Jacqueline I. Gordon and Peggy V. Church, "Overcast Sky Luminances and Directional Luminous Reflectances of Objects and Backgrounds under Overcast Skies," Appl. Opt. 5, 919-923 (1966)
Two sky luminance distributions are given for overcast sky above snow-covered terrain, and directional luminous reflectance data are presented which were obtained under these skies. Luminous reflectances computed from Krinov spectral reflectance data for a variety of natural terrains measured under overcast are also included.
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Snow, with rain crust (a crust formed by falling rain which does not freeze upon falling)d
51
0
0.67
0.67
0.67
0.67
0.67
0.67
0.67
0.67
51
45
—
0.67
0.66
0.66
0.67
0.67
0.67
0.68
51
90
—
0.66
0.67
0.67
0.68
0.68
0.68
—
51
135
—
0.65
0.66
0.67
0.68
0.68
0.67
0.69
51
180
—
0.67
0.64
0.65
0.67
0.68
0.68
0.69
14.
Snow, with glazed rain crust (rain crust completely covered by a slightly undulating sheet of ice formed by freezing rain, subsequent freezing temperatures but no further precipitation)d
Snow, with rain crust (a crust formed by falling rain which does not freeze upon fallingf
52
0
0.65
0.62
0.63
0.63
0.66
0.67
0.67
0.68
52
45
—
0.66
0.66
0.67
0.68
0.66
0.68
0.68
52
90
—
0.66
0.66
0.66
0.67
0.67
0.66
0.67
52
135
—
0.66
0.66
0.67
0.69
0.70
0.70
0.73
52
180
—
0.65
0.65
0.67
0.67
0.68
0.67
0.69
18.
Snow, with glazed rain crust (rain crust completely covered by a slightly undulating sheet of ice formed by freezing rain, subsequent freezing temperatures but no further precipitation)f
52
0
0.75
0.72
0.72
0.74
0.77
0.81
0.81
—
52
45
—
0.75
0.76
0.77
0.79
0.79
0.80
—
52
90
—
0.75
0.75
0.75
0.75
0.76
0.76
—
52
135
—
0.74
0.73
0.74
0.77
0.78
0.78
—
52
180
—
0.74
0.74
0.73
0.74
0.76
0.76
—
Directional luminous reflectances of terrains 1 through 10 were computed from spectrophotometric data taken by Krinov using C.I. E. Illuminant B.
The zenith angle of the path of sight is 115°.
Computed from equations by Duntley for the luminance distribution measured by Hood on 21 May 197.
Data taken with a telephotometer (April 1960) of simulated snow having reflectance characteristics reported by Middleton and Mungall. The photometry was done in the natural lighting simulator, using the sky luminance distribution measured by Hood on 21 May 1957.
Computed from equations by Duntley for the luminance distribution measured by Hood on 24 May 1957.
Data taken with a telephotometer (April 1960) of simulated snow having reflectance characteristics reported by Middleton and Mungall. The photometry was done in the natural lighting simulator, using the sky luminance distribution measured by Hood on 24 May 1957.
Table II
Directional Luminous Reflectance of Objects under Overcast
Data taken with a telephotometer April 1960. The photometry was done in the natural lighting simulator, using the sky luminance distribution measured by Hood on 21 May 1957.
Data taken with a telephotometer April 1960. The photometry was done in the natural lighting simulator, using the sky luminance distribution measured by Hood on 24 May 1957.
Tables (2)
Table I
Directional Luminous Reflectance of Terrain Backgrounds under Overcast
Snow, with rain crust (a crust formed by falling rain which does not freeze upon falling)d
51
0
0.67
0.67
0.67
0.67
0.67
0.67
0.67
0.67
51
45
—
0.67
0.66
0.66
0.67
0.67
0.67
0.68
51
90
—
0.66
0.67
0.67
0.68
0.68
0.68
—
51
135
—
0.65
0.66
0.67
0.68
0.68
0.67
0.69
51
180
—
0.67
0.64
0.65
0.67
0.68
0.68
0.69
14.
Snow, with glazed rain crust (rain crust completely covered by a slightly undulating sheet of ice formed by freezing rain, subsequent freezing temperatures but no further precipitation)d
Snow, with rain crust (a crust formed by falling rain which does not freeze upon fallingf
52
0
0.65
0.62
0.63
0.63
0.66
0.67
0.67
0.68
52
45
—
0.66
0.66
0.67
0.68
0.66
0.68
0.68
52
90
—
0.66
0.66
0.66
0.67
0.67
0.66
0.67
52
135
—
0.66
0.66
0.67
0.69
0.70
0.70
0.73
52
180
—
0.65
0.65
0.67
0.67
0.68
0.67
0.69
18.
Snow, with glazed rain crust (rain crust completely covered by a slightly undulating sheet of ice formed by freezing rain, subsequent freezing temperatures but no further precipitation)f
52
0
0.75
0.72
0.72
0.74
0.77
0.81
0.81
—
52
45
—
0.75
0.76
0.77
0.79
0.79
0.80
—
52
90
—
0.75
0.75
0.75
0.75
0.76
0.76
—
52
135
—
0.74
0.73
0.74
0.77
0.78
0.78
—
52
180
—
0.74
0.74
0.73
0.74
0.76
0.76
—
Directional luminous reflectances of terrains 1 through 10 were computed from spectrophotometric data taken by Krinov using C.I. E. Illuminant B.
The zenith angle of the path of sight is 115°.
Computed from equations by Duntley for the luminance distribution measured by Hood on 21 May 197.
Data taken with a telephotometer (April 1960) of simulated snow having reflectance characteristics reported by Middleton and Mungall. The photometry was done in the natural lighting simulator, using the sky luminance distribution measured by Hood on 21 May 1957.
Computed from equations by Duntley for the luminance distribution measured by Hood on 24 May 1957.
Data taken with a telephotometer (April 1960) of simulated snow having reflectance characteristics reported by Middleton and Mungall. The photometry was done in the natural lighting simulator, using the sky luminance distribution measured by Hood on 24 May 1957.
Table II
Directional Luminous Reflectance of Objects under Overcast
Data taken with a telephotometer April 1960. The photometry was done in the natural lighting simulator, using the sky luminance distribution measured by Hood on 21 May 1957.
Data taken with a telephotometer April 1960. The photometry was done in the natural lighting simulator, using the sky luminance distribution measured by Hood on 24 May 1957.