US Patent 7635976 Surveying of buried pipelines

A method of surveying a pipeline is provided. The pipeline comprises a tubular member with a protective wrapping. The method comprises the steps of applying signal to the pipeline from a first location, which first location is remote from the pipeline, and measuring the signal from a second and third locations. The second and third locations are remote from the pipeline and the second location is spaced from the third location along the pipeline. The signals received at the second and third location are used to provide an indication of deterioration of the signal along the tubular member and/or wrapping between the second and third locations.