The measurement of O₂number density by absorption of Lyman α

Abstract

Measurements of O2 number density obtained from rocket observations of the absorption profile of solar Lyman α (1216 Å) have been compared with values derived from nearly simultaneous measurements of atmospheric density from other rocket techniques: grenades, falling sphere, and Pitot tube. All launches were from Wallops Island, Virginia. The atmospheric density derived from the absorption spectroscopy data is found to be about 20% less than that from the other techniques when a constant value of the absorption cross section of 1.0×10−20 cm² is used. The agreement is worse when the cross section is allowed to vary across the width of the solar line. The data in the altitude range 70–90 km are interpreted as showing that the effective value of the absorption cross section at Lyman α for O2 at 200°K and negligible pressure is about 0.8×10−20 cm².

Der Photoabsorptionskoeffizient von molekularem Sauerstoff f�r Strahlung in der Umgebung der Lyman-Alpha-Linie des Wasserstoffs

“…Eine weitere Anwendung finden Daten fiber die Photoabsorption von 0 2 in der Umgebung der LymanAlpha-Linie schlie[31ich in der Bestimmung der Dichte yon O2 in der oberen Atmosph~ire. Es ist mehrfach darauf hingewiesen worden [6,7], dab in diesem Zusammenhang sowohl die absolute Gr613e als auch die …”

Determination of O2density from Lyman α ion chambers

“…Ion chambers sensitive to solar Lyman a radiation have provided information on molecular oxygen from numerous rocket flights [Kupperian et al, 1959;Cartier et al, 1966;Weeks and Smith, 1968;Quesette, 1970;Hall, 1972;Subbaraya et al, 1972;Smith and Miller, 1974]. This technique is a basic one for measuring molecular oxygen in the 70-to 115-km altitude regime; however, there exist a number of questions about the accuracy of the technique.…”

Molecular oxygen concentrations and absorption cross sections in the thermosphere derived from extreme ultraviolet occultation profiles

“…In particular, it has been brought to our attention by a reviewer that the adjusted value at 1216,4 is in excellent agreement with the laboratory measurements of Carver et al[1977], at temperatures appropriate for these altitudes in the thermosphere. Similar values have also been reported in other atmospheric analyses [e.g.,Smith and Miller, 1974]have also been plotted as functions of the time of year in order to try to distinguish between seasonal and latitudinal effects. Although no clear seasonal variation is apparent, such an effect cannot be ruled out on the basis of this rather limited data set, since the temporal sampling was not suitable for the seasonal variation analysis.…”