Calibration demonstration system for an imaging spectrometer to provide climatequality reflectance K. Thome, J. McCorkel, J. Hair, B. McAndrew, A. Daw, D. Jennings, D. Rabin NASA/GSFC 1
Calibration Demonstration System (CDS) SOLARIS (SOlar, Lunar for Absolute Reflectance Imaging Spectroradiometer) Provide risk reduction for CLARREO (Climate Absolute Radiance & Refractivity Observatory) Demonstrate transfer-to-orbit error budget SI-traceability Technology demonstration for prelaunch calibration methods Field collections to evaluate retrievals 2
Instrument Background Offner system covering 320 to 2300 nm with 500-m GIFOV and 100-km swath width Reflectance from ratio of earth view to measurements of irradiance while viewing the sun Reflectance traceable to SI standards at an absolute uncertainty <0.3% Lunar data provide calibration verification Spaceborne version will rely on inetrcalibration to develop climate record 3
SOLARIS hardware First unit grating All aluminum optics for reduced thermal effects 4 Portion of optics and entire instrument housing and mechanical structures done in house at GSFC
SOLARIS detector home grown Wide dynamic range detector needed Silicon detector fabricated in house at GSFC Commercial HgCdTe detector hybridized at GSFC Detector with Indium Bumps ROIC Detector Hybrid in a LCC carrier Detector mounted in ceramic board 5
Climate-quality data Absolute uncertainties < 0.3% in bandintegrated albedo TRUTHS (Traceable Radiometry Underpinning Terrestrial- and Helio- Studies) CLARREO (Climate Absolute Radiance and Refractivity Observatory) 6
Why climate quality besides for climate? Climate quality achieved through SI-traceable, well-characterized, high-accuracy sensors SI-traceable data do not require sensors to overlap in time for time series Decouple instrument, atmospheric, and surface effects Determine real differences in sensors 7
Current calibration approaches Best sensors have reflectance accuracy of 3.6% (k=2) in mid-visible [4.2% in radiance] None of these approaches is adequate for climate-quality measurements 3.6% (k=2) 8 RTC Code Intercomparisons 1.0% (k=2) relative 0.2% (k=2) relative
Detector-based approaches for climate quality Laser-based, monochromatic, SI-traceable source with <0.09% (k=2) uncertainty Highly-accurate detector calibrates source output Laser source used to allow unfiltered detectors SOLARIS being used to show accuracy transfers to the field and hence to orbit 9
Laser-based, monochromatic, extended source Spectral Single wavelength Spatial dimension Tuning laser source through multiple wavelengths allows derivation of absolute spectral response Extended source provides spectral data across the spatial dimension 10
Laser-based collimated source Red Spectral Blue Ghost from slit reflection Provides information for instrument model and baffling Second order of 632.8 nm Image 11 Spatial
Broadband radiometric calibration still needed Absolute radiometric calibration (counts per unit radiance [CPUR]) tied to calibrated field spectrometer 12 Spectral channel 220 (627.4 nm) 3% absolute accuracy relative to field spectrometer Spatial column 545
Flight-like electronics allow error budget evaluation SOLARIS at 4 channels SOLARIS detector package allows for large dynamic range but requires linearization 13
Outside solar collections test calibration approach Spectral signal profile Spatial profile 14 Tests of other attenuators and lunar views still to come
Airborne imaging spectrometer Outdoor collections allow testing transfer to orbit of detector-based calibrations and reflectance retrieval cloud Mobile SOLARIS Red Lake Playa, Arizona 29 March 2013 Field spectrometer Landsat 8 validation experiment 15 http://earthobservatory.nasa.gov/iotd/view.php?id=80913
SOLARIS to verify detector-based error budget Error budget currently based on best available methods Demonstration of error budget reduces risk for CLARREO Reflective-band imaging spectrometers will benefit as well Percent uncertainties in reflectance; k=2 0.2% Earth:Solar Ratio Line Spread Function Artifacts Reflectance uncertainty 0.1% 0.2% 0.03% Earth View Solar View Spectral 0.3% 0.2% Solar Attenuator Factor Wavelength Calibration Artifacts 16
CDS Summary SOLARIS has been used to demonstrate key parts of CLARREO calibration Plans are to take SOLARIS to the 1% plateau Produce a NIST-reviewed, SI-traceable error budget for CLARREO-like measurements Evaluate solar irradiance calibration and lunar model verification from ground-based collects High fidelity instrument model High-fidelity sensor models will allow transfer of laboratory characterization to orbit SOLARIS will show detector-based methods can be used to characterize imaging spectrometers Stray light Absolute radiometric calibration 17