Abstract

When transmittance of the atmosphere is determined by comparing the irradiancy of a distant light source to the calculated value for the irradiancy in vacuum, the result obtained is dependent on the field of view of the receiver. Measurements of this dependence over water have been made at sea level. For an uncollimated source, the results for any wavelength in the visible and near ultraviolet regions of the spectrum are represented approximately by the relation

Tθ=T+0.5(1T)(1eθ),
where Tθ is the transmittance at a particular wavelength measured with an instrument having a field of view θ radians in diameter, and T is the transmittance which would be obtained if unscattered light alone were accepted by the measuring equipment.

Observations have been made in several wavelength regions between 3600A and 6235A for atmospheres in which the transmission for visible light was between 0.35 and 0.85 per sea mile. Two-mile and nine-mile optical paths were used. Observations of Tθ through the nine-mile path were made with a fixed field of view 13.5 degrees in diameter, and those through the two-mile path were made with several values of θ between 5° and 25°.

© 1952 Optical Society of America

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References

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  1. W. E. K. Middleton, J. Opt. Soc. Am. 39, 576 (1949).
    [Crossref]
  2. Langmuir and W. F. Westendorf, Physics 1, 273–317 (1931), discussed several interesting problems of diffusion of light through fog.
    [Crossref]
  3. Pearson, Koomen, and Tousey, (February, 1951);Bull. Am. Meteor. Soc. 33, 117 (1952).

1949 (1)

1931 (1)

Langmuir and W. F. Westendorf, Physics 1, 273–317 (1931), discussed several interesting problems of diffusion of light through fog.
[Crossref]

Koomen,

Pearson, Koomen, and Tousey, (February, 1951);Bull. Am. Meteor. Soc. 33, 117 (1952).

Langmuir,

Langmuir and W. F. Westendorf, Physics 1, 273–317 (1931), discussed several interesting problems of diffusion of light through fog.
[Crossref]

Middleton, W. E. K.

Pearson,

Pearson, Koomen, and Tousey, (February, 1951);Bull. Am. Meteor. Soc. 33, 117 (1952).

Tousey,

Pearson, Koomen, and Tousey, (February, 1951);Bull. Am. Meteor. Soc. 33, 117 (1952).

Westendorf, W. F.

Langmuir and W. F. Westendorf, Physics 1, 273–317 (1931), discussed several interesting problems of diffusion of light through fog.
[Crossref]

J. Opt. Soc. Am. (1)

Physics (1)

Langmuir and W. F. Westendorf, Physics 1, 273–317 (1931), discussed several interesting problems of diffusion of light through fog.
[Crossref]

Other (1)

Pearson, Koomen, and Tousey, (February, 1951);Bull. Am. Meteor. Soc. 33, 117 (1952).

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Figures (5)

F. 1
F. 1

Schematic diagram of instrument used for field of view measurements.

F. 2
F. 2

Family of curves showing relationship of Tθ/T vs wavelength for 2 sea mile path at various values of visual transmission and 25° field of view.

F. 3
F. 3

Family of curves showing relationship of Tθ/T vs diameter field of view at several wavelengths.

F. 4
F. 4

Family of curves showing relationship of Tθ/T vs wavelength for 9 sea mile path at various values of visual transmission.

F. 5
F. 5

Series of curves showing comparison between measured and calculated spectral transmission.

Tables (3)

Tables Icon

Table I Calculation of f(θ) for θ=25 degrees (λ=5600A).

Tables Icon

Table II Calculation of f(θ) for 0<θ≤25°.

Tables Icon

Table III T computed from aurole measurements calculated transmission.

Equations (11)

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T θ = T + 0.5 ( 1 T ) ( 1 e θ ) ,
T = 1 S ,
T θ = T + S = 1 when θ = 180 ° ,
T θ = T when θ = 0 ° .
T θ = T + ( 1 T ) f ( θ ) , 1 T = S , f ( θ ) = 1 when θ = 180 ° , f ( θ ) = 0 when θ = 0 ° .
T θ = T + ( 1 T ) g f ( θ ) .
T θ / T = 1 + 1 T T g f ( θ ) .
T θ T = 1 + 0.5 ( 1 T T ) ( 1 e θ ) .
1 T T
0.5 1 T T
0.5 1 T T f ( θ )