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Reflected Solar Calibration Demonstration System - SOLARIS
K. Thome, D. Jennings, B. McAndrew, J. McCorkel, P. ThompsonNASA/GSFC
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Calibration Demonstrator System SOlar, Lunar for Absolute
Reflectance Imaging Spectroradiometer (SOLARIS) Technology demonstration of
• Design and production of optics
Depolarizer technology Test prelaunch calibration
methods Evaluate reflectance retrieval Demonstrate transfer-to-orbit
error budget showing SI-traceability
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CDS – Overall goalsCalibration demonstrator provides tests of
laboratory characterization approaches Robust, portable tunable-laser facility including
transfer radiometers with sufficient spectral coverage
Broadband stray light and polarization systems of sufficient fidelity
Depolarizer technology Thermal control of attenuators and detector
needs to be proven Development of physically-based spectrometer
models including well-understood error budgets
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CDS will provide check on instrument models and reflectance retrieval approaches
Retrieve reflectance by taking the ratio of the solar irradiance and the signal from the scene Instrument model development for stray light
and other geometric effects Correction techniques for solar attenuators
Validation of reflectance done in laboratory & field Currently available laboratory equipment Compare with state-of-the art field approaches
Observations of sun and moon
CDS – Reflectance retrieval
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SI traceability and Stray Light
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Develop and check calibration protocols and methods
Path to SI traceability (source and detector standards)
Verifiable error budgets Instrument model development and
evaluation
CDS – SI traceability and transfer to orbit
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Developed a preliminary error budget based on a nominal design for the RS sensor
Key uncertainties are Geometry differences between the solar and
earth views Knowledge of attenuator behavior when
viewing sun Sensor behavior
Detector linearity Noise behavior
Polarization
Key error terms
BRDFS
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CDS Assembly with Optics
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1st Image through entire systemLine source illumination to evaluate spectral
characteristics of system October 2011 Complete optical package
coupled with COTS detector Better spatial resolution Allowed SOLARIS detector
development to continue in parallel
Interferometric tests of full optical system also took place Results match well with
predicted performance “Snap” together approach
worked extremely well
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First reflectanceCDS outside for December 2011 reflectance
measurements Ratio of scene data
(buildings, trees, cloudy sky, and clear sky ) to reference gives relative reflectance
Photo shows SOLARIS instrument with integrated optics and detector package mounted to a motorized telescope mount with the detector readout electronics
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First reflectanceImage at right is single
band System scanned in vertical
direction to create the 2-D spatial image CDS is pushbroom
design One dimension gives
spatial information 2nd dimension gives
spectral Spatial distortion caused
by oversampling in the scan direction
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First reflectanceThree-band mix of geometrically corrected
data along with COTS digital photo of scene
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First reflectance
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320 520 720 920 1120
Scal
ed re
flect
ance
Wavelength (nm)
Evergreen
00.10.20.30.40.50.60.70.80.91
320 520 720 920 1120
Scal
ed re
flect
ance
Wavelength (nm)
Asphalt
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320 520 720 920 1120
Scal
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flect
ance
Wavelength (nm)
Cloud
Red edge is in the 700-750 range
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Laboratory-based spectral calibration
Direct view of mercury lamp Diffusely reflected lamp
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Mercury lamp spectral results
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Laboratory-based radiometric calibrationSphere-based source that fills field and
apertureMean of 20 frames of sphere measurements
Mean of 20 frames of associated dark measurements
Sphere – dark
Spatial variability of output is result of operating detectors at ambient
Results in larger dark current as well
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Laboratory-based radiometric calibrationSOLARIS detector package allows for large
dynamic range but requires linearization• Based on TIRS detector package built at GSFC• Copy TIRS approach for SOLARIS data
TIRS exampleSOLARIS at 4 channels
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Lunar collectionImage of the moon collected on March 1
Evaluate spatial quality of imagery
Develop techniques for pointing and re-sampling
Blurred edge of moon is result of detector bleed over from operating with lower voltage bias
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Solar collection
SOLARIS operated with two neutral density filters giving 10-5 transmittance
Data will be used to evaluate for optical scattering effects
Tests of perforated plate attenuator coming soon
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SOLARIS + SIRCUS first light SIRCUS used for preliminary spectral
characterization on April 7
20-m fiber from SIRCUS
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SIRCUS results
Multiple single wavelength images for single SOLARIS band
Single wavelength image
Results for multiple SOLARIS bands
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CDS Integration, Test, & Cal. Flow
Performance Test with SIRCUS
Begin I&T(Blue Band)
Sun and Moon Meas.
Reflectance Test with
Diffuser and ASD
Assemble Telescope Sub Assy
Assemble OffnerSub Assy
Assemble Optics Package
Assemble Detector to Detector Housing
Assemble Detector Package (no detector)
Detector Housing
Therm/VacTest
Assemble Complete Instrument
Performance Test with SIRCUS
Begin I&T(Red Band)
Sun and Moon Meas.
Reflectance Test with Diffuser and ASD
Assemble Telescope Sub Assy
Assemble OffnerSub Assy
Assemble Optics Package
Assemble Detector Package
Assemble Complete Instrument
Detector Cal with SIRCUS
Detector Cal with SIRCUS
Calibration with SIRCUS
Calibration with Broadband
Lamps in Sphere
Calibration Round Robin
with Butler and LASP
Calibration with HIP at NIST
Field Measurements
Sun and Moon Measurements
Complete Instrument Model
Component Characterizations
Calibration Accuracy: 1% Calibration Accuracy: 0.3%
Calibration Accuracy: 3%
Build Instrument Control System
Build Instrument Purge/VacSystem
Complete Instrument Control System Software
Current status
FY 2012
FY 2013
FY 2014
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SummaryGoal for FY 2012 is to demonstrate a 2-3%
calibrated instrument with error budget Blue box CDS completed in October 2011 with
prototype grating and uncooled detectors Verification of laboratory and scene accuracies
awaits improvements to detector cooling package expected by May
Final version of grating recently delivered Solar and lunar measurements have been
made Initial SIRCUS-based spectral response just
completed Will deliver a quantitative error budget
Red box CDS will be completed by end September
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SummaryPlans for FY 2013 and beyond concentrate on
taking SOLARIS to the 1% plateau Timing depends on actual funding allocations
Personnel numbers may limit some development Susceptible to hardware failures Improvement to laboratory calibration are funding
dependent Successful CDS effort will
Develop and test sensor model development Demonstrate error budget for reflectance retrieval Produce a peer-reviewed SI traceability for CLARREO-
like measurements Evaluation of absolute solar irradiance calibration Lunar model verification from ground-based collects
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SOLARIS CDS will play a key role demonstrating CLARREO-quality error
budgets Collaborative efforts with NIST will continue to be critical “Operational” use of SIRCUS Extension to wavelengths >1 micrometer Broadband calibration approaches (HIP)
Calibration approaches will be demonstrated Laboratory calibration protocols Error budget demonstration
Reflectance retrieval Stray light characterization Instrument model assessment
Summary