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Geolocation Tuning and Status

Geolocation Accuracy of Available Data Problems E-W, N-S Centering Discrepancies Comparing with RGP Axis Misalignments Mirror Offsets Future. Geolocation Tuning and Status. Martin Bates GIST 19, 27 Aug 2003. Geolocation Accuracy of Available Data.

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Geolocation Tuning and Status

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  1. Geolocation Accuracy of Available Data Problems E-W, N-S Centering Discrepancies Comparing with RGP Axis Misalignments Mirror Offsets Future Geolocation Tuning and Status Martin Bates GIST 19, 27 Aug 2003

  2. Geolocation Accuracy of Available Data • Only good to 2-4 pixels (particularly E-W) • Why ? • E-W centering problems (more later…) • Geolocation tuning not keeping up with NRT flow of data (particularly sensor swaps) 14 Aug (ESU 2) 29 Jul (ESU 1)

  3. N/S Variations 14 Aug 30 Jun 01 Jun (No SEVIRI)

  4. Geolocation Accuracy of Available Data

  5. TSOL Problems Diurnal variation  0.5 - 2 pixels Magnitude and phase changes with time Midnight wobble Jump at sensors swaps Magnitude ~ 3 pixels Phase of diurnal variation also changes

  6. Measure earth centering using GGSPS + correct for it Need 2 stage processing, robust centering algorithm, accuracy ~ 0.2 pixels ? EUM provide RAL with TSOL predictions in NRT/data from IMPF EUM provide RAL with TSOL evolution model EUM have investigated ARs related to TSOL anomalies. Not fully understood, but diurnal variations thought to be related to spin axis tilt EUM solution would be more accurate and would make life easier – preferred option is a hybrid of ii and iii with coefficients provided for a model valid over 10 days to an accuracy of ~0.1 pixel Should be discussed with Alcatel at next MSG progress meeting (10-11 Sep). TSOL Solutions

  7. N/S Discrepancies with RGP Array seems compressed N/S

  8. E/W Discrepancies with RGP (1) Discrepancies E/W at top & bottom of array (rotation ?)

  9. E/W Discrepancies with RGP (2) Down to oblique viewing by Meteosat at western edge ?

  10. Specifically MSG spin to MSG structure Bigger than expected: ~ 0.3 degrees (spec < 0.15 degrees) Consequences (depends on orientation): Shift in line of sight N/S (up to ~ 4 pixels) already tuned away Increased pixel smear N/S (up to (2π/15) x δ 1.8 pixels) But orientation is currently unknown (flight dynamics team at EUMETSAT trying to measure this) Size/orientation can change at each manoeuvre Axis Misalignments

  11. Mirror Offset • Mirror faces observed in fine limb scans to be slightly (0.098 pixels) non-parallel (E-W) • Hardware correction (offset) applied 15 Jul 2003 at 14:00 • Software correction needs to be applied (during any reprocessing) for data prior to this

  12. What do we do next ?? ALCATEL/EUMETSAT meeting Sept 10/11: more information on possibility of TSOL model Improve centering algorithm Complete survey of existing data Develop ad-hoc corrections in time for end of sun avoidance period i.e. tune for both ESUs – implement rapid means of switching; code diurnal variation as sinusoid with time dependent amplitude (+ phase ?) Will be better but still far from perfect Code mirror offset correction for data prior to 15 July (in case reprocess data); measured MSG-GERB alignment RMIB discrepancies (rotation, compression N/S) ? Future

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