Gravity waves are ubiquitous in the Earth's atmosphere transporting energy and momentum between regions. GWIM is a satellite instrument that will use airglow intensity variations to measure gravity wave parameters. A major interest lies in the correlation of the presence of gravity waves with their sources near the surface or in the lower atmosphere. The specific airglow emissions were chosen because of their high radiance and their low susceptibility to contamination by moonlight scattered from clouds. GWIM consists of four nadir-looking imagers, one each for signal and background for each of the two emissions. The field of each imager will be 175 km cross-track by 80 km along the track. An integration time of about ten seconds is required to achieve the required signal-to-noise ratio. To prevent image smearing due to the effects of satellite motion and the rotation of the earth, GWIM will operate in snapshot mode with an exposure time of about 0.25 second followed by on-board shift-and-add. GWIM is being considered for flight as part of the payload of EQUARS, a Brazilian satellite planned for launch into a near equatorial orbit in 2007.
Gaussian modulated sinusoids are used in S-transform to extract time-local and space-local spectral information. Similar data sets recorded at neighboring spatial locations may be used with cross spectral analysis to determine frequency localized velocity spectrum. The 2D S-transform is used in image analysis for space localized wavenumber spectra. Local changes in the image spectrum are used to define textural boundaries on images. This paper summarizes several of the research projects involving S-transforms currently in progress at the University of Western Ontario including the application of the 2D S-transform to texture analysis, recognition, and the classification of images.
2D local spectral information can be obtained form an image using Instantaneous Wavevector (IW). This 2D function is a vector quantity found by taking the gradient of the phase of the analytic image. Several synthetic images will be presented to illustrate the utility of IW analysis, and its application to OH airglow images will be discussed. The IW of an image gives us the dominant wavevector present at any point in the image. The amplitude of the analytic image gives us the magnitude of this component, and the phase differences of the analytic image between successive images allow us to infer the velocity of these waves. This method is used to determine phase velocities of internal waves from Hydroxyl airglow data. The instrument used, UWOSCR, is a scanning radiometer in the near infra-red, taking an 256 pixel image of the OH airglow every minute.
The local spectral information of the continuous wavelet transform with Morlet wavelets can, with slight modification, be used to perform 'local' cross spectral analysis with very good time resolution. This 'phase correction' absolutely references the phase of the wavelet transform to the zero time point, thus assuring that the amplitude peaks are regions of stationary phase. Thus phase differences between the 'local spectra' of time series from two spaced receivers can be used to infer time lags as a function of frequency. This method is used to determine apparent phase velocities of atmospheric gravity waves from hydroxyl airglow data. The instrument used, UWOSCR, is a scanning radiometer in the near infra-red, taking a 256 pixel image of the OH airglow every minute. Pixel-to-pixel time lags are used to determine the phase velocity as a function of frequency and time.
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