Laboratory simulation of light-focusing by water-surface waves
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A laboratory system has been developed to simulate wave-induced irradiance fluctuations that occur in the top few metres of the sea under sunny surface conditions. A principle of operation is that the fluctuations are produced after refraction of light by water waves generated in the tank. Simulated irradiance consists of repetitive high-amplitude “flashes” resulting from a lens-effect of the waves. Statistical properties of flashes are similar to those recorded at sea. In our laboratory simulation, the flashes that exceed an amplitude level of 1.5 Ē (where Ē is the time-averaged irradiance) have a mean frequency of about 230 min-1, and a typical duration of 5 to 20 ms. The frequency of the flashes decreases exponentially with increasing amplitude level. The system simulates timeaveraged irradiance comparable to full sunlight at shallow depths (∼800 μmol quanta m-2 s-1 over the visible spectral region), and provides light with a reasonable spectral composition. The simulation method was designed for studying responses of phytoplankton, but applications involving optical aspects can also be foreseen.
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