Abstract: A method and apparatus for detecting small shifts in optical wavelength is provided. Light having a known wavelength is directed towards a target volume in the atmosphere. Light reflected from the target volume is received and mixed with differentially delayed copies of itself to produce three interference signals. The interference signals are taken at delays spanning one-half the wavelength of the transmitted signal. The intensity of the signal at the three different delays is measured simultaneously, from which the wavelength of the reflected signal can be determined.

Abstract: A method and device is provided for determining the direction and speed of wind in the atmosphere by means of a laser-Doppler anemometer, wherein only values measured in a sector of about 100.degree. and less of an azimuth scan are supplied or fed to a multiple-peak finder of a measuring device. In order to attain a high processing speed, flowing differentiation takes place by means of digitally operating systems. In order to eliminate the influences from clouds, haze, fog and the like in the measuring device, several frequency maximums are always traced in the multiple-peak finder, whereby in each case a preceding maximum is related to a trailing maximum until the trailing maximum is smaller than the preceding maximum. Because of the attainable high-speed sector scanning, the measuring device can be used for the determination of multiple wind peaks caused by clouds and/or fog echoes, or at an installation site where the measuring range is highly restricted, or also for detecting aircraft wake vortices.