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Quality control study for SMOS data / Flags analysis

Quality control study for SMOS data / Flags analysis. C. Gabarró , J. Martínez, E. Olmedo M. Portabella , J. Font and BEC team J . Boutin & N. Martin, LOCEAN J.L. Vergely, ACRI-st. Flagging combination Cases.

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Quality control study for SMOS data / Flags analysis

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  1. Quality control study for SMOS data / Flags analysis C. Gabarró, J. Martínez, E. Olmedo M. Portabella, J. Font and BEC team J. Boutin & N. Martin, LOCEAN J.L. Vergely, ACRI-st

  2. Flagging combination Cases • Analysis of the best combination of L2 flags on L2 and L3 data quality: focus on the usefulness of Chi2 probability flag and galactic noise flag. • L2 comparison with ARGO floats data by selecting data with: • +/- 50 Km between SMOS & ARGO • +/- 5 days between SMOS & ARGO • L3 SMOS SSS with/without flag sorting compared with in situ optimal interpolation maps (ISAS/IFREMER) • Four different flags combinations have been tested at L2 and L3. The RMS (mean/std) and also number of points are important. • Three periods of time: • February -> low galaxy effect • March 2011 ascending -> large effect of galaxy • August -> large galaxy effect

  3. Tested flags • Fg_ctrl_chi2_P: main goodness of fit indicator; flag on SSS is raised if the probablility that an anomaly occurs about the fit is >95% or less than 5% (too good fit adjustment) • Fg_ctrl_gal_noise: galactic noise flag; flag on SSS is raised if 10% of Tb along a dwell are discarded from the SSS retrieval (e.g. because they are affected by a scattered galactic noise >4K) = since these Tbs are removed from SSS retrieval, retrieved SSS should remain usable (although noisier) • In L2OS v5 Fg_gal_noise included in the Fg_ctrl_poor_geophysical and Fg_ctrl_chi2_P in Fg_ctrl_poor_retrieval

  4. Fg_ctrl_chi2 and Fg_ctrl_chi2_P filters description L2P handles two different flags related with distribution: ())+ ( Where: are the Nm observations performed at different angles T represents the transposition operation is the variance/covariance matrix for Tb are different parameters to be retrieved are the a priori knowledge of parameters (ontained from models or satellites, auxiliary information is the variance/covariance matrix for these parameters

  5. Fg_ctrl_chi2 and Fg_ctrl_chi2_P filters description Two different flags are associated to the the residual of the cost function: Fg_ctrl_chi2 Fg_ctrl_chi2_P • When then Fg_ctrl_chi2 is set to 1=>BAD QUALITY; (Tg_Chi2 = 1.35 (corresponding to Fg_ctrl_chi2_P for N=50) => redundant with Fg_Chi2_P for N>50 and not statistically relevant because it does not take into account theoretical distribution of Chi2 as a function of Nm => Better to use Chi2_P • Fg_ctrl_chi2_P based on the theoretical expected distribution of Chi2 (gamma function). By default 5%<Tg_chi2_P<95% (i.e. with level 2 processor scaling 50 <Dg_Chi2_P<950) • Tested thresholds: • Low thresholds: 0%, 5% (default), 25%, 50%, 75% • High thresholds: 25%,50%,75%,95% (default), 100%

  6. Fg_ctrl_chi2_P filter description Dg_chi2_P_X=GAMMq(Nm/2, Chi2*Nm /2) If Tg_chi2_P_min < Dg_chi2_P_X < Tg_chi2_P_max =>Fg_ctrl_chi2_P=0 => GOOD QUALITY Otherwise Fg_ctrl_chi2_P=1 => BAD QUALITY Sometimes the Chi2 distribution does not match well with the theoretical one => useful indicator of problems for future studies..... Comparison of density functions (real->red theoretical->blue): Nm=33 Nm=97 Nm=137 >95% GOOD QUALITY >95% >95% GOOD QUALITY GOOD QUALITY BAD QUALITY BAD QUALITY BAD QUALITY BAD QUALITY BAD QUALITY <5% <5% <5%

  7. Fg_ctrl_chi2 & Fg_ctrl_chi2_P Most of the points filtered out by Fg_ctrl_chi2 are at the edges of the swath (for N<50)

  8. <SSSsmos-SSSargo> becomes very negative for Chi2P>95% Chi2P>95% QWG10, 4-6 Feb. 2013

  9. Std(SSSsmos-SSSargo) Chi2P>95% Chi2P<95% Chi2P<75% Std increases when Chi2P>95% => flag is useful for removing bad retrievalStd larger for 75%<Chi2P<95% =>Chi2_P good indicator of SSS quality Std remains at low values for Chi2P<75% QWG10, 4-6 Feb. 2013

  10. Number of SMOS measurements: about 20% with Chi2P>95% All Chi2P 75%<Chi2_P<95% Chi2P>95% QWG10, 4-6 Feb. 2013

  11. SMOS SSS March 2011 asc orbits Galactic noise flag: Qualitative effect on SMOS SSS maps:Application of the flag suppress numerous SSS in latitudinal bands => large noise and missing pixels in these areas (e.g. In Southern hemisphere March 2011, ascending orbits)No obvious SSS bias when removing the flag QWG10, 4-6 Feb. 2013

  12. Galactic noise flag: Qualitative effect on SMOS SSS maps:Application of the flag suppress numerous SSS in latitudinal bands => large noise and missing pixels in these areas (e.g. In Southern hemisphere March 2011, ascending orbits)No obvious SSS bias when removing the flag SMOS-ISAS SSS March 2011 asc orbits QWG10, 4-6 Feb. 2013

  13. Quantitative effect of Galactic noise flag on SMOS SSS: comparison with ARGO SSS over global OceanSSS averaged over +/-5days, +/-50km around ARGO) Number of colocations Flag tested Flag not tested QWG10, 4-6 Feb. 2013

  14. Quantitative effect of Galactic noise flag on SMOS SSS: comparison with ARGO SSS (Global Ocean)(SMOS SSS averaged over +/-5days, +/-50km around ARGO) Mean difference SSSsmos-SSSargo Flag tested Flag not tested QWG10, 4-6 Feb. 2013

  15. Quantitative effect of Galactic noise flag on SMOS SSS: comparison with ARGO SSS (Global Ocean)(SMOS SSS averaged over +/-5days, +/-50km around ARGO) Std difference SSSsmos-SSSargo Flag tested Flag not tested QWG10, 4-6 Feb. 2013

  16. Quantitative effect of Galactic noise flag on SMOS SSS: comparison with ARGO SSS in S. subtropical Pacific (10°S-30°S)(SMOS SSS averaged over +/-5days, +/-50km around ARGO) Number of colocations Flag tested Flag not tested QWG10, 4-6 Feb. 2013

  17. Quantitative effect of Galactic noise flag on SMOS SSS: comparison with ARGO SSS in S. subtropical Pacific (10°S-30°S)(SMOS SSS averaged over +/-5days, +/-50km around ARGO) Mean difference SSSsmos-SSSargo Flag tested Flag not tested QWG10, 4-6 Feb. 2013

  18. Quantitative effect of Galactic noise flag on SMOS SSS: comparison with ARGO SSS in S. subtropical Pacific (10°S-30°S)(SMOS SSS averaged over +/-5days, +/-50km around ARGO) Std difference SSSsmos-SSSargo Flag tested Flag not tested => We propose to remove Fg_Ctrl_gal_noise from Fg_poor_geophysical QWG10, 4-6 Feb. 2013

  19. Flagging combination Cases The following cases have been analyzed at L2 & L3: • Case 1: NO filtering by anything & Xswath=300km • Case 2: RFI=1, High_wind=1 (>12m/s), Poor_ret=1, Poor_geo=1, Xswath=300km:v5 Ctrl_poor_.. flags filtering • Case 3: RFI=1, High_wind=1, Poor_ret=1 , Poor_geo=1 (- gal_noise) , Xswath=300km • Case 4: RFI=1, High_wind=1, Poor_ret=1 (-chi2), Poor_geo=1 (- gal_noise ) , Xswath=300km

  20. ASC/DES orbits 21-30 August [-60,60] L2-ARGO ASC Same number of points only 300km of swath considered Since only 300 Km are considered here GP with CHI2 set are already filtered by CHI2_P. number of points decrease for fg_ctrl_gal_noise & not better RMS DES 1: No filter 2: poor_geo +poor_ret 3: poor_ret=1, poor_geo=1 (- gal_noise) 4: poor_ret=1 (-chi2), poor_geo=1 (- gal_noise )

  21. ASC/DES orbits 21-30 August [-60,60] L2-ARGO Same number of points only 300km of swath considered ASC mean & STD (L2-ARGO) mean & STD (mean(L2)-ARGO) DES number of points decrease for fg_ctrl_gal_noise -> not better values 1: No filter 2: poor_geo +poor_ret 3: poor_ret=1, poor_geo=1 (- gal_noise) 4: poor_ret=1 (-chi2), poor_geo=1 (- gal_noise )

  22. ASC+DES 21-30 August [-60,60] ASC+DES L2-ARGO mean & STD (L2-ARGO) mean & STD (mean(L2)-ARGO) 1: No filter 2: poor_geo +poor_ret 3: poor_ret=1, poor_geo=1 (- gal_noise) 4: poor_ret=1 (-chi2), poor_geo=1 (- gal_noise )

  23. ASC/DES orbits 21 Feb-2 Mar [-60,60] L2-ARGO ASC DES 1: No filter 2: poor_geo +poor_ret 3: poor_ret=1, poor_geo=1 (- gal_noise) 4: poor_ret=1 (-chi2), poor_geo=1 (- gal_noise )

  24. ASC+DES orbits 21 Feb-2 Mar [-60,60] L2-ARGO ASC+DES 1: No filter 2: poor_geo +poor_ret 3: poor_ret=1, poor_geo=1 (- gal_noise) 4: poor_ret=1 (-chi2), poor_geo=1 (- gal_noise ) Similar results for region [-30,30]

  25. ASC/DES orbits August/Feb [-10,10] February August ASC DES NOW pseudo L3 similar BIAS & less STD 1: No filter 2: poor_geo +poor_ret 3: poor_ret=1, poor_geo=1 (- gal_noise) 4: poor_ret=1 (-chi2), poor_geo=1 (- gal_noise )

  26. CONC LUSIONS • Better results are obtained when NOT using Fg_ctrl_gal_noise, both at Level 2 and Level 3 analysis -> this filters out many good points during some periods of time. • We consider flag Fg_ctrl_Chi2 should not be used because is theoretically incorrect (should depend on Nm) and GP with bad retrieved are already filtered by Fg_ctrl_Chi2_P. • Large variability on the L2 SMOS data is observed at high latitudes (-40, -60). • Still some land sea contamination is observed.

  27. mean(L2) – ARGO : Pseudo L3 (mean(L2 SSS) – ARGO) L2 SMOS data with the same ARGO float measurement are averaged -> pseudo L3 Land Sea contamination Effect or RFI? STD (SMOS) per ARGO Large variability are high latitudes 5- 24 june 2011 (reprocessed data)

  28. Extra slides QWG10, 4-6 Feb. 2013

  29. Definition of Fg_ctrl_poor_retrieval & Fg_ctrl_poor_geophysical in v500 If (Fg_ctrl_many_outliers(igp) = = true or Fg_ctrl_sunglint(igp) = = true or Fg_ctrl_moonglint(igp) = = true or Fg_ctrl_gal_noise(igp) = = true or Fg_ctrl_gal_noise_pol(igp) = = true or Fg_ctrl_num_meas_low(igp) = = true or Fg_sc_TEC_gradient(igp) = = true or Fg_sc_suspect_ice(igp) = = true or Fg_sc_rain(igp) = = true ) then Fg_ctrl_poor_geophysical (igp) = true If (Fg_ctrl_retriev_fail(igp) = = true or Fg_ctrl_range(igp) = = true or Fg_ctrl_sigma(igp) = = true or Fg_ctrl_chi2(igp) = = true or Fg_ctrl_chi2_P(igp) = = true or Fg_ctrl_marq(igp) = = true or Fg_ctrl_reach_maxiter(igp) = = true) Then Fg_ctrl_poor_retrieval(igp) = true

  30. ASC/DES orbits 21-30 August [-30,30] ASC DES 1: No filter 2: poor_geo +poor_ret 3: poor_ret=1, poor_geo=1 (- gal_noise) 4: poor_ret=1 (-chi2), poor_geo=1 (- gal_noise )

  31. ASC/DES orbits 21 Feb-2 Mar [-30,30] ASC DES 1: No filter 2: poor_geo +poor_ret 3: poor_ret=1, poor_geo=1 (- gal_noise) 4: poor_ret=1 (-chi2), poor_geo=1 (- gal_noise )

  32. Analysis on L3 MAPS ON DESCENDING GALACTIC NOISE FLAG ON Descending & August L3 Maps 1ºx1º SMOS-ARGO [-60,60] [-30,30] -0.15 -0.15 Mean Mean(L3-ARGO) Mean(L3-ARGO) -0. 50 -0. 50 0.9 1.0 STD STD(L3-ARGO) STD(L3-ARGO) 0.55 0.4 Best results

  33. Fg_ctrl_chi2 filter description • When then Fg_ctrl_chi2 is set to 0=>GOOD QUALITY • When then Fg_ctrl_chi2 is set to 1=>BAD QUALITY • PROBLEM: depends on Nm, but is constant for all Nm (Nm: number of measurements). Comparison of distribution functions (real->grey theoretical->green): PORTION OF DISGARDED POINTS IS NOT ALLWAYS THE SAME Nm=97 Nm=33 Nm=137 Xi2/Nm>1.35 ALL THESE POINTS ARE FILTERED Xi2/Nm>1.35 ALL THESE POINTS ARE FILTERED Xi2/Nm>1.35 ALL THESE POINTS ARE FILTERED

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