抄録
We made a magnetic anomaly map in the eastern margin of the Japan Sea using seaborne magnetic data collected during five cruises of R/V Hakurei-maru. The contours of this map are at 25 nT intervals. They are much smaller than those of the seaborne magnetic maps published previously by the Geological Survey of Japan. On a map using a procedure without cross-point control, unnatural contours are usually showed, which results from relatively large discrepancies at cross-over points of the survey lines compared with the small contour-interval. To solve this problem, we applied a cross-point control method which had been used commonly for processing airborne magnetic data. An offset of each track line was determined to minimize the sum of the square of difference at each cross-over point. The causes of the discrepancies at cross-over points include diurnal variation, secular variation, measurement error, positioning error, and ship's magnetization. It is difficult to separate these components from observed data. The crosspoint control method is hence useful for processing seaborne magnetic data as well as airborne data.
