1. A computer-implemented method of discriminating a subsurface from a surface sound-generating target in the water, comprising: receiving sound generated by the sound-generating target with a sound receiver at a known depth in the water; identifying an arrival angle of the sound generated by the sound-generating target; generating a probability density function about the measured arrival angle having a corresponding plurality of sound arrival angles; mapping the probability density function about the measured arrival angle to a probability density function of vertex depths; and calculating a probability that the depth of the sound-generating target is greater than a threshold depth by integrating the probability density function of vertex depths, wherein the identifying the generating the mapping, and the calculating are performed by one or more processors.