Computational systems and methods to be carried out by the computational systems for determining streamer-depth bias during exploration-seismology experiments are disclosed. An exploration-seismology vessel tows a number of streamers that form a smoothly varying data acquisition surface located beneath a fluid surface. In one aspect of this disclosure, the method determines a set of image points that represent a profile of the fluid surface above each streamer. The image points are determined based on pressure and velocity wavefields measured at dual sensors of the streamer. The method then determines an elevation parameter of the image points that minimizes DC offset in a spectral domain of the image points. The elevation parameter corresponds to the streamer-depth bias and can be used to correct for the streamer-depth bias in subsequent calculations of a fluid-surface profile.