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HIRS Status Update

HIRS Status Update. C. Cao, R. Chen, A. Pearlman, and S. Uprety August 17, 2010. HIRS Calibration S tatus U pdate. Highlights MetOP HIRS/IASI comparisons HIRS is more stable than AVHRR Nonlinearity re-analysis Thermal vacuum data re-analysis HIRS re-calibration for FCDR

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HIRS Status Update

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  1. HIRS Status Update C. Cao, R. Chen, A. Pearlman, and S. Uprety August 17, 2010

  2. HIRS Calibration Status Update Highlights • MetOP HIRS/IASI comparisons • HIRS is more stable than AVHRR • Nonlinearity re-analysis • Thermal vacuum data re-analysis • HIRS re-calibration for FCDR • Visible channel calibration pre/post-launch discrepancies

  3. HIRS/IASI-Spectral Match • IASI: 8461 spectral samples between 645.0 cm-1 and 2760 cm-1 (15.5 µm and 3.63 µm); HIRS :19 channels from short wave to long wave. The IASI measurements are convolved with HIRS SRF to simulated HIRS measurements for all 19 IR channels.

  4. HIRS/IASI-Spatial Match • IASI: scan rate: 8s, IFOV @ Nadir: 12km, and spectral sampling interval of 0.25 cm-1 ; HIRS: scan rate: 6.4s, IFOV@ Nadir: 10km. • IASI and HIRS measurements are collocated with navigation data, for which the distances between the nearest IASI/HIRS pairs are required to be less than 5km. • The biases between IASI and HIRS are generally consistent for different orbits based on studies of many orbits. Example results for an MetOp orbit start from 09:11am at July 18, 2009 is presented here.

  5. BT Comparison-Long Wave Channels(one sample orbit) • BT averaged every 8 IASI scan lines • Mean biases are within 0.3K for most channels • Scene temperature dependence found for some channels BT bias BT Diff (HIRS-IASI) K UTC hour of the Day

  6. BT Comparison-Short Wave Channels • Mean biases are within 0.3K for most channels, with some dependence on scene temperature BT Diff (HIRS-IASI) K delta count radiance UTC hour of the Day

  7. Non-Linear HIRS Calibration Test • Channel 8 is shown as an example • Adding a non-linear term to HIRS calibration canreducesthe biases

  8. HIRS Re-calibration for FCDR • Funded by NCDC to support the HIRS FCDR especially for the cloud time series using CO2 slicing (P. Menzel) • Recent progress at Wisconsin in resolving the discrepancies between high and low clouds from NOAA-14 to -15 through spectral shift • Plans: • Phase 1: Improve HIRS calibration on MetOp to match IASI (radiometric model, SRF, non-linearity, etc) (in progress) • Phase 2: Re-calibrate HIRS back to NOAA-14 • Phase 3: Re-calibration HIRS back to NOAA-6 • Provide the improved calibration to the Wisconsin team

  9. HIRS Visible Band CalibrationCheck at the Dome C Site • Investigation suggest that the discrepancy is due to prelaunch/postlaunch differences in spaceview count • Since the prelaunch coefficients are used for the operations, this discrepancy is causing the problems for NOAA-19/HIRS • The prelaunch spaceview count values (~-3140,  handbook, Rev. A, May 2006, page 6-28) are significantly different from that of the postlaunch values (~-2839) • Contacted NASA and ITT to find explanation for the large differences in spaceview count between pre and postlaunch

  10. Summary • MetOp HIRS is more stable than AVHRR relative to IASI • Residual biases can be further reduced with nonlinearity correction • Further calibration improvements is being made with a radiometric model, re-analysis of T/V data, and spectral response function re-analysis • Working closely with Wisconsin team to support the HIRS FCDR development • Pre/post-launch calibration discrepancy for the visible channel needs to be resolved working with the vendor

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