Post on 12-Jan-2016
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
QuickTime™ and aVideo decompressor
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.
QuickTime™ and aSorenson Video decompressorare needed to see this picture.
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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are needed to see this picture.
QuickTime™ and aVideo decompressor
are needed to see this picture.
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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0
2
4
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Fig04_cj.opj
EOS VXR UA VNIR GSFC LXR
(a)
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0
2
4
6
EOS VXR UA VNIR GSFC LXR
(b)
-6
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0
2
4
6
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
-4
-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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-2
0
2
4
6
EOS VXR UA VNIR GSFC LXR
(f)
Fig07_cj.opj
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-10
-5
0
5
10
15
EOS SWIXR UA SWIR
(a)
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-5
0
5
10
15
EOS SWIXR UA SWIR
(b)
100
x (L
B, X
R /L
B, S
IS -
1 )
-30
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-10
-5
0
5
10
15
EOS SWIXR UA SWIR
(c)
800 1000 1200 1400 1600 1800 2000 2200 2400-35
-30
-25
-20
-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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0
1
2
3
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(a) i = 0°
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-3
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0
1
2
3
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(b) i = 30°
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-2
-1
0
1
2
3
4
-60 -40 -20 0 20 40 60
GSFC
JPL
SBRS
UA
(c) i = 45°
-4
-3
-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)