# Behaviour of Magnetic Fields Underwater

• I
• sjr
In summary: The ocean is a very large body of water and its physical characteristics can have a big impact on the way magnetic fields behave. There are a lot of factors that can play into this, like the presence of currents, the salt content of the water, and so on.The decay rate of a magnetic field depends on a lot of different things, like the material it's located in, the shape of the field, the orientation of the field, and the magnetic field's strength.There are two main types of propagation in magnetic fields: longitudinal and transverse. Longitudinal propagation is the waves that move along the direction of the field, and transverse propagation is the waves that move perpendicular to the direction of the field.
sjr
TL;DR Summary
Expected decay rate and speed of magnetic field changes underwater.
I've been trying to pick up the fundamentals of electromagnetic theory and I reckon I'm doing alright, but I've run into a some questions about how magnetic fields behave in an anisotropic fluid medium like the ocean. There is an awful lot of conflicting information online. Ultimately, I'd like to be able to detect magnetic field anomalies at a range of up to 100m under the water as accurately as possible.

A couple of questions:

1. The rate at which the strength of a magnetic field decays with distance remains somewhat unclear to me. I understand there are near field and far field implications, and in general the field strength will decay at a cubic rate. Can someone offer me a clear explanation of the expected rate of magnetic field decay with distance in a medium like the ocean, and how it's affected by conductivity, permittivity and permeability, and so on? This part I haven't figured out yet.

2. The 'propagation' of magnetic field changes in the ocean. Consider a basic problem. A point source ##O## lies in the ocean and directly ahead of it there is a sensor ##A## a range ##r##. We then activate a magnetic field at ##O##. Assuming it is capable of doing so, how long will it take the sensor ##A## to detect a resultant change or 'front' in its vicinity? I'm consistently reading very different answers to this question.

If you could offer me any guidance on this I'd really appreciate it :)

Welcome to PF.

sjr said:
I've been trying to pick up the fundamentals of electromagnetic theory and I reckon I'm doing alright, but I've run into a some questions about how magnetic fields behave in an anisotropic fluid medium like the ocean.
Why do you say that you think that conductive seawater is anisotropic with respect to magnetic fields? And are you expecting a strong interaction, or a weak interaction?

https://svs.gsfc.nasa.gov/12450

I should have worded that line differently, I wasn't specifically referring to magnetism.

I'm interested in how physical characteristics of seawater may cause magnetic fields to behave slightly differently in the ocean than they would in free space. I'm not making any assumptions at all right now, I'm just trying to make sense of the all the conflicting stuff I'm reading.

## 1. How do magnetic fields behave underwater?

Magnetic fields behave differently underwater compared to in air or on land. The presence of water can affect the strength and direction of the magnetic field, as well as its ability to propagate through the medium.

## 2. Can magnetic fields be detected underwater?

Yes, magnetic fields can be detected underwater using specialized equipment such as magnetometers. These devices can measure the strength and direction of the magnetic field, allowing scientists to study its behavior and changes over time.

## 3. Do magnetic fields underwater have an impact on marine life?

There is ongoing research on the potential effects of magnetic fields on marine life. Some studies suggest that certain marine animals, such as sharks and sea turtles, may use magnetic fields for navigation and orientation. However, more research is needed to fully understand the impact of magnetic fields on marine life.

## 4. How do man-made magnetic fields, such as those from underwater cables, affect the behavior of magnetic fields underwater?

Man-made magnetic fields can have a significant impact on the behavior of magnetic fields underwater. These fields can disrupt natural magnetic fields and affect the behavior of marine animals that rely on them for navigation. Additionally, man-made magnetic fields can interfere with scientific research and equipment that relies on accurate measurements of natural magnetic fields.

## 5. Can the behavior of magnetic fields underwater be predicted?

While scientists have a good understanding of the general behavior of magnetic fields underwater, there are still many factors that can affect their behavior, such as the composition of the water and the presence of man-made magnetic fields. Therefore, it is difficult to predict the exact behavior of magnetic fields in a specific underwater environment without further research and data.

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