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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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Scal

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Wavelength (nm)

Evergreen

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320 520 720 920 1120

Scal

ed re

flect

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Wavelength (nm)

Asphalt

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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