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Many techniques are available for extracting a 2D velocity field from a fluid flow which has been seeded with some small tracer particles. In general, two images are taken in rapid succession with a known time spacing between them. If the distance these tracer particles have moved between images is then measured, a simple calculation of distance over time gives the velocity. (More information should be available here on particle tracking soon!) In this case, the microencapsulated liquid crystals themselves can be used as the tracer particles; and the color of the tracked particles recorded to make the temperature measurement.
A (really squished down) vector field showing the velocity at the 17,000 points that were tracked between two images. The direction of the lines indicates the direction of flow; line color indicates the local temperature (again, black is coolest, then red, green, and finally, blue is the warmest). Blowing up a section near the lower-right of the above field shows the density of the velocity measurements. One can also see that there are exceedingly few bad vectors (those mistracked by the tracking software). The color of the particles in an interesting mosaic. One can clearly see the downward moving plume on the right and the buoyant upwelling on the left.
geophysics