CTD, or Conductivity-Temperature-Depth, is an oceanographic instrument used to measure the physical properties of seawater. It collects data on the conductivity, temperature, and depth of the water, which helps scientists understand ocean dynamics, including salinity and density variations. This information is crucial for studying marine ecosystems and climate change. The CTD device is typically deployed from research vessels and can be lowered to various depths in the ocean. It often includes additional sensors to measure parameters like dissolved oxygen and chlorophyll, providing a comprehensive view of the underwater environment and its health.