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Presenter: Kurt Thome

Presenter: Kurt Thome. Reflected Solar Suite Kurt Thome , Jason Hair & RS Team. Deputy Project Scientist. RSS Requirements. Requirements includes inter-calibration. RSS Level 2 Requirements. Spectral range: 320 – 2300 nm Spectral sampling: ≤4 nm Spectral resolution: 8 nm

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Presenter: Kurt Thome

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  1. Presenter: Kurt Thome Reflected Solar Suite Kurt Thome, Jason Hair & RS Team Deputy Project Scientist

  2. RSS Requirements Requirements includes inter-calibration

  3. RSS Level 2 Requirements • Spectral range: 320 – 2300 nm • Spectral sampling: ≤4 nm • Spectral resolution: 8 nm • Sampling interval at nadir from 600 km orbit: 0.5 km • Spatial resolution per sample: • 70% of energy from within a 0.5 km x 0.5 km area • ≥ 95% within a 1.0 km x 1.0 km area • Swath width at nadir from 600 km orbit: >100 km • SNR values for a single sample (defined for a typical radiance, Ltyp, based on a reflectance of 0.3 and incident solar zenith angle of 75 degrees): • SNR> 20 for wavelengths 320 – 380 nm • SNR> 33 for wavelengths 380 – 900 nm • SNR> 20 for wavelengths 900 – 2300 nm • Polarization sensitivity for 100% polarized input: • <0.25% (TBD) below 1000 nm and • <0.75% (TBD) at other wavelengths • Radiometric calibration accuracy: 0.3% of albedo (integration of reflectance across all wavelengths) and within individual bands Requirements

  4. Original RSS Instrument Concept Detector Plane Thermal Radiators • 3x Optical Packages • Blue Channel 320-640nm • Red Channel 600-1200nm • NIR (Near Infra-Red) 1150-2300nm Heat Pipes Instrument Support Platform Attenuator wheel Control Electronics (On S/C) Main Electronics Box (On S/C) Sensor Design

  5. RSS Instrument Concept Design • Commonality of design of three boxes aids in calibration • All-aluminum materials including telescope optics • Offner design • Cooled focal planes tailored for each spectral region • Depolarizers reduce impact of scene polarization • Attenuator wheel for reducing solar irradiance for reflectance retrieval Instrument Optical Bench Telescope Optics Depolarizer Assembly Attenuator Wheel Detector Electronics Detector Assembly Sunshield Single box layout

  6. CLARREO-1RSIS Goals • Develop modified instrument concept to coincide with a “single” instrument spacecraft • Reduce the instrument mass • Fit within funding caps and profiles provided by the project • Meet all of the RS science requirements including intercalibration • Proposed solution – reduce three boxes to two boxes • Assume a development plan for CLARREO-1 consisting of • 1 Breadboard • 1 Prototype/EDU • 1 Flight Unit • The development plan for RSIS on CLARREO-2 depends on what is developed for CLARREO -1

  7. 2-box design • The RSIS instrument concept for an RSIS dedicated spacecraft revolves around a two spectrometer approach • Blue spectrometer remains the same • Silicon-based detector • 320 to 640 nm • Single order grating • Red and NIR spectrometers combined • 600 to 2300 nm • Dual order grating; multi-blazed • HgCdTe detector • Dual attenuator wheel • Combining the Red and NIR channels into one spectrometer leverages the capability of the MCT detector

  8. Why not 2-box from the start? • Three-box approach was chosen for several reasons • Lowest overall risk • Simpler design, fabrication, build, and test/calibration • Higher component TRL • Detectors had flight history • Depolarizers and attenuators could be tailored spectrally • Characterization/calibration more straightforward • 2-box approach satisfies many of these • Increased risk to the calibrate the Red/NIR spectrometer due to the increased stray light from the dual order grating • Mitigate attenuator spectral sensitivity through multiple attenuator wheels • The specific impacts of the dual order system will have to be evaluated though the breadboard program

  9. Two-box concept • 2x Optical Packages • Blue Channel 320-640nm • Red/NIR Channel 600-2300nm Detector Plane Thermal Radiators Instrument Support Platform Attenuator wheel Control Electronics (Inside S/C) Main Electronics Box (Inside S/C)

  10. Two-box approach

  11. GPS Antennas GNSS-RO POD Antenna Star Trackers

  12. Instrument • Mass:  67 kg CBE, 86kg with 28% confidence factor • Power:  96 W Avg, 118 W Peak CBE, 125 W Avg, 153 W Peak with 30% confidence factor • Data Rate:  Still being reviewed, but it looks like an allocation of 100 Gbits/day and 150 Mbps Data Rate to the SSR would provide good margin with a 30% confidence factor • Thermal Radiator: 0.1m^2 mounted on the side of the S/C • Spacecraft pointing control: 360 arcsec control, 72 arcsecknowledge • Spacecraft roll slew rate: up to 2 deg/s • Planned Orbit: 609km • Mechanical Interface: 2 spectrometers mounted to the top of the S/C, 2 Electronics boxes (Main EB, and Attenuator Wheel EB) mounted inside S/C, thermal radiator mounted to S/C cold side • Electrical Interface:  LVDS connection to SSR, 1553 or 422 communication bus

  13. Reflectance Retrieval • Baseline approach to reflectance retrieval is ratio of earth-view data to solar-view data • Single detector scans entire solar disk • Response of ith detector is • Bidirectional reflectance distribution function (BRDF) is Level 1 Science requirement is stated in terms of a reflectance retrieval

  14. Operating Modes • Reflectance retrieval, calibration and inter-calibration requirements lead to three basic operating modes • Solar Calibration • Nadir Data Collection • Inter-calibration of LEO/GEO assets (avg. 2x per orbit) • Verification of calibration drives the need for Lunar Views Three basic operating modes for RSS instrument

  15. On-Orbit, Solar Calibration • Solar calibration allows for • Correction of degradation of sensor response • Temporal degradation of detectors and optics • Detector-to-detector changes • Evaluation of stray light • Solar view is non-trivial • Irradiance source rather than radiance source • 50,000 times higher energy level • Requires attenuating approaches Reflectance retrieval uses direct solar view

  16. Attenuators for Solar Calibration Mode • Attenuators provide the 50,000x reduction in solar energy • All approaches are spectrally dependent • Pinhole Aperture • Diffraction effects lead to spread of solar “image” • Small-sized aperture affects diffraction grating dispersion • Perforated Plate • Avoids materials degradation problems • Trade on size and number of holes relative to attenuation and beam uniformity • Neutral Density Filters • Attenuate using either absorption or interference effects • Temporal degradation needs evaluation Direct solar view requires an attenuating mechanism

  17. Calibration overview • CLARREO reflectance retrieval relies on the ratio of the benchmark data to the solar data • Account for temporal variability in sensor • Can be converted to absolute radiance using a known solar irradiance • Need to include uncertainties in sensor characterization • Straylight changing • Sensor solid angle (footprint) • Sensor aperture • Attenuator area • Detector response uncertainties • Nonlinearity • Polarization • Flat field correction

  18. Full Calibration

  19. Single-Multiple Image Calibration • Each attenuator must be used for solar views • Lunar verification follows similar scanning

  20. Flat-Fielding Calibration

  21. Calibration Approach • Characterize the sensor to SI-traceable, absolute radiometric quantities during prelaunch calibration • Watt • Irradiance mode • Radiance mode • Determine geometric factors for conversion to reflectance • On-orbit calibration “validates” the prelaunch calibration • Solar and lunar views used to determine temporal changes • Key is to ensure prelaunch calibration simulates on-orbit sources • Absolute irradiance calibration for solar view • Simulated geometry of solar and lunar views for stray light • Successful transfer to orbit achieved when sensor behavior can be accurately predicted Simulating and predicting on-orbit sources is basis of calibration

  22. Meeting L1 Measurement Requirements • The effort is determining the measurements needed to satisfy/understand the development of the sensor model • Preliminary independent study indicated CLARREO Reflected Solar requires nearly order of magnitude improvement in radiometric accuracy • Dominant error sources identified as stray light and attenuator characterization • Efforts to reduce these error sources rely on • Minimizing sensor complexity • Choosing appropriate approaches for SI traceability • Emphasizing calibration throughout sensor development lifecycle RS Calibration

  23. Calibration Overview * Measurements to achieve SI traceability for transfer to orbit

  24. Calibration overview • Attenuator verification relies on trending of lunar views without attenuator • Compare to trend of sensor output while viewing sun with attenuator in place • Different trend behavior indicates attenuator issue • Comparison of solar irradiance reported by CLARREO to other on-orbit sensors indicates whether absolute calibration is maintained in going to orbit • Indicates whether geometric factors are well understood (attenuator area) • Stability of absolute detector response • Relative response measured in laboratory compared to that derived on orbit for consistency • Artifact determination • Sun and moon provide sharp boundaries for stray light, ghosting • Stellar and planetary sources provide point sources for evaluation of spatial response • Polarization sensitivity assessed using earth-view scenes (e.g., ocean views at large angles) • Non-linearity evaluated by varying attenuators • Size of source effect is most difficult to issue to understand

  25. SIRCUS Traceability • SIRCUS provides a feasible option for simulating on-orbit sources • Absolute response • Stray light • SIRCUS relies on a set of well-understood tunable lasers • Variety of techniques used to condition laser output • Output characterized by CLARREO Transfer Radiometer and monitors on sphere • Provides a monochromatic source that can achieve 0.1% absolute uncertainty * POWR – Primary Optical Watt Radiometer Meeting L1 Measurement Requirements

  26. SIRCUS and CLARREO • Ultimate goal is to have a portable SIRCUS-like facility for calibration of RS instrument • Portability needed to ensure its use at a vendor facility • Necessary to achieve needed accuracy • SIRCUS-like facility includes • Monochromatic source • Irradiance • Radiance • Cover full spectral range of CLARREO • Broadband transfer radiometers • Monitor output of source • Transfer radiometer #1 – VNIR • Transfer radiometer #1 - SWIR • Maintain traceability to NIST laboratories • Transfer radiometer #2 – VNIR • Transfer radiometer #2 - SWIR Meeting L1 Measurement Requirements

  27. Inclusion of SIRCUS for CLARREO • Including a SIRCUS-like source in the preflight calibration chain permits preflight, absolute radiometric calibration of solar view to better than 0.2% • Diagram below gives top-level error sources and expected error budget Meeting L1 Measurement Requirements

  28. Broadband Approaches • Sources calibrated in SIRCUS-like measurements are limited in bandpass • Small regions of wavelength can be tested • Cannot calibrate all CLARREO spectral and spatial detectors simultaneously • Hyperspectral Image Projector (HIP) currently under development at NIST would provide a broadband source • Can match desired spectral source • Traceablity can be achieved through a SIRCUS-like calibration • Also provides opportunity to develop a solar simulated source • SIRCUS and HIP can be replicated at a CLARREO facility HIP schematic Meeting L1 Measurement Requirements

  29. Technology Development/Path to 0.3% • Clearly the key technology developments are • SIRCUS facility • RS Transfer Radiometer • A SIRCUS-based absolute calibration in radiance is currently demonstrated by NIST at the 0.2% accuracy • Stray light is readily characterized by a SIRCUS-based calibration • Polarization sensitivity measurements are also feasible with SIRCUS • Focus on developing broadband calibration techniques • HIP can be used to bridge the broadband gap • More development to understand the accuracy • Prototype development scheduled to be complete in 18 months • Characterization of filtered transfer radiometers by SIRCUS also permits extension to broadband sources • Significant technology development is not required but rather advancements in current approaches are needed • Robust, portable SIRCUS facility • Transfer Radiometers with sufficient spectral coverage • Broadband stray light and polarization systems of sufficient fidelity Requirements Compliance

  30. Error Budget • Radiometric calibration requirements of RSS instrument can be met with currently-available approaches • Requires inclusion of NIST-based methods • Detector-based transfer radiometers • Narrow-band SIRCUS aproaches • HIP-based scene projections Meeting L1 Measurement Requirements

  31. Calibration Flow Requirements Verification Launch • Thermal/Vac Test • Survival - Balance Requirements Verification Environmental Test Acceptance Review Delivery to Payload I&T Environmental Test • Thermal/Vac Test • Survival - Balance Environmental Test Requirements Verification Environmental Test Requirements Verification Payload Delivery to Spacecraft I&T • Thermal/Vac Test • Survival - Balance Requirements Verification Environmental Test Requirements Verification Environmental Test • Thermal/Vacuum Test • Thermal/Vacuum Test • Thermal/Vacuum Test Ground Operations Calibration Stability Check Calibration Stability Check Calibration Stability Check Assemble FLT Optics Package (NIR Band) Assemble FLT Optics Package (Blue Band) Assemble FLT Instrument (3 Boxes) Deep Calibration Subsystem/ Component Measurements Assemble FLT Optics Package (Red Band) Deep Calibration In-Orbit Calibration Payload I&T Subsystem/ Component Measurements Deep Calibration Spacecraft I&T Post-Launch Checkout Subsystem/ Component Measurements Validation Post-Launch Operations RS Calibration

  32. Trade Studies Completed • Aperture and Grating Quantity Trade Study • Proceed with 3 Aperture, 3 Grating Design • Lowest overall Risk • Simpler design, fabrication, build, and test • Lower cost • Higher component TRL • Detector Material Trade Study • Blue Band Material Selected – Silicon; Red and NIR Band Material Selected – MCT (substrate removed) • Only consider main-stream detector technology • Only consider materials with flight history • Meets Spectral Requirement • Wavelength Range Trade Study • Spectral range to cover from 320 to 2300 nm • Upper limit chosen due to loss of signal from reduced solar irradiance and strong water vapor and carbon dioxide absorption • Short-wavelength limit chosen to provide sufficient spectral range for accurate retrieval of total shortwave flux • Polarization Requirements Trade Study • Polarization sensitivity <0.50% below 1000 nm and <0.75% at other wavelengths for a 100% polarized input  • Value required to limit uncertainty in benchmark data set to contribute <0.1% of total radiometric calibration budget Trade Studies

  33. Radiometric Performance Margin: Ltyp; Sun View; Lmax Worse case detector temps Inst #1 270K Inst #2 250K Inst #3 230K Per pixel SNR requirement 11 7 7 Requirements Compliance

  34. Polarization Sensitivity Compliance Add text description; label requirements lines; define DOLP Dual-Double Wedge Depolarizer with OA at 90, Wedge angles clocked at 45  Requirements Compliance

  35. Phase A plans • Phase A breadboard and EDU development requires a parallel development of calibration GSE • Calibration development plan also includes development of calibration methods and protocols applicable for flight instruments • Calibration development plan follows Phase A plans to reduce instrument risks and close trades • Solar/earth view ratio for reflectance • Laboratory capability to provide irradiance (point) source and radiance (extended ) source • Solar- and lunar-based measurement capability • Geometric characterization of sensor field of view • Attenuator characterization • Spectral transmittance • Aperture-area measurements • Path to SI traceability (source and detector standards) • Narrow-band source (SIRCUS) • Broad-band source (HIP) • Transfer radiometers • Stray light modeling capability • Polarization sensitivity measurement • Component-level depolarization characterization • System-level polarization sensitivity • Focal plane and grating characterization • Uniformity • Stability • Noise

  36. Breadboard Plan Characterization and Calibration Component Fabrication, Procurement Component Characterization Optical Package Assembly Performance Test and Calibration Earth, Sun, Moon Measurements Component Fab, Procure Long Lead Procurement Start (Detector, Grating, Depolarizer) Layout & Analysis Comp. Charact. Optics Package Assembly Perf. Test, Cal. Calibration (incl. NIST) Earth, Sun, Moon Meas. March 2012 Oct 2011 Aug 2010 May 2011 Dec 2011 July 2012 Aug 2011 April 2012 Long Lead Procurements Layout and Analysis • Description • Detectors • Depolarizers • Gratings • Risk Reduction • Items available when other parts ready • Description • Develop a breadboard based on the blue band spectrometer • Risk Reduction • Allows lower cost breadboard development using Si detectors • Focuses effort on component and calibration risk mitigation • Description • Measure Performance • Detectors • Depolarizers • ND Filters • Gratings/Optics • Risk Reduction • Validate analytical performance models with measured performance • Measure Detector noise levels, Validate noise reduction by averaging • Evaluate stray light • Description • Calibrate with a NIST traceable FEL Lamp • Flat Panel, Spherical Integrator Cal. • Risk Reduction • Begin NIST traceable calibration • Begin developing cal. processes • Description • Measure Sun and Earth to generate Reflectance • View Moon and Sun • Risk Reduction • Begin to validate operations approaches • First time that Sun and Earth will be viewed to generate Reflectance • Description • Continue cal. evaluation with GSFC facilities • Calibrate with SIRCUS at NIST • Risk Reduction • Continue NIST traceable calibration to higher accuracies • Begin developing cal. processes • Evaluate the ability to calibrate the design

  37. Breadboard Plan • Breadboard plan was modified slightly in March • Build an optical package starting with the Blue band (320-1150 nm) design • Blue band selection will allow achievement of more objectives than any other band (items 1,2,4,5, and 6) quicker, with possibly lower cost options for detectors • Build optical package for the Red/NIR band (600-2300 nm) designs • Evaluate detector options based on cost, with the possibility of a stepped approach of cheaper vs. more functional detectors to begin a stepwise learning and testing approach based on available budget • The optical package would have a feature for using attenuators • Validate reflectance retrievals in laboratory and field • NIST-based measurements to evaluate calibration techniques and error budgets • Breadboard objectives • Demonstrate the ability to view the sun and the scene and output reflectance by taking the ratio of the Solar irradiance and the measured value • Feasibility of attenuation methods: perforated plate, pinhole plate, neutral density filters • Develop and check calibration protocols and methods • Path to SI traceability (source and detector standards) • Demonstrate the ability to design and produce optics, with the optics in the Blue band (320-1150 nm) being the most challenging • Demonstrate ability to minimize polarization sensitivities • Demonstrate the ability to control and characterize stray light including multiple-order gratings • Demonstrate the ability to measure shortwave IR (600-1200nm) (Red) • Demonstrate the use of detector technology • Validate ability to control thermal stability • Make measurements past 900nm

  38. Calibration Development Plan • Phase A breadboard and Prototype development requires a parallel development of calibration GSE • Calibration development plan also includes development of calibration methods and protocols applicable for flight instruments • Calibration development plan follows Phase A plans to reduce instrument risks and close trades • Solar/earth view ratio for reflectance • Laboratory capability to provide irradiance (point) source and radiance (extended ) source • Solar- and lunar-based measurement capability • Geometric characterization of sensor field of view • Attenuator characterization • Spectral transmittance • Aperture-area measurements • Path to SI traceability (source and detector standards) • Narrow-band source (SIRCUS) • Broad-band source (HIP) • Transfer radiometers • Stray light modeling capability • Polarization sensitivity measurement • Component-level depolarization characterization • System-level polarization sensitivity • Focal plane and grating characterization • Uniformity • Stability • Noise

  39. NIST Standards Development FY 2011 FY 2012 FY 2013 FY 2014 Procure tunable lasers to cover desired wavelength range (320nm – 2300nm) Design a portable version of the NIST SIRCUS facility Outcome: Provides monochromatic source that can achieve 0.1% absolute accuracy of irradiance sources Complete Testing SIRCUS Assemble SIRCUS facility Design DMD-based spectrally tunable calibration source Outcome: Provides a broadband source that can reproduce expected reflected solar brightness levels and spatial distributions Assemble DMD Complete Testing DMD Outcome: Enables SI-traceable radiance comparisons in the UV, visible, and near-infrared Construct/Test CXRs (coverage from 320 nm to 2300 nm) Complete testing of CXRs Design CXRs

  40. Breadboard and SIRCUS • Activities of breadboard relevant to SIRCUS • Develop and check calibration protocols and methods • Path to SI traceability • Detector-based methods • Demonstrate the ability to control stray light • Demonstrate the ability to measure shortwave IR (600-1200nm) (Red) • Development of SIRCUS-like facility takes place during breadboard work • Not necessary to complete SIRCUS for breadboard • Necessary to understand how it would be used • Higher fidelity error budget

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