Depths shown on the geospatial profiles and two-way travel (TWT) times shown on the printable profile images are relative to the Chirp towfish position, not to the sea surface. Furthermore, the raising or lowering of the towfish during a survey (to avoid obstacles or follow relief) produces relative shifts in multiple reflections seen in the profile, which can confuse geologic interpretations. Any elevation change of the towfish is recorded in the logbooks and identifiable on the subbottom profiles by steep, abrupt shifts in the seafloor return.