Multispan optical fiber system and techniques for improved distributed acoustic sensing

A method of operating a distributed acoustic sensing system, comprising:

• launching an outbound distributed acoustic sensing (DAS) signal from a DAS transmitter of a DAS station through an optical fiber, over at least one span;
• receiving a backscatter Rayleigh signal, based upon the outbound DAS signal, at a DAS receiver;
• performing at least one processing operation to increase a sensing sensitivity during the launching the outbound DAS signal and the receiving the backscatter Rayleigh signal;
• and
• using a receiver power tracker, selectively attenuating or reducing an amplification of the power of the backscatter Rayleigh signal, received from a beginning of the at least one span in comparison to a power of the backscatter Rayleigh signal from an end of the at least one span, opposite to the beginning, wherein the receiver power tracker comprises an optical programable attenuator having an attenuation that is relatively larger at the beginning of the at least one span, wherein the attenuation gradually decreases to zero at the end of the at least one span;
• or an optical pre-amplifier having a relatively smaller current or relatively smaller gain for the backscatter Rayleigh signal from the beginning of the at least one span, and a relatively larger current or relatively larger gain for the backscatter Rayleigh signal, when coming from an end of the at least one span.

A distributed acoustic sensing system, comprising:

• a distributed acoustic sensing (DAS) station, comprising:
• a DAS transmitter, arranged to launch an outbound DAS signal through an optical fiber, over at least one span;
• a DAS receiver, arranged to receive a backscatter Rayleigh signal, based upon the outbound DAS signal;
• a first acousto-optic modulator (AOM), arranged to receive the outbound DAS signal;
• a first amplifier, to receive a first output signal of the first AOM and to increase an intensity of the outbound DAS signal;
• a second AOM, arranged to receive an output of the first amplifier;
• and
• a narrow bandwidth optical filter, arranged to receive an output from the first amplifier, wherein the narrow bandwidth optical filter has a bandwidth, the bandwidth being between 1 GHz and 10 GHz
• a receiver power tracker, arranged to attenuate or reduce an amplification of the backscatter Rayleigh signal, from a beginning of the at least one span wherein the receiver power tracker comprises an optical programable attenuator having an attenuation that is relatively larger at the beginning of the at least one span, wherein the attenuation gradually decreases to zero at an end of the at least one span;
• or an optical pre-amplifier having a relatively smaller current or relatively smaller gain for the outbound DAS signal from the beginning of the at least one span, and a relatively larger current or a relatively larger gain for the outbound DAS signal, when coming from an end of the at least one span.