courses is a difficult point in ship magnetic field analysis. The method based on the special

situation of the magnetic signature at the typi- cal measurement points under the keel of ship can

solve this problem easily and clearly. According to the magnetic field measurements in two

headings of 180° difference，the sum of the longitudinal and the transverse magnetism of the ship

can be separated. At the typical measurement points under the keel of a ship，the longitudinal and

vertical components of the magnetic fields of the sum of the longitudinal and the transverse

magnetism of the ship come from the longitudinal induced magnetism，and the transverse component of

the magnetic fields comes from the transverse induced magnetism. Finally，the decomposition of ship

induced magnetism and magnetic fields in oblique courses is realized.