Abstract

On March 13, 1959, the infrared solar spectrum from 1 to 10 μ was recorded at altitudes up to 90 000 ft by means of a balloon-borne spectrometer flown in conjunction with a biaxial pointing control. The amount of water vapor present at these altitudes was also measured by means of a frost-point hygrometer.

Infrared absorptions depend not only on the amount of absorbing material traversed by the radiation but also on its pressure environment. Various methods have been advanced for predicting the absorption that would be suffered by radiation traversing a slant path in the atmosphere. Carpenter et al. have shown that the absorption should be equivalent to that suffered by radiation traversing a constant pressure path through an amount of absorbing gas given by

ue=h1h2α(h)αsρ(h)dh

Kinetic theory predicts that if temperature effects are neglected α=(P/Ps)αs. Thus,

ue=h1h2P(h)Psρ(h)dh,

which is equivalent to that predicted by Curtis. The laboratory studies of Howard et al. indicate that for constant pressure paths

ue=0x(PPs)kρ(x)dx,

where k varies from band to band. This suggests that α=(P/Ps)kαs and that ue should be calculated from

ue=h1h2(P(h)Ps)kρ(h)dh.

The absorptions were calculated for the 1.4-μ, 1.9-μ, and 6.3-μ bands using both expressions, the hygrometer data, and the laboratory data of Howard et al. Comparison of the calculated and observed absorptions indicates that the expression

ue=h1h2(P(h)Ps)kρ(h)dh

gives better agreement with the observed values.

© 1961 Optical Society of America

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