Method for determining at least one speed component of a fluid stream

A method for determining at least one speed component of a fluid stream, for laser Doppler anemometry, the method comprising at least the steps of:

• providing at least a first part-beam and a second part-beam;
• directing the first part-beam along a first optical path and directing the second part-beam along a second optical path onto a superimposition region within the fluid stream so that the first optical path and the second optical path intersect in the superimposition region;
• detecting a Doppler-shifted first part-beam scattered light signal, which was back-scattered by tracer particles in the fluid stream in the superimposition region, at least partially following the first optical path;
• detecting a Doppler-shifted solid angle scattered light signal, which was scattered by the tracer particles in the superimposition region into a path different at least from the first optical path and from the second optical path,
• determining a first speed component of the fluid stream in the superimposition region from the Doppler-shifted first part-beam scattered light signal;
• determining a total speed of the fluid stream in the superimposition region from the Doppler-shifted solid angle scattered light signal;
• and
• determining a first direction of movement of the first speed component of the fluid stream in the superimposition region from the first speed component and the total speed.