Paper Summary
Marine seismic surveying in the Arctic presents many challenges. Conducting streamer surveys in the presence of high ice concentrations eliminates the ability to safely tow a conventional GPS
tail buoy. When conducting 2D surveys under these conditions, the tail buoy is typically removed, which leaves only compasses as a means to calculate the cable position.
Compass data must be corrected for declination caused by the Earth’s magnetic field. As a first order correction to the raw compass bearings, the navigation software can apply a gridded declination. That is, a gridded World Magnetic Model (WMM) or Enhanced Magnetic Model (EMM) declination is applied as the seismic vessel sails through the model. However, this method is not adequate at high latitudes, due to temporal variations in the Earth’s magnetic field. Instead, a shipboard declinometer has been developed that measures real-time magnetic declination, which is then applied to the cable compasses in an open traverse from the vessel to the tail.
On November 1, 2012, the declinometer observed a geomagnetic event in the Beaufort Sea during which the peak declination changed 12 degrees (12°) in 6 minutes. Magnetic observatories at Point Barrow and Deadhorse confirmed the event. This article discusses the improvement of real-time declinations over modeled declinations for marine seismic streamer positioning in the Arctic.