Hi all.

Any clues on where to find figures for magnetic field attenuation trough seawater ?

As at different depths/temperatures/paths, will a compass become less sensitive to earth magnetic field ?

"Any clues on where to find figures for magnetic field attenuation trough seawater ?"

Yes, the biggest clue is that you can't find a figure/ table for it.

Can you think of a reason for that?

 

The next question might well be: what do they make submarine hulls from?

That's not how magnetic fields work. They don't attenuate as they pass through a material - they go from one pole of a magnet to the other. The field in a medium will be modified by the value of the permeability.

A permanent magnetic field, for instance Earth's one, is not attenuated by seawater. You can use the compass.

 

An AC magnetic field is attenuated. At rather low frequency, when the distance is well under a wavelength, the attenuation depends on water's conductivity, hence on salinity mainly. If the distance clearly exceeds a wavelength, no pure magnetic field exists, but rather an electromagnetic field, for which the attenuation of E and B is measured and follows an exp(). Consider a few cm for exp(-1) at 1GHz, varying as sqrt(F) more or less.

 

Radiocomm with submarines is done at very low frequency like 10kHz, with huge antennas from an aeroplane in the vicinity.

I'd be interested in seeing a compass that can follow a 1GHz magnetic field.

I'd be interested in seeing a compass that can follow a 1GHz magnetic field.

 

 

That would surely be interesting, but Enthalpy has not suggested one exists. The earth's field is DC and he was discussing an EM wave at 1 GHz.