Abstract

Shadows of leaves and other objects that can float on the surface of still or slowly flowing water such as a pond or a gently flowing stream have shapes that frequently look nothing like their boundaries because of meniscus effects. Menisci can either refract light into the shadow region making it brighter, or away from it extending the area of darkness. Generally speaking one will find both effects in the shadows of leaves with complicated outlines. In this paper we present an approximate theoretical model for the light intensity in these shadow regions with results of laboratory experiments and computer simulations matching our calculations. The calculations indicate a minimum depth for the water of $\sim 10\mathrm{cm}$ for typical floating leaves at which caustic structures form in the shadows. For depths significantly less than this, the shadows will more or less match the outline of the leaf. But for depths much greater the shadows will be significantly different, often not looking anything like the leaf itself.

© 2015 Optical Society of America

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