Abstract
Abstract. The potential danger caused by glacier margin lakes and the related risk of glacier lake outburst floods (GLOF) increases constantly due to glaciers retreating in many parts of the world. Reasons for this development are on the one hand the new formation and enlargement of glacier margin lakes due to melt water. On the other hand, retreating and thinning glacier tongues lead to a decrease of the back pressure against the dammed glacier lakes. The paper describes the design of a photogrammetric GLOF monitoring system, based on monoscopic image sequence analysis for automatic detection of water level changes. The presented approach for measuring the water line in an image sequence is based on directional edge detection in LoG-filtered image data. After that, the water level is determined by a transformation of image measurements into object space based on orientation parameters of the camera and a geo-referenced lake basin model. The model can for instance be determined by photogrammetric methods after a GLOF; it may also be determined portion-wise by analysing shore lines at various water levels. Camera orientation parameters are determined by a local GPS-supported photogrammetric network. Comparing the determined water level changes with reference data provided by a water gauge, the precision is estimated in the order of one decimetre. A major challenge is the automatic detection of the water line in image sequences under varying light and visibility conditions. The paper will also discuss promising approaches such as multispectral images as well as a statistical analysis of grey value changes over short image sequences to eliminate disturbing reflections on the rough water surface.
Highlights
The glacier retreat in Chile is one of the main reasons for the increase of glacier lake outburst floods
The water level changes derived from the detected water lines in the monoscopic image sequences need to be scaled, and an absolute height reference for the measurement values has to be provided
The approximate values for the water line detection are derived from the previous images; a very strong water level change during the night time or in long-lasting times of poor visibility may result in a distinctive water line offset
Summary
The glacier retreat in Chile is one of the main reasons for the increase of glacier lake outburst floods. In April 2008, the ice dammed glacier lake Cachet II drained catastrophically the first time and caused an immense damage by flooding parts of the Colonia River valley. 2013) of the drained Lago Cachet II and its drainage path to Baker River (USGS). Lago Cachet II is located in the Northern Patagonian Ice Field in Chile It is dammed on its southern lakeside by the Colonia Glacier and contains a water volume of approximately 200 Mio m3 (Casassa et al, 2008). During a GLOF event, the water drains over a distance of 8 km through a tunnel forming at the bottom of the Colonia Glacier and flows down the Colonia River to the confluence with Baker River (figure 1)
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