A bearing error in the VHF Omni-Range due to sea surface reflection

The VHF Omni-Range (VOR) is a short-range air navigation system providing an aircraft with its bearing relative to the ground station. The authors describe how interference brings about course fluctuation, and predict the error numerically. They limit the consideration to SSB Doppler VOR (SSB-DVOR). The authors note the interaction between the intrinsic error, and that created by the interference. The generation mechanism of the intrinsic error is examined in order to obtain the parameters relating to the error. The uniform geometrical theory of diffraction (UTD) is applied to derive the accurate parameters. The effect of the interference on these parameters is then closely studied. An assumption is presented to account for the bearing error by the interference. A formula based on the assumption is applied to several examples to compare the results with measurements. A couple of methods to decrease the course error are also proposed