Redundant data from independent over-thehorizon radar systems can increase track accuracy by providing more independent "looks" at the target. With proper geometry, complementary radar system can aid in resolving uncertainties in the coordinate registration through the various ionospheric modes. Systematic positional differences between tracks from the separate radars can be used to improve the estimation of ionospheric heights. In operational systems, targets are tracked by multiple over-thehorizon radars in overlapping coverage areas. In this paper, we consider the case of two over-the-horizon radars. The main algorithm is designed to hand-off range bias errors from one radar's ionospheric mode to a second radar. It is expected that the resultant algorithmic development based on the work described in this paper will improve track positional accuracy by more than 50%.

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Relocatable Over-the-Horizon Radar (ROTHR) is a long range, bi-static, high frequency radar surveillance system tasked with tracking air targets over large land and ocean areas. The long ranges, together with the relatively low altitudes of the targets, require that the radar look beyond the line-of-sight, in other words, over-the-horizon (OTH). This is accomplished by refracting the signal off the ionosphere t o points beyond the horizon. In order to quant.ify the performance of the data fusion of multiple OTH radar tracks, several Measures of Effectiveness (MOEs) have been developed which correspond to the unique technical challenges facing a single OTH radar tracking system. This paper describes appropriat,e MOEs arising from OTH technical issues relating to ionospheric mode identification, crossing targets, and low Doppler targets. These MOEs were chosen to be sensitive to the performance that would be expected by fusing data fiom two OTH radar systems having overlapping coverage.