A detection system comprising: (i) an optical fiber, the optical fiber having (a) a length L≧1 km; (b) beat length between 10 m and 100 m; and (c) beat length uniformity over any distance of at least 100 m within the length L is characterized by standard deviation σ, where |σ|≦10 m; (ii) an OTDR coupled to the fiber and including (a) a radiation source providing pulsed radiation to the fiber, (b) a detection system capable of detecting radiation that is backscattered back through the fiber; and (iii) at least one polarizer situated between the fiber and the detector, such that the backscattered radiation passes through the polarizer before reaching the detector.