Mesospheric airglow perturbations offer a method of observing fast (long vertical wavelengths, &lgr;z and short horizontal wavelengths, &lgr;h) atmospheric gravity waves (AGWs) propagating through the mesosphere. In a recent study, wave phase speeds (and &lgr;h) have been deduced from the airglow observations and Doppler corrected using lidar winds [Swenson et al., 1999>. Combining these measurements with the dispersion relationship, wave momentum and energy fluxes were calculated. The observed waves have intrinsic phase speeds which are not linearly related to &lgr;z for short &lgr;h as is assumed in the commonly applied approximation to the dispersion relation. This corrected dispersion relationship is graphically presented along with imager measurements of AGWs and an estimate of error in the wave momentum flux related to this term. The observed waves with &lgr;h<20 km are found to be near the high-frequency limit for vertical propagation, suggesting they may be ducted, evanescent, or close to the point of total internal reflection. ¿ 2000 American Geophysical Union