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Impact of ambient O 2 (a 1 Δ g ) on satellite‐based laser remote sensing of O 2 columns using absorption lines in the 1.27 µm region
Author(s) -
Sharp William E.,
Zaccheo T. Scott,
Browell Edward V.,
Ismail Syed,
Dobler Jeremy T.,
Llewellyn Edward J.
Publication year - 2014
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2013jd021324
Subject(s) - airglow , laser , radiation , absorption (acoustics) , noon , backscatter (email) , optics , materials science , physics , atmospheric sciences , telecommunications , computer science , wireless
Determination of CO 2 mixing ratio columns from space using Laser Absorption Spectroscopy (LAS) requires simultaneous measurements of CO 2 number density columns and knowledge of the dry atmospheric surface pressure. One approach to determining the surface pressure is to make an LAS column measurement of O 2 number density in the 7857.3–7921.7 cm −1 (1.27 µm) region of the O 2 ( 1 Δ) state. A complicating factor in the LAS O 2 measurement is the presence of a permanent but spatially variable natural source of airglow from the O 2 ( 1 Δ) state. In addition, the laser radiation can induce stimulated emission from the ambient O 2 ( 1 Δ) state and also cause stimulated absorption and emission from the ground state O 2 molecules as the laser beam passes through the atmosphere. Finally, the upwelling surface‐reflected solar radiation is an additional source of background radiation. The effects of these additional radiation sources on the LAS measurement of O 2 are examined. The surface‐reflected solar radiation produces the largest background at 3 orders of magnitude more intense than the laser backscatter signal, while the airglow is of the same order of magnitude as the laser backscatter. The stimulated emission from ambient O 2 (a 1 Δ g ) is found to be about the same order of magnitude as the laser radiation. These effects are evaluated under noon, twilight, and midnight conditions at midlatitudes, the equator, and the pole. The stimulated emission is in the same direction and in phase with the laser signal, its contamination of the LAS O 2 measurement prevents a full sunlight determination of surface pressure.