High-Precision, High-Resolution Measurements of Absorption in the Oxygen A-Band

Abstract

Issues arising in the application of high-resolution, high-precision spectroscopy to remote sensing are discussed in the context of deriving surface pressure from absorption in the O2 A-band. This application requires spectral resolution approaching 1 cm?1 and noise not exceeding 0.1%. The authors establish the theoretical limit to signal-to-noise ratio and establish tolerances on mechanical and thermal stability for a grating spectrograph. The tolerances are tight, but not impossibly so. Two experiments are described to test the effects of atmospheric noise generated by turbulence in the lower atmosphere. In the first experiment, the air mass along the path of the solar beam was tracked with an error equivalent to less than 0.1 kPa in surface pressure. In the second experiment, the optical path from the sun to the spectrograph was extended with an O2 absorption cell whose pressure could be modulated to simulate changes in atmospheric pressure. Changes as small as 0.1 kPa were detected clearly.