An instrument system that includes an elongate body, an optical fiber, and a controller is provided. The optical fiber is operatively coupled to the elongate body and has a plurality of strain sensors provided on the optical fiber. Each of the plurality of strain sensors has a reflectivity, wherein one of the plurality of strain sensors has a different reflectivity than another one of the plurality of strain sensors. The controller is operatively coupled to the optical fiber and adapted to: receive one or more signals from the plurality of strain sensors; and determine a position of the elongate body based on the one or more signals.