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Photogrammetric image sequence processing to determine change in active lava flows

Robson, S; James, MR; (2007) Photogrammetric image sequence processing to determine change in active lava flows. In: Proceedings of the 2007 Annual Remote Sensing and Photogrammetry Society (RSPSOC2007). Remote Sensing and Photogrammetry Society: Newcastle.

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Abstract

Understanding the processes involved with the advance of lava flows is critical for improving hazard assessments at many volcanoes. Here, we describe the application of computer vision and oblique photogrammetric techniques to visible and thermal images of active lavas in order to investigate flow processes at Mount Etna, Sicily and on pahoehoe flows in Hawaii. Photogrammetric surveys were carried out to produce repeated topographic datasets for calculation of volumetric lava flux at the flow-fronts. Photogrammetry is an established technique for the investigation of change in landform over time, relying typically on vertical aerial imagery or more unusually, on oblique imagery from aircraft or terrestrial platforms. This paper describes experiences in processing data from terrestrial digital photogrammetric surveys of lava flows acquired with digital photogrammetric SLR cameras at a number of sites which have active lava flows. In each case the objective was to ascertain flow evolution over time using a sequence of oblique imagery, captured from multiple locations. Data processing was carried out using VMS software to solve the imaging geometry and to deliver seed points for stereo and multi-photo matching. Stereo matching was carried out using UCL’s gotcha matching package which incorporates a combination of pyramidal and Otto-Chau region growing algorithms to produce topographic models which were then automatically image draped for visualisation within VMS software. For the Hawaii data, sequences of image pairs in which the lava field advanced over time were evaluated using the pyramidal features of the gotcha matcher in order to allow the propagation of seed points from one temporal image pair to the next. Because of the four-level pyramid chosen, this process could utilise sub-sampling of the 6MP resolution of the input images in order to account for camera vibrations caused by the environment. At each temporal epoch the orientation of each image was refined by tracking features in stable terrain. Example results will be shown demonstrating tracking through a 36 minute sequence. Such results allowed the computation of volume flux which could then be used to validate flux measurements calculated using cooling trends from thermal images.

Type:Proceedings paper
Title:Photogrammetric image sequence processing to determine change in active lava flows
Event:Remote Sensing and Photogrammetric Society, Annual Conference, Newcastle, September 2007
UCL classification:UCL > School of BEAMS > Faculty of Engineering Science > Civil, Environmental and Geomatic Engineering

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