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OTT sensitivity study and Sun correction impact J. Gourrion and the SMOS-BEC team

OTT sensitivity study and Sun correction impact J. Gourrion and the SMOS-BEC team SMOS-BEC, ICM/CSIC. OTT sensitivity. DPGS OTT Impact on OTT quality of different factors : Galactic signals Number of snapshots used Apparent drift ( or temporal integration window width )

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OTT sensitivity study and Sun correction impact J. Gourrion and the SMOS-BEC team

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  1. OTT sensitivity study and Sun correction impact J. Gourrion and the SMOS-BEC team SMOS-BEC, ICM/CSIC

  2. OTT sensitivity • DPGS OTT • Impacton OTT quality of differentfactors: • Galacticsignals • Number of snapshotsused • Apparentdrift (or temporal integrationwindowwidth) • Experimentsdesignedtoremove inter-dependence • OTT qualitycriterion: stability,level of dependenceonthesubset of data

  3. OTT sensitivity • Force independence of factor 2 (constant number of snapshots N) and 3 (use a 12-days period) • Galactic potential contamination detection: threshold on the incident field (3.5 to 8 K) • For each threshold value, N snapshots are randomly selected, and an OTT computed • Using the lowest threshold value as reference, we compute the OTT rms increase due to increasing galactic contamination Impact of galactic contamination

  4. OTT sensitivity • Forceindependence of factor 1 (strictgalacticfilter) and 3 (use a 12-days period) • Forthreedifferentperiods, thereferencesituationisgivenbytheoverallnumber of availablesnapshotsafterfiltering. • thenumber of snapshotsisprogressivelyreduced, snapshots are randomlyselected and correspondingOTTs are computed • OTT rmsincreaseiscomputed as a function of snapshotnumberreduction factor and averagedoverthe 3 datasets (consistencychecked) Impact of number of snapshots

  5. OTT sensitivity • Force independence of factor 1 (strict galactic filter) and 2 (constant number of snapshots N) • The temporal window width is increased from 6 days to 48 days • In each case, N snapshots are randomly selected, and an OTT computed • Using the shortest temporal window as reference, we compute the OTT rms increase due to increasing data inconsistency Impact of apparent drift

  6. OTT sensitivity • As expected, the number of snapshots used to compute the OTT should be kept as high as possible, the upper limit being set by other constraints • Galaxy presence in the snapshots used to compute the OTT may induce large errors in the characterization of systematic instrument/reconstruction biases (up to 0.4 K rms at X- and Y-pol) • Apparent instrumental drift can induce significant errors. If not canceled, numbers provided should help defining the OTT recomputation period. Summary

  7. Direct sun correction impact Using DPGS file : SM_OPER_MIR_SC_F1B_20100803T131914_20100803T141314_340_001_0

  8. Direct sun correction impact Using DPGS file : SM_OPER_MIR_SC_F1B_20100803T131914_20100803T141314_340_001_0

  9. Direct sun correction impact Using DPGS file : SM_OPER_MIR_SC_F1B_20100803T131914_20100803T141314_340_001_0 * 0.1-0.2 K shift * no impact on latitudinal variations

  10. Direct sun correction impact Using DPGS file : SM_OPER_MIR_SC_F1B_20101110T031502_20101110T040900_340_001_0

  11. Direct sun correction impact Using DPGS file : SM_OPER_MIR_SC_F1B_20101110T031502_20101110T040900_340_001_0

  12. Direct sun correction impact Using DPGS file : SM_OPER_MIR_SC_F1B_20101110T031502_20101110T040900_340_001_0 1K impact on latitudinal variations

  13. Summary • Variability of the distribution of observed geophysical conditions inside the FOV, when computing the OTT, may introduce inconsistencies in the modified brightness temperatures • Adequate snapshot selection procedure enables to reduce consequent biases in the retrieved salinities. The procedure requires much more data than one half-orbit. • The residual SSS anomalies are highly reduced when using a roughness-improved forward model (IQR divided by 2, Y-pol) • In terms of salinity, X-pol is much noisier than Y-pol. • To further reduce the SSS errors: • work on the roughness description and more generally on the forward model • improve the inversion method from the present linear approach

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