1. A fiber optic sensing device comprising: an optical fiber including at least two fiber cores spaced apart so that mode coupling between the fiber cores is reduced; wherein each fiber core has an associated Rayleigh scatter signature and different segments of each fiber core correspond to a portion of the associated Rayleigh scatter signature; a frequency domain reflectometer coupled to the optical fiber configured to obtain a Rayleigh scatter pattern associated with each of multiple fiber segments from each core; and a computing device configured to determine a spectral shift of the Rayleigh scatter pattern associated with each of multiple fiber segments from each core and to use the determined spectral shift for the Rayleigh scatter pattern associated with each of multiple fiber segments from each core in determining a strain parameter for each of the multiple fiber segments from each core and in determining a position and/or shape of a portion of the fiber based on the determined strain parameters.