Transcript A global infrared land surface emissivity database

A global infrared land surface emissivity
database
Suzanne Wetzel Seemann, Eva Borbas, Robert Knuteson, Elisabeth Weisz,
Jun Li, and Hung Lung Huang
CIMSS Seminar
December 8, 2006
Applications requiring a global land surface
emissivity
Our goal is to produce a methodology for integrating the best information
on land cover and surface emission on a high spatial (5km), high
spectral (1 wavenumber), and high temporal (daily) that can be updated
to support real-time operations and research for future instruments,
including:
•
•
3.
4.
GOES-R Proxy data set generation
GOES-R Surface characterization for TOA radiance calculations.
Current Applications/Users:
GOES-R/NPOESS TrainingSelected
set (IROther
surface
emissivity) for ABI retrieval
•
Assimilation
of radiances
land
(JCSDA)
GOES-R/NPOESS background
field required
forover
1-D
var
data
•
Climate Monitoring SAF (EUMETSAT)
assimilation
•
Cloud and Ozone retrieval from SEVIRI (EUMETSAT)
Synthetic
ozone
•
AIRS Retrieval of Dust Optical Depths (UMBC/ASL)
•
IASI-Metop Cal/Val (CNES, France)
(statistical) retrievals •of atmospheric
temperature,
Retrieval of hot spot
data from AATSRmoisture,
(ESA/ESRIN)and
Energy
balance
fromAIRS
ASTERradiances
over glacier (Univ of Milan)
from MODIS MOD07•• and
UW
IMAPP
AIRS trace gas retrieval for pollution monitoring
•
(Stellenbosch University, South-Africa)
•
Education (Seoul National Univ.; NTA, Konstantin)
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Sensitivity of calculated BT to land surface
emissivity
Is emissivity important? In what spectral regions?
Band 29 (8.6mm)
Band 31 (11mm)
Band 33 (13.4mm)
Difference between BT calculated using the prototype-CRTM model with
emis = 1.0 minus emis = 0.95 for 3 Aqua MODIS bands. Each of the 8583
points represents a forward model calculation for one land SeeBor profile,
and the colors correspond to the land surface type (IGBP ecosystem
category)
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BT calculated with
Emis = 1.0 minus
that calculated
with Emis = 0.95
BT calculated with
Emis = 1.0 minus
that calculated with
Baseline Fit (BF)
Emissivity
Average differences for 8583 land SeeBor profiles of BT for Aqua MODIS IR bands 25,
and 27-36 (left) and all 2378 Aqua AIRS channels (right). Each symbol (MODIS) and
dot (AIRS) represents the average BT difference over all profiles for one channel.
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Sensitivity of retrieved atmospheric products to
land surface emissivity: TPW
TPW % difference retrieved using a training
data set with two different surface emissivities.
emis = 1.0 minus emis = 0.95
MOD07 retrievals used Terra radiances for
314 clear sky cases at the ARM SGP site
between April 2001 and August 2005.
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emis = 1.0 minus BF emis
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Sensitivity of retrieved atmospheric products to
land surface emissivity: T, q profiles
Temperature K
Land and coastlines
(1402 profiles)
Barren/desert
(242 profiles)
Profiles retrieved using the IMAPP
AIRS algorithm (Elisabeth Weisz).
Mixing Ratio g/kg
Land and coastlines
(1402 profiles)
Barren/desert
(242 profiles)
Mean absolute differences between collocated
radiosondes and retrievals with:
• emis = 1.0 minus emis = 0.95 (dashed)
• emis = 1.0 minus BF emis (solid)
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Emissivity in regression retrievals of atmospheric
properties
• The MODIS MOD07 synthetic regression retrieval algorithm uses 11 IR channels to
retrieve atmospheric profiles of temperature and moisture, total precipitable water vapor
(TPW), total ozone, lifted index, surface skin temperature.
• The algorithm uses clear-sky radiances measured by MODIS over land and ocean for
both day and night. To compute the synthetic radiances from the profile training dataset to
train the regression, surface emissivity values must be assigned to each profile.
Mean (solid) +/- 1 stdev
(dashed) for emissivity
assigned to the NOAA-88
training profiles in ATOVS and
early MODIS retrieval
algorithms
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In the past, constant value or
pseudo-random emissivity spectra
have been assigned to the training
data for retrieval of atmospheric
temperature and moisture
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For Comparison:
Laboratory measurements of selected materials from UCSB
(compiled by Dr. Zhengming Wan, MODIS Land Team):
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One option for emissivity is the MODIS MOD/MYD11 operational land
surface emissivity product but it is not at high enough spectral resolution
MODIS IR
Channels
20
22
23
25
27
28
29
30
31
32
33
34
35
36
wavelength
(mm)
3.8
3.9
4.0
4.5 6.7
7.3
8.6
9.7
11
12
13.3
13.6
13.9
14.2
X
X
X
X
X
X
X
X
X
X
X
X
Channels in
MOD07
Channels
with
Emissivity
in MOD11
X
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X
X
X
X
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To fill in the spectral gaps in MYD11 emissivity data, high spectral resolution
laboratory measurements from the MODIS/USCB and ASTER
emissivity libraries are used:
•
•
High spectral resolution (wavenumber resolution between 2-4cm-1),
Not necessarily true representations of a global ecosystem as seen from
space.
The key to deriving a global emissivity database lies in the combination of
the high spectral measurements made in the laboratory and moderate
spectral resolution satellite observations of actual ecosystems.
There are a number of ways to combine the two. One approach, termed the
“baseline fit” method is introduced here. Another effort is underway to
generate a high spectral resolution emissivity dataset that uses principal
component analysis to combine the laboratory data with MOD/MYD11
observations (Eva Borbas) .
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Baseline Fit Methodology for Deriving Land
Surface Emissivity
We use selected laboratory measurements of emissivity to derive
a baseline conceptual model of emissivity and MODIS MYD11
measurements to adjust the emissivity.
First, we selected 10 inflection points, or hinge points that are important in
characterizing the *shape* of a spectrum
Then, we developed a set of fitting rules to adjust the emissivity at these
wavelengths based on the observed MOD/MYD11 values. The rules were
developed based on careful inspection of and testing with 321 high spectral
resolution laboratory-measured emissivity spectra.
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Conceptual model of a land surface emissivity spectrum
that was used to build the baseline fitting rules
• Spectra typically slope up more steeply from 4.3 to 5mm, then less steeply
from 5 to 7.6mm.
• In the 5-7mm region, the spectra typically slopes more steeply from 5-5.8mm,
then levels off.
• Due to a lack of information from MOD11 in the 5-8mm region, one value
must be held constant in some cases. A value of 0.976 was used for the 7.6mm
emissivity based on an average over the laboratory spectra.
• Many, but not all, spectra have a broad reduction in emissivity centered
around 8.6mm.
• If MOD11 emissivity at 8.6mm is greater than 0.97, these cases typically
have relatively flat emissivity spectra, often with all emissivities higher than 0.97.
• The emissivity beyond 12mm (the last wavelength for which MOD11 data is
available) is assumed to have a constant slope for all spectra equal to a rise of
0.01 over 3.5 microns. This is based on inspection of the laboratory data.
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Results of applying the baseline fit procedure to MYD11 emissivity
at 4 locations.
The baseline fit spectra
are shown by the solid,
dotted, dashed, and
dash-dot lines and the 6
input MYD11 emissivity
values as the symbols.
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Evaluation of the Baseline Fitting Procedure
Lab emis (black solid lines) was sampled at only the MYD11 wavelengths
(vertical dotted lines) and input to the baseline fitting procedure.
The result is the baseline fit emissivity (blue dashed).
Sliced Santa
Barbara Sandstone
Tropical Soil,
Zimbabwe, Africa
Granodiorite
Laurel Leaf
Page, Arizona
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Altered
Volcanic Tuff
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Average differences between 321 laboratory spectra and emissivity derived by the baseline
fit method (blue). Differences are also shown for a constant emissivity of 1.0 (black) and
those derived by linear interpolation between MYD11 wavelengths (red).
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Impact of BF Emissivity on MODIS and AIRS
Retrieved Temperature and Moisture
TPW (mm) at the ARM SGP site from Terra MODIS MOD07 (red), GOES-8 and -12
(blue), and radiosonde (black), with the ground-based ARM SGP MWR for 313 clear
sky cases from 4/2001 to 8/2005.
MOD07 Statistics
bias = -0.04 mm
rms = 2.49 mm
n = 313
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MOD07 Statistics
bias = 1.9 mm
rms = 3.76 mm
n = 313
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Sahara Desert: Terra MODIS ascending
(nighttime) passes on 1 August 2005
MOD07 TPW with emis = 0.95
MOD07 TPW with Baseline Fit emis
NCEP-GDAS TPW analysis
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A closer look at one of the Sahara desert
granules
Emis = 0.95
Emis = 1.0
BF Emis
MODIS MOD07 TPW for the 5 minute Terra granule beginning at 21:40 UTC on
August 1, 2005.
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Some examples from the database…
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Global BF emissivity for 6 wavelengths, August 2002
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3.7 mm
4.3 mm
5 mm
8.3 mm
10.8 mm
14.3 mm
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BF Emissivity in the Sahara Desert region for August 2003
4.3 mm
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8.3 mm
10.8 mm
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Land Surface Emissivity Time Series
February
Monitoring
seasonal land
changes in a
region: 4.3mm
BF land
surface
emissivity
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August
May
November
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Monitoring
changes over
time at 10 point
locations:
8.3mm BF land
surface
emissivity
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Future Work and Limitations
The baseline fit emissivity database is tied to the accuracy of MYD11. Future work will apply a similar
methodology to operational emissivity products from other platforms such as AIRS for comparison.
Monthly temporal resolution is not be sufficient for some applications. MYD11 L3 daily or 8-day global
emissivity fields can be used to create BF emissivity with higher temporal resolution.
Spectral information between the inflection points is an approximation and will not be sufficient for some
applications. Work is ongoing on a new version using a principal component analysis combining the
MODIS MOD11 emissivity with laboratory measurements of emissivity. The dataset is based on a
regression relationship between the observed MOD11 emissivity data and the principal components of
selected laboratory spectra (Eva Borbas).
Work to compare the baseline fit database with ground-based measurements is planned. Work to
comparison of this dataset with emissivity derived from other sources (AIRS, SEVIRI) is ongoing (Leslie
Moy).
Dataset available at http://cimss.ssec.wisc.edu/iremis
Contact [email protected]
Draft of paper submitted to JAMC September 2006 available upon request
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