1. Geolocation Tuning and Status Geolocation Accuracy of Available Data Problems –E-W, N-S Centering –Discrepancies Comparing with RGP –Axis Misalignments –Mirror Offsets Future 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 Aug30 Jun 01 Jun (No SEVIRI)

4. Geolocation Accuracy of Available Data StartEndESUTuning 03 Aug 10:4415 Aug 23:592Good 20 Jul 07:1403 Aug 10:441E/W bad 07 Jul 08:1420 Jul 07:142Good 23 Jun 09:2607 Jul 08:141E/W bad. N/S discrepancies 20 Jun 12:3523 Jun 09:261/2N/S very bad… poor orbit/att data 14 Jun 17:1820 Jun 12:35(1)No data 12 Jun 13:2414 Jun 17:181E/W bad. N/S discrepancies 09 Jun 23:5912 Jun 13:242E/W good. N/S discrepancies 28 May 09:4509 Jun 23:591E/W bad. N/S discrepancies, particularly 30 May – 02 Jun (no SEVIRI) 25 May 00:2528 May 09:251/2No data 24 May 00:0025 May 00:252E/W good. N/S discrepancies

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

6. TSOL Solutions 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).

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. Axis Misalignments 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

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. Future 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) ?