SMOS-BEC – Barcelona (Spain)

Preliminary analysis on the processing of fused temperatures with L2PP

BEC team

SMOS Barcelona Expert CentrePg. Marítim de la Barceloneta 37-49, Barcelona SPAINE-mail: smos-bec@icm.csic.esURL: www.smos-bec.icm.csic.es

SMOS-BEC 2

Contents and objectives

Objectives:1. To assess the “radiometric accuracy” of fused TBs2. To compare retrieved salinities from SMOS and fused TBs3. To analyze the inversion residuals from fused TBs for QC purposes

Contents:• Brief description of the fusion process• Some modifications of L2P processor• Fused TBs “radiometric accuracy” assessment• Retrieved salinity quality analysis and intercomparison• Filtering analysis on L2 product from fused TBs• Summary and conclusions

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Brief description of the fusion process

Algorithm: Tb from DPGS L1C is fused with OSTIA SST (OSTIA data: http://ghrsst-pp.metoffice.com/pages/latest_analysis/ostia.html)

• Compute OTT and apply it to L1C in the ARF (Antenna Reference Frame)• Convert Tb in TOA (Top Of the Atmosphere) and with the Earth Reference

Frame• Convert Tb to ground level (Bottom Of the Atmosphere, BOA )• Use Singularity Analysis to fuse SST with Tb

• Convert resulting Tb back to antenna level in the ARF• Process new L1C file using L2PP 5.5

Zone under study: Latitude in [-30o,0o] and longitude in [-1500,-1200] (zone 122)Dates: February 6-16 2012. Ascending orbits.We have always used BEC salinity model (SSS3)

References related with fusion:Turiel, A., Sole, J., Nieves, V., Ballabrera-Poy, B., and Garca-Ladona, E. (2008a). Tracking oceanic currents by singularity analysis of microwave sea surface temperature images. Remote Sensing of Environment, 112(5):2246-2260. Earth Observations for Terrestrial Biodiversity and Ecosystems Special Issue.

Turiel, A., Yahia, H., and Perez-Vicente, C. (2008b). Microcanonical multifractal formalism geometrical approach to multifractal systems: Part I. singularity analysis. J. Phys. A: Math. Theor., 41(1).

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Some modifications of L2P processor

4

We have used DPGS L2P processor for the salinity computationA few modifications have been tested for fused TB processing:

• (M1): Change of TB filter before salinity computation: RFI filter has been modified:• Point in risk of RFI:

• Criterion for temperature deletion for points in risk of RFI:

(same formula than for outlier but M=3 for RFI and M=5 for outlier)

• (M2): Above TB filter before salinity computation (pre-filter) not considered

• (M3): Cost function background term (constraints) not accounted for

measmeas N

i

imeas

i

meas

N

i

imeas

i

meas NKTBTB

N 1

2)(2)(mod

1

2)()(mod )(

1)(

1

meas

meas

N

iNi

measi

imeas

i

KTBTB

12)(2)(

mod

2)()(mod )(

)()()(mod

imeas

imeas

i MTBTB 2)(2)(mod

)()(mod

imeas

iimeas

i MTBTB

parammeasN

jjparam

jprior

jN

iimeas

i

imeas

i PPTBTB

12)(

2)()(

12)(2)(

mod

2)()(mod

)()(

measN

iimeas

i

imeas

i TBTB

12)(2)(

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SMOS-BEC

TB quality analysisPolarization H

SMOS TB

Fused TB

Polarization H

measTBTB mod

Sigma of fused TBs

decreases by a factor 4

with respect to the sigma of

SMOS TBs

Polarization V

Polarization 3

Polarization 4

Polarization V

Polarization 3

Polarization 4

Radiometric accuracy

SMOS TB

Fused TB

We compute the standard deviation and the mean of

as function of the incidence angle

TBmeas represents SMOS nominal TBs or fused TBs

TBmod is evaluated at retrieved parameters both for nominal and fused TBs

Computations with M1 software.

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Salinity quality analysis

COMPARISON OF SALINITIES

We have computed salinity with and without cost function constraints (M3)

We compare the RETRIEVED salinities from SMOS and fused TBs

We compare the salinity with ARGO buoys.

Comparison of L2 salinity in a neighbourhood of 15km and 1day

Fused TB (no priors) Fused TB (priors) SMOS TB (no priors)

SMOS TB (priors) Climatology February

Climatology March

SMOS TB (priors) Fused TB (no priors)

Fused TB (priors)

COMPARISON WITH ARGO

In general, fused TBs result in narrower salinity distributions and of higher quality (w.r.t. ARGO)

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Filtering analysis on L2 product from fused TBs

We test two kinds of filters:

POST-FILTERS: flag grid points with poor quality retrieved salinities

Fg_ctrl_retrievFg_ctrl_suspect_RFIFg_sc_high windFg_ctrl_rangeFg_ctrl_sigmaFg_ctrl_chi2_PFg_ctrl_reach_maxiter Fg_ctrl_marqFg_ctrl_many_outliersFg_ctrl_sunglintFg_ctrl_moonglintFg_ctrl_num_meas_lowFg_sc_TEC_gradientFg_sc_suspect_iceFg_sc_rain

PRE-FILTERS: remove TB measurements before salinity retrieval

RFI pre-filterOutlier pre-filter

We have performed the following situations:1. We have fitted the sigma associated to fused TBs with a 5

degree polynomial ( ) as function of incidence angle and polarization

2. We have considered two different values for the total error associated to the fused TBs:

a)b)

3. For each one of these two configurations, we compute salinity with standard pre-filter criteria (L2P processor) and without RFI-Outlier pre-filter (M2 software)

4. For every set of resulting salinity we have analyzed the salinity accuracy without any post-filter applied to the results; with all post-filters minus Fg_ctrl_chi2_P ; with all post-filters

fit

fitmeas 22mod

2.022mod fitmeas

SMOS-BEC

Filtering analysis on L2 product from fused TBs

NO pre-filter and fit NO pre-filter and 2.0 fit

Pre-filter and fit Pre-filter and 2.0 fit

We compute the mean and the peak of the residuals distribution as function of the number of measurements used in the salinity computationThe peak should be close to the identity for having distributions close to the theoretical Chi2 distributionsNormalized distributions should be centered at one for a proper Fg_ctrl_Chi2_P application

Centered distributions and peak close to identity 2.0 fit

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Filtering analysis on L2 product from fused temperatures

COMPARISON WITH ARGO (no pre-filtering)COMPARISON WITH ARGO (pre-filtering)

Statistics of ARGO comparison (no pre-filtering):

Statistics of ARGO comparison (prefiltering):

No post-filtering All post-filtering without Fg_ctrl_Chi2_P All post-filtering

No post-filtering All post-filtering without Fg_ctrl_Chi2_P All post-filtering

Pre-filters improvesstandard

deviation but decreases the number of final “good” points

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Final comparison of salinities

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Summary and conclusions

• The radiometric accuracy of fused TBs decreases by a factor 4 (approximately) with respect to SMOS TBs

• The fused TBs can be processed with L2P processor.

• Preliminary ARGO comparisons show higher quality retrieved salinities from fused TBs than from SMOS TBs

• Remarks & future work on fused TBs• Improve rad. accuracy estimation (e.g., discern

short/long)• Improve QC (e.g., Chi2-based, normalization w.r.t.

N_meas and cross-track location)• Further test unconstrained cost function