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Several systematic effects that can influence SBAS and GPS time transfers are discussed. These include: ionospheric delays, multipath, and signal-to-noise ratio. Estimates for the magnitude of these effects are given., See also ADM001507. Presented at Annual Precise Time and Time Interval (PTTI) Planning Meeting (34th), held on 3-5 December 2002, in Reston, VA. The original document contains color images.

The FAA is currently developing the Wide Area Augmentation System (WAAS), a GPS Satellite-based Augmentation System (SBAS) that will be used for navigation within the National Airspace System (NAS). WAAS consists of a multitude of ground reference stations and several geo-stationary communication satellites. The geo-stationary satellites will be broadcasting a "GPS"-like signal that can be used as a supplementary navigational signal and that will also contain GPS health status and correction data. The WAAS also offers a significant tool to the timing community. There are several unique advantages of using the WAAS or any SBAS for frequency and time transfer: (1) The geo-stationary satellites are always in view. They never set like the GPS and GLONASS satellites. This offers the ability for multiple sights to be permanently "phase-locked" together by locking themselves to the common WAAS signal. (2) They do not have any intentional distortions like the GPS SA dither. (3) WAAS system computes and broadcasts orbit and clock corrections for all GPS satellites in view thereby substantially removing the effects of SA on GPS. (4) The geo-broadcast signals are cesium-based, generated and controlled by the WAAS network of cesium-based GPS receivers. (5) The WASS network computes a real-time observational ionospheric delay model for the coverage area. This model is broadcast over the WASS signal so that an L1 single frequency user can make local corrections. This paper describes an initial attempt at time transfer using the WAAS test transmissions currently broadcast from the INMARSAT Atlantic Ocean Region - West (AOR- W) satellite. The clocks being compared are the master clock at USNO Washington and the master clock at NRC Ottawa. A 30-day data set is examined. It was obtained from dual frequency GPS/WAAS NovAtel receivers that were set up at both institutions. Comparisons are made between UTC(USNO), UTC(NRC), GPS time, and WAAS Network Time (WNT)., See also ADM001481. Presented at the Annual Precise Time and Time Interval (PTTI) Meeting (31st), held in Dana Point, CA on 7-9 December 1999. Published in the proceedings of the meeting, p191-202, 1999. Prepared in collaboration with NovAtel, Inc., Calgary, Alberta; Innovative Solutions International, Inc., Vienna, VA; and National Research Council, Ottawa, Ontario.

Two-Way Satellite Time and Frequency Transfer (TWSTFT) is the most accurate and precise method of comparing two remote clocks or time scales. The accuracy obtained is dependent on the accuracy of the determination of the non-reciprocal delays of the transmit and the receive paths. When the same transonders in the satellite at the same frequencies are used, ten the non-receiprocity in the earth stations is the limiting factor for absolute time transfer., Presented at the Annual Precise Time and Time Interval Applications and Planning Meeting (27th) held in San Diego, CA on 29 November-1 December 1995. Published in the Proceedings of the Annual Procise Time and Time Interval Applications and Planning Meeting (27th), p359-372, 1995.