A method of distributed acoustic sensing includes providing a fiber optic distributed acoustic sensing system having a cable. A straight optical fiber extends parallel to a longitudinal axis of the cable along the cable length. A helically wrapped optical fiber extends along the cable length. The method includes transmitting optical signals into and receiving backscattered signals out of the optical fibers consisting of a component of said optical signals which component has been backscattered from impurities or inhomogeneities in the optical fibers, observing changes in the backscattered signals caused by axial stretching and compressing of the optical fibers caused by an incident wave, comparing the backscattered signals of the straight optical fiber and the helically wrapped fiber, and determining, based on the comparing of the backscattered signals, a direction of wave propagation of the incident wave with respect to the fiber axis for detecting broadside waves and axial waves distinguishably.