Advanced digital processing for amplitude and range determination in optical RADAR systems [fusion reactor inspection]

An amplitude modulated laser radar has been developed by the Italian Agency for New Technologies, Energy and the Environment (ENEA) for periodic in-vessel inspection in large fusion machines. The viewing system is based on a transceiving optical radar using a radio frequency (RF) modulated single-mode 840-nm wavelength laser beam. The sounding beam is transmitted through a coherent optical fiber to a probe, on the tip of which a focusing optics and suitable scanning system, using a silica prism, steers the laser beam in order to obtain a complete 3-D mapping of the in-vessel surface. This paper describes the digital signal processing system used to modulate the laser beam, as well as to measure both the amplitude of the backscattered laser beam and the phase difference between it and the modulation signal. This information, together with the information on the scanning system position, are acquired and then used by the visualization system to produce both 2-D and 3-D images. The system is based on VME boards and directly acquires and processes in real-time three 79.5-MHz RF signals by using a digital receiver and four digital signal processors. The system principles, the mathematical algorithm, and the system architecture are described hereafter.