an overview of solar reflectance remote sensing methods for earth science applications
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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 - PowerPoint PPT PresentationTRANSCRIPT
An Overview of Solar Reflectance Remote Sensing Methods for Earth Science Applications
S. Platnick
Laboratory for AtmospheresNASA Goddard Space Flight Center, Greenbelt MD USA
SORCE Science Team MeetingSonoma CA
5 December 2003
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
Measurement
Example Instruments
Heritage Current/Recent Future
Spectral, Spatial (radiometric imagers)
AVHRR, Landsat TM, SPOT (CNES), CZCS
MODIS, GLI (JAXA, ADEOS-II), ATSR (UK, ERS-1,2), ASTER (Japan), ETM+, SeaWiFS, MERIS (ESA, Envisat)
VIIRS (NPP, NPOESS)
Directional MISR (imager),ATSR, ASTER, POLDER
APS (Glory)
Polarization POLDER(CNES, ADEOS-I,II)
APS, PARASOL (CNES, A-train)
Solar Reflectance Satellite Measurement Summary (incomplete)
S. Platnick, SORCE, 5 Dec 2003
Key: Instrument development/management (other than US)Satellite platform
S. Platnick, SORCE, 5 Dec 2003
MODTRAN, absorption transmittance only
H2O =
O2
O2
--O3--
O2
CO2
CH4 N2O
CO2
Spectral regions of interest
VIS SWIR
MWIRSWIR
NIR
S. Platnick, SORCE, 5 Dec 2003
MODTRAN, absorption transmittance only
MODIS (Terra, Aqua)nominal band locations
– ocean color/phytoplankton/ biogeo. chemistry
– general purpose window bands (land, aerosol, clouds)
cloud particle size
fire detection
– water vapor bands
S. Platnick, SORCE, 5 Dec 2003
MODTRAN, absorption transmittance only
AVHRRnominal bands locations
(channel 1, 2, 3)
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.)
S. Platnick, SORCE, 5 Dec 2003
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are needed to see this picture.
Click Here to See Movie
S. Platnick, SORCE, 5 Dec 2003
QuickTime™ and aVideo decompressor
are needed to see this picture.MODIS 0.86 µm albedo, mid-late
July 2001
MODIS land classification
map (MOD12)
urban
S. Platnick, SORCE, 5 Dec 2003
1.0
0.00.0 0.25 0.5
Aerosol Optical ThicknessFin
e A
ero
sol
Fra
ctio
n
MODIS Aerosol Product - daily examples from 2001(MOD04, L3 1° gridded, Kaufman, Tanre, Remer, et al.)
QuickTime™ and aSorenson Video decompressorare needed to see this picture.
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Click to See Movie
MODIS Cloud Product – thermodynamic phase(MOD06, L3 0.1° gridded, Terra, 21 Nov 2003;
modis-atmos.gsfc.nasa.gov)
S. Platnick, SORCE, 5 Dec 2003
Ice
Liquid
Uncertain
S. Platnick, SORCE, 5 Dec 2003
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
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
MODTRAN, absorption transmittance only
MISR (Terra)nominal bands locations
9 cameras ± 70 deg views
MISR 9-camera animation over southern Florida(true-color composite)
S. Platnick, SORCE, 5 Dec 2003
Click to See Movie
S. Platnick, SORCE, 5 Dec 2003
MODTRAN, absorption transmittance only
polarizationchannels
POLDER(CNES, ADEOS-I,II)CCD array, rotating
filter wheel
Cloud Observations with AirPOLDER(19 minutes of data, Proteus Aircraft, CRYSTAL-FACE, 3 July 2002)
1520 UTC
1539
S. Platnick, SORCE, 5 Dec 2003
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Cloud Observations with AirPOLDER(19 minutes of data, Proteus Aircraft, CRYSTAL-FACE, 3 July 2002)
(figs. courtesy of Jerome Riedi, U. Lille, France)
S. Platnick, SORCE, 5 Dec 2003
RGB: 865(pol), 865(total), 763(total) Total radiance RGB: 865, 763, 443 nm
Click to See Movie Click to See Movie
Calibration for reflectance-based remote sensing
S. Platnick, SORCE, 5 Dec 2003
Fundamental measurement is bidirectional reflectance not radiance,defined for some spectral band as:
where, = viewing zenith angle0 = solar zenith angle
I() = spectral radiance (intensity) measured in viewing directionF0, = solar spectral irradiance
Calibration approaches:
1. Radiance calibration + solar spectral irradiance table —> reflectance2. On-board reflectance calibration (e.g., MODIS, MERIS, etc.)3. Other: vicarious calibration (ground-based validation), lunar observations, inter-satellite comparisons, etc.
R ,0 I
cos 0 F0,
**
* useful for stability as well as absolute cal
Reflectance uncertainty is:
1. Radiance-based approach
S. Platnick, SORCE, 5 Dec 2003
dR
R
dII
dF0
F0
I difficulties compared with F0, :
– 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!)
Integrating Sphere calibration intercomparison(relative to SBRS SIS100 sphere cal)
S. Platnick, SORCE, 5 Dec 2003
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Fig04_cj.opj
EOS VXR UA VNIR GSFC LXR
(a)
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2
4
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EOS VXR UA VNIR GSFC LXR
(b)
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2
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EOS VXR UA VNIR GSFC LXR
(c)
100
x (L
B, X
R /L
B, S
IS -
1 )
-6
-4
-2
0
2
4
6
EOS VXR UA VNIR GSFC LXR
(d)
400 500 600 700 800 900-6
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-2
0
2
4
6
EOS VXR UA VNIR GSFC LXR
(e)
Wavelength [nm]
400 500 600 700 800 900-6
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0
2
4
6
EOS VXR UA VNIR GSFC LXR
(f)
Fig07_cj.opj
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-5
0
5
10
15
EOS SWIXR UA SWIR
(a)
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0
5
10
15
EOS SWIXR UA SWIR
(b)
100
x (L
B, X
R /L
B, S
IS -
1 )
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-5
0
5
10
15
EOS SWIXR UA SWIR
(c)
800 1000 1200 1400 1600 1800 2000 2200 2400-35
-30
-25
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-15
-10
-5
0
5
10
15
EOS SWIXR UA SWIR
(d)
Wavelength [nm]
800 1000 1200 1400 1600 1800 2000 2200 2400-35
-30
-25
-20
-15
-10
-5
0
5
10
15
EOS SWIXR UA SWIR
(e)
100
(L X
R/L
SIS -
1)
100
(L X
R/L
SIS -
1)
wavelength (nm)wavelength (nm)
Butler et al., J. Res. NIST, 108, May-June 2003.
EOS VXRUA VNIRGSFC LXR
(figs. courtesy of Jim Butler, NASA GSFC)
water vapor bands
EOS SWIXRUA SWIR
Reflectance uncertainty is:
S. Platnick, SORCE, 5 Dec 2003
dR
R
dII
dF0
F0
1. Radiance-based approach, cont.
F0, 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
MODIS(backup to refl. cal.)
personal useMODTRAN
Landsat ETM+ASTER
MODIS band-averaged reflectance differencerelative to MODTRAN solar irradiance spectrum (Kurucz)
S. Platnick, SORCE, 5 Dec 2003
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
1. Radiance-based approach, cont.
MODIS Terra granulecoastal Chile/Peru (18 July 2001, 1530 UTC)
uncertain ice liquidwater
noretrieval
phaseretrieval
RGB true-color composite
S. Platnick, SORCE, 5 Dec 2003
S. Platnick, SORCE, 5 Dec 2003
3.7 µm retrieved re (Thekaekara)
MODIS Terra granule, coastal Chile/Peru (18 July 2001, 1530 UTC)
ice cloudsre (KABGP - Thekaekara)
-1.0
-1.5
-2.0
40
32
24
16
8
0
2. Reflectance-based approach(MODIS example, VIS-SWIR)
S. Platnick, SORCE, 5 Dec 2003
MODIS Solar Diffuser Stability Monitor instrument (integrating sphere, 9 filters, 0.4-1 µm; views sun w/screen & panel)
MODIS Spectralon diffuser panel
toscan mirror
20.5 20.7
58.1
Sun
SDSM
SD
optional 7.8 % screen (bands 8-16 saturate w/o screen)
1.4 % screen
calibration schematic
Laboratory panel BRDF measurements (relative to NIST)Spectralon at =633 nm
S. Platnick, SORCE, 5 Dec 2003
(figs. courtesy of Jim Butler, NASA GSFC)
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1
2
3
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(a) i = 0°
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1
2
3
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(b) i = 30°
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0
1
2
3
4
-60 -40 -20 0 20 40 60
GSFC
JPL
SBRS
UA
(c) i = 45°
-4
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-2
-1
0
1
2
3
4
-60 -40 -20 0 20 40 60
Viewing Angle [deg]
(d) i = 60°
Laboratory
Spectralon, = 633 nm
Figure 11
viewing angle (deg)
Laboratory
Diff
ere
nce
re
lativ
e t
o N
IST
(%
)
Early et al., J. Atmos. Oceanic Tech., 17, August 2000.
MODIS Solar Diffuser Degradation
S. Platnick, SORCE, 5 Dec 2003
(fig. courtesy of Bill Barnes, Jack Xiong, NASA GSFC)
Satellite Instruments w/Solar Diffusers (incomplete?)
S. Platnick, SORCE, 5 Dec 2003
• 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)
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
Extras
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
S. Platnick, SORCE, 5 Dec 2003
MODTRAN, absorption transmittance only
Landsat TMnominal bands locations
(1, 2, 3, 4, 5, 7)
S. Platnick, SORCE, 5 Dec 2003
MODTRAN, absorption transmittance only
ASTER (Terra)NASDA/JAXA
dual views
S. Platnick, SORCE, 5 Dec 2003
MODTRAN, absorption transmittance only
MOPITT (Terra)2.2-2.4 µm bands,nominal locations(gas correlation
radiometry)
COCH4
MODIS Aerosol Product - global animation, 2001(MOD04, L3 1° gridded, Kaufman, Tanre, Remer, et al.)
QuickTime™ and aSorenson Video decompressorare needed to see this picture.
S. Platnick, SORCE, 5 Dec 2003
1.0
0.00.0 0.25 0.5
Aerosol Optical ThicknessFin
e A
ero
sol
Fra
ctio
n
Click to See Movie
Land surface polarization(RGB: 2250, 865, 410 nm color composite, RSP a/c instrument)
(figs. courtesy of Brian Cairns, NASA GISS/U. Columbia)
S. Platnick, SORCE, 5 Dec 2003
Reflectance Polarized Reflectance
Color composite 443-670-865 nm
Namibia
Stratocumulusover the ocean Scattering Angle
Same scene in polarized light• Polarization features less affected by multiple scattering than total radiance
(figs. courtesy of Bréon, François-Marie, LSCE, France)
Cloud Observations with POLDER
S. Platnick, SORCE, 5 Dec 2003
ToScan Mirror
20.5 20.7
58.1
Sun
1.44% Screen
SDSM
SD
Optional 7.8% Screen(Bands 8-16 saturate w/o screen)
SDSM Views:Sun, SD, Dark
MODIS calibration schematic
MODIS Instrument Degradation/Drift
S. Platnick, SORCE, 5 Dec 2003
MODIS Instrument Degradation/Drift
S. Platnick, SORCE, 5 Dec 2003
(fig. courtesy of Bill Barnes, Jack Xiong, NASA GSFC)