CTD systems are central tools in oceanography. They measure the conductivity, temperature, and depth of seawater. From these values, salinity, density, and other physical properties can be derived. The data collected are crucial for better understanding ocean currents, climate changes, and marine habitats.
What does CTD actually stand for? CTD stands for Conductivity, Temperature, and Depth. A typical CTD system consists of multiple sensors mounted on a rosette with water sampling bottles (Niskin bottles). The system is lowered into the depth via a cable, continuously transmitting measurement data to a onboard computer. During the ascent, targeted water samples are collected from various depths. Depending on the depth, a measurement cruise lasts between two and five hours.
Besides ship-based systems, compact CTD sensors are used on autonomous platforms. These operate independently and are utilized for long-term observations:
Water Column Profilers perform repeated vertical measurements and are often equipped with additional instruments such as acoustic current meters (ACM).
Spray Gliders move along preprogrammed routes through the sea and regularly transmit their data.
Floats (e.g., Argo) record temperature and salinity profiles and passively follow ocean currents.
Autonomous Underwater Vehicles (AUVs) navigate independently through the ocean and can be used for complex missions.
CTDs can be combined with additional measurement technology. This includes oxygen sensors, ADCPs for current measurement, or Niskin bottles for chemical analysis of water samples.
Unlike ship-based CTDs, autonomous systems do not provide water samples for calibration. Therefore, the long-term stability of sensors is especially important. In greater depths where water properties remain constant for long periods, the measurement data can be compared with historical reference values.
STS offers reliable pressure sensors for use in CTD systems. They are designed for high measurement depths, corrosion-resistant, and highly energy-efficient—ideal for long-term use on autonomous platforms.
Advantages:
High measurement accuracy with low power consumption
Robust, saltwater-resistant materials
Compact design for use in mobile systems
Stable performance over long deployment periods