Almerian R. Boileau and Jacqueline I. Gordon, "Atmospheric Properties and Reflectances of Ocean Water and Other Surfaces for a Low Sun," Appl. Opt. 5, 803-813 (1966)
Measurements of illuminance at sea level, directional luminous reflectances of ocean water and other surfaces, atmospheric beam transmittance, and path luminance for a day with an unobscured, low sun are presented. These data are applicable for visibility calculations for downward paths of sight.
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.
5. Snow, with glazed rain crust (rain crust completely covered by a slightly undulating sheet of ice formed by freezing rainfall followed by warm rain, subsequent freezing temperatures but no further precipitation)e
Data are from Flight 105.
Value not available, near to direct reflectance from sun.
Computed from equations by Duntley3 for the lighting condition prevailing for Item 1 in this table.
Value not computed since sky luminances near sun are poorly defined.
Data taken with a telephotometer April 1960 of simulated snow having reflectance characteristics reported by Middleton and Mungall.4 The photometry was done in the natural lighting simulator, using the sky luminance distribution from Flight 105.
Data interpolated graphically.
Data taken with a goniophotometer at Naval Ordnance Test Station, China Lake, California, in July and August 1962. The spectral reflectance of a sample of the dirt was measured with a Hardy spectrophotometer. Using CIE illuminant B, chromaticity coordinates were x = 0.370, y = 0.361, z = 0.269; dominant wavelength = 580 mμ; excitation purity = 10%.
Table II
Unidirectional Luminous Reflectance bR0(0,180°,0°) of Ocean Background: Vertically Downward Path of Sight
Description
Sun zenith angle
Zenith angle θ of path of sight
Wind speed (m/sec)
0
1
2
4
7
10
13
16
19
1. Ocean water, infinite optical depth (white water not included in averaging)a
77.3
180
0.0152
0.0147
0.0147
0.0148
0.0149
0.0150
0.0150
0.0152
0.0158
Computed from equations by Duntley3 for the lighting condition prevailing for Item 1, Table I.
Table III
Directional Luminous Reflectance tR0(0,θ,φ) of Surfaces
Data were taken with a goniophotometer on 5 February 1958.
Data were taken with a telephotometer. The photometry was done in the natural lighting simulator, using the sky luminance distribution from Flight 105.
Table IV
Measured and Equivalent Attenuation Lengths, and Ratio of Altitude to Equivalent Attenuation Length
Attenuation length L(z) was recorded continuously as a function of altitude from 20,000 ft (6.10 km) to 1000 ft (0.305 km) during descent of airplane at 1000 ft (305 m per min). The 100-ft to 1000-ft data were taken directly afterward during an ascent where the airplane was again held in a level attitude. These data are shown in Fig. 2. Attenuation lengths from 20,000 ft to 60,000 ft (6.10 km to 18.3 km) are computed using density ratios derived from Radiosonde data on temperature and pressure. Extrapolation from 60,000 ft to ∞ was made assuming an optical standard atmosphere.
The quantity 1/
(z) is equal to Elterman’s mean attenuation coefficient Ka(h), and the two quantities z/
(z) and Ka(h) · h1 may be used interchangeably.
The value of z/L(z) where z = ∞ was calculated from the sea level to space transmittance obtained from measured and extrapolated attenuation length data.
Table V
Path Luminance Br*(z,θ,0°),a Lower Sky in Azimuth of Sunb
Parenthetical symbols: photometer altitude z, zenith angle θ, and azimuth applicable to table.
Zenith angle of sun during flight 77.3°.
In using these tables, it has been found that above 10,000 ft altitude increments of 5,000 ft and 10,000 ft are satisfactory.
The tabulated value in ft-L multiplied by 10.76 gives the value in apostilbs.
Path luminances from 0–20,000 ft altitudes for zenith angles from 95° to 180° were calculated by means of Eq. (1), Duntley et al.2
Path luminances for altitudes above 20,000 ft were extrapolated as follows: (1) path functions for 20,000 ft B*(20,000,θ,φ) were calculated from flight data and Eq. (10) of Duntley et al.2; (2) path functions above 20,000 ft were calculated in 100-ft increments, in proportion to atmospheric density computed from Radiosonde data; (3) path luminances above 20,000 ft Br*(z,θ,φ) were calculated by means of Eq. (17) of Duntley et al.2
Table VI
Path Luminance Br*(z,θ,±45°),a Lower Sky, 45° from Azimuth of Sunb
5. Snow, with glazed rain crust (rain crust completely covered by a slightly undulating sheet of ice formed by freezing rainfall followed by warm rain, subsequent freezing temperatures but no further precipitation)e
Data are from Flight 105.
Value not available, near to direct reflectance from sun.
Computed from equations by Duntley3 for the lighting condition prevailing for Item 1 in this table.
Value not computed since sky luminances near sun are poorly defined.
Data taken with a telephotometer April 1960 of simulated snow having reflectance characteristics reported by Middleton and Mungall.4 The photometry was done in the natural lighting simulator, using the sky luminance distribution from Flight 105.
Data interpolated graphically.
Data taken with a goniophotometer at Naval Ordnance Test Station, China Lake, California, in July and August 1962. The spectral reflectance of a sample of the dirt was measured with a Hardy spectrophotometer. Using CIE illuminant B, chromaticity coordinates were x = 0.370, y = 0.361, z = 0.269; dominant wavelength = 580 mμ; excitation purity = 10%.
Table II
Unidirectional Luminous Reflectance bR0(0,180°,0°) of Ocean Background: Vertically Downward Path of Sight
Description
Sun zenith angle
Zenith angle θ of path of sight
Wind speed (m/sec)
0
1
2
4
7
10
13
16
19
1. Ocean water, infinite optical depth (white water not included in averaging)a
77.3
180
0.0152
0.0147
0.0147
0.0148
0.0149
0.0150
0.0150
0.0152
0.0158
Computed from equations by Duntley3 for the lighting condition prevailing for Item 1, Table I.
Table III
Directional Luminous Reflectance tR0(0,θ,φ) of Surfaces
Data were taken with a goniophotometer on 5 February 1958.
Data were taken with a telephotometer. The photometry was done in the natural lighting simulator, using the sky luminance distribution from Flight 105.
Table IV
Measured and Equivalent Attenuation Lengths, and Ratio of Altitude to Equivalent Attenuation Length
Attenuation length L(z) was recorded continuously as a function of altitude from 20,000 ft (6.10 km) to 1000 ft (0.305 km) during descent of airplane at 1000 ft (305 m per min). The 100-ft to 1000-ft data were taken directly afterward during an ascent where the airplane was again held in a level attitude. These data are shown in Fig. 2. Attenuation lengths from 20,000 ft to 60,000 ft (6.10 km to 18.3 km) are computed using density ratios derived from Radiosonde data on temperature and pressure. Extrapolation from 60,000 ft to ∞ was made assuming an optical standard atmosphere.
The quantity 1/
(z) is equal to Elterman’s mean attenuation coefficient Ka(h), and the two quantities z/
(z) and Ka(h) · h1 may be used interchangeably.
The value of z/L(z) where z = ∞ was calculated from the sea level to space transmittance obtained from measured and extrapolated attenuation length data.
Table V
Path Luminance Br*(z,θ,0°),a Lower Sky in Azimuth of Sunb
Parenthetical symbols: photometer altitude z, zenith angle θ, and azimuth applicable to table.
Zenith angle of sun during flight 77.3°.
In using these tables, it has been found that above 10,000 ft altitude increments of 5,000 ft and 10,000 ft are satisfactory.
The tabulated value in ft-L multiplied by 10.76 gives the value in apostilbs.
Path luminances from 0–20,000 ft altitudes for zenith angles from 95° to 180° were calculated by means of Eq. (1), Duntley et al.2
Path luminances for altitudes above 20,000 ft were extrapolated as follows: (1) path functions for 20,000 ft B*(20,000,θ,φ) were calculated from flight data and Eq. (10) of Duntley et al.2; (2) path functions above 20,000 ft were calculated in 100-ft increments, in proportion to atmospheric density computed from Radiosonde data; (3) path luminances above 20,000 ft Br*(z,θ,φ) were calculated by means of Eq. (17) of Duntley et al.2
Table VI
Path Luminance Br*(z,θ,±45°),a Lower Sky, 45° from Azimuth of Sunb
Add to BibSonomy