the snowman cometh

The cold/warm/cold weather continues with a wee snow fall this evening; I went out to get my road bike to put it on the turbo trainer and stopped to get a couple of pictures. Not much to it yet.

The multiple exposures of the snowflakes is rather nice and is demonstrates what I used to do: the sodium lamps are flashing at 100Hz and as my exposure was 1/10th s I should have 10 images per flake (count 'em, it's correct). Now, if we know that the street lamp head is about 60cm long we can make a guess as to how fast the flakes are falling; it looks like about 3m/s, probably a bit less due to perspective. The larger and fluffier the flake, the slower the fall will be. That, in a nutshell, is particle image velocimetry (PIV).