Level 1B Operational Processing

1. Level 1B Operational Processing GRAS Team at EUMETSAT

2. Operational Processing: Setup / Events PPF 2.16 running since July 2010 tracking down to -250km SLTA from Oct 2010 onwards overlap configuration changed, thus no more double occultations now observed ADA now operational (not all orbits) Orbits affected by geomagnetic storms (often avoided POD reset by context transfer) First ever Metop collision avoidance maneuver on 1st of May 2011 PPF 2.17 under development since Dec 2010, running on GS2: fixing zeros in some 2.16 output fields azimuth angle at tangent point included in output fields some other orbit, data stuff L2 extrapolation optional (updates / improvements under investigation, see later presentations) with new configuration (should improve mitigation of solar storms) planned for GS1 next week Instrument software update to 1.9 on 5th of May (wrong ephemeris usage) Instrument software update to 1.10 ~2 months until delivery (tracking improvement) Slide: 2

3. Operational Processing: # of Occultations GRAS shows very solid performance, very few instrument issues detected and potentialsoftware updates are evaluated. Manoeuvre GRAS PPF 2.16 (no QC) and COSMIC provided number of occultations / day over last year S/W Update Slide: 3

4. Operational Processing: Issues • Current processor issues: • no raw sampling / open loop and wave optics processing • orbit affected by data flow interruptions, magnetic storms, etc. This leads to degraded data for several hours, often requiring manual intervention.

5. Operational Processing: Antarctic Dump • ADA Station: • additional Antarctica download station (operational service started June 2011, all orbits in 2014)

6. MetOp-A Status • DHSA: Redundant CCU I/O Board. Further investigation of I/O Board planned following a possible future PLSOL outage. • HRPT:B unit in restricted operation. Complete longitudinal coverage zone active since 18th January (No transmission at higher latitudes in both hemispheres) • AMSU A1: Channel 7 is declared failed • MHS channel degradations – now on highest possible gain – products may be impacted starting in 2012. • A-DCS: frequency complaints - no requests to stop operations. • GOME throughput loss investigation – ongoing .

7. Detailed view on GRAS / Processing Anomalies

8. Operational POD between July 2010-June 2011 • 17 POD resets (compared to 21 from July 2009 to June 2010) • Missing L0 data (CDA, PGF, GS...) 4(9) • Manoeuvres 4(2) • GSN 1(2) • Instrument 8 • USO clock slip 5(2) • Unphysical Pseudo-ranges 1(1) • Divergence of navigation solution 0(1) • SLTA change 1*(2) • Upload of software version 1(1) • Unknown ancillary packet type 8 1(0) • Every reset: 4hours of products flagged as degraded • Solar Storms (along track biases) ~4 degraded periods * SLTA change done during OOP Manoeuvre (Oct 2010)

9. Instrument – Phase Slips PLL • All but one are very close to a multiple of 200ns (most are 400 ns) corresponding to 5Mhz USO frequency • Triggers reset on operational POD • No impact on batch prototype ~560ns ~400 ns

10. Instrument – Phase Slips PLL • Plots show the POD clock bias estimation of GRAS, removing a one degree polynomial ~400 ns ~400 ns

11. Instrument – Phase Slips PLL • Plots above and below show PLL phase slip as observed in the Level0 data ~800ns ~200ns

12. Degradation due to misbehaviour of sequential estimator during solar storms • Strongest event, beginning of March2011. • Until this point temporary solution was to move a converged state from G2 to G1 • Decided to try different history fading times configuration

13. Degradation due to misbehaviour of sequential estimator during solar storms • Finally reduce fading time from ~30 orbits to ~5 orbits • Small increase of noise during quite periods; no along track biases during storms • Currently being tested in g2, and will soon go operational

14. GSN degradation due to large clock offset (Nov 2010) • GRAS monitoring was showing reduction of accepted measurements, and increase of wRMS.

15. GSN degradation due to large clock offset (Nov 2010) • Station clock ‘jump’ introduced a large clock drift, when realigning clock products • Has been added to GSN daily quality report for easier identification if re-occurrence • GSN has put in place mechanism to avoid re-occurrence

16. Degradation due to wrong estimation of clock bias • Clock bias estimation irregularity in GRAS POD causing large systematic biases in GRAS level 1b products • Caused by unphysical Pseudoranges which are not rejected in the 2nd SRIF run • Manual reset of the second SRIF run was needed • Better data cleaning for SRIF is being put in place • Low elevation pass

17. Instrument – Navigation Solution • 9th February 2010, GRAS reported invalid navigation (second time after 10th July 2008). Many GPS outage result in larger Navigation orbit error (peak) • Software patch (GOBS 1.9) to avoid the issue uploaded 5th May 2011 • 1 GPS manoeuvre on the day of the upload (navigation solution not affected) • Note that not all the GPS manoeuvres/outages affect the navigation solution PRN 26 Unusable NANU 2011033 GOBS 1.9 uploaded to GRAS Not investigated PRN 29 Manoeuvre NANU 2011032 PRN 11 Manoeuvre NANU 2011037

18. Instrument Related Issues • Data gaps in • raw sampling data • closed loop C/A data • Low L2 SNR “issue” • …and putting it into perspective • SNR Comparison GRAS vs. COSMIC / CHAMP / GRACE

19. Data Gaps (rising) 28°N, 155°E 37°N, 147°E 20 0 -20 SLTA [km] -40 -60 9°N, 120°E -80

20. Closed Loop Data Gaps in Rising Occ’s SLTA of highest gap in C/A carrier phase data (from October 2007) About 33% of rising occultations are affected, 16% in total Will have to live with this in “historic” data; workarounds and maybe a fix in the GRAS firmware in the future Also: (more or less) all occultations have gaps in the RS part due to C/A code tracking losses

21. Low L2 SNR • C/A SNR < 200 for ≤ 1% of all occultations • P2 SNR < 50 for ≤ 7% of all occultations • Most pronounced in rising • no geographic distribution • GRAS tracks wrong portion of the code (“sidelobe tracking”) • in effect: large number of cycle slips in L2 phase data • Retrievals are either significantly noisier, or not useful at all; will flag these profiles as ‘bad’ (and work on cycle slip corrections if we find the time)

22. Upcoming Solutions Short term: According to RUAG, all three problems are related to overly conservative settings of configuration parameters for loss-of-lock indicators in the CL carrier phase tracking loop loss-of-lock indicators in the C/A code during RS Acquisition thresholds for P1/P2 codeless tracking Unfortunately, changing these parameters requires a firmware patch Request to implement parameter changes in onboard software has been issued to industry in late November; still waiting for completion of paperwork (at industry!), to be implemented as GOBS v1.10 (~September?) Long term: Changes in tracking state machine? -> ESA study to be kicked off Post-GRAS: Decoupling of RS and L2 tracking? -> ESA study to be kicked off

23. (Un-?) solution: Raising SLTA Threshold Initially: Considered raising upper SLTA boundary for rising occultations to cover C/A data gaps with RS L2 only available above 15-20 km requires extrapolation of ionospheric correction (implemented in v2.17, but problems identified) requires further system modification at GRAS SAF to keep products at CAF and SAF consistent (nearly done) Unfortunately, raising SLTA led to an increase (+ 6%) in the number of occultations with failed L2 acquisition Will probably wait for results of GOBS v1.10 patch… …or might require a further GOBS patch

24. SNR in Perspective 0.7% 49.3% 6.2% 50.2%

25. SNR in Perspective (cont’d)

26. GRAS SNR vs. COSMIC, CHAMP, GRACE

27. GRAS SNR vs. COSMIC, CHAMP, GRACE (cont’d) • GRAS data shows drop in C/No / SNR for NH; expected as noise is higher in the NH. • No similar signature in COSMIC, CHAMP or GRACE data. • Tom Meehan: JPL receivers use nominal No in their SNR calculation, not measured • Should we re-address the SNR calculation and presentation to allow for a more realistic / physical comparison with the US receivers?