TIME-LAPSE CAMERA IMAGES FOR OBSERVATION AND VISUALIZATION OF SNOW LINES ON GLACIERS IN HIGH ASIA
ISBN 978-85-88783-11-9
Authors
1Schröter, B.; 2Buchroithner, M.
1TECHNISCHE UNIVERSITÄT DRESDEN Email: benjamin.schroeter@tu-dresden.de
2TECHNISCHE UNIVERSITÄT DRESDEN Email: manfred.buchroithner@tu-dresden.de
Abstract
Glaciers are characteristic elements of high mountain environments and represent key indicators for the ongoing climate change. The covering snowpack considerably affects the glacier-ice surface temperature and thus the meltdown of the glaciers which in recent decades has been accelerating worldwide. Therefore, the detailed investigation as well as the accurate delineation of the actual snow line – here defined as the fluctuating lower altitudinal boundary of a snow-covered area – are of high importance. Between 2009 and 2014 there have been several field campaigns to different glaciers on the Tibetan Plateau within the framework of the joint Sino-German research projects “TiP” (Tibetan Plateau: Formation – Climate – Ecosystems) and “WET” (Variability and Trends in Water Balance Components of Benchmark Drainage Basins on the Tibetan Plateau). The best observed glacier among those is Zhadang Glacier which is located in the western Nyainqentanglha Mountain Range in the central part of the Tibetan Plateau (30°28.24’ N, 90°38.69’ E). The glacier is debris-free, covers an area of 2.0 km2, has a length of 2.2 km and flows from 6,090 to 5,515 m a.s.l. Recent measurements have shown that the whole glacier is below the equilibrium line altitude (ELA) and experiences significant glacier volume loss. Two terrestrial cameras were installed there and have been continuously operating between May 2010 and September 2012 generating 6,225 images of Zhadang Glacier with a frequency of three resp. six images per day. The result is a globally unique dataset. In order to use this dataset for snow line mapping all images had to be georeferenced and orthorectified. The biggest challenge was the problem of the shifting camera positions due to deformations of the ground (melting und refreezing) and hence the offset in the image coordinates. This was resolved by combining the manual orthorectification of one image per week and a subsequent application of a spline interpolation to determine the changed image coordinates. The actual orthorectification was finally realized by applying a fully automated batch processing of all images. The most favorable image of each day, i.e. with the best illumination and the lowest amount of cloud cover/shadows, was chosen for the manual snow line mapping process. The final aims were both the calculation of the mean elevation of the snow line for every day of the data collecting period materialized by intersecting the mapped snow lines with resampled SRTM 3 data as well as their dynamic visualization. Considering the fact that there were several weeks either with full snow cover (especially DJFM) or without any snow (especially JJAS) this aim could be achieved. The results are currently being used for the evaluation of a glacier mass balance model developed at RWTH Aachen, Germany. The most recent field campaign is currently taking place at Halji Glacier south of Gurla Mandhata in northwestern Nepal on the southern edge of the Tibetan Plateau (30°15.80’ N, 81°28.16’ E, 5,730 - 5,270 m a.s.l., ELA = 5,660 m a.s.l.), another benchmark area of the before mentioned “TiP” and “WET” projects. The main objective is the recovery of the image data collected by a terrestrial time-lapse camera system and an automated weather station installed there in December 2013. The hardware setup of the camera system has been transferred to Halji Glacier and is similar to the system that had been successfully operating on Zhadang Glacier. The expected 2000 images will be processed with an improved version of the orthorectification algorithm applied to the Zhadang Glacier images and the transient snow line will be detected. A remarkable result is the proof of the existence of intense ablation due to snow drift and sublimation on Zhadang Glacier during the winter months (DJFM). This strongly affects the onset of the melting period during the summer months (JJAS). The extent of the snow free areas on the glacier is currently being mapped.