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LO calibration frequency impact on ocean salinity

LO calibration frequency impact on ocean salinity. V. González, C. Gabarró, J. Martínez, M. Portabella, J. Font and BEC–TEAM SMOS Barcelona Expert Centre Pg. Marítim de la Barceloneta 37-49, Barcelona SPAIN E-mail: jfont@icm.csic.es URL: www.smos-bec.icm.csic.es. Decimation study using MTS.

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LO calibration frequency impact on ocean salinity

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  1. LO calibrationfrequency impact on ocean salinity V. González, C. Gabarró, J. Martínez, M. Portabella, J. Font and BEC–TEAM SMOS Barcelona Expert Centre Pg. Marítim de la Barceloneta 37-49, Barcelona SPAIN E-mail: jfont@icm.csic.es URL: www.smos-bec.icm.csic.es

  2. Decimation study using MTS • Assessment of the LO calibration frequency impact on TB. • Data acquired at 2min and decimated at 6min and 10min. • Descending orbit over Pacific: 20100325T040821. • All the comparisons are relative to the 2min LO calibration frequency data. • Only AF-FOV grid points

  3. TB maps @ 38-40º in the AF-FOV TBH10min-TBH2min TBV10min-TBV2min MIRAS-TS [K]

  4. L1pp: TB maps @ 38-40º in the AF-FOV L1PP_3.5

  5. TB_10min-TB_2min AF-FOV MIRAS-TS L1PP_3.5 TB10min – TB2min H-pol V-pol

  6. TB maps @ 38-40º in the AF-FOV TBH6min-TBH2min TBV6min-TBV2min MIRAS-TS

  7. TB_6min-TB_2min AF-FOV MIRAS-TS L1PP_3.5 TB6min – TB2min H-pol WARNING: different K scale V-pol

  8. SSS 24-25 march 2010 57 orb SSS 10min – 2min

  9. SSS 24-25 march 2010 57 orb SSS 6min – 2min

  10. Conclusions • The present LO calibration frequency has a clear impact on TB (larger in V-pol) and SSS. • TB differences between LO-10min and LO-2min have a global STD of 0.47 K (1.1K in N. Atlantic, 0.21 K in Pacific) • Differences in SSS (filtered by good retrieval flag): global STD 0.48 psu (0.94 psu in N. Atlantic, 0.20 psu in Pacific) • Accuracy requirement for L2 SSS is 1.2 psu. We don’t know yet the actual retrieval error, but the low calibration freq can represent in average 0.5 psu of additional error!! • SMOS SSS requirements will likely never be met with LO being calibrated at 10 min intervals

  11. On statistics • During 10 minutes 500 SMOS snapshots are acquired • Calibrating LO every 10 min means loosing up to 8 snapshots, then the error in building an L3 map by averaging L2 products (wrt no calibration) increases by sqrt (500)/sqrt(492) = 1.008 • Calibrating every 2 min, 40 snapshots maximum are lost, the L3 error increases by sqrt(500)/sqrt(460) = 1.043 • Going back to one orbit, the increase of usable snapshots @10 min compared to @2 min implies an error reduction of sqrt(492)/ sqrt(460) = 1.034 • This 3.4% reduction on the required SSS error means 0.04 psu • We showed that calibrating @2 min instead of @10 min implies an error reduction by 0.48 psu in global average

  12. Histogram SSS WORLD Global L2OS output When filtering by Fg_poor_retrieval=1 STD (SSS10-SSS2)= 0.48 psu

  13. SSS differences: best & worst cases PACIFIC Lat=[-50,10] Lon=[-180,-110] Lat < -50º

  14. TB maps @ 23-25º in the AF-FOV TBH10min-TBH2min TBV10min-TBV2min MIRAS-TS [K] 15

  15. L1pp: TB maps @ 23-25º in the AF-FOV L1PP_3.5

  16. L1pp: TB maps @ 38-40º in the EAF-FOV L1PP_3.5 EAF

  17. L1PP: TB differences for 1 orbit EAF-FOV L1PP_3.5 EAF

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