The novel use of imaging riometers to observe mesospheric gravity waves is described. Imaging riometers respond to changes in the absorption of cosmic radio noise in the ionospheric D-region which enables them to detect the compression and rarefaction of the atmosphere at ~90 km altitude generated by the passage of gravity waves. A considerable advantage of this method is that, unlike conventional techniques which rely on imaging faint optical emissions from the airglow layer at ~87 km altitude, riometers remain operative under daylit, moonlit or cloudy conditions. This is particularly important for research into gravity wave forcing of mesospheric temperature at polar latitudes in summer when continuous 24-hour daylight prevails. An example in which the same wave event is characterized in co-located airglow imager and imaging riometer shows good agreement between the two instruments.