Doppler velocimeter

Abstract

A heterodyne velocimeter system includes an illumination laser that illuminates a moving object with a coherent, laser beam. The laser illumination is reflected from the object as separate wavefronts (referred to as the signal light) and is passed through a range-focus lens pair, a polarizer element and through a partially reflective, partially transmissive element onto a plurality of separate light sensitive elements of a sensor which are referred to as pixels. A second source of laser illumination, such as a second laser provides a reference light beam that is directed onto a local oscillator scatter mask. The light beam from the second laser is scattered into separate wavefronts by the scatter mask and they are focussed by a lens onto the partially reflective partially transmissive element which reflects them onto the separate pixels of the sensor where they are individually mixed with the separate signal light wavefronts from the object. Thus light reflected from the other points of the moving object are similarly directed as signal light onto the pixels of the sensor and mixed with corresponding reference light wavefronts from the scatter mask to provide a two-dimensional array of emission points from local oscillator scatter mask is imaged onto the sensor to serve as the local oscillator for the reflected wavefronts at each pixel.