CTD

CTD is an acronym used in several fields, most notably oceanography and medicine. In oceanography, a CTD refers to an instrument package that measures conductivity, temperature, and depth as a function of depth in the ocean. These measurements are used to derive salinity and to profile other water properties with depth. A typical CTD setup includes sensors for conductivity, temperature, and depth (derived from pressure), and often auxiliary sensors for dissolved oxygen, chlorophyll fluorescence, turbidity, and pH. CTD data are collected during shipboard casts, often from a rosette equipped with Niskin bottles to sample water at discrete depths. The resulting vertical profiles support studies of water mass structure, thermohaline stratification, and ocean circulation, and are essential for calibrating climate and ocean models. Salinity is calculated from conductivity using the practical salinity scale or, for some applications, absolute salinity.

In medicine, CTD can stand for connective tissue disease, a broad category of autoimmune disorders that affect connective tissues such as skin, joints, and organs. Examples include systemic lupus erythematosus, scleroderma (systemic sclerosis), polymyositis, dermatomyositis, and Sjögren syndrome. Symptoms are diverse and may involve fatigue, joint pain, skin changes, Raynaud’s phenomenon, and organ involvement. Diagnosis typically combines clinical assessment with serologic testing for autoantibodies and, when needed, imaging or functional studies. Treatments vary by condition and may include immunosuppressive medications, corticosteroids, and supportive care aimed at reducing inflammation and managing organ-specific complications.