Surface geometry, thickness changes and flow fields on creeping mountain permafrost: Automatic extraction by digital image analysis

Aerial photogrammetry is an established tool for area-wide mapping and moni toring of permafrost geometry, thickness changes and surface creep. This st udy applies commercial software for the automatic generation of elevation m odels from digital imagery and presents a newly developed tool for digital measurement of surface displacements from repeated orthophotos. The accurac y and duality of automatically-derived geometry and velocity data are compa red to conventionally-derived elevation and velocity data from the Muragl r ock glacier in the Swiss Alps. The analysis reveals that for thickness chan ges and velocities digital photogrammetry provides at least the same accura cy as the difference data. Under unfavourable terrain and image conditions, such as steep slopes, shadows or snow cover, the reliability of the automa tically-derived data is significantly lower than the operator-measured ones . Copyright (C) 2000 John Wiley & Sons, Ltd.