About L2OS v6 improvement wrt L2OS v5

N. Martin – J.L. Vergely - J. Boutin

Descending orbits resultsIn L2 v6 => latitudinal biases are reduced wrt L2 v5

due to TEC

Slides from QWG 13TEC retrieval in L2 reduces latitudinal biases in

descending orbits(tests conducted using same L1c)

SMOS SSS - ISAS SSS: descendingPCTVAR<80% (exclude regions with no ARGO) and 700km far from land

L2V550OTT L1cTEC – L1cTECprior – TEC dwell retr.

L2V611b, OTT L1cTEC – A3TEC ‘prior’ -no TEC dwell retr.

L2V550OTT A3TEC on - L1cTEC prior –TEC dwell retr.

Global: mean=0.11 (std=0.39)[45S45N;180W180E] : mean=0.05 (std=0.32)[30S30N;180W180E] : mean=-0.01 (std=0.29)

L2V550OTT L1cTEC – L1cTECprior – TEC dwell retr.

L2V611b, OTT A3TEC on- A3TEC prior – no TEC dwell retr.

The TEC retrieval in L2OS improves retrieved SSS compared with ISAS SSS.

L2V611b, OTT A3TEC on- A3TEC prior – no TEC dwell retr.

Global: mean=0.00(std=0.36)45S-45N: mean=-0.01 (std=0.29)30S-30N: mean=-0.02 (std=0.27)

Suntail flag in L1c v620

X. Yin1,2, J. Boutin2, J. Vergely3 , P. Spurgeon1

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1. ARGANS2. LOCEAN3. ACRI-ST

Thanks to L1 team for providing L1C v620 product.

Aims: 1.Validate the new suntail flag

2.Define the methodology at L2 to be used to flag data affected by sun

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1) Data• 5 days ascending and descending orbits in May 2011 and November 2012, L1C v620 and L2OS v612• L2OS without Suntail filtering processed by ARGANS• L2OS with Suntail filtering processed by LOCEAN

2) Method2.1 Part1 : Validation of TB radiometric accuracy

std(Tbsmos-Tbmodel) wrt radiometric accuracy

The grid points in the FOV with number of measurements less than 30 are discarded

2.2 Part 2: Validation of SSS and Chi2p flagging

Comparisons of monthly SSS w.r.t ISAS, and intercomparisons between SSS (CTRL_Chi2p flag) with or without filtering with L1 Suntail flag

Consider only Tbs 1000km away from coasts to avoid land contaminationSMOS SSS flags used

CONTROL FLAGS :

check to be set to 1 : CTRL_ECMWF

check to be clear to 0 :

CTRL_MANY_OUTLIERS;CTRL_SUNGLINT;CTRL_MOONGLINT;CTRL_REACH_MAXITER;CTRL_MARQ;

CTRL_CHI2_P;CTRL_SUSPECT_RFI

SCIENCE FLAGS :

check to be set to 1 : SC_LOW_WIND;SC_LAND_SEA_COAST1

check to be clear to 0 : SC_ICE;SC_SUSPECT_ICE

+Dg_af_fov>130

Part1 Validation of TB radiometric accuracy

Ratio of std(Tbsmos-Tbmodel) wrt theoretical radiometric accuracy computed between 0N and 30N

The grid points in the FOV with number of measurements less than 30 are discarded

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Descending orbits in the northern hemisphere are strongly affected in November 2012 (eclipse period)

[std (TB-Tbmodel)/rad_acc.] of 1 orbit (20121118) in open ocean between 0N and30N

Suntails in FOV

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No filtering Suntail + Sun point

Suntail and Sun point flag remove some regions with strong Sun contamination. However, vertical stripes outside suntails are still seen in FOV (due to imperfect sun correction?).

Ratio: StdTB/Ra

Std(TBsmos-TBmodel)i.e. StdTB

X pol.

Y pol.

Theoretical Radiometric accuracy i.e. Ra

Vertical stripes outside Suntails can be seen in FOV (due to imperfect sun correction?).

Same as previous slide except for 10 orbitsLong integration snapshots with filtering

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Ratio: StdTB/Ra

Std(TBsmos-TBmodel)i.e. StdTB

X pol.

Y pol.

Theoretical Radiometric accuracy i.e. Ra

Vertical stripes outside Suntails can be seen in FOV (due to imperfect sun correction?).11

Same as previous slide except for 10 orbitsshort integration snapshots with filtering

With filtering

X pol.

Y pol.

Long integration snapshots, Ratio: StdTB/Ra, 10 orbits

Without filtering

12Suntail flag and Sun point flag remove some data contaminated by Sun, but they are not enough to flag ripples outside the tails.

Suntails in FOV

13

Ascending orbits in May 2011 (Sun alias in bottom left of FOV)TB of 1 orbit (20110526) in the OTT region (45S and 5S by black box)

No filtering Suntail + Sun point

The impact of Sun is much smaller in May than in November. Suntail and Sun point flag remove regions with contamination (maybe too much).

Ratio: StdTB/Ra

Std(TBsmos-TBmodel)i.e. StdTB

X pol.

Y pol.

Theoretical Radiometric accuracy i.e. Ra

Suntail and Sun point flag remove regions with contamination.14

Same as previous slide except for 10 orbitsLong integration snapshots with filtering

Ratio: StdTB/Ra

Std(TBsmos-TBmodel)i.e. StdTB

X pol.

Y pol.

Theoretical Radiometric accuracy i.e. Ra

15

Same as previous slide except for 10 orbitsshort integration snapshots with filtering

Suntail and Sun point flag remove regions with contamination.

Conclusion and discussion of Part 1 (TB validation)

1. For ascending orbits in May with Sun alias in the bottom left of FOV, Suntail and Sun point flag remove regions with contamination but maybe too much.

Question: Do we need to filter TB flagged by Suntail before SSS retrievals for ascending orbits given that impact of Sun is much smaller than the descending orbits in November?

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Be careful about the vertical tail in the FOV due to the Suntail flag. No or few TB can be used for SSS inversion along dwell lines near the vertical tail! More details in part 2.

2. For descending orbits in November with Sun alias in the left side of FOV, vertical stripes outside suntails, especially for X(H) pol., can be seen in FOV (due to imperfect sun correction?). The Suntail flag itself is not enough to flag those vertical stripes.

Part 2 SSS and Chi2p

1. Comparisons of SMOS SSS w.r.t ISAS (monthly in situ interpolated maps)

2. Intercomparisons between SSS maps obtained with or without filtering L1c TB with Suntail flag and after cheching the L2OS Chi2P flag(chi2P : good TB fit if chi2P high. Chi2P > 0.05 in current processor. )

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181. When applying Suntail filtering, no SSS are retrieved along the vertical Suntail. Also, SSS near the vertical tail are quite different to those retrieved in other parts of the swath. 2. Nothing strange can be seen in SSS along the vertical tail when no Suntail filtering is applied.

SSSwithfilt-SSSISAS SSSnofilt-SSSISAS SSSwithfilt-SSSnofilt

Suntails in FOV

One ascending orbit in May 2011 (Sun alias in bottom left of FOV)SSS of one orbit (20110526)

With L1c suntail filtering

Without L1c suntail filtering

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SSSnofilt-SSSISAS, mean=-0.03, std=0.65

SSSwithfilt-SSSISAS, mean=-0.06, std=0.72

SSSnofilt-SSSwithfilt , mean=0.03, std=0.36

1. When applying Suntail filtering, SSS near the vertical tail are quite different to those in other parts of the swath 2. Nothing strange can be seen in SSS along the vertical tail when no Suntail filtering is applied.

Comparison of monthly SMOS SSS with ISAS (May 2011)

20When applying L1c Suntail filtering, less dwell lines are filtered by the L2OS Chi2P flag => more SSS are retrieved in the northern hemisphere ... but they suffer from strong impact of Sun (low biases).

SSSwithfilt-SSSISAS SSSnofilt-SSSISAS SSSwithfilt-SSSnofilt

Suntails in FOV

One descending orbits in November 2012 (eclipse period) SSS of one orbit (20121118)

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SSSnofilt-SSSISAS, mean=-0.02, std=0.79

SSSwithfilt-SSSISAS, mean=-0.22, std=0.86

SSSnofilt-SSSwithfilt , mean=0.05, std=0.38

When applying Suntail filtering, more SSS are retrieved in the northern hemisphere (middle panel) than when the L1c Suntail flag is not filtered, but they are systematically biased (more details in slide 21).

Extra slides: In case Sun alias does not appear in the FOV(descending orbits in May 2011)

The vertical Suntail still appears in the FOV even if the Sun alias is not in the FOV. There is few valid TB near the vertical tail (figure left). SSS near the tail are strange (middle panel in the maps below).

SSSnofilt-SSSISAS, mean=0.03, std=0.65

SSSwithfilt-SSSISAS, mean=0.00, std=0.70

SSSnofilt-SSSwithfilt , mean=0.03, std=0.33

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Extra slides: In case Sun alias does not appear in the FOV(ascending orbits in November 2012)

SSSnofilt-SSSISAS, mean=-0.18, std=0.72

SSSwithfilt-SSSISAS, mean=-0.14, std=0.76

SSSnofilt-SSSwithfilt , mean=-0.04, std=0.37

SSS near the tail are strange (middle panel in the maps below) when applying Suntail filtering.

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Conclusion and discussion of Part 2 (SSS): should we use L1c suntail flag in L2OS

1. All ascending orbits and descending orbits during the non eclipse period.For ascending orbits in May with Sun alias in the bottom left of FOV, Sun contamination is weak. When applying Suntail filtering, SSS near the vertical tail appear noisy and biased. This is not observed when no Suntail filtering is applied. The sam e is observedfor the period when the Sun alias is outside EAFFOV (vertical tail still present in the FOV).We recommend not to apply the L1c Suntail flag in the L2OS

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Conclusion and discussion of Part 2 (SSS)

2. Descending orbits during the eclipse period: When applying L1c suntail flag, more SSS are retrieved in the northern hemishpere but they are strongly biased compared with ISAS SSS (-0.66), while SSSsmos-SSSisas of ascending orbits is -0.27. We recommend not to apply the Suntail flag in the L2OS descending orbits during the eclipse period because the L2OS Chi2P flag better removes biased retrieved salinities when no L1c suntail filtering is applied

0-40N: SSSasc,nofilt -SSSISAS, mean=-0.27, std=0.72

0-40N: SSSdesc,withfilt -SSSISAS, mean=-0.66, std=0.88

L2OS threshold optimisation

20 June 2014, PM26

JL Vergely, J. Boutin, P. SpurgeonACRI-ST,LOCEAN, ARGANS

RFI/outlier detection

Aim : To improve the thresholds of the L2OS

processor to be applied on TB measurements in order to remove outliers.

About thresholds : should be independent on L1c quality

products

Thresholds to be testedtest for outlier detection (dwell test)nsig

test for out of range TB detection (FOV test)Tm_out_of_range_affov Tm_out_of_range_eaffovTm_out_of_range_stokes3_affovTm_out_of_range_stokes3_eaffovTm_out_of_range_stokes4_affovTm_out_of_range_stokes4_eaffov

test for oscillation TB detection (FOV test)Ts_stdTs_std_stokes3Ts_std_stokes4

Other tests : max of iteration

Tests conditions|X_swath| < 400 km (& sig_SSS<1.35)Coast > 1000 km-40° < lat < 40°

SSS ref: ISAS near real time (MyOcean)PCT_var < 80

Day : 1,2,3,4,5/5/2013, L1C v550L2OS proc : v600 (CATDS processing chain)

Indicators / SSS quality filter- chi2P : good TB fit if chi2P high. Chi2P > 0.05

in current processor. - mean(SSS SMOS – SSS Coriolis) and std(SSS

SMOS – SSS Coriolis) - X = (SSS SMOS – SSS Coriolis)/SSS_error. X

should be close to a Gaussian law with mean(X)=0 and std(X)=1. Does not depend on SSS accuracy (close to the ratio between empirical error and theoretical error).

Chi2P and RFI

Chi2P, 5/5/2013, asc

Percentage of RFI contamination : january 2012, asc

nsig : outlier test at ‘nsig’ sigma

Outlier detection.Dwell test.TB removed if :

|TBsmos – TBmodel – DA| > nsig.rad_noiseDA = mean dwell correction

Current value : 5Tested values : 2, 3, 4, 5

nsig full ocean

Bad fit Good fit

nsig full ocean

Expected distribution

Centred reduced variable

4 sigmas test

Queue distribution : outliers

nsig full ocean

No Chi2P filter in L2OS

Chi2p > 0.05

Mean and std(X)

nsig = 2

nsig full ocean Mean and std(X)

nsig = 3

No Chi2P filter in L2OS

Chi2p > 0.05

nsig full ocean Mean and std(X)

nsig = 4

No Chi2P filter in L2OS

Chi2p > 0.05

nsig full ocean Mean and std(X)

nsig = 5

No Chi2P filter in L2OS

Chi2p > 0.05

nsig full ocean

nsig=2: Many outliers at 4 sigmas

nsig : coast (1000km)

nsig coast

Expected distribution

nsig coast

No specific filter

Chi2p > 0.05 & sigSSS < 1.35

Mean and std(X)

nsig = 2

nsig coast

No specific filter

Chi2p > 0.05 & sigSSS < 1.35

Mean and std(X)

nsig = 3

nsig coast

No specific filter

Chi2p > 0.05 & sigSSS < 1.35

Mean and std(X)

nsig = 4

nsig coast

No specific filter

Chi2p > 0.05 & sigSSS < 1.35

Mean and std(X)

nsig = 5

nsig coast

nsig=2 : very biased !!

nsig=2: Many outliers at 4 sigmas

5 day processing

1,2,3,4,5/05/2013; nsig = 2, 3, 4, 5 Dwell test.TB removed if :

|TBsmos – TBmodel – DA| > nsig.noiseDA = mean dwell correction

Current config : nsig = 5

Without LS mask. chi2P > 0.05nsig=2

nsig=3

nsig=4

nsig=5

Preliminary Conclusions Chi2P (or chi2) is improved with TB filtering but SSS

biases increase. No TB filtering requiered ? It helps for coast (only for some

threshods) but not for open ocean. The current configuration of L2OS has very high

thresholds which filter almost nothing. A configuration with 0 TB filtering gives almost the same results as the current configuration. In the future ‘almost’ will have to be quantified and decide whether we should adapt the current L2OS configuration

The best quality SSS is obtained when filtering is only done at SSS level from Dg_chi2P, but this is at the expense of the number of retrieved SSS. For L2OS v7, envisage several steps/filtering? 1-no L1c filter - only Chi2P => best SSS; 2-in pixels eliminated by -1-, filter L1c, then retrieve SSS => degraded SSS quality.

Use of Tm_out_of_range ? Algorithm to be improved (need to be normalized by radiometric accuracy) and tested again ?

Extra slides

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Tm_out_of_range_affov or eaffov (polar X,Y,3,4)

Snapshot removed if at least one TB is an outlier :

|TB smos – TB model| > Tm_out_of_range

Problem because the test is applied directly on the TBs and not on the TBs normalised by the radiometric noise

X and Y from short and long integration timeCurrent value : 50 K for affov and 100 K for

eaffovTested value : 10, 20, 30, 40 K

Tm_out_of_range_affov full ocean

Tm_out_of_range_affov full ocean

No specific filter

Chi2p > 0.05 & sigSSS < 1.35

Tm = 10K

Tm_out_of_range_affov full ocean

No specific filter

Chi2p > 0.05 & sigSSS < 1.35

Tm = 40K

Tm_out_of_range_affov full ocean

Tm_out_of_range_eaffov full ocean

Tm=10K :

Little bit better but lost of accuracy

No significative change

(with Tm_out_of_range_affov = 12)

Tm_out_of_range_stokes3_affov full ocean

Tm=6K :

Little bit better

-> try to work in dual pol mode ?

No significative change

(with Tm_out_of_range_affov/eaffov = 12/18)

No significative change

(with Tm_out_of_range_stokes3_affov = 8)

Tm_out_of_range_stokes3_eaffov full ocean

Tm_out_of_range_stokes4_affov full ocean

No significative change

(with Tm_out_of_range_stokes3_affov/eaffov = 8/16)

Tm_out_of_range_stokes4_eaffov full ocean

No significative change

(with Tm_out_of_range_stokes3_affov/eaffov = 8/16 & Tm_out_of_range_stokes4_affov = 10)

Ts_std thresholds

Snapshot is removed if :rms((TB smos –TB model)/ra) > Ts_std

rms((TB smos –TB model)/ra) is expected to be close to 1 (if OTT well applied)

Current value = 2.5

Ts_std full ocean

Ts_std=1.5 :

Little bit better

Ts_std_stokes3 full oceanTs_std=0.5 or 1 :

Too low

Too biased

No significative improvement

Ts_std_stokes4 full ocean

No significative improvement

Ts_std=1 :

Too low

Too inaccurate

Comparison current configuration and configuration without thresholds

Comp current/without thres. full ocean

current conf

Chi2p > 0.05 & sigSSS < 1.35

Comp current/without thres. full ocean

without filter

No signicative change

Chi2p > 0.05 & sigSSS < 1.35

Comp current/without thres. full ocean

A little bit better without thresholds

Comp current/without thres. coast

Without thresholds : better for 4 sigmas SSS

Iteration number

2 modes !!

Iteration numberSignature TEC ?

RFI or island ?

Hot spot

Global improvement using iterMax

Small global effect.

What about specific area ?

4 zones with RFI/coast contamination

Pacific

Pacific + coast

Atlantic

Indian ocean

4 zones with RFI/coast contamination

Pacific

Pacific + coast

Atlantic

Indian ocean

iterMax = 5

Itermax=5 is too low : lost of accuracy

Low bias

Gulf of Bengal

iterMax = 10

good accuracy

iterMax = 15

No significative change comparatively to 10

iterMax = 20

iterMax=20 (current)

iterMax=15

iterMax=10

iterMax=5

Stripes