www.argans.co.uk SMOS L2 Ocean Salinity From CH/JLV/JB TN: typical N. Atlantic RFI pattern in salinity (left), typical oscillations in TBs (right) Outliers & RFI
www.argans.co.uk SMOS L2 Ocean Salinity 0317 outlier detection algorithm for pol = 0 to 3 /* Stokes 1..4 */ for each measurement if abs((Tbsmos[pol] – Tbmodel[pol]) – correction[pol]) > 5 * σTB then outlier[pol, meas] = TRUE where correction = median (Tbmeas - Tbmodel) σTB = √ (σTB_radiometric_noise 2 + σTBmodel 2 ) Outliers & RFI Outlier detection in L2OSPP and its usefulness in RFI detection and correction – HENOCQ et al, SMOS L2OS technical note, 28/02/11 Some Tests close to Greenland New algorithm more consistent and effective (below outliers=filled points) A B A B With L2OSPP v3.17With new algorithm Refinements: - If no RFI, 3 sigma sorting may discard good measurements : Add a first step at gridpoint level for identifying the risk of outliers (see TN) Future work: -use « up and down evolution » of (Btmeas– BTmodel) over a dwell to detect RFI
www.argans.co.uk SMOS L2 Ocean Salinity 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_noise 2 + TBmodel 2 ) / 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 Outliers & RFI
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 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... Outliers & RFI