Since their development in 1959 [Little and Leinbach, 1959], riometers have been used throughout the world for the detection of VHF radio noise absorption in the ionosphere. However, one of the problems in using a riometer is that of having to derive a quiet-day curve for the installation before the magnitude of absorption events can be determined. The quiet-day curve has a quasi-sinusoidal variation with a period of one sidereal day (about 23h 56m) for a fixed installation on the ground because the cosmic noise background is scanned at this rate by the rotation of the earth with respect to the stars. The amplitude of the quiet-day curve depends on the latitude of the installation and the elevation of the antenna beam.