, TIME, GLOBAL POSITIONING SYSTEM.

Subject Categories : Radiofrequency Wave Propagation

Distribution Statement : APPROVED FOR PUBLIC RELEASE