A fiber optic sensing (FOS) system and method. The system may include one or more interrogator units and a proximal wavelength division multiplexer (WDM) and a distal WDM optically connectable to the one or more interrogator units, an upgoing transmission fiber, a down-going transmission fiber, and one or more downhole sensing fibers. The method may include transmitting one or more light pulses from an interrogator unit, multiplexing the one or more light pulses from the interrogator unit with a proximal WDM into an upgoing transmission fiber and a down-going transmission fiber, and receiving the one or more light pulses with a distal WDM. The method may further include multiplexing the one or more light pulses from the upgoing transmission fiber and the down-going transmission fiber into one or more downhole sensing fibers and receiving backscatter light from at least one of the one or more downhole sensing fibers.