Abstract: Ultrasonic imaging techniques are subject to interference from whiteout, a component at insonification frequency in the image signal. A technique for separating the image signal from whiteout by mixing the received ultrasonic radiation with another frequency is described. In one form using an electron beam to scan a transducer mosaic the beam is modulated and mixing occurs between the transducer and a signal plate. A filter connected to the signal plate selects a mixing product containing the image signal and rejects the insonification and beam frequencies.