Some field-data examples are in Figures and . These results are not surprising. A dominant local plane is removed, and noise or the second-from-strongest local plane is left. 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 on paper (which has a lesser dynamic range than video), I recolored the white residual with a short triangle filter on the time axis.
The residual in Figure 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.