THE STABILITY OF A PERMANENT TERRESTRIAL LASER SCANNING SYSTEM – A CASE STUDY WITH HOURLY SCANS

Abstract. The stability of the permanently installed terrestrial laser scanner (TLS) in a high mountain environment at Hintereisferner glacier, Ötztal Alps, Austria, is tested. From previous studies it is already known that the uncertainty of the permanent setup results from scanning geometry, atmospheric conditions and instrumental limitations. This study focuses on the instrumental limitations related to the lack of perfect stability of the TLS. A case study is performed with hourly scans over the glacier and the data of the internal inclination sensors are read. A comparison of the scanning data with the inclination data shows that the TLS at Hintereisferner is affected by both high-frequency vibrations and coarser movements. The high-frequency vibrations cause radial stripes in the data, and cannot be corrected, as the internal inclinations sensors of the TLS measure at a frequency of 1 Hz, whereas pulses are emitted at effectively 23 kHz. The coarser movements are indicated by the measurement of roll and pitch with the internal inclination sensors and can be corrected by manually georeferencing the data.

In order to complete the uncertainty assessment of a permanent long-range TLS system in a high mountain environment, future work will concentrate on the impact from the scanning geometry and from the atmospheric variables. The finalised uncertainty assessment is crucial to derive the smallest magnitude at which snow (re)distribution can be detected and, thus, significantly will improve the treatment of snow cover dynamics in future glacier mass balance research.