modis surface albedos and distribution of global ecosystem types

MODIS Surface Albedos and Distribution of

Global Ecosystem Types

Eric G. Moody1,2, Michael D. King1, Steven Platnick1,3, Crystal Schaff4

1NASA Goddard Space Flight Center2Emergent IT, Inc.

3University of Maryland Baltimore County4Boston University

Outline• Motivation• Issues with original albedo scheme• New Ecosystem-Albedo seasonal model• Description of ecosystem classifications• Implementation of new model• Summary and future directions

Eric G. Moody [email protected] 2

Motivation• Retrieval of Cloud Optical Properties (MOD06OD)

– Computes optical thickness and effective radius using White-Sky surface albedos at wavelengths of 0.659, 0.865, 1.24,

1.6, 2.1, and 3.7 microns.– Inaccurate albedo value will enhance or attenuate

reflectance.– Can cause retrieval failures and unreasonable/unphysical results.

• Preparation for consistent year processing.• Pre- and post-launch White Sky Surface Albedo scheme

flagged for update.


Original Albedo Scheme

• Scheme used IGBP ecosystem classifications as a surrogate for albedo.– eg. Table of albedos for each ecosystem.

• Albedo data obtained from CERES/SARB.• Issues with the scheme:

– Broad-banded data.• Led to key bands having same surface albedo.

– No seasonal variation in albedo.• Ecosystem with growth cycles not represented.

– Coarse resolution CERES IGBP global ecosystem map.• 1 degree resolution left signatures


Design Parameters• Fine resolution (10km) IGBP ecosystem and albedo data.• Albedos at wavelengths of interest.• Seasonally dependent albedo data set.

• Sufficient data to generate global albedo maps.-OR-

• Sufficient data to create an ecosystem-albedo surrogate.


MODIS-Land Products.• Drs. Alan Strahler and Crystal Schaaf

– Boson Univ. Center for BRDF/Albedo Research• MOD12 - Ecosystem Classification

– 10 km resolution, globally.– Includes updates of IGBP classifications.

• MOD43B - BRDF/Albedo Product– 10 km resolution, 16-day global composites.– Includes White-Sky Albedos at specific

wavelengths of interest.


Sufficient Data Available?

• NO (at the time of consistent year code delivery).

• Only 2 data sets certified for quantitative use.– Spanned October, 2000.


Preliminary Analysis.• Create seasonal ecosystem-albedo scheme if:

– Northern and Southern Hemispheres differ statistically.– Sufficient data samples for each ecosystem type.– Ecosystem-Albedo correlate.

• Analysis– Compute statistics for “latitude belts” of varying sizes

• Mean, standard deviation, and sample size• Albedos at various wavelengths, for each ecosystem type.

• Results– All three criteria met.


Model Description.

• Tropics, no seasonal effect.• Seasonally dependant.• Transition region.


Model Data.• Seasonally Dependent Regions.

– Northern Hemisphere values assumed to be winter albedos at the winter solstice.

– Southern Hemisphere values assumed to be summer albedos at the summer solstice.

– Sinusoidal fit of these albedos to simulate seasonality.• Tropical Region (no seasonal effects)

– Albedos at various bands computed for ecosystem types• Transition Region (some seasonal effects)

– Linear fit between tropical and north/south albedos.


IGBP Ecosystem Classifications• Forests:

– Evergreen Needle and Broadleaf, Deciduous Needle and Broadleaf, and Mixed

• “Savannas”– Closed and Open Shrublands, Woody Savanna, Savanna,

Grasslands• Other Vegetation

– Permanent Wetlands, Urban and Buildup, Cropland and Cropland Mosaics

• Miscellaneous:– Permanent Snow/Ice, Tundra, Barren/Sparse, and Water Bodies


Global Ecosystem Distribution


Forest Ecosystem Distribution


Savanna Ecosystem Distribution


Other Vegetation Distribution


Miscellaneous Distributions


Ecosystem Distribution - Forest Breakdown.

Evergrn needle frt3.2%

Evergrn broad frt6.0%

Decid needle frt0.8%

Decid broad frt0.9%

Mixed forest6.6%

Perm Snow/Ice34.6%

Barren/sparse veg8.6%

Tundra2.1%

Open shrublands13.8%

Cropland5.3%

Grasslands5.5%

Savanna3.2%

Woody savannas4.0%

Perm wetland0.2%

Closed shrublands0.8%

Urban & buildups0.1%

Forests18%

Cropland mosaics4.3%


Ecosystem Distribution - Savanna Breakdown.



Woody savannas4.0%

Savanna3.2%

Grasslands5.5%

Perm Snow/Ice34.6%

Tundra2.1%

"Savannas"27%



Decid needle frt0.8%Decid broad frt

0.9%Mixed forest

6.6%Perm wetland

0.2%

Cropland5.3%





Ecosystem Distribution - Other Vegetation.



Woody savannas4.0%

Savanna3.2%

Grasslands5.5%

Perm wetland0.2%

Cropland5.3%



Perm Snow/Ice34.6%


Tundra2.1%

Vegetation9.8%

Evergrn needle frt3.2%Decid needle frt

0.8%

Decid broad frt0.9%

Mixed forest6.6%



Ecosystem Distribution - Miscellaneous.


Woody savannas4.0%

Perm Snow/Ice34.6%


Tundra2.1%

Cropland5.3%



Grasslands5.5%

Perm wetland0.2%

Savanna3.2%

Decid needle frt0.8%


Mixed forest6.6%

Decid broad frt0.9%



Misc.45.3%


Winter Albedo Means (winter solstice).

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0.05

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0.35

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0.5 1 1.5 2 2.5 3 3.5 4Wavelength (µm)

Albedo

Evergrn needle frt

Evergrn broad frt

Decid needle frt

Decid broad frt

Mixed forest


Summer Albedo Means (summer solstice)

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0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Wavelength (µm)

Albedo

Evergrn needle frt

Evergrn broad frt

Decid needle frt

Decid broad frt

Mixed forest


Forest Winter (W) and Summer (S) Albedo Means

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0.5 1 1.5 2 2.5 3 3.5 4Wavelenght (in microns)

Albedo

Evergrn needle frt - WEvergrn broad frt - WDecid needle frt - WDecid broad frt - WMixed forest - WEvergrn needle frt - SEvergrn broad frt - SDecid needle frt - SDecid broad frt - SMixed forest - S


Winter Albedo Means (winter solstice).

0.00

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0.35

0.5 1 1.5 2 2.5 3 3.5 4Wavelength (µm)

Albedo

Closed shrublands

Open shrublands

Woody savannas

Savannas

Grasslands


Southern Hemisphere Albedo Means

0.00

0.05

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0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Wavelength (µm)

Albedo

Closed shrublands

Open shrublands

Woody savannas

Savannas

Grasslands


Combined winter (W) and summer (S) albedos.

0.00

0.05

0.10

0.15

0.20

0.25

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0.5 1 1.5 2 2.5 3 3.5 4Wavelength (in microns)

Albedo

Closed shrublands - WOpen shrublands - WWoody savannas - WSavannas - WGrasslands - WClosed shrublands - SOpen shrublands - SWoody savannas - SSavannas - SGrasslands - S


Winter (W) and Summer (S) Albedos.

0.00

0.05

0.10

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0.20

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0.35

0.40

0.5 1 1.5 2 2.5 3 3.5 4Wavelength (microns)

Albedo

Perm wetlands - WCroplands - WUrban & built-up - WCropland mosaics - WPerm wetlands - SCroplands - SUrban & built-up - SCropland mosaics - S


Standard Deviations.

• Albedo means at various wavelengths and times of year, for all ecosystem types, are within 7%.

• Majority are within 3%• Suggests a reasonable correlation between ecosystem and

albedo.

Southern HemisphereWavelength (in microns) 0.659 0.865 1.24 1.64 2.1Average % Error 2.21% 1.61% 1.52% 1.78% 2.31%Max % Error 4.10% 4.59% 6.30% 6.60% 7.18%

Northern HemisphereWavelength (in microns) 0.659 0.865 1.24 1.64 2.1Average % Error 2.56% 2.11% 1.90% 2.14% 2.58%Max % Error 4.84% 4.20% 4.79% 4.87% 5.99%


Cropland - Seasonal Albedo Spectra.

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 50 100 150 200 250 300 350 400Julian Day

Albedo

0.659 micron0.865 micron1.24 micron1.64 micron2.14 micron3.7 micron


Albedo Movies•Loops through bands 0.65, 0.86, 1.24, 1.64, 2.1, and 3.7•Loops through seasonal equinox and solstice, progressing from Julian days 91, 173, 293, 356

Ecosystem Color Scheme•Pink = Crops•Green = Trees•Yellows = Barren/Deserts•Blues = Savannas


QuickTime™ and aVideo decompressor

are needed to see this picture.





Albedo Movies•Loops through bands 0.65, 0.86, 1.24, 1.64, 2.1, and 3.7•Loops through seasonal equinox and solstice, progressing from Julian days 91, 173, 293, 356QuickTime™ and a

Video decompressorare needed to see this picture.


Conclusions• Improved surface albedo data for use in consistent

year processing.• Provided albedo and ecosystem data sets at a finer

resolution.• Added seasonal variability.• Provided albedos at specific wavelengths of

interest.• Ecosystem can be used as a surrogate for albedo.


Future Directions

• Use a full year’s data (from consistent year) to improve ecosystem and albedo statistics.

• Investigate global albedo maps.• Investigate ecosystem-albedo surrogate.

• ISRSE presentation, April 2002.• Publish this work with BU group.

modis surface albedos and distribution of global ecosystem types

Documents

ecosystemalbedo correlate

igbp ecosystem classifications

albedo schemescheme

dependent albedo data

global albedo maps

data sets

data available

winter albedos