1. An apparatus for measuring a surface of an object, comprising: a measuring unit configured to transmit a measurement signal in a direction towards the object and to determine, based on a reflected signal resulting from the transmitted measurement signal, a plurality of voxels, wherein each voxel comprises a phase and a magnitude of the reflected signal and one or more spatial coordinates, wherein the spatial coordinates comprise a Z-axis, which corresponds to a depth within the object, and an X-axis and a Y-axis, which are disposed perpendicular to the Z-axis and to each other, and wherein the plurality of voxels comprises a plurality of series of voxels along the Z-axis, each series of voxels along the Z-axis having a same X-coordinate and a same Y-coordinate; and a surface-determining unit comprising (a) a magnitude-determining unit configured to determine a voxel of a maximum magnitude for each series of voxels along the Z-axis, (b) a phase-determining unit configured to determine, for each maximum magnitude voxel, phases of at least three voxels comprising the maximum magnitude voxel and voxels that are adjacent thereto, (c) an angle-determining unit configured to determine, for each maximum magnitude voxel, a normal vector based on the respective phases, and (d) a surface-reconstructing unit configured to determine the surface of the object based on the spatial coordinates of the voxels of maximum magnitude and the respective normal vectors.