an overview of solar reflectance remote sensing methods for earth science applications s. platnick...

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


MODTRAN, absorption transmittance only

H2O =

O2

O2

--O3--

O2

CO2

CH4 N2O

CO2

Spectral regions of interest

VIS SWIR

MWIRSWIR

NIR



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



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.)


QuickTime™ and aVideo decompressor

are needed to see this picture.

Click Here to See Movie



are needed to see this picture.MODIS 0.86 µm albedo, mid-late

July 2001

MODIS land classification

map (MOD12)

urban


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.


Click to See Movie

MODIS Cloud Product – thermodynamic phase(MOD06, L3 0.1° gridded, Terra, 21 Nov 2003;

modis-atmos.gsfc.nasa.gov)


Ice

Liquid

Uncertain


MODIS Cloud Product – optical thickness(MOD06, L3 0.1° gridded, Terra, 21 Nov 2003;



MODIS Cloud Product – particle effective radius(MOD06, L3 0.1° gridded, Terra, 21 Nov 2003;




MISR (Terra)nominal bands locations

9 cameras ± 70 deg views

MISR 9-camera animation over southern Florida(true-color composite)


Click to See Movie



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






Cloud Observations with AirPOLDER(19 minutes of data, Proteus Aircraft, CRYSTAL-FACE, 3 July 2002)

(figs. courtesy of Jerome Riedi, U. Lille, France)


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


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


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)


-6

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Fig04_cj.opj

EOS VXR UA VNIR GSFC LXR

(a)

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(b)

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(c)

100

x (L

B, X

R /L

B, S

IS -

1 )

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(d)

400 500 600 700 800 900-6

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(e)

Wavelength [nm]

400 500 600 700 800 900-6

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(f)

Fig07_cj.opj

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EOS SWIXR UA SWIR

(a)

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0

5

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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

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EOS SWIXR UA SWIR

(c)

800 1000 1200 1400 1600 1800 2000 2200 2400-35

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0

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EOS SWIXR UA SWIR

(d)

Wavelength [nm]

800 1000 1200 1400 1600 1800 2000 2200 2400-35

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-5

0

5

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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:


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)


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


1. Radiance-based approach, cont.

MODIS Terra granulecoastal Chile/Peru (18 July 2001, 1530 UTC)

uncertain ice liquidwater

noretrieval

phaseretrieval

RGB true-color composite



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)


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


(figs. courtesy of Jim Butler, NASA GSFC)

-4

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0

1

2

3

4

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(a) i = 0°

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-3

-2

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1

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(b) i = 30°

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GSFC

JPL

SBRS

UA

(c) i = 45°

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0

1

2

3

4

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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


(fig. courtesy of Bill Barnes, Jack Xiong, NASA GSFC)

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)

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


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)• ???




Landsat TMnominal bands locations

(1, 2, 3, 4, 5, 7)



ASTER (Terra)NASDA/JAXA

dual views



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.)



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)


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


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


MODIS Instrument Degradation/Drift


(fig. courtesy of Bill Barnes, Jack Xiong, NASA GSFC)

an overview of solar reflectance remote sensing methods for earth science applications s. platnick...

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