On a spatial smoothing technique for multiple source location

This correspondence presents an alternate proof for the spatial smoothing technique recently proposed for multiple source location. Specifically, it is proved that the number of subarrays required to ensure a nonsingular covariance matrix is m + 1 where m is the nullity of the source covariance matrix. Also, it is shown that this number can be reduced if a specific basis can be found for the null eigenspace of the covariance matrix satisfying certain properties.