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Abstract
Abstract. This paper presents a comprehensive method for the determination of glacier surface motion vector fields at high spatial and temporal resolution. These vector fields can be derived from monocular terrestrial camera image sequences and are a valuable data source for glaciological analysis of the motion behaviour of glaciers. The measurement concepts for the acquisition of image sequences are presented, and an automated monoscopic image sequence processing chain is developed. Motion vector fields can be derived with high precision by applying automatic subpixel-accuracy image matching techniques on grey value patterns in the image sequences. Well-established matching techniques have been adapted to the special characteristics of the glacier data in order to achieve high reliability in automatic image sequence processing, including the handling of moving shadows as well as motion effects induced by small instabilities in the camera set-up. Suitable geo-referencing techniques were developed to transform image measurements into a reference coordinate system.The result of monoscopic image sequence analysis is a dense raster of glacier surface point trajectories for each image sequence. Each translation vector component in these trajectories can be determined with an accuracy of a few centimetres for points at a distance of several kilometres from the camera. Extensive practical validation experiments have shown that motion vector and trajectory fields derived from monocular image sequences can be used for the determination of high-resolution velocity fields of glaciers, including the analysis of tidal effects on glacier movement, the investigation of a glacier's motion behaviour during calving events, the determination of the position and migration of the grounding line and the detection of subglacial channels during glacier lake outburst floods.
Highlights
IntroductionTerrestrial photogrammetry has been an important measurement method for glaciology research
For almost a century, terrestrial photogrammetry has been an important measurement method for glaciology research
In Schwalbe et al (2016) a case study is presented where the high temporal resolution of the motion fields of the Colonia Glacier allow for an analysis of the tunnel formation and collapse in relation to the changing water level of the lake Cachet II obtained from a glacier lake outburst flood (GLOF) early warning camera
Summary
Terrestrial photogrammetry has been an important measurement method for glaciology research. Because of further technical improvements of digital cameras and developments in automatic image matching techniques, terrestrial image sequence analysis has become a valuable tool for the investigation of glaciers during the last 20 years. The simple use of time-lapse cameras as a visual observation tool may already be a great help for environmental investigations Beyond that, they have the potential to deliver precise measurements with high temporal and spatial resolution when applying appropriate photogrammetric image sequence processing techniques. In this paper we want to present a detailed methodological concept for the determination of motion vector fields from terrestrial time-lapse image sequences. 3 we discuss the suitability and possible areas of the application of the method for the examples on the basis of different glaciology research pilot studies that were conducted applying the presented time-lapse measurement method and image sequence analysis approach
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