Terrain Analysis and Digital Mapping of Parental Material Using Object-Based Image Analysis (OBIA)

Detailed mapping of subsurface characteristics at broad spatial scales is one of the fundamental challenges in geoscience. Because of their distinct physical attributes (e.g. hydraulic conductivity, grain-size), the spatial distribution of parent materials is critical to our understanding of hydrologic and geomorphic processes. Parental material is a controlling factor in the movement and storage of shallow groundwater, and its mapping across catchments should prove useful in determining sediment source areas. In the context of the Canadian Shield, deposit variability is defined by glacial and post-glacial deposit processes that occurred during the retreat of the Late Wisconsinan Laurentide Ice Sheet following the Last Glacial Maximum (18-21 ky BP). New remote-sensing techniques now allow for quick acquisition of precise geographical information at broad spatial scales. Among these new technologies, LiDAR elevation data and derived sub-meter resolution digital elevation models (DEMs) can be used to identify subtle landforms and landscape features, even in vegetated areas where ground surface is cloaked by canopy cover. Here, we present our methodology for detailed mapping of parental materials across upstream catchments of a Precambrian shield. Local assessment of parental materials has been obtained through intrusive methods (i.e. coring, excavation). These field measurements have then been related to landscape topographic attributes obtained from terrain analysis of a high-resolution LiDAR DEM via OBIA. This two-step method consists of (i) segmentation of the landscape into homogeneous objects based on various topographic and optical metrics representing the Earth's surface (e.g. elevation, slope, Earth's curvature, reflectance); and then (ii) classification of each object following topographic statistics and their associated parent material as defined from field sampling. This research contributes to a broader integrated study of hydrogeomorphic and hydroecologic processes in Precambrian shield headwater catchments.