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An Overview of Solar Reflectance Remote Sensing Methods for Earth Science Applications

An Overview of Solar Reflectance Remote Sensing Methods for Earth Science Applications. S. Platnick Laboratory for Atmospheres NASA Goddard Space Flight Center, Greenbelt MD USA. SORCE Science Team Meeting Sonoma CA 5 December 2003. Outline

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An Overview of Solar Reflectance Remote Sensing Methods for Earth Science Applications

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  1. An Overview of Solar Reflectance Remote Sensing Methods for Earth Science Applications S. Platnick Laboratory for Atmospheres NASA Goddard Space Flight Center, Greenbelt MD USA SORCE Science Team Meeting Sonoma CA 5 December 2003

  2. Outline • Solar reflectance remote sensing - a brief overview of passive solar techniques (excluding UV) • space-borne/aircraft techniques and instruments • examples w/emphasis on atmosphere (clouds and aerosols) • Radiometric calibration • radiance vs. irradiance • Solar spectral irradiance issues • use/misuse of irradiance data sets • 3.7 µm spectral band

  3. Solar Reflectance Satellite Measurement Summary (incomplete) Key: Instrument development/management (other than US) Satellite platform S. Platnick, SORCE, 5 Dec 2003

  4. H2O = --O3-- O2 O2 O2 VIS NIR SWIR MWIR SWIR CO2 CH4 N2O CO2 MODTRAN, absorption transmittance only Spectral regions of interest S. Platnick, SORCE, 5 Dec 2003

  5. – general purpose window bands (land, aerosol, clouds) – ocean color/phytoplankton/ biogeo. chemistry – water vapor bands cloud particle size fire detection MODTRAN, absorption transmittance only MODIS (Terra, Aqua) nominal band locations S. Platnick, SORCE, 5 Dec 2003

  6. MODTRAN, absorption transmittance only AVHRR nominal bands locations (channel 1, 2, 3) S. Platnick, SORCE, 5 Dec 2003

  7. MODIS Land Surface Albedo, band 2 (0.86 µm)global animation for 2001, 16 day averages(derived from operational product MOD43, E. Moody, et al.) Click Here to See Movie S. Platnick, SORCE, 5 Dec 2003

  8. MODIS land classification map (MOD12) urban MODIS 0.86 µm albedo, mid-late July 2001 S. Platnick, SORCE, 5 Dec 2003

  9. 1.0 Fine Aerosol Fraction 0.0 0.0 0.25 0.5 Aerosol Optical Thickness MODIS Aerosol Product -daily examples from 2001(MOD04, L3 1° gridded, Kaufman, Tanre, Remer, et al.) Click to See Movie S. Platnick, SORCE, 5 Dec 2003

  10. MODIS Cloud Product – thermodynamic phase(MOD06, L3 0.1° gridded, Terra, 21 Nov 2003; modis-atmos.gsfc.nasa.gov) Uncertain Ice Liquid S. Platnick, SORCE, 5 Dec 2003

  11. MODIS Cloud Product – optical thickness(MOD06, L3 0.1° gridded, Terra, 21 Nov 2003; modis-atmos.gsfc.nasa.gov) S. Platnick, SORCE, 5 Dec 2003

  12. MODIS Cloud Product – particle effective radius(MOD06, L3 0.1° gridded, Terra, 21 Nov 2003; modis-atmos.gsfc.nasa.gov) S. Platnick, SORCE, 5 Dec 2003

  13. MODTRAN, absorption transmittance only MISR (Terra) nominal bands locations 9 cameras ± 70 deg views S. Platnick, SORCE, 5 Dec 2003

  14. MISR 9-camera animation over southern Florida(true-color composite) Click to See Movie S. Platnick, SORCE, 5 Dec 2003

  15. MODTRAN, absorption transmittance only polarization channels POLDER (CNES, ADEOS-I,II) CCD array, rotating filter wheel S. Platnick, SORCE, 5 Dec 2003

  16. 1520 UTC 1539 Cloud Observations with AirPOLDER(19 minutes of data, Proteus Aircraft, CRYSTAL-FACE, 3 July 2002) S. Platnick, SORCE, 5 Dec 2003

  17. Cloud Observations with AirPOLDER(19 minutes of data, Proteus Aircraft, CRYSTAL-FACE, 3 July 2002) Click to See Movie Click to See Movie RGB: 865(pol), 865(total), 763(total) Total radiance RGB: 865, 763, 443 nm (figs. courtesy of Jerome Riedi, U. Lille, France) S. Platnick, SORCE, 5 Dec 2003

  18. * * * useful for stability as well as absolute cal Calibration for reflectance-based remote sensing • Fundamental measurement isbidirectional reflectance not radiance, • defined for some spectral band as: • where, •  = viewing zenith angle, 0 = solar zenith angle • I() = spectral radiance (intensity) measured in viewing direction • F0, = solar spectral irradiance • Calibration approaches: • 1. Radiance calibration + solar spectral irradiance table —> reflectance • 2. On-board reflectance calibration (e.g., MODIS, MERIS, etc.) • 3. Other: vicarious calibration (ground-based validation), lunar observations, inter-satellite comparisons, etc. S. Platnick, SORCE, 5 Dec 2003

  19. 1. Radiance-based approach Reflectance uncertainty is: • Il difficulties compared with F0,l : • Lack of spaceborne absolute radiometery for imagers (e.g, absolute detectors, electrical substitution radiometers) • low energy(narrowband), short pixel dwell time (especially scanners, ~300 µs for MODIS 1km bands) • even if possible (microbolometer), would have to measure solid angle FOV in addition to aperture area • Difficulty in transferring standards, e.g., standard irradiance lamp transferred to radiance via diffuse plate to integrating sphere • Fortunately, remote sensing needs typically much less stringent than energy budget measurements (though stability still critical!) S. Platnick, SORCE, 5 Dec 2003

  20. EOS SWIXR UA SWIR EOS VXR UA VNIR GSFC LXR Integrating Sphere calibration intercomparison(relative to SBRS SIS100 sphere cal) 100 (LXR/LSIS - 1) 100 (LXR/LSIS - 1) wavelength (nm) wavelength (nm) water vapor bands Butler et al., J. Res. NIST, 108, May-June 2003. (figs. courtesy of Jim Butler, NASA GSFC) S. Platnick, SORCE, 5 Dec 2003

  21. MODTRAN Landsat ETM+ ASTER personal use MODIS (backup to refl. cal.) 1. Radiance-based approach, cont. Reflectance uncertainty is: • F0,l from published compilations and/or measurements: • 1974 NASA spectrum (Thekaekara, 1974 ): UV/VIS [CV-990 flights, Thekaekara (1969), JPL a/c program, Drummond (1967-68)], NIR-MWIR [3 published papers] • 1981 WRC spectrum: 0.3-1.25 µm [Neckel and Labs (1981) Jungfraujoch, spectral improvement, absolute pinned to WRC solar constant], Other spectral regions [Smith and Gottlieb (1974), Heath and Thekaekara (1977), Arvesen et al. (1969)] • 1984, Neckel and Labs: 0.33-1.25 µm (improved spectral w/Kitt Peak FTS, not absolute) • 1995, Kurucz: UV-SWIR compilation using Jungfraujoch, Kitt Peak, JPL/ATMOS, …; adopted by MODTRAN • 1998, 2002, Thuillier et al.: UV-SWIR, ATLAS SOLSPEC, SOSP EURECA • 20??: SORCE SIM S. Platnick, SORCE, 5 Dec 2003

  22. MODIS band-averaged reflectance differencerelative to MODTRAN solar irradiance spectrum (Kurucz) S. Platnick, SORCE, 5 Dec 2003

  23. 1. Radiance-based approach, cont. • NOTE: A very uncomfortable uncertainty in the 3.7 µm band solar irradiance! Data sources include (?): • Thekaekara et al. (1974) – at 100 nm spectral resolution • Kondratyev, Andreev, Badinov, Grishechkin, and Popova (1965) – at 3.0, 3.6, 4.0 µm • ? Farmer and Norton (1989), Farmer et al. (1994), Livingston and Wallace (1991) • Example comparison between KABGP & Thekaekara et al. at 3.6 µm shows irradiance difference of about 15%, e.g., • Thekaekara et al. = 1.4 mW-cm-2-µm-1 • KABGP = 1.2 mW-cm-2-µm-1 S. Platnick, SORCE, 5 Dec 2003

  24. MODIS Terra granulecoastal Chile/Peru (18 July 2001, 1530 UTC) phase retrieval RGB true-color composite uncertain ice liquid water no retrieval S. Platnick, SORCE, 5 Dec 2003

  25. 40 -1.0 32 24 -1.5 16 8 0 -2.0 3.7 µm retrieved re (Thekaekara) Dre (KABGP - Thekaekara) ice clouds MODIS Terra granule, coastal Chile/Peru (18 July 2001, 1530 UTC) S. Platnick, SORCE, 5 Dec 2003

  26. calibration schematic Sun 1.4 % screen optional 7.8 % screen (bands 8-16 saturate w/o screen) MODIS Spectralon diffuser panel 58.1 SDSM to scan mirror SD 20.5 20.7 MODIS Solar Diffuser Stability Monitor instrument (integrating sphere, 9 filters, 0.4-1 µm; views sun w/screen & panel) 2. Reflectance-based approach(MODIS example, VIS-SWIR) S. Platnick, SORCE, 5 Dec 2003

  27. Difference relative to NIST (%) viewing angle (deg) Laboratory Laboratory panel BRDF measurements (relative to NIST)Spectralon at l=633 nm Early et al., J. Atmos. Oceanic Tech., 17, August 2000. (figs. courtesy of Jim Butler, NASA GSFC) S. Platnick, SORCE, 5 Dec 2003

  28. MODIS Solar Diffuser Degradation (fig. courtesy of Bill Barnes, Jack Xiong, NASA GSFC) S. Platnick, SORCE, 5 Dec 2003

  29. Satellite Instruments w/Solar Diffusers (incomplete?) • Used for primary calibration • – MODIS, MERIS (?) • Used for trending • – MISR, SeaWiFS (primary methods are vicarious calibration) • Not used • – ETM+ (due to apparent diffuser degradation relative to vicarious calibration and pre-flight cal) S. Platnick, SORCE, 5 Dec 2003

  30. Solar Remote Sensing Summary • Fundamental measurement needed for geophysical retrievals typically reflectance (not radiance) • Absolute calibration not as stringent as irradiance energy budget requirements, but stability critical for climate monitoring • New generation of satellite sensors w/on-board solar reflectance panels, flown with varying degrees of success • Accurate solar spectral irradiance needed across the solar spectrum • – Radiance-based calibration methods —> reflectance • – Intercomparison of reflectance and radiance-based methods • – Traceability of reflectance-based radiometry to MKS standards • 3.7 µm band for cloud re retrievals: heritage(AVHRR) and new (MODIS, CERES group) studies subject to unknown solar irradiance uncertainty S. Platnick, SORCE, 5 Dec 2003

  31. Extras

  32. Solar satellite-borne techniques missing from the table: • Temporal (Geosynchronous imagers) • Solar occultation (transmittance) measurements for stratospheric trace gases • NASA New Millenium technology demonstrations (EO-1) • ??? S. Platnick, SORCE, 5 Dec 2003

  33. MODTRAN, absorption transmittance only Landsat TM nominal bands locations (1, 2, 3, 4, 5, 7) S. Platnick, SORCE, 5 Dec 2003

  34. MODTRAN, absorption transmittance only dual views ASTER (Terra) NASDA/JAXA S. Platnick, SORCE, 5 Dec 2003

  35. MODTRAN, absorption transmittance only MOPITT (Terra) 2.2-2.4 µm bands, nominal locations (gas correlation radiometry) CH4 CO S. Platnick, SORCE, 5 Dec 2003

  36. 1.0 Fine Aerosol Fraction 0.0 0.0 0.25 0.5 Aerosol Optical Thickness MODIS Aerosol Product - global animation, 2001(MOD04, L3 1° gridded, Kaufman, Tanre, Remer, et al.) Click to See Movie S. Platnick, SORCE, 5 Dec 2003

  37. Land surface polarization(RGB: 2250, 865, 410 nm color composite, RSP a/c instrument) Reflectance Polarized Reflectance (figs. courtesy of Brian Cairns, NASA GISS/U. Columbia) S. Platnick, SORCE, 5 Dec 2003

  38. Cloud Observations with POLDER Stratocumulus over the ocean Scattering Angle Namibia Color composite 443-670-865 nm Same scene in polarized light • Polarization features less affected by multiple scattering than total radiance (figs. courtesy of Bréon, François-Marie, LSCE, France) S. Platnick, SORCE, 5 Dec 2003

  39. MODIS calibration schematic Sun SDSM Views: Sun, SD, Dark 1.44% Screen Optional 7.8% Screen (Bands 8-16 saturate w/o screen) SDSM 58.1 To Scan Mirror SD 20.5 20.7

  40. MODIS Instrument Degradation/Drift S. Platnick, SORCE, 5 Dec 2003

  41. MODIS Instrument Degradation/Drift (fig. courtesy of Bill Barnes, Jack Xiong, NASA GSFC) S. Platnick, SORCE, 5 Dec 2003

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