1. Apparatus for detecting obstacles in the path of a work vehicle upon which said apparatus is mounted comprising: transducer means for producing radiant energy having a central axis of propagation, receiving reflected produced radiant energy, and controllably producing an obstacle detected signal in response to receiving said reflected produced radiant energy; rotatable reflector means for controllably projecting said produced radiant energy radially outwardly from said work vehicle and receiving said reflected produced radiant energy along substantially the same path, said rotatable reflector means including a central axis of rotation and an optical reflector member rotatably disposed along said axis of rotation; encoder means for controllably producing an enable signal in response to said optical reflector member being rotatably positioned at any one of a plurality of predetermined rotational positions about said axis of rotation; and zone control logic means for receiving said obstacle detected signal and said enable signal and producing a vehicle control signal only in response to the simultaneous presence of said enable signal and said obstacle detected signal.