Second captain Lambros Katsenis navigates the research vessel (R/V) Aegaeo. Navigation is an important part of deep-sea science. The R/V Aegaeo is equipped with a satellite-based differential global positioning system (DGPS) that determines its location on Earth. GPS does not work underwater so scientists and technicians must use other methods to determine underwater location. Image courtesy of Project PHAEDRA 2006, WHOI, HCMR, Thera Foundation, NOAA.