Abstract
Performance of a new shipboard three-component magnetometer system utilizing a GPS (Global Positioning System) attitude sensor was compared with that of a conventional system using a gyrocompass for ship's heading and a pitch/roll sensor constituted by accelerometer and fibre-optics gyro. Response of the GPS attitude sensor is quick enough for shipboard magnetic measurement. During "figure-8 turns" for measuring ship's magnetization, difference in heading between the two systems varied about 1° systematically with heading. Differences in pitch and roll changed at about 1° depending on the turning directions. This is most likely caused by error in the gyros due to acceleration during the turns. Previously it was known that significant bias often occurred in each component of magnetic vector anomalies after the correction of ship's magnetization. The significant error in attitude determination during "figure-8 turns" as well as viscous remnant magnetization are responsible for the bias. Significant error of about 0.5° at maximum remains in gyrocompass for 30 to 60 minutes after a turn, and this causes strange fluctuation in Y (east) component of magnetic vector anomalies at the beginning of each survey line. GPS attitude sensor can overcome these problems, and increase the accuracy of shipboard magnetic vector measurement.
