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On-orbit Cross-calibration of AM Satellite Remote Sensing Instruments Using the Moon

On-orbit Cross-calibration of AM Satellite Remote Sensing Instruments Using the Moon. International Workshop on Radiometric & Geometric Calibration Grand Casino Gulfport Hotel Gulfport, MS 39501 December 4, 2003 Jim Butler NASA’s GSFC Code 924 Laser Remote Sensing Branch

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On-orbit Cross-calibration of AM Satellite Remote Sensing Instruments Using the Moon

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  1. On-orbit Cross-calibration of AM Satellite Remote Sensing Instruments Using the Moon International Workshop on Radiometric & Geometric Calibration Grand Casino Gulfport Hotel Gulfport, MS 39501 December 4, 2003 Jim Butler NASA’s GSFC Code 924 Laser Remote Sensing Branch Greenbelt, MD 20771 Phone: 301-614-5942 Fax: 301-614-6744 E-mail: James.J.Butler@nasa.gov

  2. Acknowlegements • Tom Stone-USGS Flagstaff • Hugh Kieffer-USGS Flagstaff (emeritus) • Bob Barnes-SAIC • Bob Kozon-NASA’s GSFC Mission Ops and his entire team • Carol Johnson, Steve Brown, Ted Early-NIST • Stu Biggar, Kurt Thome-U of Arizona

  3. Advantages: +Appropriate radiance range for Earth-viewing instruments +Photometric properties are virtually invariant (<10-8/yr) +Spectrally bland (from returned Apollo samples) +Accessible to spacecraft regardless of orbit +Useful as a common transfer source between spacecraft Disadvantages -Non-uniform reflectance and complex photometric behavior -Satellite instrument lunar views may require a spacecraft attitude maneuver •MISR, ASTER, ALI, Hyperion, SeaWiFS, & MODIS (Earth view port) on 4/14/03 •MODIS (Space view port) 8 to 12 times a year w/ no maneuver The Moon as an On-orbit Calibration TargetThe Moon has advantages (+) and disadvantages (-) when used as a satellite instrument calibration target. The Moon is equivalent to a 6 km target from a 705 km orbit

  4. On-orbit Lunar Viewing by AM Constellation Instruments on April 14, 2003 AM Constellation Spacecraft & Instruments

  5. i h g f e d c b a

  6. On-orbit Lunar Viewing by AM Constellation Instruments on April 14, 2003 • Instrument Lunar Viewing Times (UT) 1. ALI MS/Pan 1 21:39:47 2. ALI MS/Pan 2 21:44:34 3. ALI MS/Pan 3 21:49:19 4. Hyperion 21:54:31 5. MISR Df camera 22:01:38 6. MISR Cf camera 22:02:33 7. MISR Bf camera 22:04:05 8. MISR Af camera 22:06:23 9. MODIS 22:09:24 10. MISR An camera 22:09:34 11. ASTER SWIR 22:09:34 12. ASTER VNIR-nadir 22:09:34 13. MISR Aa camera 22:12:46 14. ASTER VNIR-aft 22:13:22 15. MISR Ba camera 22:15:04 16. MISR Ca camera 22:16:37 17. MISR Da camera 22:17:33 18. SeaWiFS 22:34:14

  7. X spacecraft End Start Hyperion 1 MS/PAN3 MS/PAN2 MS/PAN1 1.26° 41.5° Pitch Roll 0.75° Yspacecraft EO-1 Lunar Maneuver

  8. ASTER 560nm Band MODIS 645.5nm Band MISR 672nm Band

  9. Robotic Lunar Observatory (ROLO) and the Lunar Irradiance Model • Goal: provide on-orbit stable and accurate radiometric calibration at solar reflectance wavelengths using the Moon • Two 20 cm, 1m focal length Richey-Chretien telescope systems • VNIR: • 512 square Si-CCD • 23 filters • SWIR: • 256 sq. HgCdTe • Identical to NICMOS on Hubble • 9 filters • Calibration (absolute accuracy is TBD) • 12” sq Spectralon™ panel + 1000W irradiance standard lamp • Irradiance of spectrophotometric standard star Vega • External 0.4 m dia. collimator + light source calibrated for radiance

  10. Robotic Lunar Observatory (ROLO) Irradiance Model • The ROLO Irradiance Model is used to compare on-orbit lunar measurements made by satellite instruments over a wide range of lunar phase and libration. • Empirical model based on 5+ years of lunar observations • ~85,000 lunar images; >106 star images • 32 bands: 23 VNIR, 9 SWIR • ±90º lunar phase coverage14 coefficients for each band, 4 are wavelength coupled. • Typically 14 coefficients and >1000 data points per band. • Smooth wavelength interpolation. NOTE: The ROLO lunar image database is unique and extensive. The substantial spatial, phase angle, and wavelength coverage are far beyond any published prior work.

  11. Applications of the ROLO Lunar Irradiance Model • The irradiance model has been used to: • Determine relative differences in the radiometric scales of satellite instruments () • Determine long-term degradation in the radiometric responsivity of satellite instruments () • Determine band to band radiometric differences in satellite instruments () • Validate the absolute radiometric scales of satellite instruments (accuracy is TBD)

  12. Determining Relative Radiometric Differences Between Instruments Using the Moon -Absolute accuracy of ROLO measurements is TBD -Relative differences between instruments due to 1. Use of different solar irradiance spectra 2. Different approaches in calculating integrated lunar radiances from instrument lunar images 3. Inherent differences/uncertainties in instrument calibrations

  13. Determining Relative Radiometric Differences Between Instruments Using the Moon -Comparison of MODIS instruments at three different lunar phases. 1. MODIS Terra: 1 through Earth view port + 25 through Space view port (2 angles of inc. on scan mirror). 2. MODIS Aqua: 10 through space view port.

  14. Determining Relative Radiometric Differences Between Instruments Using the Moon -Average of all lunar views for each instrument: SeaWiFS (70); ALI (29); MODIS Terra (26); Hyperion (9); MISR (1)

  15. Determining Long-term Degradation in the Radiometric Responsivity of Satellite Instruments SeaWiFS -Correcting for correlated time jitter (left), a clear asymptotic degradation trend is seen in Bands 7 and 8 (right). -Degradation information determined through repeated lunar views is used in the generation of SeaWiFS standard data products.

  16. Determining Long-term Degradation in the Radiometric Responsivity of Satellite Instruments ALI

  17. Determining Band-to-band Differences in Satellite Instruments MODIS Terra & Aqua Band-to- band Differences MISR An Camera Band-to-band Differences -Results from 5 VC expts. + 1 lunar view (4/14/03) -Normalized VC and lunar results show identical band-to-band trends -Lunar and U of A results show similar band-to-band trends -Absolute scale not established in lunar case

  18. Summary and Conclusions • On-orbit satellite instrument calibration/characterization using the Moon complements current on-board and vicarious calibration approaches. • Effective in long-term trending of degradation of instrument radiometric response • Useful in determining relative radiometric differences between instruments • Useful in determining band-to-band radiometric differences within instruments • Absolute calibration of lunar system needs additional work • Analysis of calibration/characterization data obtained in Sept/Oct at Flagstaff • Detailed analysis of atmospheric correction codes • The lunar irradiance model is currently running at GSFC • The Moon (i.e. lunar views + model) is a viable prospect for meeting NPP/NPOESS global change/climate monitoring goals “All you have to do is look at the Moon.” Hugh Kieffer “Once you look at the Moon, you may see amazing things.” Hugh Kieffer

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