“…Then (1) can be rewritten as (2) where f, s and n are the vector versions of f(k), s(k), n(k), and n(k), respectively. The imaging operator G, defined as (3) is a (typically, underdetermined) matrix operator consisting of N φ linear convolution matrices. Thus, a unique minimum-norm least-square estimate (denoted by ŝ below) of the scatterer vector s can be expressed as (4) where PIO is a pseudoinverse operator [17], [25] equal to (5) The superscripts * , t , and † represent conjugate, transpose, and generalized inverse operators, respectively.…”