Page 36 - Marine Magnetometer Processing

Cables and Pipes Cables and pipes are considerably longer than they are wide and produce effects on the Earth’s magnetic field which are larger than would be expected from the small mass of steel they are made from. Figure 32A shows the effect of a magnetometer run over a collection of power cables with steel armour on the outside; the large but narrow anomaly peaks are typical for this kind of target. The cables are close together so their magnetic effects overlap which makes it difficult to count how many there are in that area. One survey within Plymouth Sound detected a particularly unusual cable that produced a huge magnetic anomaly of nearly 15000nT (Fig. 32B right). Figure 32A-B: A series of cables giving large magnetic anomalies (left) and a particularly large 14485 nT anomaly (right) Marine Magnetometer Processing \[35\] © 3H Consulting Ltd