See Zaron, "Laser Doppler velocimetry of a flowing soap-water film using a modified computer mouse." American Journal of Physics, 84(10):810--813, 2016.
What you will find here:
./Catalog/ -- A brief write-up and summary of calibration experiments and experiences making meaurements of the velocity of a flowing soap water film.
./Data/ and ./DataGood/ -- Example data, time series and transects.
./Software/ -- Drivers for reading the mouse device and storing the results in data files.
./README -- Some instructions to help get started with the ./Software/.
./Muse/ -- An old web site documenting some of my efforts.
The measurement principle of the PLN20** devices requires the scatterers to lie in a well-defined plane. Because of this, I was never able to use the device to measure velocity in water, and I am no longer investigating it. As demonstrated in the manuscript, though, it is completely viable for measuring velocity in the plane of a flowing water film. The primarily limitation for quantitative work is the difficulty of precisely the distance between the sensor and the flow plane.