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The Three Dimensional Universe with GAIA Paris-Meudon, October 4-7, 2004

Gaia First Look: Description and Status Report. The Three Dimensional Universe with GAIA Paris-Meudon, October 4-7, 2004.

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The Three Dimensional Universe with GAIA Paris-Meudon, October 4-7, 2004

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  1. Gaia First Look:Description and Status Report The Three Dimensional Universe with GAIAParis-Meudon, October 4-7, 2004 Stefan Jordan, Uli Bastian, Helmut Lenhardt, Hans Bernstein, Sonja Hirte (Astronomisches Rechen-Institut, Heidelberg) & Michael Biermann (Landessternwarte, Heidelberg) Acknowledgement:- GIS routines by Lennart Lindegren (LL-37)- simulation data from Barcelona group (Eduard Masana et al.)

  2. Often heard here: • GAIA is a self calibrating instrument GST13, ESTEC, 2004-09-13

  3. Often heard here: • GAIA is a self calibrating instrument • This is true …. GST13, ESTEC, 2004-09-13

  4. Often heard here: • GAIA is a self calibrating instrument • This is true …. • However, GIS possible only after 6 months GST13, ESTEC, 2004-09-13

  5. Often heard here: • GAIA is a self calibrating instrument • This is true …. • However, GIS possible only after 6 months • Gaia can only solve for calibration, attitude and source parameterssimultaneously. GST13, ESTEC, 2004-09-13

  6. The basic problem • It is difficult to immediately assess proper functioning of all elements (on the μas level) • But very important, else risk of losing many months of data and mission time. Some compromise must be found GST13, ESTEC, 2004-09-13

  7. Overall QL/FL Scheme • Quick Look (QL) - ESOC • Science Quick Look (Sc-QL) – ESOC + FL task Sc-QL monitor Sc-QL evaluator • Early science processing steps - Core Processing Ingestion, cross-matching, initial data treatment • First-Look pre-processing (FLP) - FL task ODIS (one-day iterative solution)* or ring solution • Detailed First Look (DFL) - FL task First-Look monitor First-Look evaluator * formerly called 1-day GIS GST13, ESTEC, 2004-09-13

  8. Scan directions and location on the sky Different scan directions: Across-scan unknowns solvable Equal scan directions: Across-scan unknowns undefined RGC Scan circles at the node: different scan directions 90 deg off the node: only one scan direction GST13, ESTEC, 2004-09-13

  9. Two basic ways of attack • Some reduced variant of GIS, now named „ODIS“, One-Day Iterative Solution • Direct solution of the full problem of the 1-day astrometric reduction, named „Ring Solution“ being performed in parallel Note: Neither way can produce a full astrometric solution. GST13, ESTEC, 2004-09-13

  10. ODIS versus Ring Solution • Ring Solution:- allows to easily and clearly detect and remove the degeneracies- can in principle produce full covariances- may be much more demanding in terms of storage and computing • ODIS:- a block-iterative scheme does not necessarily show its degeneracies- a block-iterative scheme does not necessarily converge- the degeneracies are not easily pinned down GST13, ESTEC, 2004-09-13

  11. First-Look Preprocessing using Ring Solution:Direct elimination of source unknowns Sources Attitude Cal. x x 0 6 000 000 0 6 000 f u l l 900 GST13, ESTEC, 2004-09-13

  12. ODIS versus Ring Solution • Ring Solution:- allows to easily and clearly detect and remove the degeneracies- can in principle produce full covariances- may be much more demanding in terms of storage and computing • ODIS:- a block-iterative scheme does not necessarily show its degeneracies- a block-iterative scheme does not necessarily converge GST13, ESTEC, 2004-09-13

  13. Data volume, computing time Initial estimates for 24 hours of data, using (various) present-day 2 GHz Pentium III (4 GByte memory) PCs • About 5 GByte of observed data • →50 million parameters (attitude, calibration parameters, source parameters, global parameters) • Computing time (extrapolated to 50 million elementary observations) without data base overhead: • Ring solution: 1600 hours • ODIS:40 hours At time of GAIA: faster computers Parallelization possible! GST13, ESTEC, 2004-09-13

  14. Lessons already learned • Either FLP method (ODIS or ring solution) needs a „zeroth“ iteration to identify the degenerate dimensions • Either FLP method can conveniently use quaternions in the RGC system for the attitude representation (GAIA-SJ-002) • Convergence behaviour of ODIS depends on block sequence, on block size, on block composition, .....We‘ll use more than 4 blocks (split AL/AC), and omit the ‚global‘ block (GAIA-SJ-001) • In smaller test runs: distribution of observations over time interval very important GST13, ESTEC, 2004-09-13

  15. ODIS Iterations Before first iteration: FOV 1 FOV 2 observed-computed (along-scan)/μas -23000 sources -125000 elementary “observations” large scale calibration wrong GST13, ESTEC, 2004-09-13

  16. ODIS Iterations After first iteration: observed-computed (along-scan)/μas large scale calibration adjust GST13, ESTEC, 2004-09-13

  17. ODIS Iterations After second iteration: observed-computed (along-scan)/μas large scale calibration adjusts GST13, ESTEC, 2004-09-13

  18. ODIS Iterations After 24 iteration: observed-computed (along-scan)/μas large scale calibration adjusted… GST13, ESTEC, 2004-09-13

  19. ODIS Iterations After 50 iteration: observed-computed (along-scan)/μas large scale calibration adjusted… GST13, ESTEC, 2004-09-13

  20. ODIS Iterations After 50 iteration: observed-computed (along-scan)/μas large scale calibration adjusted…but GST13, ESTEC, 2004-09-13

  21. ODIS Iterations observed-computed (along-scan)/μas Both FOV after 50 iteration: time/days large scale calibration GST13, ESTEC, 2004-09-13

  22. ODIS Iterations observed-computed (along-scan)//μas FOV 1 after 50 iteration: time/days large scale calibration GST13, ESTEC, 2004-09-13

  23. ODIS Iterations observed-computed (along-scan)/μas FOV 2 after 50 iteration: time/days large scale calibration GST13, ESTEC, 2004-09-13

  24. ODIS Iterations Before first iteration: FOV 1 FOV 2 observed-computed (along-scan)/μas large scale calibration wrong GST13, ESTEC, 2004-09-13

  25. ODIS Iterations Only CCD calibration observed-computed (along-scan)/μas If we do it right… GST13, ESTEC, 2004-09-13

  26. ODIS Iterations After 2 iteration observed-computed (along-scan)/μas If we do it right… GST13, ESTEC, 2004-09-13

  27. ODIS Iterations After 1 iteration observed-computed (along-scan)/μas If we do it right… GST13, ESTEC, 2004-09-13

  28. ODIS Iterations After 5 iteration observed-computed (along-scan)/μas If we do it right… GST13, ESTEC, 2004-09-13

  29. ODIS Iterations After 10 iteration observed-computed (along-scan)/μas If we do it right… GST13, ESTEC, 2004-09-13

  30. Lessons already learned (cont.) • No across-scan instrument calibration possible within a short amount of time • →Commissioning and initial in-orbit calibration would greatly benefit from a „zero-nu-dot“ scanning mode (i.e. scan axis remaining on the ecliptic, at 50 degrees from the sun) GST13, ESTEC, 2004-09-13

  31. “Zero-nu-dot mode” Coverage of the ecliptic pole area about 8000 stars Note: z-axis of the satellite points toward the top (on day 1); sun is either 50º to the right or 50º to the left of it. GST13, ESTEC, 2004-09-13

  32. Lessons already learned (cont.) • Commissioning and initial in-orbit calibration would greatly benefit from a „zero-nu-dot“ scanning mode (i.e. scan axis remaining on the ecliptic, at 50 degrees from the sun) • This will provide us with a first calibration also across-scan • Needed: Pre-GAIA astrometric observations of some 8000 stars around the ecliptic poles GST13, ESTEC, 2004-09-13

  33. Lessons already learned (cont.) • Commissioning and calibration would greatly benefit from an „AC calibration“ CCD sampling mode (i.e. strongly reduced across-scan binning in AF; in practical terms this can be implemented by temporarily using the WY00 windows over a larger magnitude range) GST13, ESTEC, 2004-09-13

  34. First-Look Preprocessing using ODIS: Preliminary concept • First, produce a global solution for the along-RGC unknowns only, already omitting those stars with only 1 FoV transit. • In this process, collect the list of actual scan directions for each star • For those stars with sufficiently differing scan directions, solve across-scan coordinates in subsequent solutions. • For all across-scan attitude unknowns collect the number of stars with across-scan solutions contributing to them. • For those across-scan attitude unknowns with sufficiently many such stars contributing, make a first solution. • In all further iterations, omit or „Huber away“ discordant observations, using all unknowns selected before. • After first GIS: the first+last of these steps suffice (probably) GST13, ESTEC, 2004-09-13

  35. The first look task is not a closed session – collaboration is welcome END GST13, ESTEC, 2004-09-13

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