Orienting paleomagnetic drill cores using a portable GPS compass

Abstract

Abstract A portable Global Positioning System (GPS) compass was devised for orienting paleomagnetic drill cores and field test measurements were conducted. Orientation of drill cores has been done by magnetic compasses, sun compasses, and backsighting using landmarks. We modified a lightweight marine GPS compass to be mounted on an orientation device and directly measure azimuths, and compared them to measurements made with a magnetic compass, sun compass, and backsighting. Tests on our campus for a site with open sky above showed a root-mean-squared (rms) error of $$0.39^\circ$$ 0 . 39 ∘ , which is less than what is noted on the specifications of the GPS compass, and a difference of $$-\,0.1^\circ \pm 1.1^\circ$$ - 0 . 1 ∘ ± 1 . 1 ∘ (average ± rms) between the GPS and sun azimuths for 11 direction measurements. However, the site between buildings showed an average deviation of $$11.4^\circ$$ 11 . 4 ∘ from the sun azimuth due to multipath effects. When tested on drill core sampling of historical lavas in a volcanic island, the GPS azimuths were deviated only by $$0.4^\circ \pm 2.3^\circ$$ 0 . 4 ∘ ± 2 . 3 ∘ from the sun azimuths at a flat coastal site with open sky above, indicating that the GPS azimuths are as accurate as the sun azimuths. On the other hand, the GPS compass could not provide azimuths at vertical outcrops in forests due to the small number of satellites captured and multipath effects. If other Global Navigation Satellite Systems (GNSS) satellites are captured and false signals caused by multipath are eliminated, portable GNSS compasses, which operate regardless of rock type, weather, or geographic situation, would replace other methods of orienting drill cores. Graphical Abstract