Abstract: A system and method for dynamically calibrating a distributed fibre optic sensing system is disclosed. The calibration system includes a light source for generating pulses of coherent light, an optical fibre arranged at least partly in a ground soil region to guide the light and a photo detector for detecting scattered light returning from the optical fibre in dependence of time. The method includes obtaining information from which a temporal change of an acoustic transfer characteristic of the ground soil region is derivable and calibrating a distributed acoustic sensing system based on the changed acoustic transfer characteristic.