Uncertainty assessment of multi-temporal airborne laser scanning data: A case study on an Alpine glacier

In glaciology, volumetric changes from multi-temporal digital elevation models (DEMs) serve to validate and calibrate glacier mass balances from traditional in situ measurements. In this study, we provide a thorough uncertainty assessment of multi-temporal airborne laser scanning DEMs based on: (a) applying a statistical error model, (b) comparing laser echoes to reference points and surfaces, and (c) developing a physical error propagation model. The latter model takes into account the measurement platform characteristics, components of the measurement process, and the surface properties. Such a model allows the estimation of systematic and stochastic uncertainties for single laser echoes, as well as for distributed surfaces in every part of the study site, independent of the reference surfaces. The full error propagation framework is applied to multi-temporal DEMs covering the highly undulating terrain in the Findelengletscher catchment in Canton Valais, Switzerland. This physical error propagation model is able to reproduce stochastic uncertainties in accordance with measurements from reference surfaces. The high laser point density in the study site reduces the stochastic uncertainties over the whole glacier area to negligibly small values. However, systematic uncertainties greatly influence the calculation of mass changes and lead to corrections of the thickness change of up to 35%.