Abstract: A method and apparatus for determining the rate of angular rotation of a rotating object comprising directing a beam of substantially coherent electromagnetic radiation towards the rotating object (80); detecting speckles generated by electromagnetic radiation (60) scattered from the object; and determining the transit time of the detected speckles; wherein the field of electromagnetic radiation (60) scattered from the object is Fourier-transformed by an optical Fourier-transforming system (20); and subjective speckles (71) of the Fourier-transformed electromagnetic radiation (70) are detected in at least two detection regions (12, 13) positioned in a detector plan (9) substantially parallel with and located in or near the Fourier-plane (10) of the Fourier-transforming system (20).

Abstract: The disclosed invention is a measurement device for use in determining wind turbulence in the atmosphere, such as the cross-wind velocity and strength of refractive turbulence in a localized region. In the preferred embodiment, the device is comprised of: a telescope for collimating the light received from the light source, the telescope placed in front of a pair of spatially filtered optical receivers and focussed at infinity; a pair of gratings; a collecting lens, placed behind the gratings to collect the spatially filtered light; a photodetector to collect the light; an amplifier to amplify the signal received from the photodetector, and; a spectrum analyzer to analyze the interference pattern created by the gratings. The device uses the information contained in the light as it is scattered into its various Fourier components as the light passes through the atmosphere.