Resolving ambiguous direction of arrival of weak meteor radar trail echoes

Abstract. Meteor phenomena cause ionized plasmas that can be roughly divided into two distinctly different regimes: a dense and transient plasma region co-moving with the ablating meteoroid and a trail of diffusing plasma left in the atmosphere and moving with the neutral wind. Interferometric radar systems are used to observe the meteor trails and determine their positions and drift velocities. Depending on the spatial configuration of the receiving antennas and their individual gain patterns, the voltage response can be the same for several different plane wave Directions Of Arrival (DOA), thereby making it impossible to determine the correct direction. Noise can create the same effect even if the system contains no theoretical ambiguities. We propose a method for interferometric meteor trail radar data analysis using coherent integration of the signal spatial correlation to resolve DOA ambiguities. We have validated the method by a combination of Monte Carlo simulations and application on 10 minutes of measurement data (174 meteor events) obtained with the Sodankylä Geophysical Observatory SKiYMET all-sky interferometric meteor radar. We also applied a Bayesian method to determine the true location of ambiguous events in the data set. In 26 out of 27 (~ 96 %) ambiguous cases, the coherently integrated spatial correlation gave the correct output DOA as determined by Bayesian inference. In the one case that was mis-classified there were not enough radar pulses to coherently integrate for the method to be effective.