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 December 4, 2003 Jim Butler NASA’s GSFC Code 924 Laser Remote Sensing Branch Greenbelt, MD Phone: Fax:

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

The Moon as an On-orbit Calibration Target The Moon has advantages (+) and disadvantages (-) when used as a satellite instrument calibration target. 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 is equivalent to a 6 km target from a 705 km orbit

On-orbit Lunar Viewing by AM Constellation Instruments on April 14, 2003 AM Constellation Spacecraft & Instruments SatelliteOptical Instruments Altitude (km)Orbital Inclination (deg) Equatorial Crossing Time (LST) EO-1ALI Hyperion Atm. Corrector :01 Landsat-7ETM :05 SAC-CMMRS HRTC HCS :15 TerraMODIS MISR ASTER MOPITT CERES :30 SeaStarSeaWiFS :00

a b c d e f g h i Terra EventElapsed time (min) a. Maneuver start0 b. Zero pitch accel.3.03 c. Nadir at Earth’s limb7.37 d. Nadir at Moon11.90 e. Midpoint of maneuver17.95 f. Nadir at Earth’s limb28.53 g. Maneuver end35.54 h. Terra enters sunlight41.6

On-orbit Lunar Viewing by AM Constellation Instruments on April 14, 2003 Instrument Lunar Viewing Times (UT) 1. ALI MS/Pan 121:39:47 2. ALI MS/Pan 221:44:34 3. ALI MS/Pan 321:49:19 4. Hyperion21:54:31 5. MISR D f camera22:01:38 6. MISR C f camera22:02:33 7. MISR B f camera22:04:05 8. MISR A f camera22:06:23 9. MODIS22:09: MISR A n camera22:09: ASTER SWIR22:09: ASTER VNIR-nadir22:09: MISR A a camera22:12: ASTER VNIR-aft22:13: MISR B a camera22:15: MISR C a camera22:16: MISR D a camera22:17: SeaWiFS22:34:14

EO-1 Lunar Maneuver MS/PAN1MS/PAN2MS/PAN3 Start Y spacecraft 1.26° 0.75° 41.5° Pitch Roll End Hyperion 1 X spacecraft

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

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 W irradiance standard lamp –Irradiance of spectrophotometric standard star Vega –External 0.4 m dia. collimator + light source calibrated for radiance

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; >10 6 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.

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)

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

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.

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)

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.

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

Determining Band-to-band Differences in Satellite Instruments MISR A n 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 MODIS Terra & Aqua Band-to- band Differences -Lunar and U of A results show similar band-to-band trends -Absolute scale not established in lunar case

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