地磁気極近くでの海流観測: コンパスの問題について

抄録

Accurate ocean current measurements near the magnetic dip pole have been carried out in the multi-year ice area of the central Arctic Ocean using ice-drifting buoy, J -CAD (JAMSTEC Compact Arctic Drifter). Because of weakness of the magnetic direction reference near the magnetic dip pole, we need to look more carefully into the compass malfunction in order to obtain accurate ocean current. Using the observational data from J-CAD 6 in 2003, we attempted heading data comparisons of attached compasses with azimuthal data calculated from GPS buoys. Results show that Watson Compass, which is 3-dimensional magneto-metric compass attached on the same cage of WorkHorse 300 kHz ADCP (WH-ADCP), can measure the correct heading with an accuracy of 4 degree over the entire J-CAD 6 trajectory. On the other hand, we found that WH-ADCP compass illustrated good results of heading measurements under the condition which the horizontal magnetic intensity is higher than 3000 nT. Also, we investigated a non-linear response of WH-ADCP compass from a comparison with Watson Compass, which are attached on J-CAD 4 in 2002. A non-linearity response of WH-ADCP compass was found with amplitude of ~20 degrees under the condition which the horizontal magnetic intensity is higher than 3000 nT. However, we can conclude that the heading data from WH-ADCP would be useful with an accuracy of 5 degrees after understanding the non-linear response of each compass.