Underwater fluorescence photography in the presence of ambient light

Abstract

Fluorescence photography is traditionally done in dark conditions owing to the relatively low level of the fluorescence emission compared to ambient light levels. Working in the dark can be awkward, especially underwater, and the ability to do the photography during the day would be an advantage. Recent experiments have demonstrated that with the appropriate off-the-shelf camera and lighting technology it is possible to make high-quality fluorescence images in the presence of moderate levels of ambient light. The factors that affect this technique are the ambient light and the specifics of the equipment being used. For the ambient light, the important factors are the inherent optical properties of the water body, depth at which the photography is being done, time of day, cloud cover, and subject orientation and location (insofar as they create shadowing). For the equipment, the important factors are the camera's flash synchronization speed, flash intensity, flash duration, detector sensitivity, and the spectral characteristics of fluorescence barrier filters. The range of conditions under which this technique can be used was determined by modeling. Results are presented for the relatively clear waters of a tropical reef (Bahamas) and the relatively turbid waters of New England. This method of fluorescence photography allows collection of fluorescence images under daylight conditions, rather than at night or with enclosures to create artificial darkness, and thus is much more practical and applicable in the field.