where G^k−1≡[g(r^1,e^1)...g(r^k−1,e^k−1)] is formed from the array manifold estimates (g(r^i,e^i)=h(r^i)e^i) of the previous k - 1 recursions and ΠG^k−1⊥≡(I−G^k−1(G^k−1TG^k−1)−1G^k−1T) is the projector onto the left-null space of G^k−1. The recursions are stopped once the maximum of the subspace correlation in (13) drops below a minimum threshold.
