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Thermal IR Considerations for use of Moon as On-Orbit Calibration Source

Thermal IR Considerations for use of Moon as On-Orbit Calibration Source. Joe Tansock Alan Thurgood Ray Russell. Outline. Comparison of lunar radiance to earth upwelling radiance Lunar radiance spectral content Lunar spectral radiance comparison with Planck curves

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Thermal IR Considerations for use of Moon as On-Orbit Calibration Source

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  1. Thermal IR Considerations for use of Moon as On-Orbit Calibration Source Joe Tansock Alan Thurgood Ray Russell

  2. Outline • Comparison of lunar radiance to earth upwelling radiance • Lunar radiance spectral content • Lunar spectral radiance comparison with Planck curves • Christensen bands and Silicon Dioxide (SiO2) • Comparison of Christensen and Silicon Dioxide bands with earth viewing sensor bands • Lunar surface temperature gradients • Full moon brightness temperature gradient • Lunar temperature transitions • Lunar advantages and challenges • Further discussion on thermal IR calibration

  3. Thermal Parameters • Lunar parameters that affect thermal emission1 • Max Lunar Surface Temp (day) (123 deg C, 396 K) • Mean Lunar Surface Temp (day) (107 deg C, 380 K) • Mean Lunar Surface Temp (night) (-153 deg C, 120 K) • Min Lunar Surface Temp (night) (-233 deg C, 40 K) • Emissivity ~93% • Earth Surface Temperatures • For comparison to estimated earth upwelling radiance • Cool (2 degrees C, 275 K) • Warm (32 degrees C, 305 K) 1. Hamilton @ SolarViews.com

  4. 10-3 10-4 Radiance (W / cm2 sr m) 10-5 10-6 3 10 30 Wavelength (m) Comparison of Lunar Radiance and Cool Earth Upwelling Radiance

  5. 10-3 10-4 Radiance (W / cm2 sr m) 10-5 10-6 3 10 30 Wavelength (m) Comparison of Lunar Radiance and Warm Earth Upwelling Radiance

  6. Lunar Spectral Radiance • Skylab S191 Visible-Infrared Spectrometer, T. L. Barnett and R. D. Juday, 1977

  7. Lunar spectral radiance comparison with Planck curves

  8. Christensen Bands and Silicon Dioxide Bands • Spectrophotometric Observations of MU CEPHEI and the Moon from 4 to 8 microns, R. W. Russell, et al, 1974 Christensen band • Christensen band • ~ 6.5 to 8 microns • Silicon dioxide band • ~ 9 microns?

  9. Comparison of Christensen and Silicon Dioxide bands with earth viewing sensor bands

  10. Lunar Surface Temperature Variations • The Infrared Moon, R. W. Shorthill, 1969

  11. Full Moon Brightness Temperature Gradient • The Sunlit Lunar Surface, J. M. Saari and R. W. Shorthill, 1972

  12. Lunar Surface Temperature Variations • The Infrared Moon, R. W. Shorthill, 1969

  13. Lunar Heating and Cooling • The Sunlit Lunar Surface, J. M. Saari and R. W. Shorthill, 1972

  14. Lunar Calibration Advantages • Advantages • With dedicated satellite maneuvers, the moon can be viewed as a long-term on-orbit calibration source • Existing resource if proven useful for Thermal IR applications • Except for Christensen and SiO2 bands, the spectral distribution of lunar thermal IR emission is similar to Planck function • Many challenges may be overcome by requiring specific lunar region views, spatial averaging, specific viewing geometry and lunar phase • Further evaluation required

  15. Lunar CalibrationChallenges • Challenges • Sunlit Lunar surface is one to two orders of magnitude brighter than typical earth upwelling radiance • Lunar surface exhibits large temperature variations • 70 to 80 K across sunlit surface of full moon • Large number of Isotherms with magnitudes greater than 1 K across craters, mountains, etc. • Calibration of spectral regions containing Christensen and SiO2 bands may be challenging? • A thorough understanding of lunar temperature transition from day-night and night-day will be required • Specific viewing geometry (limited to specific regions of the moon and lunar phase will be required. May limit the number of viewing opportunities given a specific earth orbit • Repeatability? Existing data sets? • Detailed thermal IR lunar model will be required • A method of lunar calibration and ongoing validation will be required • Additional investment (effort, time and possibly other resources) will be needed to convince ourselves the moon can be used as a high quality thermal IR cal source

  16. Further discussion on thermal IR calibration • Recoverable instrument to calibrate/validate moon or other sensor systems • Free-flier launched and retrieved by launch vehicles supporting the space station • Other recoverable systems • Mid-air retrieval used by NASA or DOD • Ocean recovery using GPS • NIST traceable transfer radiometer and blackbody as payload on Ballon flights • NIST traceable transfer radiometer and blackbody as payload on Aircraft systems • Others?

  17. Further discussion on thermal IR calibration (cont) • Challenges for using blackbody as in-flight calibration source • Need BB with long term radiance stability (I.e. emissivity and temperature stability) • Stable effective emissivity over long period of time • Deep cavity and/or imbedded surface monitoring device • Deep cavity designs typically require more power, space and weight than other options like stimulators, etc. • Long life and stable temperature monitoring • Can’t rely on temperature sensors by themselves • Anchor temperature to fixed points (for example Gallium at 29.76 deg C) • SDL is working with Russians to investigate and hopefully demonstrate the use of fixed points in space environment

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