Abstract: A contour mapping system including compensation for the heave or vertical displacement of a ship due to wave and swell effects, and for correcting errors due to such effects in depth or bottom contour measurements of a body of water. Vertical acceleration A(s) of the ship, measured by a gravity meter accelerometer, is filtered according to the following Laplace transform equation by a cascaded series of filters to yield ship vertical displacement .DELTA.D(s) due solely to heave: ##EQU1## WHERE: .tau..sub.G = GRAVITY METER FILTER BREAKPOINT.omega..sub.f = filter transfer function breakpoint frequency.zeta. = filter transfer function damping constant.tau..sub.f = filter transfer function cut-off breakpointThis series of filters accomplishes attenuation of noise, such as is caused by gravity, vertical coriolis, vertical vibration or electrical noise, in the acceleration signal, and double integration of the remaining acceleration signal.