Surface mass balance monitoring of an alpine glacier using GNSS Interferometric Reflectometry

Abstract Assessing glacier surface mass balance (SMB) is essential for evaluating glacier response to climate change. However, traditional in situ measurement methods are labour intensive and often lack the temporal and spatial resolutions required to fully constrain SMB models. Here, we explore the potential of the Global Navigation Satellite System Interferometric Reflectometry (GNSS-IR) technique which exploits reflected satellite signals to track surface height changes for continuous SMB estimation. Using data from 13 GNSS stations operating between 2019 and 2021 on Glacier d’Argentière (French Alps), we compare GNSS-IR-derived SMB with estimates from snow pits, wooden stakes, continuous ice-melt measurements using a SmartStake device, and a degree-day model. We demonstrate that the GNSS-IR technique can reliably estimate SMB values that closely match independent in situ measurements, while also offering the advantages of spatial integration and long-term time series that capture both snowfall events and snow/ice melt. We show that glacier surface roughness and antenna height, when the glacier is snow-free, strongly influence uncertainties, which can be reduced to as little as 2 cm d −1 using a smoothing filter. Finally, we demonstrate that the GNSS-IR technique can further constrain the degree-day factor, particularly its temporal evolution throughout the ablation season.