. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. S. JOHNSEN ET AL. brasiliensis) have many small photophores that evenly illu- minate the ventral surface, most have a smaller number of isolated photophores that produce uneven illumination U'.,t,>.. Fig. 2d). Thus, even if the photophores match the spectrum and intensity of the downwelling light perfectly, the coun- terilluminator will be visible when viewed at a distance that allows these individual sources to be discerned. To inves- tigate this problem, the effects of the intervening water and the viewer's visual acuit
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. S. JOHNSEN ET AL. brasiliensis) have many small photophores that evenly illu- minate the ventral surface, most have a smaller number of isolated photophores that produce uneven illumination U'.,t,>.. Fig. 2d). Thus, even if the photophores match the spectrum and intensity of the downwelling light perfectly, the coun- terilluminator will be visible when viewed at a distance that allows these individual sources to be discerned. To inves- tigate this problem, the effects of the intervening water and the viewer's visual acuity on the perceived image of the counterillumination must be understood. This study examines the effects of underwater light scat- tering and visual acuity on the perceived images of coun- terillumination signals. The effects are modeled with Monte Carlo methods and image transfer theory, using data col- lected from water types ranging from shallow coastal water to the deep mesopelagic zone (800 m). Three visual sys- tems, with high, medium, and low acuity, are also exam- ined. The goal is to determine under which conditions counterilluminators are still visible and what implications this has for both camouflage and visual detection under low-light conditions. Materials and Methods General principles of image transfer The perceived image of a counterilluminating animal viewed from a distance is affected by three factors: absorp- tion and scattering by the water and the acuity of the viewer's eye. The water and associated particulates poten- tially dim and blur the image, and the acuity of the eye determines the resolution of the perceived image. The effect of the first factor is generally modeled in the following way. First, the optical effects of the water on the image of a point source are calculated. The image of a point source is known as the point spread function (PSF) (Mertens and Replogle, 1977). The point source is then convolved with a given image to determine the appea
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
