Images of the variations of OH intensities have been recorded by a three-station network of scanning radiometers in southwestern Ontario during the period from May until September 1998. The ensemble of gravity waves seen in all three instruments is 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. In order to understand these results a model of the transmission of gravity waves through the atmosphere was employed. The gravity waves observed by the OH Scanning Radiometers (OHSCRs) are assumed to originate in the troposphere with an isotropic spectrum, meaning that the average wave amplitudes are equal in all directions. The gravity waves propagate upward where they will undergo a selection process owing to the effect of the background winds. Using the horizontal winds from the Horizontal Wind Model (HWM-93), the transmission of gravity waves from a tropospheric source is modeled and shown to be consistent with the observations. The strong zonal winds account for the summer eastward and winter westward propagation, but it is the tidal components of the meridional wind that account for the northward tendency of wave propagation (and the corresponding relative absence of southward propagating waves). In order to further validate the transmission, model winter measurements from the OHSCR data set are examined and shown to be consistent. ¿ 2001 American Geophysical Union