# What is the use of HV or VH polarization in Radar?

Radar is a common tool in remote sensing, it is a so-called active instrument, hence it emits and receives energy. Modern Syntethic Aperture Radar (SAR) systems are capable of both transmitting and receiving polarized waves. The most common polarizations are horizontal $$(H)$$ and vertical $$(V)$$ polarization, although other ones exist. Using H and V leads to 4 possible combinations of emitting and receiving signals:

$$HH, VV, HV, VH,$$

which is read as transmitted first, received later (i.e. $$HV$$ means transmitting horizontally polarized waves and receiving only vertical polarized waves).

I can relatively easily imagine the use of the $$HH$$ and $$VV$$ copolarized waves. They should be easier reflected by object that have a longish geometric structure. Large $$VV$$ and small $$HH$$ would probably indicate tower-like structures and small $$VV$$ and large $$HH$$ should indicate bridge-like structures.

However it is not obvious to me what structure would reflect a cross-polarized wave $$HV$$ or $$VH$$ stronger than $$HH$$ or $$VV$$? Furthermore, what is the difference between an object that reflects $$VH$$ and an object that reflects $$HV$$?

• cool question!! – uhoh Mar 10 at 13:19
• @uhoh thank you, i think its not that obvious! My collaborator seemed to use it in a very empirical fasion (ie trial and error of all possibilities) and couldnt give an intuition. I even checked a remote sensing textbook and it did not answer the question, despite mentioning the existence of the HV and VH polarizations.... – ckrk Mar 10 at 16:17