RealTime and Near RealTime GPS Products and Services from Canada

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Real-Time and Near Real-TimeGPS Products and
Services from Canada

• Y. Mireault, P. Tétreault, F. Lahaye, P. Collins,
  M. Caissy
• Geodetic Survey Division, Natural Resources
  Canada (GSD/NRCan)
• http//www.geod.nrcan.gc.ca
• IGS Analysis Center Workshop 2008
• June 2-6, 2008
• Miami Beach, Florida, USA

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Outline

• NRCan Ultra Rapid Products (EMU)
• CSRS Precise Point Positioning Service (CSRS-PPP)
• Canadian RT GPS Tracking Network
• Canadian High Precision RT GPS Wide-Area
  Correction Service (GPSC)
• Final Notes

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1. NRCan Ultra Rapid Products (EMU)
1.1 Description

• Orbits and clocks for RT/NRT usage
• Covers 48h, i.e. 24h estimated and 24h predicted
• Produced every hour
• 1h delay for orbits and 1.5h delay for clocks
• Submission to IGS every 6h
• Predicted orbits used in GPSC
• Estimated orbits and 30-sec satellite clocks used
  in NRT PPP

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1.2 Some Highlights
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1.3 Precision
() Orbit and Clock Median RMS when compared to
IGS Rapid (IGR) (a) Orbits and clocks are used in
NRT PPP (b) Orbits are used in GPSC
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2. CSRS Precise Point Positioning (PPP)
2.1 Description

• A Web based global positioning service for single
  GNSS datasets (currently GPS only GLONASS
  planned)
• Initiated in the Fall of 2003 as next-day service
  (17h delay)
• Delay reduced to 90min (May 2008) using NRCan
  Ultra Rapid orbits and 30sec clocks
• Process static or kinematic (both with single or
  dual frequency data)
• Use of IGS IONEX grids for single frequency
  processing

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2.2 CSRS-PPP Usage
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2.3 CSRS-PPP Static Positioning Corrections (wrt
IGS05)
Statistics based on processing of 30 secs data
from 24 hour files for ALGO DRAO RESO SASK STJO
for GPS Week 1470
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2.4 CSRS-PPP Kinematic Positioning Variations
(wrt IGS05)
Statistics based on processing of 30 secs data
from 24 hour files for ALGO DRAO RESO SASK STJO
for GPS Week 1470
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3. Canadian RT GPS Tracking Network
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4. GPSC Canadian High Precision RT GPS
Wide-Area Correction Service
4.1 Description (1/2)

• Pseudorange Phase Processing from IGS-RT
  RT-CACS Stations
• P3 r(Xsta,Xsat) c ( dtsta dtsat ) dtrop
  e
• L3 r(Xsta,Xsat) c ( dtsta dtsat ) dtrop
  lN e
• Xsat provided by EMU (1h cycle) IGU (6hr
  cycle) predictions
• dtsta, dtsat,dtrop,N estimated in real-time
• Enhancement of the current code-based system

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4.1 Description (2/2)

• Modeled Effects
• Earth ocean tides
• Station satellite absolute PCV
• Relativity
• ITRF station velocity
• Phase wind-up
• Parameters Estimated
• Station and satellite clocks (white noise
  parameters wrt VRC)
• Station troposphere ZPD (random-walk)
• Constant (float) ambiguities
• RT High Precision Correction Stream
• Xsat-BRD _at_ 120sec (linear over 240sec)
• dtsat-BRD _at_ 2sec

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4.2 GPSC Results
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4.3 GPSC Development

• Status
• Access to 50 real-time stations globally
• Finalizing stress-tests application robustness
  improvements
• IOC targeted for Fall 2008 ? Pilot Project / ESS
  activities
• Further Refinements to the Phase-based Algorithm
  Models
• YAW model (Kouba, GPS Solutions (online))
• Un-differenced integer ambiguity resolution with
  decoupled clocks
• Define BRD-independent orbit messages
• Define messages for troposphere-mapping grid,
  satellite DCBs
• Define messages required for PPP ambiguity
  resolution

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4.4 Day-Boundary Clock Jumps / Decoupled Clocks
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5. Final Notes

• IGS Ultra Rapid Combination
• Push it to a 3h cycle? Ultimate goal of 1h cycle?
• Reduce delay from 3h to 2h?
• Need more AC clock solutions to improve precision
  and accuracy!
• Global RT GPS Tracking Network
• Would provide faster data for Ultra Rapid
  orbits/clocks turnaround
• Need for 30sec satellite clocks for Rapid and
• Ultra Rapid products (NRT users such as PPP)

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• Information on decoupled clocks
• Isolating and Estimating Undifferenced GPS
  Integer Ambiguities,
• Paul Collins, GSD, NRCan
• Presented at the Institute of Navigation, NTM
  2008, San Diego,
• January 28-30 2008, session D3.
• Look also for the corresponding paper in the ION
  TNM proceeding.

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Statistics based on processing of 5 min data
from 24 hour files for ALGO for GPS Week 1470
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Statistics based on processing of 5 min data
from 24 hour files for ALGO for GPS Week 1470
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2.5 CSRS-PPP Static Positioning Corrections (wrt
IGS05)
Hours
Statistics based on processing of 30 secs data
from 24 hour files for ALGO DRAO RESO SASK STJO
for GPS Week 1470
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Real-Time and Near Real-Time GPS Products and
Services from Canada

• Y. Mireault, P. Tétreault, F. Lahaye, P. Collins,
  M. Caissy
• Geodetic Survey Division, Natural Resources
  Canada (NRCan
• Natural Resources Canada (NRCan) has been
  involved in producing and promoting GPS Real-Time
  (RT) and Near Real-Time (NRT) products and
  services for more than 10 years. Key products
  and services, like 1Hz GPS station data, Ultra
  Rapid GPS orbits/clocks, GPS Precise Point
  Positioning (PPP) and GPS corrections (GPSC),
  have been developed and refined over the past
  several years. This presentation will focus on
  current RT and NRT products and services
  developed by NRCan and made available to users in
  Canada and world wide.
• First, a description of the RT GPS tracking
  network covering Canadian territory and used
  within GPSC will be given. Next, NRCans hourly
  Ultra Rapid GPS satellite orbit and 30-sec
  satellite clock estimation strategy will be
  presented. Then, we will discuss NRCans PPP, a
  free online post-processing service using IGS and
  NRCans orbits/clocks and IGS IONEX products to
  allow GPS users world wide to compute
  better-accuracy positions from their single/dual
  frequency datasets observed in static/kinematic
  mode. Finally, an overview of the RT GPS
  wide-area correction service (GPSC) distributed
  nationally through the Canada-wide DGPS will be
  given.