Comparing alpine watershed attributes from LiDAR, Photogrammetric, and Contour‐based Digital Elevation Models

Abstract

Abstract:As part of an alpine hydrological study in the Canadian Rocky Mountains, three digital elevation model (DEM) data sets were obtained for the purpose of watershed characterization. The data sources were: (1) archived public access BC TRIM (Terrain Resource Information Management) 1 : 20 000 contour vectors; (2) stereo aerial photography DEM with a derived point spacing between 5 m and 20 m; (3) airborne LiDAR (light detection and ranging) with point spacing from 1 m to 4 m. GIS layers of terrain and watershed attributes were created for each of the three DEM data sets at grid cell resolutions of 5 m and 25 m. Watershed attributes investigated were: DEM elevation, area, hypsometry, and stream network topology. In areas of lower relief and forest cover, the TRIM contour DEM contained topological errors at both 5 m and 25 m resolutions due to the poor representation of terrain from widely spaced contours. The photo DEM introduced obvious stream topology errors at 25 m due to the inability of the photo DEM to discern subtle terrain beneath forest canopies. The photo and TRIM DEMs overestimated basin hypsometry relative to the LiDAR watersheds at highest elevations due, in part, to their inability to represent the inside of gullies and steps associated with geological strata. In the case of the photo DEM, selectively digitizing break lines such as cliff edges, while missing shadowed areas, led to the creation of an interpolated surface that was biased towards the outer extremities of the terrain. Conversely, relative to the photo-based datasets, the LiDAR DEM better captured the inside of gullies and steps while under-sampling break line features, leading to a bias in the interpolated surface towards internal terrain extremities. As would be expected, the quality and resolution of the terrain data increased from BC TRIM to photo to LiDAR. If modelling watersheds within the Canadian Rockies at the meso scale and above, BC TRIM (or equivalent) 1 : 20 000 contour vectors would be most appropriate given availability and cost considerations. The benefits of LiDAR are apparent if higher resolution and more accurate watershed attribute information is needed detailing first-order hydrological channel features on steep shadowed mountain slopes or zero-order hill-slope depressions beneath forest canopies. Such landscape features provide preferential storages for winter snowpack in mountainous watersheds, suggesting that in the future LiDAR might be a tool of choice for snowpack resource monitoring in these regions.

Brief Communication: Low-cost, on-demand aerial photogrammetry for glaciological measurement

“…Typical estimates of vertical RMS errors from airborne LiDAR data used in glaciological applications are below 0.2 m (e.g. Arnold et al, 2006;Hopkinson et al, 2009;Pope et al, 2013), which is not drastically different from the preliminary estimates shown here. Planimetric accuracies reported in the current study are also similar to those reported by Arnold et al (2006), and Hopkinson et al (2009), who both estimated XY accuracies as being between 0.3 m and 0.4 m. Furthermore, use of a metric camera might reduce some of the errors, and given the growing availability and shrinking size of these cameras, this is a logical next step for UAV payloads.…”

Measuring glacier surface roughness using plot-scale, close-range digital photogrammetry

“…Hopkinson, 2004;Avian and Bauer, 2006;Kerr and others, 2009;Kassalainen and others, 2011;Nield and others, 2013). From such data, DSMs and surface profiles can be retrieved at sub-centimetre horizontal and vertical resolution over intermediate (<200 m) scan distances.…”

The influence of terracettes on the surface hydrology of steep-sloping and subalpine environments: some preliminary findings

“…6). These are believed to be spurious features and probably represent a product of the way in which topographic data are converted to raster data (Hopkinson et al, 2009). A possible way in which this problem will be avoided in future is discussed in Sect.…”