The magnetometer measures magnetic induction (magnetic field intensity), during an ocean exploration. It is used to survey the seafloor’s geological features but also to detect the presence of ferro magnetic material due to shipwrecks and disposed contaminants.

What are magnetometers

A magnetometer is a scientific instrument used for measuring the strength of magnetic fields. For example, the device can be used to find variations in the magnetic field of the ocean floor.

Higher magnetization levels are caused by the presence of ferrous (unoxidized) iron on the seafloor, either from a shipwrecked boat made of steel or a volcanic rock containing grains of magnetite. The remains of a wooden ship can sometimes also be detected. This because of objects made of iron or ballast stones containing magnetite.

Scientists can also use the total magnetic field measurements to estimate the age and thickness of volcanic lava flow at mid-ocean ridges and ocean island hot spots, locate pipelines, undersea cables and bridge foundations.

How do magnetometers work

The Earth’s magnetic field is generated by the electric currents of iron and nickel at its core and the strength of this field can be measured by magnetometers using various methods and types of sensors. During a survey the magnetometer is towed behind the research vessel or mounted on a submersible or ROV.

The magnetometer samples the field strength at a rate that can vary a bit depending on application. Often a sample rate of one to ten reading per second is used. The field strength of the background level can vary but the presence of something ferrous (containing iron), like a ship hull fragment, an anchor, or a geological formation of basalt will create a significant change that can easily be detected.

Illustration of a Magnetometer Survey. Credit: Wessex Archaeology

What happens next?

Magnetometer data is collected with corresponding latitude/longitude position data from a GPS and processed to create a map of the local variations in the magnetic field. To determine the cause of the detected anomality a classification is required. This can be done by divers or other complementary methods.

Why is it important?

A magnetometer is an excellent tool to search and map the location of contaminations where there are an iron-oxide component present. Especially when larges areas have to be surveyed and other methods like soil sampling would be too tedious and cost ineffective.

About the images
RWMT work with nation states, government agencies and institutions on sensitive and often classified operations. Also, the tools we use are constantly being evaluated and changes depending on the nature of the operation. Because of this, we have sometimes chosen to show example images of the tools we use, rather than images from actual projects.

Used for

Detecting variations in the Earth’s magnetic field

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