Oceanographic Instruments

Since the invention of boats and the need to recognize the seas, ocean explorers have relied on rustic instruments to measure and observe the ocean. The Vikings used a lead weight with a hollow underside, which was attached to a line . Once the weight collected a sample of the ocean floor, it was brought back to the ship for further examination. Similar instruments, called Baillie sounding machines, were utilized to collect samples from the sea floor, during the Challenger expedition between 1872-1876. Modern oceanographers use a number of sophisticated instruments and research ships to study the oceans.

One of the main pieces of equipment that oceanographers use for the study of the ocean is a platform or research ship. A research ship is equipped with a variety of instruments to measure temperature, water current, turbidity, salinity, tides, waves, Oxygen, pH, and for collecting water samples and sea floor sediments. Other instruments, such as submersibles, remote controlled vehicles and autonomous robots equipped with photographic equipment help oceanographers study the oceans. A research ship offers oceanographers comfortable living and working places, which allow  them to stay in open sea for several months.

Sounding weight

The sounding weight was one of the first instruments used for the exploration of the sea floor. The sounding weight consisted of a tube at the base which absorbed the sea floor sediment when it reached the ocean bottom. More advanced sounding weights were utilized during the Challenger expedition between 1872-1876, although the main objective and function was the same; to explore the sea floor and collect biological samples. Other instruments, such as dredges and scoops were used in the same way to collect biological samples of the seabed.

Water-sampling bottles

To measure the properties, including salinity, and concentrations of dissolved gases such as CO2 and oxygen, of a sample of sea water, different types of plastic and metal bottles are used. Two of these bottles are the Nansen bottle and the Niskin bottle. The sampling bottles are lowered down in a wire down the water column. When water enters the bottles, a messenger, which is a metal weight, slides down the wire, closing the bottles. Several bottles may be attached along the wire at different distance intervals and closed in succession by a messenger released by the next bottle above them. After sample bottles are lifted up, the water samples are drawn for analysis and storage.


A CTD is an essential instrument in oceanography. A CTD is mounted on a metal frame known as a rosette, with Niskin sampling bottles added to it. The CTD instrument is lowered down into the ocean water by a wire to predetermined depths, and is connected to a computer on board the ship by a conducting cable, allowing instant data visualization on a screen. The instrument contains a number of sensors to measure salinity, which is derived from electrical conductivity, temperature and depth, derived from the recording of pressure. A CTD may include other sensors attached to it, such as those to measure dissolved gases, pH and chlorophyll.

Van Veen Gran Sampler

The Van Veen Grab Sampler is a small instrument to gather sediment samples from the ocean floor. This instrument has two levers with shovel-like mechanisms at their ends. The shovel-like mechanism functions as a pair of scissors. The levers remain locked while descending to the sea bottom and unlocked upon reaching the sea floor, grabbing a sample from the deep ocean. This type of sampler is not suitable to sample living organisms, since its contents are usually washed out off the shovels before reaching the ocean surface.

Ocean currents

The simplest and most used method to measure ocean currents prior to the advent of modern technology was the Lagrangian current indicator. A Lagrangian current indicator is simply an object which can be carried by an ocean current, thus giving a measure of its distance travelled and the time covered in that distance. Glass bottles were used for this purpose at the beginning of the 19th century. Modern measurements of the ocean’s currents are made by using drifting buoys with radio transmitters attached for satellite tracking. Some drifting buoys are designed to float under the water surface, thus avoiding the friction of the wind and giving more accurate measurements of the ocean currents.

Tide gauges

One of the most important measuring instruments for operations on the coast, such as ports and city harbours is the tide gauge. Most tide gauges consist of a float that is connected to a pipe that has a counter weight on the opposite side of a shaft. The shaft rotates everytime the sea level rises or lowers. The tide gauge measuring system includes additional mechanisms to measure variations in land. In the past, sea level used to be measured by installing a graded stick on the sea floor, allowing the reading of sea level by eye.

Snow Catcher  

The snow catcher is a big bottle similar to a Niskin bottle that collects sample particles, know as marine snow, falling from the upper to the bottom of the ocean. The snow catcher is lowered to a predetermined depth by using a wire attached to it. Once at the given depth, the end caps get closed, and the water brought back to deck. On the ship’s deck, the snow catcher is left in an upright position to allow the marine samples to sit to the bottom. After the set time, the samples are taken out and analysed for classification in the ship’s laboratories.

The gravity corer

The gravity corer is a more up to date version of the sounding weight. The gravity corer consists of an open-ended tube with a weight. A mechanism releases the gravity corer into the ground, penetrating to a depth of more than 10 meters (33 ft.) into the seabed. When the gravity corer is lifted, a cylindrical sample of the sea floor is extracted. The collection of the deep ocean’s sediment cores permit scientist to examine fossils that may indicate global climate patterns in the past. A corer mounted on a drill , as the one in the vessel Joides Resolution, which is designed to extract core samples from depths of 1,500 meters (4900 ft.) below the sea floor.


Since the 1950’s echo-sounding instruments, such as a sonar, have been used to map the ocean floor. A sonar is used principally to determine the depth of the ocean floor by using an acoustic echo. Through this technique, a pulse of sound is sent from the ship; the sound pulse touches the bottom of the ocean and returns back to the place of origin on the ship. The time interval, from the time the sound pulse is sent to the time when it returns to the ship, indicates the ocean’s depth. This type of instrumentation has allowed oceanographers to map much of the ocean floor, revealing its depth and physical features.

Secchi disk

The secchi disk is an instrument for measuring the clarity of the ocean water. A secchi disk consists of a white plate of about 30 cm (11 inches) in diameter with a lead weight suspended under the disk. The secchi disk is lowered into the ocean water, always keeping an eye on it from on board. The secchi disk will get lost from sight at a determined depth. When this occurs, the depth is recorded, thus giving scientists the clarity of the water. The longer the depth at which the disk is lost from sight, the greater the clarity of the ocean water.

Submersible vehicles

The exploration of the deep ocean sometimes requires manned or unmanned vehicles known as submersibles. A submersible allows scientists to reach depths that would otherwise not be attained by divers. in 1930 a submersible vehicle known as the Bathysphere allowed scientists to reach a depth of 435 meters (1425 ft.). Subsequent submersions allowed it to reach higher depths. The Bathyscape, which was invented in 1948 allowed August Piccard, a Swiss Scientist, to try several dives at various depths; finally in 1960, the Bathyscape was able to reach the deepest dive in a submersible. Onboard the Bathyscape were Jacques Piccard and Donald Walsh, who reached a depth of 10,915 meters (35,810 ft.). Modern submersibles often have High resolution TV cameras, lights, computers thermometers, seismographs and robotic arms attached to them.

Scuba tank

Aqua-lung, also called scuba tank, is a tank containing compressed air. The scuba tank is strapped to a diver’s back and a mouthpiece, called a regulator lets the diver breath air from the tank. The mouthpiece is connected to the tank by a hose. Unlike earlier diving devices, the scuba tank allows greater mobility and longer spans of time underwater. The deepest to where a scuba diver can dive is approximately 135 meters (443 ft.) due to the increased water pressure; however, in 1979, Dr. Sylvia Earle set a record for the deepest dive, wearing a special diving suit connected by a cable to a ship, at 380 meters (1247ft.) off the coast of Hawaii.


Robots are being used by oceanographers in the exploration of the oceans. A robot does not carry people on board and it is equipped with cameras, sensors and lights, all of which are controlled by computers. A robot is connected to a surface ship through a series of cables. Other vehicles, such as remotely operated vehicles (ROV) are being used extensively in underwater exploration. Another robotic technology are the Autonomous Underwater Vehicles (AUVs), which are programmed and receive instructions from a ship above in the ocean surface.

Nutrient and chemical analysers

Many other properties of water, including nitrite, phosphate, silicic acid and ammonium, are measured by using small samples of water drawn from sampling Niskin bottles in a rosette. After a removing residue from other analysis, samples are analysed with chemical reagents. The process produces a colored compound that results from the light absorption in proportion to the nutrient concentration of the sample being analysed.

An increased interest in the oceans and the need for more acurate oceanographic instrumentation for measuring, sampling and collecting biological and chemical samples, has given rise to the development of more advanced innstruments in oceanography. Oceanographic data is stored in the data centers of most countries, and the primary international data centers for oceanography are located in the United States, China and Russia. According to CSIR National Institute of Oceanography, during the last 25 years there has been a significant improvement in the hability to study the oceans and sensors that are stationed in satellites have provided important information regarding the surface properties of the ocean.