Early results of multipath measurements on Lake Ontario (low angle radar tracking)

The authors discuss multipath measurements conducted to study the effects of environmental conditions on the accuracy of low-angle radar tracking. The data were recorded using a large synthetic antenna with an 18.4-m vertical aperture. The antenna was equipped with meteorological sensors so that both radar and meteorological measurements could be made at the same time. In addition to measuring the angles-of-arrival of the direct and indirect signals from a beacon, the antenna and the associated equipment were used to make measurements of the refractive index gradient. The measurements show that anomalous propagation conditions can greatly alter the interference pattern measured by a tracking radar. Also presented are data that were recorded under rough sea conditions. These data showed that the diffuse component of a reflected signal increased with increasing sea state conditions. This is expected and a well-known result. Reflection of a signal by a rough surface causes some of the signal to become thermalized or to take on noiselike characteristics. This was manifested by an increased noise component on the trace of the measured interference patterns with increasing sea state. A surprising result was that there was only a small overall decrease in the coherent component with increasing sea state.<>