Water transparency measurements in the deep Ionian Sea

A long optical base line spectrophotometer designed to measure light transmission in deep sea waters is described. The variable optical path length allows measurements without the need for absolute or external calibration. The spectrophotometer uses eight groups of uncollimated light sources emitting in the range 370-530 nm and was deployed at various depths at two locations in the Ionian Sea that are candidate sites for a future underwater neutrino telescope. Light transmission spectra at the two locations are presented and compared.