For non-plane wave beamforming (matched field processing), the replicas are read from an external file, and in this case this block serves only as a consistency check. The sampling in the three coordinate directions must be identical to that used for OASN in computing the replicas. Note the the depths zshould be specified in meters whereas the ranges x and y should be specified in kilometers.
For plane wave beamforming (option W), the first line defines the grazing angle interval and number of sampling points. Usually this interval ranges from (upward) to (downward). The second line similarly selects the bearing interval and number of samples. The third line is dummy (but must be included) for plane wave beamforming.