Term: Polarization signature

Definition:

A plot of the backscattered power received from specific scatterer as a function of the polarizations of the incident and scattered electromagnetic waves.

Explanation:

The polarizations are described by 4 independent variables, the ellipticity and orientation of the incident wave, and the ellipticity and orientation of the backscattered wave. However, using all four of these variables would result in a response that would be too complicated to draw or to interpret. Therefore, for simplicity, only two variables are used at a time to portray the polarization signatures – the ellipticity and orientation angle of the incident wave. This gives rise to two signatures – the co-pol and cross-pol signatures. In the co-pol case, the polarization of the scattered wave is the same as the polarization of the incident wave, while in the cross-pol case, the polarization of the scattered wave is orthogonal to the polarization of the incident wave.

Note that a backscattered wave can have many different polarizations, for a specific transmitted polarization. However, a receiving antenna is configured to receive only one polarization component of the backscattered wave, e.g. horizontal linear. This does not mean that the orthogonal component of the backscattered wave (e.g. vertical linear) does not exist – it is just not measured by this antenna at this time. For this reason, both the co-pol and the cross-pol signatures should be drawn in order to describe the polarimetric properties of a scatterer.

Polarization signatures of different terrain classes can be used to identify surface scatterers, although polarization signatures are not unique – two types of scatters can have the same polarization signature.

Related Terms:

Co-polarization signature
Cross polarization signature

Graphic 1:

Example of a polarization signature.
P = power
O = orientation angle
E = ellipticity angle