Spatial analysis of topography for glacier mapping in the Western Himalaya

Understanding climate change requires accurate assessment of the Earths cryosphere, as glacier fluctuations directly and indirectly reflect changes in radiative forcing and temperature and precipitation patterns. Direct assessment of alpine glaciers in high-mountains is notoriously difficult, and assessment from space represents the only practical alternative for assessing regional and global ice-fluctuation patterns. The mapping of debris-covered glaciers is especially problematic, as glacier surfaces exhibit spectral reflectance patterns similar to surrounding rock and sediment. Therefore, multispectral analysis of satellite imagery does not permit accurate delineation. Consequently, the use of satellite-derived topographic information and spatial analysis were evaluated for mapping the Raikot and Sachen Glaciers at Nanga Parbat mountain in the Pakistan Himalaya. Geomorphometric analyses were used to generate first- and secondorder topographic parameters. These were utilized to generate homogeneous elemental-form objects, which were evaluated for glacier mapping. Topo-sequence information was also examined and represents the slope-angle altitude function within slope facet objects. The results indicate that it is difficult to characterize the hierarchical topographic organization of glaciers using topographic parameters and elemental form objects. Even though only one level of the topographic hierarchy was attempted, elemental form objects appear to be more useful than topographic parameters, as they represent a combination of topographic information. In addition, elemental-form objects can be used to identify and map selected glacial features without further aggregation to another level in the hierarchy. Toposequence information was found to be of value in differentiating glacier versus non-glacier surfaces. Collectively these results indicate that spatial analysis of the topography can be used for glacier mapping, although accurate digital elevation models are required, along with more sophisticated approaches for quantitatively characterizing the topography. It is suggested that specific topographic primitives and glacier landforms be individually characterized and integrated into a landscape topographic hierarchy in order to accurately characterize and map debris-covered glaciers. Finally, special attention to the concept of scale must be formally accounted for in analysis procedures