Oceanography is the multidisciplinary study of the world’s oceans, encompassing the physical properties of seawater, the geology of the seafloor, and the biology of marine ecosystems. This field seeks to understand the complex processes that govern the ocean, which covers over 70% of the planet’s surface. Understanding ocean dynamics is important for predicting long-term climate patterns and supporting sustainable management of marine life. Oceanographers rely on specialized instruments and advanced platforms to acquire data across vast distances and extreme depths.
Measuring the Water Column
Direct measurement of the ocean’s properties is accomplished using instruments lowered from a research vessel to gather in situ data throughout the water column. The foundational tool for this work is the Conductivity, Temperature, and Depth (CTD) sensor. This device measures the electrical conductivity of seawater, its temperature, and the pressure, which is used to calculate depth. The measured conductivity is mathematically converted into salinity, providing scientists with the three fundamental physical properties needed to define water masses and track ocean currents.
The CTD sensor is typically integrated into a larger framework called a rosette sampler. This framework holds multiple specialized containers, known as Niskin bottles, arranged in a circular array. As the rosette is lowered, a wire transmits real-time data back to the ship, allowing operators to identify specific depths of interest. At these precise locations, a remote electronic command triggers the Niskin bottles to snap shut, capturing an isolated water sample for later chemical and biological analysis.
The rosette array often carries other electronic sensors to expand the range of measurements beyond physical properties. Optical sensors are frequently included to measure the concentration of dissolved oxygen, which gauges biological activity and habitat health. Other instruments measure chemical parameters, such as the water’s pH level and the concentrations of nutrients like nitrates and phosphates. These combined measurements provide a detailed vertical profile of the water, offering a comprehensive look at the ocean’s physical and chemical structure.
Mapping the Ocean Floor
Geological oceanography requires technology that can penetrate the water barrier to characterize the shape, or bathymetry, of the seafloor and collect physical samples of the underlying sediment. Acoustic technology, specifically sonar (SOund NAvigation and Ranging), is the primary method for mapping the terrain. Single-beam sonar systems send a single pulse of sound directly downward and measure the time it takes for the echo to return, calculating the depth at that one point.
For efficient, large-scale mapping, oceanographers utilize multibeam sonar systems, which are typically mounted to the ship’s hull. Multibeam sonar sends out a fan-shaped array of sound pulses across a wide swath of the seafloor. By measuring the time delay and angle of return for each beam, the system generates thousands of depth points per second, creating detailed, three-dimensional maps of submarine features.
The strength, or intensity, of the returning sound waves—known as backscatter—also provides information about the seafloor composition, differentiating between hard, rocky surfaces and softer, muddy sediments.
To obtain physical material from the seafloor, scientists deploy specialized coring devices. A gravity corer is a heavy, weighted steel tube that is dropped into the sediment, relying on its mass and momentum to retrieve a long, cylindrical core sample. Box corers are designed to collect large, relatively undisturbed rectangular sections of the seafloor surface. As the box penetrates the sediment, a spade mechanism seals the bottom of the sample, preserving the delicate layers for detailed study of surface processes and benthic life.
Autonomous and Remotely Operated Vehicles
Underwater vehicles allow oceanographers to explore environments too deep or remote for human divers, providing a mobile platform for advanced sensors and cameras. These vehicles are categorized into two distinct types based on their control and operation.
Remotely Operated Vehicles (ROVs)
ROVs are tethered to a ship by a cable that supplies power and transmits real-time data and video back to a surface operator. The tether allows instant control of the vehicle’s movement and manipulators, making ROVs ideal for complex, action-oriented tasks. ROVs frequently carry high-definition cameras for visual surveys and robotic arms used to collect samples or perform maintenance. Their continuous power supply means they can remain deployed for extended periods, limited only by the support vessel.
Autonomous Underwater Vehicles (AUVs)
AUVs are untethered and operate independently according to a pre-programmed mission plan. Before deployment, an AUV is instructed on its survey area, depth, and required data collection. Once submerged, it uses internal navigation systems to follow its path, collecting data on water properties, mapping the seafloor, or capturing imagery. AUVs rely on internal batteries, which restricts their mission time. However, the lack of a cable grants them greater range and flexibility to cover vast distances or survey areas inaccessible to tethered vehicles.
AUVs and ROVs often work in tandem, with an AUV performing a broad survey to identify areas of interest, followed by an ROV dive for detailed investigation. Both vehicle types can be equipped with an array of sensors, including CTDs and high-resolution imaging systems. They are particularly useful for long-term monitoring, such as tracking deep-sea currents or surveying hydrothermal vents over time.
Observing from Space
Satellites offer a unique, global-scale perspective impossible to achieve with localized, ship-based measurements. Remote sensing technology allows for the continuous monitoring of the ocean’s surface properties across the entire planet.
Sea Surface Temperature (SST)
SST is measured using infrared and microwave sensors. Infrared sensors provide high-resolution data but cannot penetrate clouds, while microwave sensors can see through clouds but offer coarser resolution. By combining data from these sensors, scientists generate daily, near-global maps of sea surface thermal patterns. This data is used to track ocean currents, monitor marine heatwaves, and study air-sea energy exchange.
Ocean Color
Satellites measure ocean color, which is an index of the light reflected from the water column. Sensors detect subtle changes in ocean color to estimate the concentration of chlorophyll, a pigment found in phytoplankton. This provides a direct measure of the ocean’s biological productivity, revealing the distribution of microscopic marine plants that form the base of the food web.
Satellite Altimetry
Satellite altimetry measures sea level height with extreme precision. Altimeter satellites emit microwave pulses toward the ocean surface and measure the time it takes for the signal to bounce back. Combining this precise timing with the satellite’s orbital position allows scientists to calculate the absolute height of the sea surface. This data is used to monitor long-term global sea level rise, track large-scale ocean circulation patterns, and observe surface wave behavior.