IMAGE SYSTEM DESIGNED TO SCAN FOR SECURITY THREATS

An imaging system comprises a transmitter (24, 25), a receiver (24, 25, 21), and a controller (20) for directing the transmitter and the receiver to scan an object in a volume. The controller determines which sub-volumes of the volume the object is located within and then performs a fine scan in those sub-volumes. This reduces overall scanning time. The controller (20) may compare a received signal sample magnitude from the initial scan with a threshold to make the decision. The initial scan may be performed with a spot size to include only one or more particular volume elements within at least some of the sub-volumes.