CERES shortwave (SW), longwave (LW), and window (WN) channel radiative
fluxes are derived from empirical Angular Distribution Models (ADMs) that
convert a measured radiance in a given Sun-Earth-satellite viewing
configuration to a top-of-atmosphere (TOA) radiative flux. The first set of
CERES ADMs were developed from 9 months of CERES TRMM SSF measurements over the
Tropics (Loeb et al., 2003a,b). These ADMs were used to generate TOA fluxes on
the CERES TRMM Edition2B SSF product. The TRMM ADMs were also used to produce
TOA fluxes for the CERES Terra Edition1A SSF product while a new set of global
ADMs based on CERES Terra data were being developed.
The new global CERES Terra ADMs are now complete and are being used to
generate TOA fluxes on the CERES Terra Edition2B SSF product (Loeb et al.,
2004). The new ADMs are based on 24 months (Mar 2000 - Feb 2002) of CERES Terra
Edition2A SSF data. The main features of the new Terra ADMs are given below.
For a more detailed description of the CERES Terra ADMs see Loeb et al.
(2004).
Empirical ADMs over snow and sea-ice.
Increased angular resolution in nonpolar regions (2 degrees).
Use of "continuous" SW and LW ADM scene types over ocean, land,
and desert.
Monthly 1 degree regional clear land+desert ADMs.
Neural network scheme to improve TOA flux estimates for footprints with
excessive "no retrievals". No retrievals can occur when imager
data is missing or when the cloud algorithm cannot provide a physical retrieval.
If the scene characteristics over 35% or more of a CERES FOV are unknown, TOA
fluxes are estimated using a neural network scheme. Approximately 3% of the
CERES data fall in this category.
The tables below provide additional details on Terra ADM scene
classification and validation results. Further details can be found in the
following CERES Science Team Meeting presentations:
A Portable Document Format (PDF) reader (such as
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CERES Terra Shortwave Channel ADMs for Different Scene Types
Scene Type
Description
Clear Ocean
Function of wind speed; Correction for aerosol optical depth included.
Cloud Ocean
Function of cloud phase; Continuous function of cloud fraction and cloud
optical depth (5-parameter sigmoid).
Land & Desert Clear
1°- regional monthly ADMs using Analytical Function of TOA BRDF
(Ahmad and Deering, 1992).
Land & Desert Cloud
Function of cloud phase; continuous function of cloud cover and cloud
optical depth; used 1°-regional clear-sky BRDFs to account for background
albedo.
Permanent Snow
Function of Cloud Fraction, Surface Brightness, cloud optical depth
Fresh Snow
Function of Cloud Fraction, Surface Brightness, Snow Fraction, cloud optical depth
Sea-Ice
Function of Cloud Fraction, Surface Brightness, Ice Fraction, cloud optical depth
CERES Terra Longwave and Window Channel ADMs for Different Scene Types
Scene Type
Description
Clear Ocean, Land, Desert
Function of Ocean, Forest, Cropland/Grass, Savanna, Bright Desert, Dark
Desert, precip. water, lapse rate, skin temperature.
Clouds Over Ocean, Land Desert
Function of precip. water, skin temp, sfc-cloud temp. diff; continuous
function of parameterization involving cloud fraction, cloud and sfc emissivity,
sfc and cloud temp.
Permanent Snow, Fresh Snow, Sea-Ice
Each a function of cloud fraction, sfc temp, sfc-cld temp diff
CERES Instantaneous SW TOA flux uncertainties for Terra and TRMM ADMs
Region
So W m-2
Terra ADMs W m-2 (%)
TRMM ADMs W m-2 (%)
Clear-Sky
All-Sky
Clear-Sky
All-Sky
Tropics
1150
5.2 (2.2)
14.3 (5.1)
7.7 (3.5)
14.3 (5.8)
Midlat
870
4.2 (3.0)
13.5 (3.9)
7.3 (5.6)
13.7 (4.1)
Polar
540
12.8 (4.3)
17.3 (5.9)
37.0 (11.7)
29.2 (9.8)
CERES Instantaneous LW TOA flux uncertainties for Terra ADMs
Region
Terra ADMs W m-2 (%)
TRMM ADMs W m-2 (%)
Clear-Sky
All-Sky
Clear-Sky
All-Sky
Tropics
3.3 (1.1)
5.1 (1.8)
3.4 (1.1)
5.3 (1.9)
Midlat
2.9 (1.0)
5.4 (2.3)
2.7 (1.0)
5.6 (2.2)
Polar
3.4 (1.6)
4.0 (2.0)
3.3 (1.4)
5.0 (2.3)
Uncertainties in Regional Mean SW TOA fluxes (24-hour averages)
December 2001
June 2002
Mean Bias
Regional RMS
Mean Bias
Regional RMS
TRMM ADMs
0.21
1.77
-0.85
1.89
Terra ADMs
-0.42
0.89
-.056
0.96
Uncertainties in Regional Mean Daytime LW TOA fluxes
December 2001
June 2002
Mean Bias
Regional RMS
Mean Bias
Regional RMS
TRMM ADMs
-0.13
1.45
0.35
1.32
Terra ADMs
-0.04
0.93
0.26
0.82
Uncertainties in Regional Mean Nighttime LW TOA fluxes
