(a) Magnitude of the depth-dependent Green’s function at a depth of 40 m at 112 Hz; (b) transmission loss at a depth of 40 m at 112 Hz; (c) magnitude of the depth-dependent Green’s function at a depth of 40 m at 118 Hz; (d) transmission loss at a depth of 40 m at 118 Hz. In panels (a) and (c), the red dashed lines indicate bottom wavenumbers. In panels (b) and (d), the blue solid curves, the red dashed curves, and the green dash-dotted curves are results by KRAKEN with an homogeneous halfspace, DGMCM with an artificial pressure-release lower boundary, and the present method, respectively.