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AFREF IGS Guidelines / Station Requirements

AFREF IGS Guidelines / Station Requirements. Rui Fernandes. DI-UBI, Univ. Beira Interior, Covilh ã, Portugal. Instituto Geofísico D. Luíz, Lisboa, Portugal. DEOS, Delft Univ. of Technology, The Netherlands. AFREF Solution.

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AFREF IGS Guidelines / Station Requirements

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  1. AFREFIGS Guidelines / Station Requirements Rui Fernandes DI-UBI, Univ. Beira Interior, Covilhã, Portugal. Instituto Geofísico D. Luíz, Lisboa, Portugal. DEOS, Delft Univ. of Technology, The Netherlands.

  2. AFREF Solution • Set of coordinate positions for a number of GNSS stations distributed by the entire African continent • AFREFxx will be linked to ITRF2008 for a certain epoch. Consequently, the coordinates will not change with time‡ • ‡this will be further discussed in • this presentation…

  3. Relation with IGS • IGS stations will be the backbone of the AFREFxxrealization by providing the link to ITRF2008

  4. Roadmap for the AFREFxxsolution • Selection of the AFREF stations What is (and will be?) an AFREFxx station? • Continuously operating • No end of operation foreseen • Reliable Internet access • Data transfer after few hours of acquisition • Data Publicly available • No restrictions to data distribution • Installation according to IGS standards • stable monument, self-centering mounting device, equipment recognized, any local ties very well determined, etc... • Uniform Distribution as good as possible • Current objective: no more than 1000Km between AFREF core stations

  5. How to implement the network? Active way Install stations to densify the AFREF network which can also be used for other applications Passive way Classify stations already installed in the framework of other projects as AFREF stations necessary cooperation/support with these projects Interaction with other applications needed

  6. Site distribution Political constraints - 61 Territories - Largest: Sudan (2 505 810 Km2) - Smallest: Melilla, Spain (12 Km2) Gambia (11 300 Km2) Every territory (definitively, every country) should have a station part of AFREF

  7. Current Situation Survey of CGPS sites: >130

  8. South AfricaTrignet + IGS Too many fiducial stations at continental scale…

  9. South AfricaTrignet + IGS HRAO+HARB and SUTM+SUTH SIMO is problematic

  10. South AfricaTrignet + IGS Final selection of stations to be processed.

  11. South AfricaTrignet + IGS Example of final selection

  12. South AfricaTrignet + IGS Example of final selection

  13. West AfricaNigeria & Benin 2 National Networks But only 5-6 stations will be necessary

  14. West AfricaNigeria & Benin Final Selection will depend of the assessment of individual stations e.g., reliability and also “political considerations”e.g., Cotonou?

  15. Towards the implementation of AFREF: results of case-studies for the computation of the reference solution R.M.S. Fernandes S. Leinen H. Farah L. Combrinck H. Khalil UBI, IDL, CGUL, Portugal DEOS, The Netherlands RCMRD, Kenya HartRAO, South Africa NRIAG, Egypt IPG, TUD, Germany Presented at IAG Meeting Buenos Aires 2009

  16. “Final” Selection – AFREF08 Position solutions was computed for a total of 47 stations.

  17. “Final” Selection – AFREF09 Some new additions but also …

  18. “Final” Selection – AFREF09 Some stations not available. Position solutions was computed for a total of 43 stations.

  19. Case Study: “Final” Selection Position solutions was computed for a total of 37 stations.

  20. AFREF08 & AFREF09 solutions 4 Independent Solutions using 4 Different Software Packages • RCMRD (Kenya) & IDL (Portugal) used GIPSY • Precise Point Positioning strategy • JPL precise orbits (no fiducial) + clock corrections • Use of ambizap algorithm to solve for ambiguities • CGC (Canary Islands) used NAPEOS • Precise Point Positioning strategy • IGS final Orbits (aligned to ITRF05) and clocks • NRIAG (Egypt) & TUD (Germany) used BERNESE • HartRAO (South Africa) used GAMIT (only AFREF08) • Network Batch strategy – simultaneous processing of all stations • a-priori IGS orbits (adjusted)

  21. AFREF08 & AFREF09 solutions 3 Different mapping approaches to align to ITRF2005 RCMRD/IDL used a global set of reference mapping stations HartRAO and NRIAG/TUD used a regional set of reference mapping stations CGC only processed the stations of interest (AFREF) using the fiducial IGS orbits (realized in ITRF2005)

  22. AFREF08 ResultsComparison Global/Regional mapping IGS sites Solution 1..n daily mapping Positions of AFRICA stations w.r.t. ITRF2005 at day 1..n

  23. AFREF09 ResultsComparison Global/Regional mapping IGS sites Solution 1..n daily mapping Positions of AFRICA stations w.r.t. ITRF2005 at day 1..n

  24. Solution Combination Comparison AFREF sites

  25. Comparison between the BERNESE & GIPSY AFREF09 AFREF08

  26. Comparison between the BERNESE & GIPSY AFREF09 AFREF08

  27. The role of tectonics…. Africa contains two major tectonic plates (Nubia and Somalia) plus some few minor tectonic blocks (e.g. Victoria) in Fernandes et al. [2004] in Stamps et al. [2008]

  28. Example: Ethiopia case Ref. Ref. • Stations located on the opposite sides of the East African Rift will move apart about 6-7 mm/yr • This is a significant change in the relative positions that must be taken into account if someone decides to use stations located on both sides to further densify the network using data collected in the future

  29. Internal consistency of AFREFxx • AFREF08 will be linked to the Nubian plate  Stations located in this plate will be stationary (no motion). • Reference stations located on other tectonic blocks will have a differential motion with respect to Nubia that should be taken into account when these stations are used for densification purposes.X(t) = X(t0) + V . t • t – sometime in futuret0 – reference epoch (01 May 2008) After the computation of the position of a new station at an epoch t, the angular velocity model must be applied backwards in order to compute the position of this station at epoch t0 (01 March 2008). This is only necessary for stations not located on Nubia.

  30. Summary • AFREFxx will be estimated using a consistent set of stations distributed by the entire continent (plus some stations located in neighborhood regions). • Almost all available CORS stations in Africa will be part of the AFREFxx solutions (the few exceptions are due to good reasons [e.g., Trignet, Nignet]). • Thecoordinatepositionsshouldbebecomputedbycombiningindependentsolutionsusingdifferent software packages. • AFREFxx will be formed by a set of coordinates linked to ITRFxx at a certain epoch together with an angular velocity model that will express the relative motions of the existing tectonic blocks in the continent with respect to the Nubian plate.

  31. And the effort will continue... THANK YOU…

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