“…In [16], one numerical method is proposed to determine both ∂D and the impedance σ(x). In [1], the authors gave a uniqueness and reconstruction formula for identifying ∂D and the impedance for a Robin-type obstacle from the far-field pattern, by applying the probe method introduced by M. Ikehata (see [10], [11], [12], [13] and [14] for example). Moreover, it has also been noticed that the probe method, the singular sources method given in [23], as well as the factorization method [15], can be applied to determine the boundaries of multiple obstacles if their boundary types are the same (sound-soft or sound-hard).…”