Apparatus, systems and methods for calculating position of marine seismic acoustic receivers, and for estimating sound velocity profile of a fluid, are disclosed. One position calculation system includes a vessel, two or more vessel hull-mounted transmitters, a plurality of acoustic receivers on a cable being deployed from the vessel into the fluid, and a calculation unit. The calculation unit may be adapted to calculate position of the receivers, and may be used in calculating the sound velocity profile in the fluid and correcting raw seismic data. It is emphasized that this abstract is provided to comply with the rules requiring an abstract, which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. 37 CFR 1.72(b).