“…For known or well characterized media this problem has been addressed using frameworks such as matched field processing (MFP), maximum likelihood methods, or migration techniques in, e.g., acoustics [1,2,3], seismology [4,5,6], and electromagnetics [7,8]. The eigen-structure of the array covariance matrix or its inverse plays an important role in these approaches, in particular for data-adaptive implementations using, e.g., MVDR or MUSIC.…”