ACME2: An extended toolbox for automated cirque metrics extraction

With the availability of improved digital elevation models (DEMs) of global coverage, the morphological analysis of large populations of glacial cirques is possible, and can be used to derive important palaeoclimate and environmental information related to the distribution and history of former glaciers. In 2017, an ArcGIS toolbox, ACME (Automated Cirque Metrics Extraction), was developed to derive 16 cirque metrics based on input cirque outlines, threshold midpoints and DEMs. ACME has been widely used in cirque morphological analysis and regional comparisons. This paper presents a revised and extended toolbox, ACME2. This extended toolbox includes new functions to automatically derive cirque threshold midpoints (cirque foci) and 49 morphometric and locational variables, with attributes related to cirque location, size, shape, altitude, slope, and aspect, including variables related to the median axis, as well as 3 input metadata attributes. ACME2 also improves the methods for calculation of the hypsometric maximum and integral, and implements a new method for plan closure to be more consistent with the original definition. All ACME2 tools are coded in Python and can be imported into ArcGIS with user-friendly interfaces. Comparisons for 155 cirques in the English Lake District and 51 in the Shulaps Range, British Columbia, indicate consistency between the ACME2-derived and manually derived metrics, with most correlations r > 0.90: none <0.70. ACME2 provides more cirque metrics and automates the whole calculation sequence with cirque outlines and DEMs. Its comprehensive approach facilitates understanding of cirque form and development in all its variety.