Marine Instrumentation

Marine Instrumentation is required for:

Instruments can be used on

Data collection instrument types

To measure hydrographic properties of the sea (temperature, salinity, oxygen, nutrients, currents, etc), instruments are required that can be lowered into the water (to the bottom, if required) to record and take sea-water samples for later analysis in the lab. Typical instruments include:

CTD

What is it and why do we use it?

A CTD stands for Conductivity, Temperature, and Depth (profiler).

Rosette sampler

Some analysis need to be done in the lab, or just to calibrate the CTD readings. For these purposes, samples of sea-water are taken by fixing a rosette sampler to the CTD. Examples can be seen in die previous figures showing the CTD.

The rosette sampler consists of a number of bottles, each with a volume of 5 – 20 litres.

 The samples can be triggered from the vessel at preselected depths.

 When the CTD+ rosette is brought back on deck, samples can be tapped from the bottles (left), and taken to the lab for processing.

ADCP

What is it and why do we use it? An Acoustic Doppler Current Profiler (ADCP). Measures flow speed and direction of water. Can be mounted on a ship or anchored on/close to the sea bed

How does it work?

ADCP Data: The image (below) shows vectors depicting current direction (arrows) and speed (relative length of vector), recorded on the RV Melville. Courtesy of Chief Scientist Dr Lisa Beal (Miami) in a study of the Agulhas Current undertaken during 2003.

XBT

How do they work?

Advantages

Disadvantages

Underway observations

Submerged difters ARGO floats

What are they and why do we use them?

Global distribution of Argo floats:

“Argo is a global array of 3,000 free-drifting profiling floats that measures the temperature and salinity of the upper 2000 m of the ocean. This allows, for the first time, continuous monitoring of the temperature, salinity, and velocity of the upper ocean, with all data being relayed and made publicly available within hours after collection.” To learn how to access this data visit http://www.argo.ucsd.edu/Argo_.


The most recent picture of the Argo array.

Surface drifters

The Global Drifter Program

Satellite-tracked surface drifting buoy observations of currents, sea surface temperature, atmospheric pressure, winds and salinity.


Image: http://www.aoml.noaa.gov/phod/dac/gdp.html

Moorings

Although the mooring instruments can capture a time series of the temperature, salinity, nutrients, oxygen, etc, the limited spatial coverage is compensated by deploying a number of moorings (referred to as an array).

Extensive arrays have been deployed as part of large climate-related programmes to study El Nino, such as TOGA (Tropical Ocean Global Atmosphere (see large number of moorings along the equator in the Pacific Ocean ). Such programmes require an enormous investment in terms of equipment, ships’ time, operational expenses and manpower.

Most of the arrays deployed by organisations in Southern Africa are in depths of a few hundred metres on the shelf. Some deep arrays in this region have been deployed by overseas research organisations.