Observing surface properties of ice sheets from satellite and airborne remote sensing techniques

Abstract

Surface processes of ice sheets such as surface melt, near-surface air temperatures, and firn (densified snow) compaction play indirect, yet critical roles in the calculation of an ice sheet’s mass balance. Surface melt contributes to ablation, fueling mass loss via runoff and destabilization of ice shelves. Near-surface air temperatures and compaction rates influence firn densification, which plays a key role in converting height changes from satellite altimetry to mass changes of an ice sheet. This work is aimed at improving surface processes of ice sheets that are otherwise challenging to observe. First, we create a dynamic, physics-based threshold of AMSR-2 brightness temperatures using a snow radiative transfer model to quantify melt across the Larsen C Ice Shelf as well as several Antarctic sites. In addition to surface melt, another critical unknown process is compaction. Snow falls and accumulates over ice sheets and ultimately compacts and densifies into firn. We quantify this mass-conserving process by tracking the evolution of the snow and firn stratigraphy across the Greenland Ice Sheet using airborne snow radar. We use an automated technique to strain, or uniaxially compress, older radar data in the vertical direction and shift it downward (simulating the process of accumulation) to match co-located newer radar data. Using this methodology, we are able to quantify and validate modelled snow accumulation and firn compaction. Additionally, we focus on spatially downscaling near-surface ice sheet temperatures from an atmospheric reanalysis dataset. We show that, using a technique informed by adjacent neighbors neural network technique, we can reduce model errors with respect to ice sheet temperature observations. These measurements of ice sheet accumulation, compaction, surface melt, and near-surface temperature improve our understanding of ice sheet surface properties and the quantification of the contribution to sea level change, as well as advancements in remote sensing techniques.