Slide 1 Scanning High-resolution Interferometer Sounder (S-HIS) Calibration and Earth Observing System (EOS) Validation Joe Taylor, F Best, N Ciganovich, R Dedecker, S Dutcher, S Ellington, R Garcia, H Howell, R Knuteson, D Laporte, C Moeller, H Revercomb, W Smith*, D Tobin, M Werner University of Wisconsin, SSEC * NASA LaRC Seventh Workshop on Infrared Emission Measurements by FTIR, Quebec City, February 2004

Slide 2 Calibration and Validation for IR radiance observations are now concerned with tenths of K, not K! High Spectral Resolution is an important part of the reason. (Goody and Haskins, J Climate 1998)

Slide 3 Topics The Scanning High-resolution Interferometer Sounder (S-HIS) Overview Recent developments (Oct present) The Atmospheric Infrared Sounder (AIRS) Radiance Cal / Val of AIRS with S-HIS

Slide 4 The Scanning High-resolution Interferometer Sounder (S-HIS)

Slide 5 UW SSEC S-HIS: Present (1) (HIS: High-resolution Interferometer Sounder, ) Spectral Coverage: LW: MW: SW: Spectral Resolution: cm cm cm cm cm -1 Interferometer Type: Resolving Power: IFOV: Field Mirror Scan: Voice coil DA plane mirror (Custom / modified Bomem DA-5) mrad (2 20 km, nadir) Programmable Longwave Midwave Shortwave CO 2 CO N2ON2O H2OH2O H2OH2O CH 4 /N 2 O CO 2 O3O3 Characteristics

Slide 6 UW SSEC S-HIS: Present (2) (HIS: High-resolution Interferometer Sounder, )

Slide 7 S-HIS: Recent Developments (OCT present) ARM - UAV Mission, Oct / Nov 2002; S-HIS on the Proteus Radiometric calibration budget Spectral band overlap Uplooking (Zenith) view Nonlinearity refinement Unfiltered interferogram storage

Slide 8 S-HIS on 1 st ARM-UAV Mission with Proteus, October 2002 Zenith view added for the Proteus integration Typically, cross-track scanning with two blackbody views

Slide 9 S-HIS on the Proteus: Remote Telemetry and Command Exciting opportunity A state-of-health application for S-HIS for this deployment Three ‘application modules’ The S-HIS UAV interface Polls for and interprets commands from the payload controller Monitors internal UDP traffic, periodically retrieving data Converts retrieved data to engineering unit, parses, and sends to payload controller Monitors for critical data storage errors The payload controller Maintains ground link Power management Relays instrument commands and data files The ground system Provides a user interface to the payload

Slide 10 S-HIS on the Proteus: New Platform, New Environment New Interfaces (mechanical, electrical, optical) Vibrational environment Thermal environment

Slide 11 S-HIS on the Proteus: New Platform, New Environment (2)

Slide 12 RSS T HBB T ABB T RFL  HBB  ABB Scanning-HIS Radiometric Calibration Budget for 11/21 case T ABB = 260K, T HBB = 310K 3-sigma Uncertainties, similar to Best, et al., CALCON 2003 for AERI

Slide 13 Scanning-HIS Radiometric Calibration Budget for 11/21 case T ABB = 260K, T HBB = 310K 3-sigma Uncertainties, similar to Best, et al., CALCON 2003 for AERI

Slide 14 Longwave (HgCdTe) Midwave (HgCdTe) Shortwave (InSb) LW/MW overlap MW/SW overlap Radiance (mW/m 2 sr cm -1 ) Wavenumber (cm -1 ) Scanning-HIS Band Overlap Agreement

Slide 15 S-HIS zenith and cross-track scanning Earth views from ~14km HBB Earth ABB Zenith

Slide 16 Calculation based on 18Z ECMWF analysis, with cm H 2 O above 14km Observed and Calculated zenith views from ~14km Calculated Observed

Slide 17 Non-linearity Refinement Band-to-band overlaps are a primary source of refinement –SW band detector is highly linear, allowing SW overlap with MW to constrain or test the MW non-linearity –MW overlap with LW can then constrain or test the LW non- linearity Currently using up-looking constraints to refine estimates of non-linearity coefficients and their uncertainties

Slide 18 Raw Interferogram Storage Current flight software: only filtered interferograms stored “Bench tested” software: raw interferogram storage –All 3 bands, interferograms truncated about ZPD –2 bands, complete interferograms Raw interferograms provide out-of-band nonlinearity signal information Applications: –Verify “defiltering” algorithm –Improved tilt correction –Improved nonlinearity characterization Future work: –All 3 bands, complete –Filtered and raw interferogram combination –Operational flight software

Slide 19 The Atmospheric Infrared Sounder (AIRS)

Slide 20 AIRS AIRS is part of the EOS Aqua instrument suite polar sun synchronous ascending 1:30 PM local Managed by NASA/JPL. Companion instruments –AMSU-A (Advanced Microwave Sounding Unit - A) –HSB (Humidity Sounder for Brazil) stopped working in March 2003 –MODIS, CERES, AMSR-E Timeline: Launched on May 4 th 2002 First L1B data made available to the science team in mid June 2002 L1B available from GSFC DAAC starting in March 2003 L2 available from GSFC DAAC starting in Sept 2003

Slide 21 AIRS Design Hyperspectral radiometer with resolution of 0.5 – 2 cm -1 (resolving power of ~1200) Spectral range: 650 – 2700 cm -1 Multi-order Infrared Grating Spectrometer passively cooled to ~153K, stabilized to 30 mK PV and PC HdCdTe focal plane cooled to 60K with redundant active pulse tube cryogenic coolers Focal plane has ~5000 detectors, 2378 channels. PV detectors (all below 13 microns) are doubly redundant. 308 K onboard blackbody and space views provides radiometric calibration Clear sky upwelling radiation calculations provide spectral calibration NEDT (per resolution element) is very good and ranges from 0.05K to 0.5K per channel

Slide 22 Radiance Validation of AIRS with S-HIS

Slide 23 A detailed comparison should account for: Instrumental noise and scene variations Different observation altitudes (AIRS is 705 km, S-HIS is ~20 km on ER2, ~14 km on Proteus) Different view angles (AIRS is near nadir, S-HIS is ~±35deg from nadir) Different spatial footprints (AIRS is ~15 km at nadir, S-HIS is ~2 km at nadir) Different spectral response (AIRS  = / 1200, S-HIS  ≈ 0.5 cm -1 ) and sampling SHIS and AIRS SRFs AIRS SHIS AIRS / S-HIS Comparisons

Slide Average SHIS data within AIRS FOV(s) & compare No attempt to account for view angle, altitude, spectral differences. 1. Compare Residuals from calculations: AIRS residual = AIRS obs - AIRS calc S-HIS residual = S-HIS obs - S-HIS calc S-HIS and AIRS calculations each completed at correct altitudes, view angles, spectral resolution and sampling. Monochromatic calculations completed using same forward model, atmospheric state, and surface property inputs. 2. Difference Residuals with Spectral Resolutions made similar AIRS residual = AIRS obs  S-HIS SRF - AIRS calc  S-HIS SRF S-HIS residual = S-HIS obs  AIRS SRF - S-HIS calc  AIRS SRF valid comparison except for channels primarily sensitive to upper atmosphere (above aircraft altitude) AIRS / S-HIS Comparison Steps

Slide 25 Terra-Aqua Experiment (TX-2002), 21 Nov 2002 time coincidence Aqua Sub- satellite track ER2 Flight track UTC UTC 1941 UTC Aqua coincidence

Slide K MODIS 12  m Band Tb(K) & near-nadir AIRS FOVs, 21 Nov 2002

Slide 27 8 AIRS FOVs used in the following comparisons 1 K MODIS 12 micron Band & near-nadir AIRS FOVs, 21 Nov 2002

Slide 28 AIRS S-HIS “comparison 0” 8 AIRS FOVs, 448 S-HIS FOVs, PC filtering

Slide 29 “Comparison 0”, 21 Nov AIRS FOVs, 448 S-HIS FOVs, PC filtering

Slide 30 36, 35, 34, AIRS minus MODIS “Comparison 2” wavenumber AIRS Observed - Calculated S-HIS Observed - Calculated AIRS S-HIS Calculated spectra in black AIRS Compared to S-HIS (LW), 21 Nov 2002

Slide “Comparison 2” AIRS Observed - Calculated S-HIS Observed - Calculated AIRS S-HIS Calculated spectra in black wavenumber AIRS Compared to S-HIS (MW), 21 Nov 2002

Slide 32 22, Different viewing angle make daytime comparisons less accurate “Comparison 2” AIRS Observed - Calculated S-HIS Observed - Calculated AIRS S-HIS Calculated spectra in black wavenumber AIRS Compared to S-HIS (SW), 21 Nov 2002

Slide 33 wavenumber (cm -1 ) ∆T b (K) Small Spectral Shift (3% of resolution) in AIRS Module-05 identified from S-HIS Validation T b (K) wavenumber (cm -1 ) Observed - calculated (K) Tobin, et al., CALCON 2003, presented S-HIS Spectral Calibration observed original calculated shifted calculated original obs-calc shifted obs-calc

Slide 34 (AIRS obs - AIRS calc )- (SHIS obs - SHIS calc ) (K) “Comparison 2”, 21 Nov 2002 Excluding channels strongly affected by atmosphere above ER-2

Slide 35 Summary The calibration uncertainty of advanced high spectral resolution observations are approaching the 0.1K desired for climate applications. The calibration uncertainty of advanced high spectral resolution observations from the S-HIS [and the NPOESS Airborne Sounder Testbed (NAST) are now proven tools for the detailed validation of satellite based observations.

Slide 36 Summary (2) High spectral resolution aircraft instrument comparisons provide a way to periodically evaluate the absolute calibration of spacecraft instruments with instrumentation that can be carefully re-calibrated with reference standards on the ground. This capability is especially valuable for assuring the long-term consistency and accuracy of climate observations, including those from the NASA EOS spacecrafts (Terra, Aqua, and Aura) and the future operational observations from the new complement of NPOESS instruments.

Slide 37 Thank You.