using rotating or oscillating beam systems, e.g. using mirrors, prisms

Full Title

Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic or electromagnetic waves, or particle emission, not having a directional significance, are being received (position-fixing by co-ordinating a plurality of determinations of direction or position lines G01S5/00) > using electromagnetic waves other than radio waves > Systems for determining direction or deviation from predetermined direction > using rotating or oscillating beam systems, e.g. using mirrors, prisms