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Study of the LO calibration frequency impact on SSS

Study of the LO calibration frequency impact on SSS. C. Gabarró, V. González, 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.

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Study of the LO calibration frequency impact on SSS

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  1. Study of the LO calibration frequency impact on SSS C. Gabarró, V. González, 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 • 57 full-pol semiorbits acquired at 2min and decimated at 4min, 6min, 10min (24-25 March 2010) • Processors used (best available): • L1PP 3.5 • L2PP 3.17 • All the comparisons are relative to the 2 min LO calibration orbits. Results are not absolute values. • Example: descending Pacific orbit 20100325T040821 • Global L1 data set • L1 statistics over Pacific and North Atlantic • Available SSS data after applying L2PP • Statistics on SSS data • Conclusions

  3. Example: TB comparison @ 38-40º TBV_10min-TBV_2min TBH_10min-TBH_2min 20100325T040821 - descending

  4. Example: TB comparison @ 38-40º TBV_6min-TBV_2min TBH_6min-TBH_2min

  5. Example: TB comparison @ 38-40º TBV_4min-TBH_2min TBH_4min-TBH_2min

  6. TB differences for 1 orbit EAF TB10min-TB2min TB6min-TB2min TB4min-TB2min

  7. TB differences AF ONLY TB10min-TB2min AF TB6min-TB2min AF TB4min-TB2min AF Very similar results for EAF or AF

  8. Data set: TB H @ inc=38-40º

  9. TB H @ inc=38-40º L1 RFI mask

  10. TB V @ inc=38-40º

  11. TB V @ inc=38-40º L1 RFI mask

  12. TB histogram PACIFIC area PACIFIC data Lat=[-50,10] Lon=[-180,-100]

  13. TB differences in PACIFIC PACIFIC Lat=[-50,10] Lon=[-180,-100]

  14. TB histogram N. ATLANTIC area N ATLANTIC data Lat=[30,90] Lon=[-70,0]

  15. TB differences in N. ATLANTIC North ATLANTIC Lat=[30,90] Lon=[-70,0]

  16. SSS data set 24-25/3/2010 57 orb Attention: Almost no clean data in N. Atlantic(L2PP filter)

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

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

  19. SSS 24-25 march 2010 57 orb SSS 4min – 2min

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

  21. Histograms SSS - PACIFIC Only Fg_poor_retrieval=0

  22. Histograms SSS – N. ATLANTIC Only Fg_poor_retrieval=0

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

  24. System requirements • R-4.5.1-008 The systematic radiometric error (including: bias, drift, periodic and other errors such as thermo-elastic effects) on the retrieved brightness temperature maps shall be lower than 1.5 K RMS at the antenna boresight and lower than 1.5´1.64 = 2.5 K RMS within 32° from boresight, after calibration • G-4.7.2-007 In order to support vicarious calibration, the system shall ensure a stability of the systematic component of the radiometric error (including: bias, drift, periodic and other errors such as thermo-elastic effects) better than 0.02 K/day.

  25. 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

  26. Remembering SSS requirements • R-4.6.2-004 The accuracy of the ocean salinity data products with a 50 km spatial resolution shall be <= 1.2 PSU.Note : This OS Level-2 accuracy requirement corresponds to :·  snapshot images (100) of one pixel taken during one single pass,·  usage of the narrow swath,·  full spatial coverage,·  ocean temperature of 277 K • G-4.7.2-005 The accuracy of the ocean salinity maps outside coastal areas, after averaging over 200 km x 200 km x 10 days space-time domain, shall be <= 0.1 PSU, after corrections by using vicarious calibration, namely by periodical imaging of one or more well-known reference sources.

  27. Onstatistics • During 10 minutes 500 SMOS snapshots are acquired • Calibrating LO every 10 min means loosing 5 snapshots, then the error in building an L3 map by averaging L2 products (wrt no calibration) increases by sqrt (500) /sqrt(495) = 1.005 • Calibrating every 2 min, 25 snapshots are lost, the L3 error increases by sqrt(500)/sqrt(475) = 1.026 • Going back to one orbit, the increase of usable snapshots @10 min compared to @2 min implies an error reduction of sqrt(495)/ sqrt(475) = 1.02 • This 2% reduction on the required SSS error means 0.02 psu • We showed that calibrating @2 min instead of @10 min implies an error reduction by 0.2 psu (clean Pacific), 0.5 psu in global average

  28. RFI PROBLEMS DETECTED ??? C. Gabarró, J. Martínez, V. Gonzalez, M. Portabella 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

  29. RFI detected by LO cal study? PLOT ONLY TB10min – TB2min >2K

  30. RFI in the LO cal ? (TBH_10min –TBH_2min)>2K (TBV_10min –TBV_2min)>2K

  31. RFI in the LO cal ? RFI in detector ? Orbit ASC 20100324T0717 Snapshot 20470787

  32. RFI in the LO cal ? RFI in detector ? TBV LO 10min TBV LO 2min If TB>220 -> set to 0 Snapshot 20470787 Orbit ASC 20100324T0717

  33. RFI in the LO cal ? MASK (TBV_10min –TBV_2min)>2K RFI TAILS??

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