A method of determining deformation in a structure around which a sensing optical fiber is helically wound, includes performing a distributed measurement at a point along the fiber, to obtain a frequency gain spectrum at that point. Performing a distributed measurement includes, adjusting a pulse width of a pulse pump signal to achieve a predefined spatial resolution and providing the pulse pump signal with adjusted pulse width in the fiber to generate scattering, which is used to obtain the frequency gain spectrum. Identifying at least two curves which, when added together, best fit the frequency gain spectrum. Identifying the frequency at which peaks of the curves occur. Determining deformation in the structure by determining deformation in the fiber at the point using a frequency at which a peak of an identified curve occurs. The amount of deformation in the fiber corresponds to the amount of deformation in the structure.