Saturday, September 09, 2006

Optical phenomena from algal film on water surface

Here are some results from the work I have done this summer on the phenomena caused by algal film on water surface.

The upper pair of photographs shows elliptical corona and the alga that caused it. Pine pollen gives the scale. This corona-type display has no other phenomena.

The lower photo shows another type of display, which exhibits Quetelet rings, brightenings around sun's reflection image, glory and fogbow. In this case there is also unidentified diffuse feature marked with arrows. In addition, fogbow and glory have spot-like brightening towards nadir. Two B&W photos of the algae causing this type of display are shown. In the lower photo the algae are possibly turned 90° in comparison to upper, showing elliptical shape. This species might be Chromulina rosanoffii. It's about 5-10 ┬Ám in size (not to scale with upper color photo) and well transparent to make glory.

These phenomena turned out to be common, at least this summer. They were most abundant on rocky Finnish archipelago islands, which harbour endless number of small rock pools.

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