Recovery of Boundaries and Types for Multiple Obstacles from the Far-field Pattern

We consider an inverse scattering problem for multiple obstacles $D=\cup_{j=1}^ND_j\subset {R}^3$ with different types of boundary of $D_j$. By constructing an indicator function from the far-field pattern of scattered wave, we can firstly determine the boundary location for all obstacles, then identify the boundary type for each obstacle, as well as the boundary impedance in case of Robin-type obstacles. The reconstruction procedures for these identifications are also given. Comparing with the existing probing method which is applied to identify one obstacle in generally, we should analyze the behavior of both the imaginary part and the real part of the indicator function so that we can identify the type of multiple obstacles