This paper describes an experimental technique which allows estimates of local turbulent properties of a shear layer to be obtained without the necessity of inserting a probe into the flow field. The probe is replaced by two beams of radiation, which pass through the entire flow field in two mutually perpendicular directions. It is shown that, although each beam independently reflects only an integral of the flow properties along the entire path between the source and detector, the covariance between the two detected signals does yield local turbulent information.

To verify the validity of the technique, experimental results are presented for the shear layer of a subsonic jet and are shown to be in good agreement with published hot-wire data.