Glacial lake inventory of Bhutan using ALOS data: Part I. Methods and preliminary results

The Advanced Land Observing Satellite (ALOS) is relatively new. Its optical sensors are capable of making high-resolution digital surface models (DSMs). For the first time, the task of constructing a regional-scale inventory of glacial lakes based on ALOS data has been undertaken. This study presents the data-processing methods and the results of validation and analysis on the ALOS-based glacial lake inventory of Bhutan in the Himalaya. The analysis based on GPS measurements taken at Metatshota lake in the Mangde Chu sub-basin, one of the glacial lakes assessed as presenting a potential flood danger, shows a validation estimate of 9.5m for the location of the ALOS-based polygon, with a root mean square of 11.7m. A comparison with digitized data from the International Centre for Integrated Mountain Development (ICIMOD) shows that positioning and evaluation of terrain changes can be significantly improved using ALOS data. Preliminary analysis of the glacial lakes in four subbasins, Mo Chu, Pho Chu, Mangde Chu and Dangme Chu, reveals that the frequency distribution of lake sizes biases towards smaller lakes. Glacial lakes 0.01–0.05 km in area account for 55% of the total number and occupy 13% of the total area. Together our results demonstrate the usefulness of highresolution ALOS data with accurate DSMs for studying glacial lakes. High priority must be given to continuously improving and updating the glacial lake inventory with high-resolution satellite data.