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Responsive Autonomous Rovers to Enable Polar Science

General

Organisation
Project start
01.01.2017
Project end
31.12.2018
Type of project
ARMAP/NSF
Project theme
Instrument Development
Project topic
Cryosphere
Instrument Development

Fieldwork / Study

Fieldwork country
Greenland (DK)
Fieldwork location

Geolocation is 0, 0

Fieldwork start
21.06.2017
Fieldwork end
23.06.2017

SAR information

Fieldwork / Study

Fieldwork country
Greenland (DK)
Fieldwork location

Geolocation is 0, 0

Fieldwork start
23.06.2017
Fieldwork end
21.07.2017

SAR information

Fieldwork / Study

Fieldwork country
Greenland (DK)
Fieldwork location

Geolocation is 0, 0

Fieldwork start
13.07.2018
Fieldwork end
24.07.2018

SAR information

Fieldwork / Study

Fieldwork country
Greenland (DK)
Fieldwork location

Geolocation is 0, 0

Fieldwork start
18.07.2018
Fieldwork end
22.07.2018

SAR information

Project details

02.12.2019
Science / project plan

.

Science / project summary
In order to determine the mass balance of the Earth’s ice sheets, and and eventual contribution of glacial melt to sea level rise, researchers must understand the spatiotemporal variations in snow accumulation and firn compaction rates. The amount of snow that falls and accumulates from year-to-year across the ice sheets acts as a hydrological sink, lowering sea level, whereas ablation or melt that runs off ice sheets acts to increase sea level. The total ice-sheet surface mass balance is primarily composed of the total mass of snow that accumulated minus the mass of runoff from ice melt Subtracting the total ice mass lost through discharge at glacier calving fronts, known as the input-output method provides the ice-sheet mass balance. This project focuses on the positive component of mass balance: snow accumulation. The ice-sheet mass balance can also be measured by monitoring changes in surface elevation from satellite borne altimeters (e.g., NASA’s ICESat and upcoming ICESat-2, ESA’s CryoSat-2). The measured elevation change is used to determine the volumetric change, which must be converted to mass through knowledge of the density of the material gained or lost. Along the periphery of Greenland in the ablation zone, the change is easily attributed to solid ice, but in the interior, the conversion from volume to mass is less straightforward. The presence of a firn layer in the accumulation zone complicates conversion to mass for a few reasons. Firstly, firn is less dense than ice. The observed elevation change is the summation of change to the firn thickness and to the underlying ice column, which must be properly partitioned to adequately assign a density to the observed change. Secondly, variations in the firn compaction rate result in surface elevation fluctuations that are not the result of a mass change. Therefore, determining the ice-sheet mass balance requires a precise understanding of the spatiotemporal variations in snow accumulation and firn compaction rates, both of which are challenging to measure frequently and at large spatial scales. While spatiotemporal measurements of snow accumulation are difficult and few, measurements of firn compaction are even rarer. In Greenland, tracking the displacements of features observed using borehole optical stratigraphy over a single year at Summit provided measurements of the vertical compaction profile of the firn. Finally, repeat measurements of the firn density profile, derived using a neutron scattering technique, along a ~500 km traverse allowed Morris and Wingham (2011; 2014) to measure strain rates as a function of depth and develop a new densification equation based on their findings. The models developed by the aforementioned studies are tuned by data ranging from a few data points to a few 10s of sites, which limits their use outside of the surveyed areas. Thus, some ground-truthing of the temporal and spatial variability of compaction rates derived from firn densification models exists, but their evaluation would benefit from a method that can easily measure compaction rates over large areas. This project aims to expand our understanding of the spatiotemporal variations in snow accumulation and firn compaction rates by using GPR towed by an autonomous rover.
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