What is the maximum distance of distributed fiber optic vibration sensing?

How long can a distributed fiber optic vibration sensing system monitor? 

60km.

In the laboratory it can support 80km, in the application site to consider the light decay and other reasons, the maximum available 60km.

To support long distances of 60km, we use a coherent detection scheme, which makes the system extremely sensitive. Raman amplifier support is also required.

If no Raman amplifier is used and only EDFA is used to amplify the optical signal, perhaps only 30km or even less can be achieved.