1 / 30

QUALITY ASSESSMENT OF GFO SENSOR AND DATA PRODUCTS

This paper presents a routine quality assessment of GFO data products, including sensor and data verifications, orbit determination and analysis, SWH and σ0 calibration, time bias and sea state bias assessment, comparisons with TOPEX, wet delay validation, and evaluation of ionosphere correction.

lesliecastillo
Télécharger la présentation

QUALITY ASSESSMENT OF GFO SENSOR AND DATA PRODUCTS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. QUALITY ASSESSMENT OF GFO SENSOR AND DATA PRODUCTS C. Shum, C. Zhao, Y. Yi, and P. Luk The Ohio State University GFO Calibration/Validation Meeting NOAA Laboratory for Satellite Altimetry Silver Spring, Maryland June 12, 2001

  2. QUALITY ASSESSMENT OF GFO SENSOR AND DATA PRODUCTS • Routine quality assessment of GFO data product • Cycle by cycle GFO sensor and data verifications: • NGDR (GfoM and GfoO) data editing summary • http://geodesy.ohio-state.edu/gfo • Restricted web: http://geodesy.ohio-state.edu/gfo/navy • Summary of sensor and data assessment • OODD and GSFC MOE orbit verifications (POE to follow) • Time tag, USO, SWH, 0, sea state bias evaluations • Radiometer, ionosphere and geophysical corrections • NGDR vs. IGDR comparisons

  3. Restricted Web: http://geodesy.ohio-state.edu/gfo/navy

  4. Summary of Data Editing Percentage for Recent GFO NGDR data Restricted Web: http://geodesy.ohio-state.edu/gfo/navy

  5. GFO VERIFICATION WEB-PAGE Restricted Web: http://geodesy.ohio-state.edu/gfo/navy

  6. GFO VERIFICATION WEB-PAGE Restricted Web: http://geodesy.ohio-state.edu/gfo/navy

  7. Averaged statistics for OSU orbit, RA time bias, range bias, sea state bias GFO-1 ORBIT DETERMINATION AND ANALYSIS *RA bias is relative to T/P MSS and negative value means range is short • Selected orbit (6-day arcs) comparison (different gravity models)

  8. Evaluation of OODD (NGDR) Orbits Using Crossovers Doppler Orbits: April 15 – May 18, 2001 data (Operational Data) Crossover range: 43 - 185 cm rms

  9. Evaluation of MOE (NGDR) Orbit Using Crossovers MOE/SLR Orbits: April 15 – May 18, 2001 data (Operational Data) Crossover range: 7.6 - 42.5 cm rms (Day 113 picked lower accuracy orbit than IGDR did)

  10. Evaluation of MOE Orbit (IGDR) Using Crossovers MOE/SLR Orbits: April 15 – May 18, 2001 data (NOAA IGDR Data) Crossover range: 10.4 - 15 cm rms

  11. SWH AND 0 CALIBRATION • Geographical SWH comparison:1 ± 14 dm GFO and ERS-2 (June 1999) • Recommended calibrations (D. Hancock, 2000): • Add 0.37 dB to 0 (1-parameter model) • Add 0.24 m to SWH (1-parameter model) • Study based on Tran et al. [2000], T/P comparisons • Buoy validations (D. Cotton, 2000): • Preliminary results with limited data • 2-parameter (bias and offset) model • Ohio State University study (Y. Yi, 2000): • Preliminary results: comparison with TOPEX • Applying Hancock biases improves buoy fit for wind-speed (0), but not SWH [D. Cotton, pc] Hancock calibration was recommended and implemented in GFO data processing

  12. COMPARISONS WITH TOPEX SWH/0 10-day Averages within 66S-66N Preliminary results indicate GFO offsets with TOPEX SWH and 0 values, confirming D. Hancock’s calibration results

  13. ASSESSMENT OF TIME BIAS AND SSB Time Tag Accuracy and Timing Stability: RA time tag accuracy assessed using crossover analysis over three Cal/Val periods and first 4 operational cycles data sets: Time Tag accuracy: 0-3 ms (cal/val), 1.5 ms (operational) USO Drift Range Correction: 15 cm since launch [Lillibridge et al., 2000; Hancock, personal communication] • Sea State Bias: • One parameter model (dependence on SWH) estimates based on crossover analysis varies over different versions of Cal/Val data (possibly due to changes of 0/SWH and imperfect modeling, such as orbits): Cal/ValI Data (1999): 4.3% SWH Cal/ValII Data (1999): 3.0% SWH Cal/ValIII Data (2000): 3.5% SWH Cal/ValIV Data (2000): unavailable Operational Data (2001): 4.7% SWH

  14. COMPARISON OF GFO MWR AND NCEP WET DELAY GFO MWR - ERS2 MWR: -11  31 mm (Dec 6-22, 1999 data) GFO MWR – NCEP Mean (mm) RMS (mm) Cycle 2 (Jan 3-19, 2001) 1.6 25.7 Cycle 6 (Mar 12-18, 2001) 3.5 24.2 Cycle 8 (April 15-May 01) 3.6 25.3 Cycle 9 (May 02-18) 2.1 24.8

  15. COMPARISON OF GFO MWR AND ERS-2 MWR (ATSR) WET TROPOSPHERE DELAY

  16. VALIDATION OF IONOPSHERE CORRECTION • Comparison of JPL and CODE GIM (Global Ionosphere Map) and IRI95, high solar activities (Sept. 00 – April 01) • CODE and JPL GIM, bias ~ 2.9 mm, rms: ~ 1.5 cm • IRI95 and CODE GIM, bias ~ -10 mm, rms: ~ 5.4 cm • IRI95 and JPL GIM, bias ~ -7.1 mm, rms: ~5.1 cm • Sea level drift error could be 0-3 mm/yr directly due to ionosphere correction error during this period • Assessment of IRI-95, GIM (CODE) versus TOPEX “truth” GIM is better than IRI-95 during high solar activities on both RMS and drift; and comparable to IRI95 during low solar activities • IRI95-T/P: 5.6 cm rms, GIM –T/P: 2.3 cm rms • (TOPEX data used: Sept 00 - Feb 01) • IRI95-T/P drift: 0.35 mm/yr (Data: 1993-1999)

  17. COMPARISON OF GFO IONOSPHERE DELAY FROM IRI95 AND JPL, CODE GIM (12/1999-2/2001)

  18. GFO Range (SSH) Data Noise Estimation • SSH (Sea Surface Height) NGDR data for July-August, 1999 (Cal/Val I) and for Aug-Oct. 2000 (days 243-259, Cal/Val IV) • Track segments ~400 sec. long (12 tracks used) • Single repeating cycles used • Method • Estimate SSH signal by cubic splines • SSH Noise = SSH - SSH Signal • Selected data in deep oceans with least variability (1 Hz data) • 11-19 mmrms in Atlantic and 18-22 mm rms in Pacific (1-3 m wave heights) • Comparison with other altimeters • ERS-2 SSH Noise: 19/27mm rms (Sep, 1997) • TOPEX SSH Noise: 11/15mm rms (Sep, 1999)

  19. GFO RANGE BIAS Bias Rel. to T/P (Cal/Val I, II, III): -3 ± 5 cm Lake Michigan GPS- Buoy Campaign (March 24, 1999): 31 ± 42 cm Note: “Precise” GDR not Available for March 24, 1999 GFO Pass

  20. COMPARISON OF NGDR AND IGDR • NGDR and IGDR MOE agree well on time tags, SWH, 0, AGC, solid Earth tide and wet troposphere delay • Ionosphere delay, ocean tide and dry troposphere delay have differences as different models were used • NGDR MOE and OOD agree perfectly on time tag, SWH, 0, AGC and all other corrections except ionosphere delay NGDR MOE and IGDR MOE orbits are not always same • Differences exist in Uncorrected Altimeter Range between NGDR MOE, IGDR MOE and NGDR OOD products • Comparisons conducted using Cycle 8 and 9 data products • Mismatch orbit (1 Hz vs 10 Hz processing) was suspected and confirmed by other studies (J. Lillibridge, S. Klingenberger, R. Vaughan et al.)

  21. GFO Sensor and Data Assessment • Estimated Doppler orbit accuracy: 30-440 cm; GSFC MOE orbit accuracy: 10-50 cm; GSFC precise orbit accuracy: 5-6 cm rms • Orbit accuracy due primarily to availability of SLR tracking • Time bias insignificant (0-1.5 ms); USO Drift is 15 cm/mission • Noise of GFO SSH (1Hz): ~19 mm; TOPEX noise: ~13 mm rms, ERS-2 noise: ~23 mm rms, over same regions • Sea state bias: ~4.7% of SWH. GFO absolute range bias: ~-3 cm • Recommend to adopt David Hancock’s suggested calibrations for SWH and 0: add 0.24 m to SWH and add 0.37 db to 0 • Wet troposphere correction: 0.2 cm bias, 2.6 cm rms (w/NCEP Model); ~1 cm bias, 3 cm rms (w/ ERS-2) • CODE GIM and IRI95 provide ionosphere corrections accurate to 1-5 cm rms during medium to high solar activities; GIM performs better during high solar activities

  22. FUTURE POTENTIAL IMPROVEMENTS • Estimation of 4- or 5-parameter sea state bias • Improved calibration of SWH and 0 needed • Crossover analysis using “best” processed data set • Barotropic ocean tide models • NAO99.2b [Matsumoto et al., 2001], GOT99.b [Ray, 2000 • Ionosphere models • GIM (CODE or JPL?), IRI2001 [Bilitza, 2001] • Dry troposphere and IB • NCEP operational, FNOC (?), ECMWF (for GDR?) • Need Wallops “internal calibration” • Concerns: USO drift “large”, inland lake/sea data quality, lack of waveform data, land-sea flag, improved center of gravity (SLR retroreflector and RA), further gravity field improvement?

  23. GFO Great Lakes data are being edited due primarily to large SSB(?)

  24. ASSESSMENT OF TIDE ERROR USING MODEL COMPARISONS

  25. Assessment Of Tide Error Using Model Comparisons (RSS of 8 constituents) • 6 recent models used: NAO99.2b, GOT99.b, CSR4.0, DW98, Delft, YATM4D • Shum et al. [2001]

  26. TIDE MODEL EVALUATIONS USING ALTIMETER SEA LEVEL DATA[Shum et al. 2001]Global coastal ocean (depth<1000m) GEOSAT (Residual rms, cm) Tide Models GM ERM ERS-1 T/P CSR3.0 52.59 111.04 26.72 21.53 YATM4d 58.43 110.96 34.60 33.56 CSR4.0 51.96 53.99 25.40 19.09 GOT99.2 46.96 48.53 25.15 17.75 NAO99 51.90 53.67 24.7017.04 Smith 47.97 47.51 32.37 33.28 • Sea Level = Altimeter SSH - OSUMSS95 • Latitude weights applied [Yi and Rapp, 1995] • Edit criteria = 1000 cm

More Related