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SMOS L2 Ocean Salinity

Level 2 Ocean Salinity QWG #8

29 May 2012

ARGANS & L2OS ESL

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SMOS L2 Ocean Salinity

Original DPGS L2OS 2009-2012 before reprocessing

Data products: retrieval performance

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SMOS L2 Ocean Salinity

Reprocessed L2OS 2010-2011

Data products: retrieval performance

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SMOS L2 Ocean Salinity

Reprocessed L2OS 2010-2011 & DPGS 2012

Data products: retrieval performance

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SMOS L2 Ocean Salinity

• Dg_sun_glint_area wrong (propagated from L1)

• bug in iterative scheme exit condition test (MAP_3_2-15)– low impact, only seen in regions of high wind speed (eg high latitudes)

• bug in DPM galactic noise flagging (PRP_9-1)– fm_gal_noise_error set when galactic map delta I (strong point

sources) > Tm_max_gal_noise_error, increasing Dg_galactic_noise_error, as a result Fg_ctrl_galactic_noise (part of Fg_ctrl_poor_geophysical) may be set sometimes when it should be clear, leading to streaks of data filtered out by the Fg_ctrl_poor_geophysical flag

L2OS v550 status

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SMOS L2 Ocean Salinity

From ATBD/DPM: exit when both convergence tests are met (i is iteration):

Convergence test 1 (threshold on chi2):If not much improvement in χ2:

abs (χi+12 − χi

2) /χi2 < δχ

Convergence test 2 (normalized step size threshold):If the relative parameter variation from one iteration to another is lower than the threshold δsig:

max[abs(pi+1-pi)/σprior] < δsig

Bug in v550 convergence test 2:max[abs(pi+1-pi)/prior] < δsig

Impact on all roughness models – iterative loop may exit too early,and wind speed vector prior (in model 1) can be negative.

Iterative scheme bug: loop exit conditions

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SMOS L2 Ocean Salinity

Iterative scheme bug: number of iterations – v550SSS1

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SMOS L2 Ocean Salinity

Iterative scheme bug: number of iterations – v552

More iterations everywhere, doesn’t exit convergence loop so quickly, more iterations in RFI near Greenland

SSS1

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SMOS L2 Ocean Salinity

Iterative scheme bug: impact of retrievals

v550 v552

SSS1 has 1% more retrievals with Dg_quality_SSS < 150(SSS2 0.5%, SSS3 1%) – minimal delta in retrieved SSS

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SMOS L2 Ocean Salinity

WS ~0m/s

Iterative scheme bug: impact of retrievals

WS prior SSS1 v552

Minimal delta in retrieved SSS1 except where WS ~0m/smaybe iterative loop stops earlier instead of wandering off...

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SMOS L2 Ocean Salinity

Iterative scheme bug: sigma SSS – v550

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SMOS L2 Ocean Salinity

Iterative scheme bug: sigma SSS – v552

Small decrease in mean(Sigma_SSS1) from 2.64 to 2.61

Also for SSS2: 2.70 to 2.66, & SSS3: 2.57 to 2.46

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SMOS L2 Ocean Salinity

Dg_sky Dg_galactic_noise_error v550 after bug fixbug setting fm_gal_noise_error

Galactic noise bug

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SMOS L2 Ocean Salinity

v550 with fm_gal_noise_error bug after bug fix

Fg_ctrl_galactic_noise (part of Fg_ctrl_poor_geophysical) may be set sometimes when it should be clear, leading to streaks of data filtered out by the poor_geophysical flag

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SMOS L2 Ocean Salinity

• v600– Galactic noise model adjustment– Tuned roughness models– Improved TEC retrieval: estimate from Stokes 3?– Extend RFI detection/mitigation algorithms?– Bug fixes

• iterative scheme exit condition test• galactic noise flagging

– Add xSwath & grid-point measurement time to UDP (2 spare fields available)– Improved schema/ADF/product version & validity checks

• Schedule?– deliver late September or early October 2012 for 2012/13 reprocessing

L2OS v600 delivery plan

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SMOS L2 Ocean Salinity

RFI detection

v550 implements a 2 step RFI outlier detection algorithm based on outlier detection, using all measurements on a grid point

Fg_ctrl_suspect_rfi set if Fm_L2_RFI > 50%

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SMOS L2 Ocean Salinity

• RFI sometimes shows an incidence angle dependency, eg north of the Azores (orbit start 20110209T064332):

• VV pol measurements below incidence angles of 40° are corrupted by RFI, presumably from further north. Above 40° retrieval could be attempted.

• Bin delta TBs by azimuth & incidence angle, test std(bin) with a threshold.– Detection ok, but mitigation poor – most VV measurements flagged

RFI detection

Std for VV pol measurements < 40° is 20 to 40

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SMOS L2 Ocean Salinity

• Results from binning std(delta TBs) by azimuth & incidence angle:– Detection ok, but mitigation poor – most VV measurements flagged – 18 day repeats do not have exact same geometry over grid points, so RFI data is in

different azimuth/elevation bins – Not clear how this post-processed RFI information can be used by L2OS – adjust

radiometric accuracy near RFI prone regions?

• Different approaches needed for different types of RFI– DEW line RFI impacts complete snapshots – filter snapshots?– Snapshot filtering used by ESL (JT), using BT threshold

– Point source RFI may be incidence angle dependent– Bin (std, L1c BT, deltaTB?) by az/el & post-process?– RFI post-processor output can be used for

• Regional specific L1 RFI mitigation if computationally expensive• Adjust thresholds/radiometric accuracy in L2OS near RFI high probability regions

RFI detection

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SMOS L2 Ocean Salinity

Some similarities in pattern, but some gaps too – snapshots not in sync?

RFI detection: angle binning20110209 &20110227:

18 day repeat

Bins: 30° azimuth 10° elevation

std(meas-model) for V pol measurements

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SMOS L2 Ocean Salinity

RFI detection: angle binning

20110206 & 20110224: 18 day repeat, but different pattern for same grid points with 3 day shift

May be large errors in std(deltaTB) for each bin: only a small number of measurements per bin.

Could repeat this study, but instead of std(deltaTB), extract L1c BTs corrected for all contributions (atmosphere, glints…) except forward model surface one (model independent). BUT: how would L2OS make use of this to improve retrievals?