Could you give a good reference to understand the Freeman-Durden classification?

I am particulary interest in detect double bounce

This is the original publication of the approach:

Chapter 6.4 Model-based Decompositions of this book explains it as well, but some background on matrices and scattering mechanisms (dihedral bodies) is required. But it directly refers to the derivation of double-bounce.

I’d personally rather search the web for some PDF slides.

The SAR EDU page is good as well: