True-amplitude migration is a new development of Kirchhoff-type migration. By using a proper weighting function, called true-amplitude weighting function, in the modified diffraction-stack operator, one can obtain a reconstructed source pulse proportional to the reflection coefficient of the target reflector. According to Schleicher et al. (1993), the true-amplitude weighting function is complex and consists of two parts. One part is the module of the complex weighting function, given by means of a 2 × 2 ray transformation submatrix called . The other is the phase factor of the complex weighting function, determined by the number of ray-branch caustics. Thus, to obtain the true-amplitude weighting function, one should compute the matrix as well as the number of ray-branch caustics.