Challenges and uncertainties in geodetic mass balance estimates for HMA glaciers using space-borne data

Glacier mass balance (GMB) is an important variable for understanding the response of glaciers to climate change. The geodetic method for GMB estimation involves comparing changes in surface elevation over time using satellite or airborne remote sensing data. One of the major advantages of geodetic mass balance is that it accounts for 3-D variability (vertical and surface) in the mass balance, however, assuming that the elevations are accurate everywhere and reference a stable geographic datum. Nevertheless, errors in the geodetic GMB can result from seasonal adjustments, density adjustments and depend heavily on image quality. Further, the relative error of the digital elevation models (DEMs) plays a crucial role than the absolute error when calculating geodetic GMB, and can induce additional uncertainties in the estimates. In a rugged terrain like that of the HMA, with most of the glaciated region in the Himalayas having sudden steep slopes and thick supraglacial debris, results of glacier-level measurements over bedrock are less accurate than those over glacier ice. Further, based on the type of DEM utilized (optical or synthetic aperture (SAR) radar-based), the uncertainty in the GMB varies from 23.3% to 52.7%, with SAR-based GMB having lower uncertainty. In this work, comparisons between different studies highlight both the utility of geodetic mass balance estimates and a possible resolution to the prominent issues (highlighted here) that can assist in circumventing the challenges in GMB assessments over the HMA region.