  Bi-periodic patterns of waves that propagate in the x direction with
amplitude variation in the y direction are generated in a laboratory. The
amplitude variation in the y direction is studied within the framework of the
vector (vNLSE) and scalar (sNLSE) nonlinear Schrodinger equations using the
uniform-amplitude, Stokes-like solution of the vNLSE and the Jacobi elliptic
sine function solution of the sNLSE. The wavetrains are generated using the
Stokes-like solution of vNLSE; however, a comparison of both predictions shows
that while they both do a reasonably good job of predicting the observed
amplitude variation in y, the comparison with the elliptic function solution of
the sNLSE has significantly less error. Additionally, for agreement with the
vNLSE solution, a third harmonic in y term from a Stokes-type expansion of
interacting, symmetric wavetrains must be included. There is no evidence of
instability growth in the x-direction, consistent with the work of Segur and
colleagues, who showed that dissipation stabilizes the modulational
instability. There is some extra amplitude variation in y, which is examined
via a qualitative stability calculation that allows symmetry breaking in that
direction.
