Prelaunch Characterization of Satellite Instruments

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Pre-launch Characterization of Satellite
Instruments

• Dr. Raju Datla
• NIST
• Optical Technology Division
• Gaithersburg, MD 20899
• Collaborators NIST Adriaan carter, Joe Rice,
  Carol Johnson, Steve Brown, Eric Shirley SDL-
  Joe Tansock

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Outline

• Calibration Planning and Implementation
• Subsystem/Component Characterization
• System Level Characterization
• Summary

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Calibration Planning

• Start as soon as possible (i.e. requirements
  definition, concept design, sensor design, etc.)
• Encourage optimum sensor design and calibration
  approach to achieve performance requirements
• Use NIST as a resource to shake out problems

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• Aperture diameter uncertainty is typically no
  better than 1 micro meter.
• NIST can measure apertures down to 3 mm
  diameter to 0.05 micro meters.
• Apertures are susceptible to unintended
  obstructions and if thin, can warp.

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3D Aperture Measurement
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Blackbody Calibration at the LBIR Facility

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Calibration Planning

• Identify instrument requirements that drive
  calibration
• Programs often start with a requirement such as
• Radiance Accuracy lt 5 absolute each band
  Between Band lt 5 relative band to band etc.
• NIST VXR 1s (2) NIST Trap Detector 1s (0.1)
• Perform trade study to determine best calibration
  approach

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Ocean Color with Sea-Viewing Wide Field of View
Sensor (SeaWiFS)

• Pre-launch Calibration Implementation
• A complete calibration and validation plan was
  developed, funded, and implemented
• Well defined measurement protocols were
  established and documented in the archival
  literature or as NASA TMs http//oceancolor.gsfc
  .nasa.gov/DOCS/
• Sensor was characterized and calibrated by the
  vendor using traditional techniques in the
  laboratory, with government oversight.

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Ocean Color with SeaWiFS Example of Rigor

• Pre-launch
• Sensor design included on orbit techniques
  (solar illuminated reflectance standard, planned
  lunar observations, channel for atmospheric
  characterization, planned observations of in situ
  vicarious calibration site)
• The development of the Marine Optical BuoY (MOBY)
  vicarious calibration facility in Lanai, Hawaii
  was supported
• NIST was funded to develop a stable, calibrated
  six channel filter radiometer (SeaWiFS Transfer
  Radiometer, SXR)

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Ocean Color with SeaWiFS Example of Rigor

• Pre-launch
• NIST calibrated the integrating sphere used to
  calibrate SeaWiFS
• NIST participated in the pre-launch radiometric
  calibration at the spacecraft integrator facility

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Subsystem/Component Measurements

• Subsystem and/or component level measurements
• Help verify, understand, and predict performance
• Minimize schedule risk during system assembly
• Identifies problems at lowest level of assembly
• Minimizes schedule impact by minimizing
  disassembly effort to fix a problem
• System/Sensor level model development and
  measurements
• Allow for the development of Measurement Equation
  and Performance prediction
• Allow for end-to-end measurements
• Account for interactions between subsystems and
  components that are difficult to predict

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Ground Calibration

• Provides complete calibration needed to meet
  related requirements
• Is performed under conditions that simulate
  operational conditions for intended
  application/measurement
• Careful in-lab calibration minimizes problems
  that arise after launch
• Minimizes risk of not discovering a problem prior
  to launch
• Promotes mission success during on-orbit
  operations
• Best to perform ground calibration at highest
  level of assembly possible
• Sensor-level at a minimum is recommended

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Example of NISTAR- Radiometer built to look at
Earth from L1
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NISTAR Has Three Spectral Bands
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NISTAR Irradiance Mode Calibration at the SIRCUS
Facility
During calibration of NISTAR at the SIRCUS
facility, the instrument was in a thermal-vacuum
chamber to simulate the space environment. It
viewed the output of a laser- illuminated
integrating sphere (green), simulating the
geometry of the view of Earth from L1.
The integrating sphere was on a translation
stage, and the laser was fiber-optically fed.
This enabled the source-to-detector distance to
be varied. For filter transmittance
measurements, the sphere was at the focus of a
collimator.
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Results and Comments

• Piece-parts filter transmittance can be off by
  0.1 or more.
• Piece-parts absolute calibration can be off by
  0.1 or more.
• System level characterization using tunable
  lasers at facilities such as SIRCUS can be used
  for higher accuracy, higher-confidence
  system-level calibration.
• Important to wedge radiometer optics (such as
  filters) to enable best SIRCUS calibration.
• At SIRCUS, absolute radiometric calibration
  traceability is through irradiance trap detector.

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Summary

• Pre-Launch Characterization