Let's talk: CTD Carousels! A CTD Carousel, also known as a CTD-rosette, is the primary tool for characterizing physical and chemical properties of sea water. The letters in the acronym 'CTD' stand for Conductivity, Temperature, and Depth, all of which are measured in real time. You will find this tool on nearly every cruise that takes place on FIO's research vessels. Once in the water, scientists are able to collect data at specific depths, allowing them to create a comprehensive water column pr