Two-dimensional spectral analysis of mesospheric airglow image data

Abstract

A technique to analyze short-period ͑Ͻ1 hour͒ gravity wave structure in all-sky images of the airglow emissions is described. The technique involves spatial calibration, star removal, geographic projection, regridding, and flat fielding of the data prior to the determination of the horizontal wave parameters ͑wavelength, velocity, and period͒, by use of standard two-dimensional Fourier analysis techniques. The method was developed to exploit the information that is now available with wide-field solid state imaging systems. This technique permits interactive and quantitative investigations of large, complex data sets. Such studies are important for investigating gravity wave characteristics, their interaction with the airglow emissions, and their geographic and seasonal variability. We study one event of this type here and present possible evidence of a nonlinear wave-wave interaction in the upper atmosphere.

Characteristics and sources of gravity waves observed in noctilucent cloud over Norway

“…In order to accurately project the NLC images, the viewing geometry of the camera, including the FOV, azimuth and elevation angles as well as rotation of the optical axis, were first calibrated using the visible stars that are manually identified in the images (Garcia et al, 1997). After the images were projected on a linear-scale grid using an optical ray tracer where the refractive index was calculated from air densities taken from MSISE-00.…”

“…In order to infer the wave parameters, we have developed a robust method using a combination of fast Fourier transform (FFT) and a least squares fitting of a sinusoidal function of the intensity data in order to quantify the horizontal wavelength, phase speed and direction of propagation of the waves in the NLC images. This method is different from the 2-D FFT method used by Pautet et al (2011), originally developed by Garcia et al (1997), to analyze the gravity waves from the Stockholm NLC images. Although this fitting method is more labor intensive and more subjective than the Pautet et al (2011) method, given the low contrast of these high latitude observations it was necessary to manually identify the wave parameters.…”

Equatorial F-region plasma depletion drifts: latitudinal and seasonal variations

“…There has been considerable improvement in their capabilities to observe very faint and low contrast nightglow emissions, due to recent advances in CCD detectors (Mendillo et al, 1997b;Garcia et al, 1997;Taylor et al, 1997;Abalde et al, 2001;Pimenta et al, 2001b;Santana et al, 2001). The images recorded with the all-sky imaging system (from the Utah State University, Taylor et al, 1997) which carried out regular observations at Cachoeira Paulista (22.7 • S, 45.0 • W; 15.8 • S dip latitude), Brazil, since 1998, provided time evolution and spatial variations of selected atomic or molecular emissions over a wide sky area.…”

“…Thus, the raw image is distorted with respect to the radius. In order to calculate the east-west drift velocities of the plasma bubbles, as a function of local time, we first transform the raw image into a geographic grid image (Cartesian coordinate system), using the linearization method described by Garcia et al (1997). Figure 1b shows an example of the transformed image, after being linearized.…”

Observations of equatorial F region plasma bubbles using simultaneous OI 777.4 nm and OI 630.0 nm imaging: New results

“…The nightglow emissions are usually very faint and sometimes may present spatial and temporal fluctuations of a few percent, which can be atthbuted to the propagation of waves or to spatial irregularities in the upper atmosphere [Garcia et al, 1997]. In August 2000, optical and ionospheric radio measurements for ionospheric and thermospheric studies were started at S•o Jos• dos Campos (23.21os, 45.86ow), Brazil, using two all-sky imaging photometers and a Canadian Advanced Digital Ionosonde (CADI) digisonde.…”