Determining all ambiguities in direction of arrival measured by radar systems
Daniel Kastinen · URSI Radio Science Bulletin · 2018
There is an ambiguity problem when using radar systems to determine the position and motion of objects. This ambiguity manifests itself for certain sensor configurations when determining the direction of arrival (DOA) of an incoming electromagnetic plane wave onto the radar. Depending on the positions of the sensors in space, a radar system can respond the same way for several different plane-wave directions of arrival, thereby making it impossible to determine the true direction of arrival. We have therefore developed a mathematical framework and a practical method for finding all ambiguities in any multichannel radar. We have used a set-intersection viewpoint to formulate an alternative form for the solutions to the ambiguity problem. The new formulation allows for an efficient implementation using the numerical Moore-Penrose inverse to find all ambiguities and approximate ambiguities. This definition led to the discovery of noise-induced ambiguities in theoretically ambiguity-free radars. Finally, we explore the possibility of using the sensor-gain patterns to resolve ambiguities and to restrict the elevation angle of a detection. This study originated in the need to resolve ambiguous meteor trajectories in data from the Middle and Upper Atmosphere Radar in Shigaraki, Japan. We have therefore used this radar as a practical example throughout the paper. Our results and methods can be used to classify ambiguities in any radar system, to design new radar systems, to improve trajectory estimation using statistical information, and to identify possibly faulty direction-of-arrival calculations and to correct them.