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GSICS GEO-AIRS/IASI Inter-Calibration Algorithm Theoretical Basis Document

GSICS GEO-AIRS/IASI Inter-Calibration Algorithm Theoretical Basis Document. X. Wu 1 , T. Hewison 2 , Y. Tahara 3 1: NOAA/NESDIS; 2: EUMETSAT; 3: JMA/MSC With Contributions from Current and Former GRWG Members

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GSICS GEO-AIRS/IASI Inter-Calibration Algorithm Theoretical Basis Document

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  1. GSICS GEO-AIRS/IASI Inter-CalibrationAlgorithm Theoretical Basis Document X. Wu1, T. Hewison2, Y. Tahara31: NOAA/NESDIS; 2: EUMETSAT; 3: JMA/MSC With Contributions from Current and Former GRWG Members D. Blumstein, C. Cao, S.-R. Chung, D. Doelling, M. Gunshor, P. Henry, T. Hewison (vice chair), X. Hu, D. Kim, M. König, J. Lafeuille, J. Liu, P. Minnis, A. Okuyama, J. Privette, B.-J. Sohn, Y. Tahara, D. Tobin, X. Xiong, L. Van de Berg, X. Wu (chair), P. Zhang, and Y. Zhang. NOAA: S.-H. Sohn, Y. Li, L. Wang, F. Yu, R. Mundakkara, G. Rancic

  2. GSICSGEO-AIRS/IASI Inter-Calibration ATBD • Ensure the comparability of satellite measurements • At different times and/or locations; • By different instruments; and • Under the responsibility of different space agencies. • Method: • Inter-calibration

  3. GSICSGEO-AIRS/IASI Inter-calibration ATBD • GSICS Members • NOAA, EUMETSAT, JMA, CMA, KMA, CNES, NASA, and NIST • Five are responsible agencies for operational meteorological satellites – GEO in particular • AIRS/IASI • Hyperspectral Sounder on LEO • Versatile for collocation in space and spectrum • Highly accurate and mutually consistent • An early priority • Adjust GEOs to be consistent with AIRS/IASI

  4. GSICSGEO-AIRS/IASI Inter-Calibration ATBD • GEO-AIRS/IASI is one of many • GSICS supports inter-calibration on other orbits, for other instruments, in other spectral regions • All are similar in some ways • Each pair is unique in some ways • Instrument characteristics • Agency priority • Hierarchical Structure • General ATBD • Purpose, Options, Selection, Implementation • Details for individual pairs on http://www.star.nesdis.noaa.gov/smcd/spb/calibration/icvs/GSICS/index.php

  5. Basis for Inter-Calibration • Calibration – quantifying the instrument responses to known signals • Ideally, two instruments should make identical measurements under identical conditions • Time, location, spatial response, spectral response, and viewing geometry. • In reality …

  6. Input Data: GEO & LEO Radiances 1. Subsetting Orbit Prediction Subset Data 2. Collocation Collocation Criteria Instrument Characteristics FOV, SRF, PSF, Ref Sys 3. Transformation Collocated Data Cloud/Clear, Day/Night, Sea/Land, Nadir/Off Nadir 4. Selection 5. Analysis Analysis Methods Results: Bias, Correction, Uncertainty A series of processes to minimize and account for any and all differences between radiance by two instruments

  7. Basis for Collocation • Three objectives of GSICS • Quantify the differences – magnitude and uncertainty • Correct the differences – empirical removal • Diagnose the differences – root cause analysis • What they mean for Data Collection • Results are based on the collocated data only • Validity for other data is assumed implicitly • Variety is good • Single pixel collocations anywhere within the GEO field of regard be collected continuously over long term for all bands. • Save as many collocations as practical

  8. Input Data: GEO & LEO Radiances 1. Subsetting Orbit Prediction Subset Data 2. Collocation Collocation Criteria Instrument Characteristics FOV, SRF, PSF, Ref Sys 3. Transformation Collocated Data Cloud/Clear, Day/Night, Sea/Land, Nadir/Off Nadir 4. Selection 5. Analysis Analysis Methods Results: Bias, Correction, Uncertainty

  9. 1. Subsetting

  10. Input Data: GEO & LEO Radiances 1. Subsetting Orbit Prediction Subset Data 2. Collocation Collocation Criteria Instrument Characteristics FOV, SRF, PSF, Ref Sys 3. Transformation Collocated Data Cloud/Clear, Day/Night, Sea/Land, Nadir/Off Nadir 4. Selection 5. Analysis Analysis Methods Results: Bias, Correction, Uncertainty

  11. 2. Collocation • Time • From Telemetry • Threshold depends on refresh rate and size of data • Location • Operational geolocation • Angle • geo_zen-leo_zen < threshold – penalize at small angle • sec(geo_zen) - sec(leo_zen) < threshold – penalize at larger angle • cos(geo_zen)/cos(leo_zen)-1 < threshold

  12. 2. Collocation

  13. 2. Collocation 13.3 um Empirical correction is helpful, although one cannot depend on that too much since this correction depends on the lapse rate

  14. Input Data: GEO & LEO Radiances 1. Subsetting Orbit Prediction Subset Data 2. Collocation Collocation Criteria Instrument Characteristics FOV, SRF, PSF, Ref Sys 3. Transformation Collocated Data Cloud/Clear, Day/Night, Sea/Land, Nadir/Off Nadir 4. Selection 5. Analysis Analysis Methods Results: Bias, Correction, Uncertainty

  15. 3a. Spatial Transform GEO FOV, may be square or overlapping Non-uniform features LEO FOV, relative to GEO FOV Collocation FOV, may depend on GEO and LEO FOVs Collocation environment, may depend on time window and wind speed

  16. 3b. Spectral Transform MTSAT-1R 6.8-um AIRS blacklist ch. SRFs of Gap channels SRFs of AIRS SRF of MTSAT SRF of super channel consists of AIRS and gap channels Weights of AIRS ch. Weights of gap ch.

  17. Input Data: GEO & LEO Radiances 1. Subsetting Orbit Prediction Subset Data 2. Collocation Collocation Criteria Instrument Characteristics FOV, SRF, PSF, Ref Sys 3. Transformation Collocated Data Cloud/Clear, Day/Night, Sea/Land, Nadir/Off Nadir 4. Selection 5. Analysis Analysis Methods Results: Bias, Correction, Uncertainty

  18. 4. Selection • Several reasons • Performance under certain conditions, e.g., night • Narrow down threshold, e.g., time window • Avoid certain conditions, e.g. sun glint • Weighted average/regression is superior than threshold • ATBD facilitates these options. No specific recommendation/discrimination

  19. Input Data: GEO & LEO Radiances 1. Subsetting Orbit Prediction Subset Data 2. Collocation Collocation Criteria Instrument Characteristics FOV, SRF, PSF, Ref Sys 3. Transformation Collocated Data Cloud/Clear, Day/Night, Sea/Land, Nadir/Off Nadir 4. Selection 5. Analysis Analysis Methods Results: Bias, Correction, Uncertainty

  20. Collocation Principles • Three objectives of GSICS • Quantify the bias – magnitude and uncertainty • Correct the bias – proper reduction • Diagnose the bias – root cause • What they mean for Data Collection • Results are based on the collocated data only • Validity for other data is assumed implicitly • Variety is good • Single pixel collocations anywhere within the GEO field of regard be collected continuously over long term for all bands. • As much as practical

  21. 5a. Analysis – Quantify Bias • Mean difference • If bias is related to scene radiance, the result will depend on sample population > 270K < 270K

  22. 5a. Analysis – Quantify Bias • Mean difference • If bias is related to scene radiance, the result will depend on sample population • Recommend regression weighted by environment uniformity • Compute the uncertainty as well • Evaluated at standard radiances

  23. 5a. Analysis – Quantify Bias

  24. 5b. Analysis – Correct Bias • GSICS Corrected radiance from GEO operational product • a, b from weighted regression • Reduced Major Axis – under investigation • Period of regression is critical

  25. 5b. Analysis – Correct Bias

  26. 5c. Analysis – Diagnose Bias • A few examples reported elsewhere • Error in spectral response function • GOES-13 Imager 13.3 m channel cold bias • GOES-11/12 Sounder Channel 15 bias • Midnight calibration anomaly • Nonlinearity correction (microwave)

  27. Summary • GEO-LEO ATBD is an important tool to achieve GSICS goal • Carefully designed through collaboration of international experts • Has been used to quantify, correct for, and diagnose the causes of biases • http://www.star.nesdis.noaa.gov/smcd/spb/calibration/icvs/GSICS/index.php for more info • Ready for more users to test and to provide feedback

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