Combined GNSS reflectometry/refractometry for automated and continuous in situ surface mass balance estimation on an Antarctic ice shelf

. Reliable in situ surface mass balance (SMB) estimates in polar regions are scarce due to limited spatial and temporal data availability. This study aims at deriving automated and continuous specific SMB time series for fast moving parts of ice sheets and shelves (flow velocity > 10 m a − 1 ) by developing a combined Global Navigation Satellite Systems (GNSS) reflectometry and refractometry (GNSS-RR) method. In situ snow density, snow water equivalent (SWE), and snow deposition or erosion are estimated simultaneously as an average over an area of several square meters and independent on weather 5 conditions. The combined GNSS-RR method is validated and investigated regarding its applicability on a moving, high lat-itude ice shelf. A combined GNSS-RR system was therefore installed in November 2021 on the Ekström ice shelf (flow velocity ≈ 150 m a − 1 ) in Dronning Maud Land, Antarctica. Reflected and refracted GNSS observations from the site are post-processed to obtain snow accumulation (deposition and erosion), SWE, and snow density estimates with a 15 min temporal resolution. Results of the first 16 months of data show a high level of agreement with manual and automated reference obser-10 vations from the same site. Snow accumulation is derived with an uncertainty of around 9 cm, SWE around 40 kg m − 2 a − 1 , and density around 72 kg m − 3 . This pilot study forms the base for extending observational networks with GNSS-RR capabilities, in particular in polar regions. Regional climate models, local snow modelling

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