First measurements of the two‐dimensional horizontal wave number spectrum from CCD images of the nightglow

A narrow wavelength band CCD camera, built at Aerospace, has been used to obtain images of the OH Meinel (6,2) band and the O 2 atmospheric (0,1) band nightglow. The field of view of the camera is approximately 100 by 100 km at an altitude of 90 km, the nominal height of the nightglow. It is shown how Fourier techniques can be applied to these data to optimally smooth the images, to identify the presence of monochromatic waves, and to obtain both the one‐dimensional and, for the first time, the two‐dimensional horizontal wave number spectrum of gravity waves passing through the emission layers. Both measures of the spectrum depend, to a certain extent, on a technique which makes use of Krassovsky's η ratio. These techniques are applied to sample data taken from May 9, 1989, during the Arecibo Initiative in Dynamics of the Atmosphere (AIDA) campaign in Puerto Rico, and from the recent Collaborative Observations Regarding the Nightglow (CORN) campaign in Illinois. While future papers will describe these data in more detail, a brief comparison is made with recent models of the two‐dimensional horizontal wave number spectra presented by Gardner et al. (1993) and Gardner (1994).