Quality control study for SMOS data / Flags analysis

QWG-10 ESRIN 4-6 February 2013

Quality control study for SMOS data / Flags analysis

C. Gabarró, J. Martínez, E. OlmedoM. Portabella, J. Font and BEC team

J. Boutin & N. Martin, LOCEANJ.L. Vergely, ACRI-st

SMOS-BEC Activities Overview, 12-June-2008, Barcelona SPAIN

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

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Flagging combination Cases


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

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Tested flags

QWG-10 ESRIN 4-6 February 2013 4 / 10

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


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_chi2Fg_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%


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.....

Fg_ctrl_chi2_P filter description

Nm=33 Nm=97 Nm=137

Comparison of density functions (real->red theoretical->blue):

>95%

<5%

BAD QUALITY

BAD QUALITY

GOOD QUALITY

GOOD QUALITY

GOOD QUALITY

>95% >95%

<5% <5%

BAD QUALITY

BAD QUALITY

BAD QUALITY


Fg_ctrl_chi2 & Fg_ctrl_chi2_P

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

% of filtered points

march june desember 2011

Fg_ctrl_chi2 17.58 16.24 27.47

Fg_ctrl_chi2_P 29.55 27.99 39.13

<SSSsmos-SSSargo> becomes very negative for Chi2P>95%

Chi2P>95%QWG10, 4-6 Feb. 2013

Std(SSSsmos-SSSargo)

Chi2P>95%Chi2P<95%Chi2P<75%

Std increases when Chi2P>95% => flag is useful for removing bad retrieval

Std 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

Number of SMOS measurements: about 20% with Chi2P>95%

Chi2P>95%

All Chi2P

75%<Chi2_P<95%

QWG10, 4-6 Feb. 2013

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

SMOS SSSMarch 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

SMOS-ISAS SSSMarch 2011 asc orbits

Quantitative effect of Galactic noise flag on SMOS SSS: comparison with ARGO SSS over global Ocean

SSS averaged over +/-5days, +/-50km around ARGO)

Flag testedFlag not tested

Number of colocations

QWG10, 4-6 Feb. 2013

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

QWG10, 4-6 Feb. 2013

Quantitative effect of Galactic noise flag on SMOS SSS: comparison with ARGO SSS (Global Ocean)



Std difference SSSsmos-SSSargo

QWG10, 4-6 Feb. 2013

Quantitative effect of Galactic noise flag on SMOS SSS: comparison with ARGO SSS in S. subtropical Pacific (10°S-30°S)



Number of colocations

QWG10, 4-6 Feb. 2013




Mean difference SSSsmos-SSSargo

QWG10, 4-6 Feb. 2013




Std difference SSSsmos-SSSargo

QWG10, 4-6 Feb. 2013=> We propose to remove Fg_Ctrl_gal_noise from Fg_poor_geophysical


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

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Flagging combination Cases


ASC/DES orbits 21-30 August [-60,60]

DES

ASC

number of points decrease for fg_ctrl_gal_noise &not better RMS

Same number of points only 300km of swath considered

1: No filter2: poor_geo +poor_ret3: poor_ret=1, poor_geo=1 (- gal_noise )4: poor_ret=1 (-chi2), poor_geo=1 (- gal_noise )

L2-ARGO

Since only 300 Km are consideredhere GP with CHI2 set are already filtered by CHI2_P.



DES

ASC

number of points decrease for fg_ctrl_gal_noise ->not better values

Same number of points only 300km of swath considered


L2-ARGO

mean & STD (L2-ARGO)mean & STD (mean(L2)-ARGO)


ASC+DES 21-30 August [-60,60]

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ASC+DES

mean & STD (L2-ARGO)mean & STD (mean(L2)-ARGO)

L2-ARGO


ASC/DES orbits 21 Feb-2 Mar [-60,60]

ASC

DES


L2-ARGO


ASC+DES orbits 21 Feb-2 Mar [-60,60]

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L2-ARGO ASC+DES

Similar results for region [-30,30]


ASC/DES orbits August/Feb [-10,10]

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DES

ASC

August February

NOW pseudo L3 similar BIAS & less STD



CONCLUSIONS

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.

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SMOS-BEC Activities Overview, 12-June-2008, Barcelona SPAIN 27 / 10

mean(L2) – ARGO : Pseudo L3

L2 SMOS data with the sameARGO float measurementare averaged -> pseudo L3

5- 24 june 2011 (reprocessed data)

Large variability are high latitudes

Land Sea contaminationEffect or RFI?

STD (SMOS) per ARGO

(mean(L2 SSS) – ARGO)

Extra slides

QWG10, 4-6 Feb. 2013


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

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ASC

DES


ASC/DES orbits 21 Feb-2 Mar [-30,30]

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DES

ASC



Analysis on L3 MAPS ON DESCENDING

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GALACTIC NOISE FLAG ON Descending & August

[-60,60] [-30,30]

-0. 50 0.9

0.4

1.0

0.55

L3 Maps 1ºx1ºSMOS-ARGO

Mean

(L3

-AR

GO

)S

TD

(L3

-AR

GO

)

-0.15

-0. 50

STD

(L3

-AR

GO

)M

ean

(L3

-AR

GO

)

-0.15

Mean

STD

Best results

SMOS-BEC Activities Overview, 12-June-2008, Barcelona SPAIN 33 / 10

Fg_ctrl_chi2 filter description

Xi2/Nm>1.35

ALL THESE POINTS ARE FILTERED

Nm=33 Nm=97 Nm=137

Xi2/Nm>1.35


Xi2/Nm>1.35


Comparison of distribution functions (real->grey theoretical->green):PORTION OF DISGARDED POINTS IS NOT ALLWAYS THE SAME

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).

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Quality control study for SMOS data / Flags analysis

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