EO4GRHO: A multi-satellite synthesis constraining the near-surface density profile of the Greenland Ice Sheet through time and space

Satellite remote sensing is one of the few ways to comprehensively monitor changes in the Greenland Ice Sheet ‘s surface conditions through both time and space. From orbit, satellites can efficiently collect repeated measurements covering the entire ice sheet surface and elucidate the processes controlling how Greenland responds to a changing climate. Active radar and passive microwave measurements are especially valuable datasets, as cloud cover or illumination conditions are not limiting factors.

In this vein, recent research has shown how near-surface properties (i.e., density and roughness) across Greenland can be derived through the Radar Statistical Reconnaissance analysis of Ku-band ESA CryoSat-2 and Ka-band CNES/ISRO SARAL surface echo powers. While this approach yields densities at individual depths in the near-surface, a fuller result would include constraining a continuous density profile as a function of depth. At the same time, L-band ESA SMOS passive microwave brightness temperatures are sensitive to the entire snow-firn-ice column. However, the inversion of brightness temperatures for a property of interest in a specific layer (e.g., snow wetness, density, etc.) requires numerous assumptions regarding the subsurface conditions.

The EO4GRHO project seeks to merge these two approaches to investigate whether the inversion of SMOS brightness temperatures using a subsurface structure pre-conditioned with results derived from the analysis of radar altimetry surface echoes (i.e., density at known depth(s)) can provide a more complete picture of how Greenland Ice Sheet near-surface densities vary with depth, time, and space. Here, EO4GRHO leverages a decade (2013-2023) of contemporaneous CryoSat-2, SARAL, and SMOS measurements, makes use of modelled brightness temperatures from the Snow Microwave Radiative Transfer model software and, finally, hundreds of in-situ measurements. The ultimate aim of EO4GRHO is to operationally produce observation-based maps and time series for the near-surface density structure of the Greenland Ice Sheet that can be incorporated in future mass balance calculations.