Abstract: In the method, a volume (5) to be measured is illuminated by a pair of light beams (3) which cross each other. The Doppler-shifted scattered light (8) originating from the particles (6) which are moved along with the flow is registered and converted into electric signals (1). The Doppler frequency of the registered scattered light (8) is used as a measure of the flow velocity. The electric signals (1) of the registered scattered light (8) are digitized and represented in the form of an image and a coherent light beam is transmitted through the image. The coherent light beam (14) is focussed in a Fourier plane (18) as a result of which a Fourier-transformed image (22) of the electric signals (1), which exhibits a dot pattern (24), is generated. The Fourier-transformed image (20) is recorded and processed further.