Determining the uncertainty of areal mean surface elevation measured with a terrestrial laser scanner and with a total station in permafrost environments near Lac de Gras, NWT, Canada

Abstract

Quantifying topographic change in permafrost environments is important because it can provide insight about the loss of excess ice. Ground-based methods that detect change in surface elevation, however, are often applied at individual points rather than over an area, giving rise to questions about their representativeness.Remote sensing methods can overcome this problem, although confounding signals may arise from changing vegetation and microtopography. Comparing remotely sensed areal surface elevation or elevation change with ground-based observations also requires areal estimates rather than point measurements. This study examines the uncertainty of mean elevation measured with a terrestrial laser scanner and with a total station on 28 plots with different surface characteristics in a tundra environment. Observations from terrestrial laser scanning and surveying with a total station are analyzed statistically to reveal confidence intervals for the derived mean elevations. In the absence of a true reference elevation for the plots investigated, the difference between both mean elevations is quantified as well as the likelihood of representing the same surface. The results provide method specific detection limits for vertical movements of small plots (15 m × 15 m) with differing surface characteristics. The difference between means derived from both methods provides additional context about how well we can define what the surface is that we are observing. On average, terrestrial laser scanning can potentially detect vertical movements in the centimeter range (1.4-24.0 cm) and the total station method in the low decimeter range (3.5-47.1 cm). For all plots, the mean elevations derived from laser scanning and total station surveying are statistically different at the 95% confidence level. Strong differences between plots exist and are influenced by surface ii characteristics.iii