SMOS L2 Ocean Salinity L2OS QWG #4: RFI 7-9 March 2011 ARGANS & L2OS ESL www.argans.co.uk SMOS L2 Ocean Salinity RFI over the ocean DEW line RFI prevents successful salinity retrieval North Pacific & Atlantic www.argans.co.uk SMOS L2 Ocean Salinity Outliers & RFI Transect at 45N +-1 Dg_num_outliers SM_TEST_MIR_OSDAP2_20110209T064251_20110209T073653_317_001_8 www.argans.co.uk SMOS L2 Ocean Salinity Outliers & RFI From CH/JLV/JB TN: typical N. Atlantic RFI pattern in salinity (left), typical oscillations in TBs (right) www.argans.co.uk Outlier detection SMOS in L2OSPP and itsSalinity usefulness in RFI detection and correction – L2 Ocean HENOCQ et al, SMOS L2OS technical note, 28/02/11 Outliers & RFI Some Tests close to Greenland New algorithm more consistent and effective (below 0317 outlier detection algorithm outliers=filled points) With L2OSPP v3.17 With new algorithm for pol = 0 to 3 /* Stokes 1..4 */ A for each measurement A if abs((Tbsmos[pol] – Tbmodel[pol]) – correction[pol]) > 5 * σTB B then Refinements: outlier[pol, meas] = TRUE - If no RFI, 3 sigma sorting may discard good where measurements : Add a first step at correction = median (Tbmeas - Tbmodel) B gridpointσTB level identifying 2 + σTBmodel2 ) = √for (σTB_radiometric_noise the risk of outliers (see TN) Future work: -use « up and down evolution » of (Btmeas– BTmodel) over a dwell to www.argans.co.uk detect RFI SMOS L2 Ocean Salinity Outliers & RFI 0318 new 2 step RFI outlier detection algorithm based on reducing outlier threshold if high probability of RFI detected for pol = 0 to 3 /* Stokes 1..4 */ if std(TBmodel[pol] - TBsmos[pol]) > 1.2 * std_theory then rfi_outlier_risk[pol] = TRUE if rfi_outlier_risk[pol] then for each measurement if abs(TBmodel[pol] - TBsmos[pol]) > 3 * rad_noise then rfi_outlier[pol, meas] = TRUE where std_theory = √ ((TB_radiometric_noise2 + TBmodel2 ) / nMeas) factor of 1.2 is 99% confidence with 100 measurements (1 + 0.18) nsig is reduced from 5 (non-RFI outlier detection threshold) to 3 www.argans.co.uk SMOS L2 Ocean Salinity Outliers & RFI 0318 new RFI outlier detection algorithm disabled SM_OPER_MIR_SCSF1C_20110209T064251_20110209T073653_346_001_1 www.argans.co.uk SMOS L2 Ocean Salinity Outliers & RFI 0318 new RFI outlier detection algorithm enabled SM_OPER_MIR_SCSF1C_20110209T064251_20110209T073653_346_001_1 www.argans.co.uk SMOS L2 Ocean Salinity Outliers & RFI Fg_ctrl_suspect_RFI = RFI outliers > 50% Danger of false positives? www.argans.co.uk delta SSS1 (RFI off – on) Impact on non-RFI retrieval? SMOS L2 Ocean Salinity Outliers & RFI RFI outlier detection algorithm disabled (left) enabled (right) SM_OPER_MIR_SCSF1C_20100802T153816_20100802T163215_344_001_1 www.argans.co.uk SMOS L2 Ocean Salinity Outliers & RFI RFI outlier detection algorithm disabled (left) enabled (right) SM_OPER_MIR_SCSF1C_20100802T153816_20100802T163215_344_001_1 www.argans.co.uk SMOS L2 Ocean Salinity Outliers & RFI – L1PP 350 0318 new RFI outlier detection algorithm enabled SM_TEST_MIR_SCSF1C_20100315T080748_20100315T090119_350_001_0 www.argans.co.uk SMOS L2 Ocean Salinity Outliers & RFI – L1PP 350 Any correlation between L1 & L2 RFI flagging? www.argans.co.uk SMOS L2 Ocean Salinity Outliers & RFI Other possible RFI detection approaches Detecting RFI induced oscillations in dwell line TBs (eg using fft) – see TN from Claire, Jacqueline & Jean-Luc (oscillations seem higher in VV?): Using L1c RFI flags? Using AUX_RFILST? CATDS use one month data in 5 degree bins per grid point... www.argans.co.uk
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