Maximum Likelihood Angle Extractor in the Presence of Sea-Surface Multipath

In the presence of sea-surface multipath, the standard monopulse ratio technique to extract elevation angle of target produces large bias. In this paper we propose a maximum likelihood (ML) angle extraction technique for low elevation targets above the sea surface, of known average signal strength having a Rayleigh fluctuation. The procedure is then modified for targets having unknown average signal strength. The resulting modified angle extractor has only a small performance degradation compared with the known average signal strength case, but it performs much better than the monopulse ratio based estimator. This angle extractor reduces the root mean square error (RMSE) by more than 50% in the signal processing stage when used for low flying target tracking scenarios. Further improvement is achieved by using the predicted average target signal power in the ML estimator. This technique can be used in dynamic scenarios where a significant reduction in the tracker RMSE performance can be achieved, as shown in the simulations presented.