Projection techniques for altitude estimation over complex multipath condition-based VHF radar

In very high-frequency (VHF) radar, the performance of low-angle target tracking is strongly affected by multipath phenomenon, especially in the case of complex terrain where exact information of reflection paths is unknown. To deal with this problem, a practical multipath signal model for VHF radar in complex terrain is presented, where both curved earth geometry and actual ground surface reflection coefficient are considered. Then, a novel altitude estimation technique based on alternating projection is proposed, where the motion or Doppler shift of a target is neglected during the observation time of one coherent processing interval. The technique applies to vertical antenna arrays which perform an interferometric estimation of the target elevation angle. Simulation results and real data analysis show that the target tracking accuracy can be efficiently improved by using the proposed algorithm under both simple and complex multipath scenarios.