physical distance.

As is shown in the bottom-right panel of Figure \[fig:f2\], there are three peaks at $\phi = -1, 0$ and $7~{\rm rad/m^2}$ in the FDF, similar to the previous case in Figure \[fig:f1\]. However, the main peak at $\phi = 0~{\rm rad/m^2}$ is attributed to the emissions in the halo with $z<0$ (see the bottom-left panel), rather than the mid plane at $z\sim 0$. The emissions in the mid plane and in the halo with $z>0$ appear in the FDF at $\phi = -1$ and $7~{\rm rad/m^2}$, respectively. Therefore, the order of peak locations is inverted in the FDF compared with that in physical space, because of the non-monotonicity of the Faraday depth. Moreover, peak amplitudes of the FDF does not straightforwardly suggest the origin of the emissions (mid-plane or halo), due to their degeneracies in a certain Faraday depth.

Figure \[fig:f3\] shows a case with an Faraday depth which is far from monotonic. It is seen that the FDF is limited to a region with small values of $|\phi|$ compared with the previous two cases. This is because the Faraday depth behaves like random-walk and does not reach large values. The relation between $\phi$ and $z$ is 