Does a material change the direction of polarization of light?

[Shadi Abdelhadi]

The polarization referes to the direction of the electric field of a light wave which is to be one direction. The unpolarized light interacts with a material in various ways such as reflection, scattering, refraction. and each of which can transform an unpolarized light into a vertically or horizontally polarized light with respect to the plane of the material. In co-polarization SAR images, there are certain features that appear VV vertically sent and vertically received images , and other features only appear in HH horizontally sent horizontally received images. Then why the need for cross-polarization systems VH, HV. How can a radar antenna that is adjusted to a vertical polarization axis receive hortizontally polarized reflected echos? How is it even possible for the direction of the electric field to change 45 degrees upon interaction with a certain material

 

[berkeman]

How is it even possible for the direction of the electric field to change 45 degrees upon interaction with a certain material

Take a simple example with dipole antennas and a simple wire reflector. Transmit a vertically polarized signal with the vertical dipole, and that EM wave encounters a wire reflector that is set at 45 degrees. That EM excites a current in the wire (less than if it were vertically oriented, but still a substantial current), which then causes EM radiation at that 45 degree angle. So yes, vertically polarized EM radiation can get rotated as part of being reflected -- it happens all the time.

 

[Andy Resnick]

Summary:: The cross-polarization principle of SAR imaging says there's an option to transmit vertically polarized echos and receive horizontally polarized echos or vice versa. Is it possible that vertically polarized light can be reflected horizontally polarized

Interesting question- I am familiar with this kind of analysis in radar/millimeter wave applications, but I think it's possible in general by considering s- and p-polarization states, which is set by the orientation of a surface relative to the direction of propagation. I tried to envision a Brewster window doing this but couldn't quite figure it out.

More generally, if the surface is rough and depolarizes incident light (or if a bulk media is turbid and scatters light), cross-polarization measurements can quantify how much depolarization is happening. The references I found online point to wind speed measurements as another application.

 

[Shadi Abdelhadi]

So if the surface is non-uniform, may depolarization occur? Or may the electric field of the incident light beam rotate 45 degrees upon interaction with the material based on its degree of roughness. Also, through the cross-polarization state, can we indicate the roughness width, height or the lay direction relative to the polarization direction of the reflected beam. I appreciate your interest.

 

[Andy Resnick]

So if the surface is non-uniform, may depolarization occur? Or may the electric field of the incident light beam rotate 45 degrees upon interaction with the material based on its degree of roughness. Also, through the cross-polarization state, can we indicate the roughness width, height or the lay direction relative to the polarization direction of the reflected beam. I appreciate your interest.

There's an enormous amount of literature on this subject going back to the 1960's:

@article{bahar1987review,
title={Review of the full wave solutions for rough surface scattering and depolarization: Comparisons with geometric and physical optics, perturbation, and two-scale hybrid solutions},
author={Bahar, Ezekiel},
journal={Journal of Geophysical Research: Oceans},
volume={92},
number={C5},
pages={5209--5224},
year={1987},
publisher={Wiley Online Library}
}

@article{khenchaf2001bistatic,
title={Bistatic scattering and depolarization by randomly rough surfaces: application to the natural rough surfaces in X-band},
author={Khenchaf, Ali},
journal={Waves in random media},
volume={11},
number={2},
pages={61--90},
year={2001},
publisher={Taylor \& Francis}
}

@article{campbell1996lava,
title={Lava flow surface roughness and depolarized radar scattering},
author={Campbell, Bruce A and Shepard, Michael K},
journal={Journal of Geophysical Research: Planets},
volume={101},
number={E8},
pages={18941--18951},
year={1996},
publisher={Wiley Online Library}
}

etc etc etc

 

[Shadi Abdelhadi]

Take a simple example with dipole antennas and a simple wire reflector. Transmit a vertically polarized signal with the vertical dipole, and that EM wave encounters a wire reflector that is set at 45 degrees. That EM excites a current in the wire (less than if it were vertically oriented, but still a substantial current), which then causes EM radiation at that 45 degree angle. So yes, vertically polarized EM radiation can get rotated as part of being reflected -- it happens all the time.

Does the rotation of the electric field polarization give any clues about the nature of the reflecting material?

 

[berkeman]

Does the rotation of the electric field polarization give any clues about the nature of the reflecting material?

What do you mean by "nature"? I suppose it might tell you a bit about how conductive the material is that the EM is getting reflected off of, but there are so many other things that affect the reflection (like size of the reflector, shape, roughness, etc.) that it would be hard to single any particular thing out.

 

[Shadi Abdelhadi]

Well, to be more specific, i study the Radar microwaves and their interactions with rocks, if the type of rock is known by other means, what should the reflected signals, having a different polarization state from the incident signal, indicate about the substrate in terms of roughness or geometry?