A method and system is described for reducing unwanted noise components/interfering targets detected through an ambiguous beam-steer direction, such as the ambiguous ‘back-lobe’ of a sensor array. A pressure sensor array 52 and a plurality of pressure gradient sub-arrays 541-N are beamformed individually at processing stages 56, 581-N to derive signals indicative of directional responses, one from each group or sub-group. The signals are scaled and weighted (60, 620-N) and processed to define a cardioid beam with nulls pointing in the ambiguous beam-steer direction.