Abstract: An infra-red scanning system with raster scan display unit operating in the visible spectrum, in which the image is scanned across a linear array of detector elements to provide a signal multiplexer with electrical signals related to the detected radiation pattern. The operation of the raster scan display unit is synchronised to the operation of the scanning system so that the horizontal time base integrator is gated according to the speed of the scanning system, and the vertical time base is gated to operate in synchronism with the multiplexer in order to minimise optical distortion in the display.