Suppressing the influences of vessel magnetism on precision of marine magnetic data

Summary Vessel magnetism is always an important factor of reducing precision of marine magnetic survey. Since the traditional model of vessel magnetism (TMVM) only depends on the magnetic heading, the corrected magnetic data are still possessed of systematic error and up-and-down slope, bringing about difficulties of data fusion for cumulating cruises. Variation of vessel induction magnetism are smallest for the network of lines towards geomagnetic northwest and northeast, and difference of vessel magnetism are smallest between the geomagnetic eastward and westward lines, but largest between the geomagnetic northward and southward lines. Therefore, suppressing the influences of vessel magnetism needs to take measures at the design of survey lines. The comprehensive model of vessel magnetism (CMVM) can take all factors into consideration, such as cable length, geomagnetic heading, geomagnetic total intensity, declination and inclination. Cross-over adjustment of main and check-up lines with different cable length will reliably separate magnetic anomaly from vessel magnetism of the model, realizing comprehensive correction of vessel magnetism. The example indicates that vessel permanent magnetism, especially its negative vertical component, could make the influences of vessel magnetism change a lot with latitude, which need to be removed with calculation and correction of the CMVM.