Method of monitoring the interior of a subsea pipeline

A method of monitoring the interior of a pipeline positioned in contact with a soil below a water mass, comprising implementation by data processing means of the following steps:

• (a) for at least one position along the pipeline, obtaining acoustic data descriptive of at least one cross-section of the pipeline at the position, acquired by a mobile acoustic acquisition device in the water mass, wherein the acoustic acquisition device comprises at least one acoustic wave source and at least one acoustic wave sensor, the acoustic data descriptive of a cross-section of the pipeline at the position being a reflected acoustic field received by the at least one sensor after generation of an acoustic field by the at least one source,
• (b) calculating, at the positions of each source and each sensor, Green's functions representative of a response to a specific acoustic emission at any point of the cross-section, then estimating at any point of the cross-section of the pipeline a relative impedance perturbation value according to the acoustic field received and to parameters of the calculated Green's functions, and
• (c) comparing the estimated relative impedance perturbation value with at least one relative impedance perturbation reference model representative of presence and/or an absence of plug in the pipeline to thereby monitor the interior of a pipeline at the at least one position.