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NOAA20 CrIS Radiometric Nonlinearity

NOAA20 CrIS Radiometric Nonlinearity. Dave Tobin , Joe Taylor, Bob Knuteson, Michelle Feltz, Lori Borg, Hank Revercomb CIMSS/SSEC, UW-Madison NASA Sounder Science Team Meeting 5 October 2018. Outline. NOAA-20 Radiometric Nonlinearity Correction equations Pre-launch characterization

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NOAA20 CrIS Radiometric Nonlinearity

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  1. NOAA20 CrIS Radiometric Nonlinearity Dave Tobin, Joe Taylor, Bob Knuteson, Michelle Feltz, Lori Borg, Hank Revercomb CIMSS/SSEC, UW-Madison NASA Sounder Science Team Meeting 5 October 2018

  2. Outline • NOAA-20 Radiometric Nonlinearity • Correction equations • Pre-launch characterization • On-orbit refinements • Cal/Val examples • NOAA-20 NEDN • Comparisons to SNPP and FOV dependence

  3. CrIS On-Orbit Radiometric Calibration Equation: LS = Re {(C’ES – C’DS) /(C’ICT-C’DS)} RICT for observed complex spectra, C, of the Earth scene (ES), Internal Calibration Target (ICT), and Deep Space (DS) views. with: • ICT Predicted Radiance: RICT = eICT B(TICT) + (1-eICT) Rreflected • Quadratic Nonlinearity Correction: C’ = C (1 + 2 a2 VDC) • Polarization Correction/Error: • with polarization coefficients prpt, scene selection mirror polarization angle δ, sensor polarizer angle α, and emission from the scene mirror BSSM. (H==ICT, C==DS). 3

  4. Quadratic Nonlinearity Correction IFGlinear + Videal = (IFGmeas + V) + a2 (IFGmeas + V)2(1)* expanding … IFGlinear = IFGmeas + 2 a2 IFGmeas + a2 IFGmeas2 + contstants(2) fft’ing, complex spectra C = FFT(IFG) … Clinear = (1 + 2 a2 V) Cmeas + a2 (Cmeas⊗Cmeas) (3) if (Cmeas⊗ Cmeas) falls out of the spectral band of interest … Clinear = (1 + 2 a2 V) Cmeas(4) • Correction therefore requires: • Estimate of quadratic nonlinearity coefficient a2 (volts-1) for each detector • Estimate of DC level voltage V (volts) at detector/preamp output due to photons/dark current, for each measured interferogram 4

  5. Example Quadratic nonlinearity correction for a typical clear sky spectrum SNPP FOV7 5

  6. Pre-launch Nonlinearity Characterization (1) Example “Diagnostic Mode” data from October 2014, bypassing the FIR filter and providing out-of-band signals in-band FFT(IFG) = C a2•FFT(IFG2) = a2 C⊗C in-band in-band • Main Findings: • SW and MW FOVs 1-8 are very linear • LW and MW9 out-of-band signals are consistent with quadratic nonlinearity • Initial a2 estimates from low wavenumber harmonic (50-300 cm-1) 6

  7. Pre-launch Nonlinearity Characterization (2) External Calibration Target (ECT) view data at six temperatures with quadratic nonlinearity correction and v113 EP a2 values ECT view (Oct 2014) BT residuals, with linear calibrations: 310K 299K 287K 260K 233K 200K 310K 299K 287K 260K 233K 200K • ECT view data used to “sell-off” prelaunch radiometric calibration accuracy, and determine a2s • a2 determinations are needed for overall radiometric accuracy but also for optimal agreement among FOVs 7

  8. On-Orbit Refinements using Earth view spectra FOV-to-FOV Brightness Temperature Differences, Longwave band: • FOV2FOV differences minimized in 680-690 cm-1 region • 21 Jan Golden Day • Differences from reference FOV 6 for near nadir FORs (13-18) • Weighted Mean of all granules wavenumber 8

  9. On-Orbit Refinements using Earth view spectra FOV-to-FOV Brightness Temperature Differences, Longwave band: • FOV2FOV differences minimized in 1580-1600 cm-1 region • 21 Jan Golden Day • Differences from reference FOV 5 for near nadir FORs (13-18) • Weighted Mean of all granules wavenumber 9

  10. Summary of a2 values NOAA20 progression SNPP/NOAA20 comparison 10

  11. SNPP/NOAA20 Differences using AIRS/CrIS SNOs • 0.1K Differences in CO2 region, most likely SNPP nonlinearity

  12. SNPP/NOAA20 Apodized Differences using AIRS/CrIS SNOs • MW FOV 9 out-of-family by ~0.1 to 0.15K. • a2 perturbations investigated for v115EP, not sufficient/implemented

  13. Outline • NOAA-20 Radiometric Nonlinearity • Correction equations • Pre-launch characterization • On-orbit refinements • Cal/Val examples • NOAA-20 NEDN • Comparisons to SNPP and FOV dependence

  14. Noise Performance and Dependence among FOVs FOV 7 corner FOVs side FOVs center FOV5 FOV 9 14

  15. Noise Performance compared to SNPP SNPP 7 N20 9 SNPP 7 NOAA20 has noticeably lower noise in the LW and MW bands, and, these estimates are from 1 March 2018, and therefore do not reflect improvements for NOAA20 MW FOVs 1–8 that occurred on on 14 August due to PGA gain adjustments. 15

  16. SNPPTime series of Daily Mean CrIS/VIIRS Differences Mean Bias (mK) Trend (mK/year) M13 88.0 ± 0.6 -0.48 ± 0.41 M15 -100.7 ± 0.1 -1.02 ± 0.05 M16 -47.7 ± 0.1 -1.92 ± 0.06 I05 -71.6 ± 0.1 -0.20 ± 0.08

  17. Example Radiance based Climate Product Upper Stratosphere (667.8 cm-1) BT Time Series (Global, Monthly): Deseasonalized Trends: 2012-2017 trends:

  18. The EndThank Youdave.tobin@ssec.wisc.edu

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