Extraction of Glacial Lakes in Gangotri Glacier Using Object-Based Image Analysis

Due to change in global mean temperature, most Himalayan glaciers have shown retreat, resulting in an increase in the number and size of glacial lakes, which may give rise to glacial lake outburst flood event. These glacial lakes typically grow from small supraglacial lakes (SGLs). Therefore, it is important to map and monitor the SGLs on a regular basis. Most of the studies have utilized medium to coarse resolution images for the extraction of glacial lakes. With the availability of high spatial resolution data, it has also become possible to map small glacial lakes. The literature suggests some studies on the use of high resolution data to map glacial lakes. However, the extraction is majorly based on simple to apply pixel-based classification methods, which results into high misclassification thereby increasing the task of manual post processing. In this study, we used a novel approach, known as object-based image analysis (OBIA), for the mapping of SGLs. A new index has also been proposed for classification of SGLs. As a case study, the SGLs of Gangotri glacier (Uttarakhand Himalayas) have been mapped from the high spatial resolution data of LISS-IV using the proposed OBIA approach. The results have been compared with those obtained from object-based normalized difference water index (NDWI) and pixel-based mapping methods. The validation of the SGLs boundaries has been carried out with respect to the manually digitized database of SGLs. A significant increase in accuracy of the mapping has been observed over the benchmarked traditional methods.