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Calibration Status for the Infrared: HIRS, AIRS, IASI, CrIS, HES PowerPoint Presentation
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Calibration Status for the Infrared: HIRS, AIRS, IASI, CrIS, HES

Calibration Status for the Infrared: HIRS, AIRS, IASI, CrIS, HES

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Calibration Status for the Infrared: HIRS, AIRS, IASI, CrIS, HES

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  1. 21 October panoramas Hank Revercomb, Fred Best, Dave Tobin, Bob Knuteson, Joe TaylorUniversity of Wisconsin - MadisonSpace Science and Engineering Center (SSEC) Calibration Status for the Infrared:HIRS, AIRS, IASI, CrIS, HES Achieving Satellite Instrument Calibration for Climate Change (ASIC3) National Conference Center 16-18 May 2006

  2. Topics Overview HIRS/MODIS/GOES (filter radiometers) AIRS on NASA Aqua(grating spectrometer), the 1st modern high resolution sounder to fly Scanning HIS (aircraft FTS) AIRS - Scanning HIS Comparisons IASI & CrIS (future LEO operational FTS) Future GOES Sounders:GIFTS (FTS) & HES (FTS or Grating) Long-term climate records: approaches

  3. A. Overview

  4. The IR is a Key Climate Indicator • Fundamental component of the Energy budget of the atmosphere • High Accuracy for establishing small trends is relatively easy to achieve, if spectral calibration is handled(Especially hot or cold Reference sources not needed) • High information content to characterize complex climate changes is possible using spectrally resolved radiances

  5. Spectral Resolving Power (/ ) IR Sounders: Past, Present,and Future(Kory Priestley to cover Total IRbroadband) Resolving Power @ 14 m (1200) HES, GOES-R (2013-) (1200) GIFTS (2009 ?) (1200/2800) IASI / CrIS(2006-2009?) (1200) AIRS(2002-) (30) GOES Sounder(1994-) – (3-Axis) (2000) HIS(1986-1998) (30) VAS(1980-) –1st Geo Sounder (Spin-Scan) (30) ITPR,VTPR(1972)/HIRS(1978-) (150-300) IRIS / SIRS(1969-70) –1st Sounders BLUE = LeoPurple = Geo Red = Aircraft

  6. Absolute Accuracy Requirements • 0.1-0.3 K* 3-sigma is now achievable, but specifications are often an order of magnitude worse • Order 1 K* has been common for weather instruments, but they too would benefit from doing better • AIRS spec was 3% (~3K longwave, 1 K mid-shortwave at 300K), but < 0.2-0.3 K 3-sigma has been achieved * brightness T at scene T

  7. Calibration Performance Summary • New generation of high spectral resolution instruments offer significantly improved absolute calibration—1 degree uncertainties replaced with concern over tenths of a degreeReasons include: • Fundamental advantage of high resolution (Goody and Haskins, J of Climate, 1998),plus accurate spectral sampling knowledge • Cavity onboard reference sources • Lower detector non-linearity from PV MCT in the longwave • High Spectral resolution will also offer greatly improved instrument-to-instrument consistency by allowing standardization of spectral sampling • But we can, and should, do even better for climate, especially by incorporating means for onboard verification of long-term accuracy (see Jim Anderson)

  8. B. HIRS/MODIS/GOES(filter radiometers)

  9. (without accounting for different spectral characteristics) MCT InSb 669-749 cm-1 2188-2600 cm-1 802 900 N2O/ CO2 O3 WV Channel # Simultaneous Nadir Overpass Mean Differencesoften larger than instrument radiometric calibration errors,because of spectral differences

  10. HIRS to HIRS Differences Spectral Response Fns (SRFs) for HIRSon NOAA 16, 17, 18 Simulated Tb differencesfrom SRF differences:spectral differences are a primary contributorto HIRS-to-HIRS Diffs challenge for climate record, even if the absolute cal is perfect ±2K from Wang, Ciren, & Cao, 2005

  11. HIRS-18 Validationwith AIRS Individual HIRS calibrationuncertainties are much smaller thanHIRS-to-HIRS differences HIRS-AIRSMean ~ 0.18 ru~0.15 K AIRS HIRS-AIRS HIRS Ch5 29 August 2005, Tropical Atlantic from Wang, Ciren, & Cao, 2005

  12. MODIS Accuracy Assessment using AIRS MODIS Band / wavelength(mm) 36 / 14.2 35 / 13.9 34 / 13.7 33 / 13.4 32 / 12.0 31 / 11.0 30 / 11.0 29 / 9.7 28 / 7.3 27 / 6.8 25 / 4.5 24 / 4.4 23 / 4.1 22 / 4.0 21 / 4.0 wavenumber

  13. T from 12 thermistors 0.987 <  < 0.9940.0014<   < 0.0035 from T/V external BB comparison Courtesy of MODIS Characterization Support Team

  14. Fantastic AIRS - MODIS Agreement for Band 22 (4.0mm)! AIRS Tb (K) AIRS minus MODIS (K) Uniform Scenes Selected AIRS HistogramMODIS Tobin, et al., 2006

  15. MODIS Band 22 (4.0mm) AIRS-MODIS mean = -0.05 K Little Dependence onScene Temperature Little Dependence onSolar Zenith Angle Little Dependence onX-track View Angle Tobin, et al., 2006

  16. Summary of AIRS-MODIS mean Tb differences Red=without accounting for convolution error Blue=accounting for convolution error with mean correction from standard atmospheres p-p Convolution Error (CE) Estimate mm Band Band Diff CE Diff Std N 21 0.10 -0.01 0.09 0.23 187487 22 -0.05 -0.00 -0.05 0.10 210762 23 -0.05 0.19 0.14 0.16 244064 24 -0.23 0.00 -0.22 0.24 559547 25 -0.22 0.25 0.03 0.13 453068 27 1.62 -0.57 1.05 0.30 1044122 28 -0.19 0.67 0.48 0.25 1149593 30 0.51 -0.93 -0.41 0.26 172064 31 0.16 -0.13 0.03 0.12 322522 32 0.10 0.00 0.10 0.16 330994 33 -0.21 0.28 0.07 0.21 716940 34 -0.23 -0.11 -0.34 0.15 1089663 35 -0.78 0.21 -0.57 0.28 1318406 36 -0.99 0.12 -0.88 0.43 1980369 > 1K errors exist in some more opaque channels Tobin, et al., 2006

  17. SRF shift may explain MODIS Calibration ErrorsShifting MODIS Band 35 (13.9 mm) by 0.8 cm-1 Worksto Remove Mean bias and Scene Tb Dependence No Shift MODIS shifted Tb diff (K) AIRS-MODIS: un-shifted, shifted SRF Spectral uncertainty appears to dominate the uncertainty

  18. GEO/LEO Intercalibration GEOs relative to AVHRR GEO – LEO (K) Comparing NOAA-15 AVHRR to a global constellation of Geostationary Imagers Calculations are used to approximately account for spectral response differences The large telescope neededfrom GEO presents othercalibration challenges ±2 K Oct ’05 May ‘06 Matt Gunshor, UW

  19. Filter Radiometer Summary • Order 1 K calibration issues are not uncommon(e.g. relative GEO comparisons) • Spectral uncertainty is one probable cause for uncertainty exceeding 1 K (e.g. MODIS results from AIRS) • Lack of reproducible spectral sampling from instrument to instrument is also a key issue for long-term climate records • New instruments with Nyquist spectral sampling and broad spectral coverage will greatly reduce this uncertainty

  20. C. AIRS on NASA Aqua(grating spectrometer), the 1st modern high resolution sounder to fly • Demonstrates key advantages of high spectral resolution for calibration accuracy

  21. AIRS 4 May 2002 Launch NASA Aqua AIRS14 June 2002 Calculated

  22. AIRS Onboard Blackbody:light trap cavity design—specular surface emissivity,  > 0.999T calibration ± 0.05 K nadir Primary T/V reference emissivity,  > 0.9999T knowledge ± 0.03 K ABB Bomem PRT temperature sensors

  23. AIRS: Other key factors • ILS knowledge:thermal/vac testing with FTS source, verified with gas cell tests • Spectral Calibration:atmosphere (rough in-flight check via parylene source) stability maintained by T control of whole spectrometer/aft optics assembly (2.2%  shift/K) • Non-linearity*:<0.3% over much of spectrum, < ~1% peak; error assumed < 0.05 K after correction • Polarization*:±worst case 0.4K (9 & 15 m);error assumed < 0.07 K after correction *from Pagano et al, ITWG, 2003

  24. peak-to-peak seasonal changes (about 5 ppm) cause brightness temperature differences of about ~0.5 K p-p in 15 m CO2 band (Caused by instrument T changes of < 0.25K) But these changes are detectable, and can be corrected with the AIRS Nyquist sampling Larrabee Strow, et al.

  25. D. Scanning HIS(aircraft FTS) Aircraft instrument offers preview of future operational instruments and validation of AIRS and future instrument calibration accuracy • Performance Estimates • Key calibration considerations

  26. CO2 Midwave NASA WB57 CH4/N2O O3 H2O Longwave H2O Shortwave N2O CO2 CO UW Scanning HIS: 1998-Present(HIS: High-resolution Interferometer Sounder, 1985-1998) Characteristics Spectral Coverage: 3-17 microns Spectral Resolution: 0.5 cm-1 Resolving power: 1000-6000 Footprint Diam: 1.5 km @ 15 km Cross-Track Scan: Programmable including uplooking zenith view Applications: • Radiances for Radiative Transfer • Temp & Water Vapor Retrievals • Cloud Radiative Prop. • Surface Emissivity & T • Trace Gas Retrievals

  27. Scanning-HIS Radiometric Calibration BudgetTABB= 227, THBB=310,11/16/02 Proteus Similar to AERI description in Best, et al., CALCON 2003 3-sigmaTb error< 0.3 K for Tb >220 K RSS ofErrors in THBB,TABB TRflHBB, ABB+ 10% of non-linearitycorrection

  28. Scanning HIS: Some key factors • ILS knowledge:fundamental instrument design(only weak dependence on geometry) • Spectral Calibration:atmosphere,stability maintained by onboard HeNe laser reference(no active temperature control required) • Non-linearity:< 2.5% longwave and midwave, negligible shortwaveerror < ~0.2 K after correction • Polarization: <0.05% (gold scene mirror)error < 0.04 K even uncorrected

  29. Atmospheric Spectral Calibration: S-HIS Atmospheric CO2 lines AIRS does similaratmospheric spectral calibration Wavenumber Scale chosen to minimize difference Estimated accuracy =1.2 ppm(1 sigma) With many samples,the 3-sigma accuracy is < 1 ppm

  30. E. AIRS - Scanning HIS Comparisons • Direct AIRS radiance validation • Mean differences generally <0.2 K with small standard deviations • Demonstrates aircraft capability for highly accurate validation of S/C obs

  31. AIRS Validation with UW Scanning HIS 1 Degree 8 AIRS FOVs used in the following comparisons(shown in MODIS 12 micron image)

  32. Direct S-HIS to AIRS comparison(without accounting for spectral & viewing differences) AIRS SHIS 8 AIRS FOVs, 448 SHIS FOVs, PC filtering

  33. “comparison 0” 8 AIRS FOVs, 448 SHIS FOVs, PC filtering S-HIS Spectrum Nyquist sampled without gaps

  34. Gulf of Mexico Validation case: 2002.11.21

  35. “Comparison 2” (21 November 2002) Excluding channels strongly affected by atmosphere above ER2 (AIRSobs-AIRScalc)- (SHISobs-SHIScalc) (K)

  36. AIRS-SHIS Summary: SW (2004.09.07) 1st Direct SW Radiance ValidationExcellent agreement for night-time comparison from Adriex in Italy

  37. F. IASI & CrIS(future LEO operational FTS) • Operational extension of AIRS will be very useful for climate applications

  38. IASI on Metop17 July 2006 launch scheduled

  39. IASI: Other key factors • Instrument Line Shape knowledge:fundamental instrument designverified with laser sources in ground testing • Spectral Calibration:atmospherestability maintained by onboard 1.54 m diode laser reference with < 1ppm validated over 14 days* • Non-linearity:< 1% longwave, negligible mid- and short-waveerror < ~0.15 K after correction*stability verifiable in orbit from out of band features • Polarization: <0.05% (gold scene mirror with overcoating)error < 0.04 K even uncorrected* * Denis Blumstein and Thierry Phulpin, cnes

  40. CrIS:AIRS Successor for NPOESS,will be equally good, or better Overall Calibration Spec: <0.4 K (Design specs: < 0.45%, LW, 0.58% MW, 0.77% SW)- Actual performance will significantly exceed specification, especially after incorporating planned NIST measurements of reference blackbodies- Non-linearity very small- Polarization effects very small Spectral Calibration: Instrument Line Shape (ILS) extremely well known and stable from first principles

  41. CrIS: Other key factors • ILS knowledge:fundamental instrument design (only weak dependence on geometry), verified with laser source and gas cell tests • Spectral Calibration:atmosphere &/or onboard Ne source;stability maintained by T control of onboard 1.55 m diode laser reference • Non-linearity:<0.1% longwave & negligible elsewhereerror < ~0.07 K even uncorrectedstability verifiable in orbit from out of band features • Polarization: <0.05% (gold scene mirror)error < 0.04 K even uncorrected