Time Transfer Research and Development at USNO

1
Time Transfer Research and Development at USNO

• CGSIC March 2004
• Presented by Jim Brad

2
RD Time Transfer Outline

• Improved GPS time transfer
• New GPS time transfer receiver evaluation
• Real Time GPS Carrier Phase Demonstration (JPL)
• Improved Standard Positioning Service (Civil)
• Improved Precise Positioning Service (Military)
• WAAS Time Transfer
• Improve Two-way satellite time transfer
• Time Transfer to US Navy Ship
• Thermal Stability Studies/Improvements

3
GPS Hardware Time Transfer Stabilitycomparison
of two high performance receivers
4
Time Transfer Test BedUSNO to USNO AMC
PPS CV
TWSTT
CP Realtime Post-processed
SPS CV
5
JPL and USNO Demonstration of Live Real Time
Carrier Phase Time Transfer
1.5E-15 at one day
See link at http//galia.gdgps.net/igdg/
6
How WAAS timing works today

• WAAS Network Time (WNT) is an average of WAAS
  reference station clocks steered to GPS time
• GPS time is steered to UTC(USNO) and is specified
  to be maintained to within 1 microsecond of
  UTC(USNO) modulo one second
• GPS broadcasts UTC corrections including leap
  second information in GPS navigation message
• Today no UTC corrections are broadcast by WAAS
• WAAS message type-12 is designated to contain UTC
  corrections. At present this message type-12 has
  not been implemented

7
Joint USNO and WAAS program was initiated in 1999
to study WAAS timing

• Investigate WAAS broadcast of UTC(USNO)
  corrections to support UTC time transfer
• Investigate using WAAS geostationary satellite as
  an independent UTC timing source
• Investigate use of the WAAS geostationary
  satellite signal as a method for improved common
  view time transfer
• Investigate improvements to WNT to better support
  time transfer
• Investigate use of the WAAS ionosphere correction
  grid data to improve time transfer

8
Modulo 1 Second
9
USNO Two-Way Satellite Time Transfer Earth
Terminals
10
TWSTT to SHIPS
11
Temperature-stable Enclosures
12
Thermal Control of TWSTT
13
Correlation of Diurnal Time Variations with
Outside Temperature Variations
14
Correlation of Diurnal Time Variations Reduced
with Better Thermal Control
Temperature
15
Future Work

• Focus on Robust Operation Center
• Improved Calibration of Time Transfer
• New GPS Calibrator (February 2004)
• Continue to Work on Time Transfer Hardware
  Stability
• Continue Work on Real Time Carrier Phase Time
  Transfer (JPL, NRCan, IGS)
• Demonstration of Two-way and GPS Time Transfer to
  Navy Ship at Sea