Re: OT: Sensor array correlation matrix - some questions

On 16 Jul, 05:14, Jerry Avins <j...@xxxxxxxx> wrote:
Rune Allnor wrote:

   ...

I don't know the operational constraints of EM vector sensors, but
I can almost guarantee that free-space EM propagation, even with a
couple of multiple paths, is all but trivial compared to even
idealized acoustic propagation scenarios.

Is that true in a homogeneous medium free of reflections?

In an infinite homogeneous space there can exist two types
of acoustic waves, P waves and S waves. These exist and
propagate independently of each other, and only interact
at reflections, when acoustic energy is converted from one
to the other.

The difference between the P waves and S waves is how the
acoustic energy interacts with the medium. P waves tend to
move the mass in line with the propagation direction, so
if the P wave propagates in the x direction the particle
movement will be along the x axis. S waves, on the other
hand, tend to move the particles transversal to the
direction of propagation. An S wave propagating in the x
direction will cause particle movement in the (y,z) plane,
the exact details depending on the polarization.

With one vector sensor one can not see the difference between
a P wave and an S wave. If you see particle movement along,
say, the y axis, this may be caused by either a P wave
travelling in the y direction or an S ave travelling in
the (x,z) plane.

This discussion above is valid in an infinite homodeneous
space.

Then introduce *one* reflecting surface, and things get
really messy as the presence of the surface means there
are both upgoing and downgoing P waves as well as S waves,
P waves are reflected as both P and S waves (and vice
versa), not to mention that other types of waves might
exist near the surface.

It's a real mess.

Rune
.

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