Some field data examples are in Figures 4 and 5. These results are not surprising. A dominent local plane is removed, leaving noise or the second from strongest local plane. These data sets fit the local plane model so well that subtracting the residual noise from the data made little improvement. These Figures are clearer on a video screen. To facilitate examination of the residual on Figure 4 on paper, I recolored the white residual with a short triangle filter on the time axis.
The residual in Figure 5 is large at the dead trace and wherever the data contains crossing events. Also, closer examination showed that the strong residual trace near 1.1 km offset is apparently slightly time shifted, almost certainly a cable problem, perhaps resulting from a combination of the stepout and a few dead pickups. Overall, the local-plane-residual shows a low frequency water velocity wave seeming to originate from the ship.