Comparison of the University of California at Los Angeles Line-by-Line Equivalent Radiative Transfer Model and the Moderate-Resolution Transmission Model for accuracy assessment of the National Polar-Orbiting Operational Environmental Satellite System’s Visible–Infrared Imager–Radiometer Suite cloud algorithms
S. C. Ou, K. N. Liou, Y. Takano, E. Wong, K. Hutchison, and T. Samec
S. C. Ou,1
K. N. Liou,1
Y. Takano,1
E. Wong,2
K. Hutchison,2
and T. Samec2
1S. C. Ou (ssou@atmos.ucla.edu), K. N. Liou, and Y. Takano are with the Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, 405 Hilgard Avenue, Los Angeles, California 90095-1565. USA
2Northrop-Grumman Space Technology, One Space Park, Redondo Beach, Los Angeles, California 90278. USA
S. C. Ou, K. N. Liou, Y. Takano, E. Wong, K. Hutchison, and T. Samec, "Comparison of the University of California at Los Angeles Line-by-Line Equivalent Radiative Transfer Model and the Moderate-Resolution Transmission Model for accuracy assessment of the National Polar-Orbiting Operational Environmental Satellite System’s Visible–Infrared Imager–Radiometer Suite cloud algorithms," Appl. Opt. 44, 6274-6284 (2005)
To support the verification and implementation of the National Polar-Orbiting Operational Environmental Satellite System’s Visible–Infrared Imaging–Radiometric Suite (VIIRS) algorithms used for inferring cloud environmental data records, an intercomparison effort has been carried out to assess the consistency between the simulated cloudy radiances–reflectances from the University of California at Los Angeles Line-by-Line Equivalent Radiative Transfer Model and those from the Moderate-Resolution Transmission Model (MODTRAN) with the 16 stream Discrete Ordinate Radiative Transfer Model (DISORT) incorporated. For typical ice and water cloud optical depths and particle sizes, we found discrepancies in the visible and near-infrared reflectances from the two models, which presumably are due to the difference in phase function (nonspherical versus Henyey–Greenstein), different numbers of phase function expansion terms (16 versus 200 terms), and different treatment of forward peak truncation in each model. Using the MODTRAN4, we also found substantial differences in the infrared radiances for optically thick clouds. These differences led to the discovery by MODTRAN4 developers of an inconsistency in the MODTRAN4–DISORT interface. MODTRAN4 developers corrected the inconsistency, which provided dramatic reductions in the differences between the two radiative transfer models. The comparison not only affects the prospective test plan for the VIIRS cloud algorithms but also should lead to improvements in future MODTRAN releases.
Steve S. C. Ou, K. N. Liou, X. J. Wang, D. Hagan, A. Dybdahl, M. Mussetto, L. D. Carey, J. Niu, J. A. Kankiewicz, S. Kidder, and T. H. Vonder Haar Appl. Opt. 48(8) 1452-1462 (2009)
You do not have subscription access to this journal. Cited by links are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
You do not have subscription access to this journal. Figure files are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
You do not have subscription access to this journal. Article tables are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
You do not have subscription access to this journal. Equations are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
Summary of Single-Scattering Properties Incorporated into LBLE, M1, M3, and M4
Model
Property
LBLE
M1
M3–M4
Ice cloud single-scattering parameters (ϖ, g, βe)
From the geometric ray-tracing method, assuming randomly oriented hexagonal ice crystals
Same as LBLE (user defined)
Same as LBLE (user defined)
Ice cloud phase function for 0.67, 1.6, and 2.25 μm
200 term Legendre polynomial expansion of the hexagonal ice crystal phase function subject to the truncation of the δ-function transmission (fδ) and the diffraction (f) peaks
H–G phase function at specified ϖ and g
Exact tabulation of hexagonal ice crystal phase function plus corresponding Legendre polynomial expansion coefficients; phase function subject to δ–M truncation
Ice cloud phase function for 3.7 and 10.8 μm
200 term Legendre polynomial expansion of the H–G phase function
H–G phase function at specified ϖ and g
H–G phase function at specific ϖ and g from the LBLE
Water cloud single-scattering parameters (ϖ, g, βe)
ɛs = 1.00, U.S. Standard Atmosphere, re = 8 μm, θ = 0°, no aerosols.
ΔR = RMODTRAN − RUCLA.
BT = B10.8μm−1 (R). Tc is cloud temperature.
Table 6
Percentage Difference [ΔR/RUCLA(%)]a of 3.7 μm Top-of-Atmosphere Radiance for Ice Cloud
Particle Size, De (μm)
Optical Depth
24
30
75
90
124
1
3.03
2.84
1.04
1.04
1.12
2
7.12
6.79
2.28
2.00
2.17
5
20.96
20.55
5.84
3.65
3.84
10
36.36
33.58
5.75
2.06
1.85
20
13.60
8.99
−0.77
−1.41
−1.57
ΔR = RMODTRAN − RUCLA.
Table 7
Percentage Difference [ΔR/RUCLA(%)]a of 10.8 μm Top-of-Atmosphere Radiance for Ice Cloud
Particle Size, De (μm)
Optical Depth
24
30
75
90
124
1
−1.67
−1.63
−0.85
−0.47
1.54
2
−3.13
−3.08
−1.54
−0.81
2.45
5
−3.67
−3.66
−2.07
−1.23
1.79
10
−1.78
−1.76
−1.21
−0.95
−0.25
20
−1.93
−1.91
−1.5
−1.37
−1.25
ΔR = RMODTRAN − RUCLA.
Table 8
Percentage Difference [ΔR/RUCLA(%)]a of 3.7 μm Top-of-Atmosphere Radiance for Water Cloud
Particle Size, De (μm)
Optical Depth
2
3
4
6
12
16
24
30
1
−0.24
−0.66
−0.70
−0.10
−0.84
−0.89
−0.88
−0.86
2
2.94
0.88
0.60
2.03
−0.95
−1.29
−1.40
−1.41
5
5.04
1.92
1.26
2.16
−1.19
−1.61
−1.80
−1.84
10
5.82
2.20
1.23
1.52
−1.50
−1.90
−2.14
−2.23
20
4.82
1.48
0.53
0.80
−1.99
−2.35
−2.54
−2.59
ΔR = RMODTRAN − RUCLA.
Table 9
Percentage Difference [ΔR/RUCLA(%)]a of 10.8 μm Top-of-Atmosphere Radiance for Water Cloud
Particle Size, De (μm)
Optical Depth
2
3
4
6
12
16
24
30
1
−0.26
−0.26
−0.29
−0.48
−0.80
−0.98
−0.13
−0.66
2
0.35
0.27
0.10
−0.43
−1.06
−1.22
−0.33
−0.70
5
0.62
0.40
0.14
−0.43
−0.97
−1.08
−0.65
−0.67
10
0.63
0.26
−0.02
−0.50
−0.98
−1.08
−0.87
−0.72
20
0.40
0.07
−0.15
−0.55
−0.94
−1.01
−0.89
−0.67
ΔR = RMODTRAN − RUCLA.
Tables (9)
Table 1
Summary of Single-Scattering Properties Incorporated into LBLE, M1, M3, and M4
Model
Property
LBLE
M1
M3–M4
Ice cloud single-scattering parameters (ϖ, g, βe)
From the geometric ray-tracing method, assuming randomly oriented hexagonal ice crystals
Same as LBLE (user defined)
Same as LBLE (user defined)
Ice cloud phase function for 0.67, 1.6, and 2.25 μm
200 term Legendre polynomial expansion of the hexagonal ice crystal phase function subject to the truncation of the δ-function transmission (fδ) and the diffraction (f) peaks
H–G phase function at specified ϖ and g
Exact tabulation of hexagonal ice crystal phase function plus corresponding Legendre polynomial expansion coefficients; phase function subject to δ–M truncation
Ice cloud phase function for 3.7 and 10.8 μm
200 term Legendre polynomial expansion of the H–G phase function
H–G phase function at specified ϖ and g
H–G phase function at specific ϖ and g from the LBLE
Water cloud single-scattering parameters (ϖ, g, βe)