Method of fibre optical distributed acoustic sensing, the method comprising: switching between a high rate fibre optical distributed acoustic sensing and a low rate fibre optical distributed acoustic sensing, the high rate fibre optical distributed acoustic sensing comprising: injecting, using a light coupler, a first coherent light pattern comprising first light into an optical cable, the optical cable having at least a first reflector pair and a second reflector pair arranged at different positions along the optical cable; injecting, using the light coupler, a second coherent light pattern comprising second light into the optical cable while first backscatter light of the first light pattern is propagating in the optical cable; detecting, using a detector, first reflected light originating from reflection of the first light pattern from the second reflector pair; and, at a different interval in time: detecting, using the detector, second reflected light originating from reflection of the second light pattern from the first reflector pair, wherein the first reflected light originating from reflection of the first light pattern from the reflectors of the second reflector pair is received at the detector during a first reception time interval, the second reflected light originating from reflection of the second light pattern from the reflectors of the first reflector pair is received at the detector during a second reception time interval, wherein the first reception time interval does not overlap with the second reception time interval, the low rate fibre optical distributed acoustic sensing comprising: injecting, using the light coupler, another first light pattern into the optical cable; detecting, using the detector, light originating from Rayleigh backscattering of the other first light pattern from different portions along the optical cable including at least one portion between reflector pairs; injecting, using the light coupler, another second light pattern into the optical cable after all the other first light pattern backscattered from all portions of the optical fibre has left the optical cable; detecting, using the detector, light originating from Rayleigh backscattering of the other second light pattern from different portions along the optical cable including the at least one portion between reflector pairs. injecting, using a light coupler, a first coherent light pattern comprising first light into an optical cable, the optical cable having at least a first reflector pair and a second reflector pair arranged at different positions along the optical cable; injecting, using the light coupler, a second coherent light pattern comprising second light into the optical cable while first backscatter light of the first light pattern is propagating in the optical cable; detecting, using a detector, first reflected light originating from reflection of the first light pattern from the second reflector pair; and, at a different interval in time: detecting, using the detector, second reflected light originating from reflection of the second light pattern from the first reflector pair, wherein the first reflected light originating from reflection of the first light pattern from the reflectors of the second reflector pair is received at the detector during a first reception time interval, the second reflected light originating from reflection of the second light pattern from the reflectors of the first reflector pair is received at the detector during a second reception time interval, detecting, using the detector, second reflected light originating from reflection of the second light pattern from the first reflector pair, wherein the first reflected light originating from reflection of the first light pattern from the reflectors of the second reflector pair is received at the detector during a first reception time interval, the second reflected light originating from reflection of the second light pattern from the reflectors of the first reflector pair is received at the detector during a second reception time interval, injecting, using the light coupler, another first light pattern into the optical cable; detecting, using the detector, light originating from Rayleigh backscattering of the other first light pattern from different portions along the optical cable including at least one portion between reflector pairs; injecting, using the light coupler, another second light pattern into the optical cable after all the other first light pattern backscattered from all portions of the optical fibre has left the optical cable; detecting, using the detector, light originating from Rayleigh backscattering of the other second light pattern from different portions along the optical cable including the at least one portion between reflector pairs.