Correcting GIS-based slope aspect calculations for the Polar Regions

Slope aspect is an important geomorphic parameter. The aspect of a slope controls its solar irradiation, thus affecting a wide diversity of processes (for a partial review see Moore et al. 1991). Slope aspect can be calculated from a digital elevation model using one of several GIS-based algorithms (e.g. Moore et al. 1991, Burrough & McDonnell 1998). These algorithms are designed for mid-latitude regions, calculating slope aspect as an angle relative to grid north. In polar regions, however, this approach suffers from two problems: 1. In the commonly-used polar stereographic projections, grid north is parallel to either the prime meridian (for the south pole) or the meridian at 180° (for the north pole) while geographic north varies with longitude. 2. In the polar regions, the direction of geographic north can vary significantly over a relatively small area.