Images of the variations of OH nightglow intensities have been recorded by a three-station network of scanning radiometers in southwestern Ontario during the period from May until September 1998. Each radiometer performs a 16 by 16 point raster scan of the night sky every minute, turning itself on and off when the solar depression angle is <6¿. The horizontal phase velocity, horizontal wavelength, and frequency of the internal gravity waves are derived from the OH intensity measurements using joint time-frequency analysis techniques, including the S transform, localized cross-spectral analysis, and generalized instantaneous frequency. The ensemble of gravity waves seen in all three instruments are analyzed and observed to have a strong dependence in their propagation direction with the majority of waves seen at each of the three sites having a horizontal wave vector in the northeast direction. The most common parameters observed for horizontal phase speed is 45 m/s, horizontal wavelength is 25 km, and period is 10 min. ¿ 2001 American Geophysical Union