Inversion algorithm development for passive electromagnetic detection of line sources

Abstract

The position of installed submarine power cables is often not accurately known for several reasons. The precise knowledge of the cable position is important for the maintenance process and necessitates the need for cable tracking systems. Current systems are in many cases imprecise and have a short sensing distance, limited to a few meters. A device with better accuracy and sensing range is in demand for enhancing the cable maintenance process. Three new inversion algorithms are introduced which invert the passive electromagnetic _eld created from an injected signal in the target cable. The cable is treated like a line source. This can be seen as an inverse source location _nding problem, while the source time signature is known. The algorithms are tested on synthetic data, modeling a power cable in homogeneous sea water with noise. Several parameters like sensor array, dip angle of the cable and relative position to the system are analyzed. The inuence of soil and the sea surface are studied on synthetic data created from a numerical three-layer forward model. Additionally, a prototype is developed, and di_erent processing schemes are presented and compared. The system is tested with di_erent inversion algorithms on a _eld cable on land. A solution is found which can determine the cable position accurately in sea water with noise terms for a distance up to 6 m. However, this system is highly sensor array dependent. A second inversion method gives a smaller sensing range of 5m but can be used with more versatility. In a di_erent modeled scenario without noise terms, the cable is buried in marine sediments and air is on top of a layer of sea water. The sensors are in the sea water layer. The soil has a great impact on the accuracy of the inversion. In some cable-system-orientations, the absolute error caused by the layered earth exceeds 1 m. The prototype is successfully tested on a _eld cable for di_erent scenarios. An inverted cable position in a global reference frame can be obtained by including a motion sensor.