  This work is concerned with an inverse scattering problem of determining
unknown scatterers from time-dependent acoustic measurements. A novel
time-domain direct sampling method is developed to efficiently determine both
the locations and shapes of inhomogeneous media. In particular, our approach is
very easy to implement since only cheap space-time integrations are involved in
the evaluation of the imaging functionals. Based on the Fourier-Laplace
transform, we establish an inherent connection between the time-domain and
frequency-domain direct sampling method. Moreover, rigorous theoretical
justifications and numerical experiments are provided to verify the validity
and feasibility of the proposed method.
