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Preliminary analysis on the processing of fused temperatures with L2PP

Preliminary analysis on the processing of fused temperatures with L2PP. BEC team SMOS Barcelona Expert Centre Pg. Marítim de la Barceloneta 37-49, Barcelona SPAIN E-mail: smos-bec@icm.csic.es URL: www.smos-bec.icm.csic.es. Contents and objectives. Objectives:

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Preliminary analysis on the processing of fused temperatures with L2PP

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  1. Preliminary analysis on the processing of fused temperatures with L2PP BEC team SMOS Barcelona Expert Centre Pg. Marítim de la Barceloneta 37-49, Barcelona SPAIN E-mail: smos-bec@icm.csic.es URL: www.smos-bec.icm.csic.es

  2. Contents and objectives • Objectives: • To assess the “radiometric accuracy” of fused TBs • To compare retrieved salinities from SMOS and fused TBs • 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

  3. 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). 3

  4. Some modifications of L2P processor • We have used DPGS L2P processor for the salinity computation • A 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):AboveTB filter before salinity computation (pre-filter) not considered • (M3): Cost function background term (constraints) not accounted for

  5. TB quality analysis Polarization H We compute the standard deviation and the mean of as function of the incidence angle TBmeas represents SMOS nominal TBs or fused TBs TBmodis evaluated at retrieved parameters both for nominal and fused TBs Computations with M1 software. Polarization H SMOS TB Fused TB Polarization V Polarization V Polarization 3 Polarization 3 Sigma of fused TBs decreases by a factor 4 with respect to the sigma of SMOS TBs Radiometric accuracy SMOS TB Fused TB Polarization 4 Polarization 4

  6. Salinity quality analysis • We compare the salinity with ARGO buoys. • Comparison of L2 salinity in a neighbourhood of 15km and 1day We have computed salinity with and without cost function constraints (M3) We compare the RETRIEVED salinities from SMOS and fused TBs COMPARISON WITH ARGO COMPARISON OF SALINITIES 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) In general, fused TBs result in narrower salinity distributions and of higher quality (w.r.t. ARGO)

  7. Filtering analysis on L2 product from fused TBs We test two kinds of filters: POST-FILTERS: flag grid points with poor quality retrieved salinities PRE-FILTERS: remove TB measurements before salinity retrieval Fg_ctrl_retriev Fg_ctrl_suspect_RFI Fg_sc_high wind Fg_ctrl_range Fg_ctrl_sigma Fg_ctrl_chi2_P Fg_ctrl_reach_maxiter Fg_ctrl_marq Fg_ctrl_many_outliers Fg_ctrl_sunglint Fg_ctrl_moonglint Fg_ctrl_num_meas_low Fg_sc_TEC_gradient Fg_sc_suspect_ice Fg_sc_rain • RFI pre-filter • Outlier pre-filter • We have performed the following situations: • We have fitted the sigma associated to fused TBs with a 5 degree polynomial ( ) as function of incidence angle and polarization • We have considered two different values for the total error associated to the fused TBs: • a) • b) • 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) • 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

  8. Filtering analysis on L2 product from fused TBs We compute the mean and the peak of the residuals distribution as function of the number of measurements used in the salinity computation The peak should be close to the identity for having distributions close to the theoretical Chi2 distributions Normalized distributions should be centered at one for a proper Fg_ctrl_Chi2_P application NO pre-filter and NO pre-filter and Pre-filter and Pre-filter and Centered distributions and peak close to identity

  9. Filtering analysis on L2 product from fused temperatures COMPARISON WITH ARGO (pre-filtering) COMPARISON WITH ARGO (no pre-filtering) Statistics of ARGO comparison (no pre-filtering): Pre-filters improves standard deviation but decreases the number of final “good” points All post-filtering All post-filtering without Fg_ctrl_Chi2_P No post-filtering Statistics of ARGO comparison (prefiltering): No post-filtering All post-filtering without Fg_ctrl_Chi2_P All post-filtering

  10. Final comparison of salinities

  11. 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 salinitiesfrom 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 11

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