In Distributed Acoustic Sensing (DAS), a fiber-optic cable is used as a distributed seismic sensor, with channels representing successive short sections of the fiber, spaced at defined intervals along the 1D fiber axis. Typically, the positions of these channel are assumed to be known and to coincide with the cable´s position. In reality, a fiber-optic cable contains many fibers that are not perfectly straight and are thus longer than the cable itself. Additionally, the cable may feature some degree of curvature even though it was deployed with the intention of a straight line. Consequently, the real channel spacing differs from the theoretical one and may vary alongside the cable axis. On land usually a tap test is carried out before the start of the DAS acquisition to determine the exact channel locations. DAS with marine horizontal cables has recently been used for various offshore applications including seismic imaging. To avoid errors in the seismic image, a precise receiver location is required. For many marine fiber optic cables, the position is known to some extent but may be subject to inaccuracies. In this paper, we propose a traveltime-based inversion workflow to determine a more accurate fiber position on the seafloor. Moreover, we show that we can resolve an unknown time shift, between the acquisition and the recording system, in addition to the fiber position.