Abstract
The elevation of ice sheets changes due to climate change, and satellite altimetry is the preferred tool for measuring ice sheet-wide height changes. In situ validation is needed to ensure the quality of the observed elevation changes, but the cost often limits the amount of in situ data which can be collected. As more tourists are accessing the ice sheets, citizen science might provide in situ data in an environmentally friendly and cost-efficient way. Here, we investigate the opportunistic kinematic global positioning system (GPS) profiles across the Greenland ice sheet, collected by the American-Icelandic expedition on the Greenlandic icecap 2018. The collected GPS data are in good agreement with the widely used NASA’s Operation IceBridge Airborne LiDAR data measured within ± 10 days, with an average difference of 10.7 cm ± 11.7 cm. The main difference is attributed to changes in the compaction of the snow while driving and changes in the tires’ pressure. The kinematic GPS data are then compared with data from the European Space Agency’s CryoSat-2 mission. Here, an average bias of 92.3 cm ± 65.7 cm in the two records is observed between the spring CryoSat-2 and the truck GPS data obtained largely in the dry-snow zone. This suggests that the surface penetration of Ku-band radar on the Greenland ice sheet and the observed magnitude are consistent with the literature. Finally, we compared the 2018 GPS data to a profile obtained in 2005 near Kangerlussuaq, West Greenland. Here, the records show an average ice-elevation decrease of 9 m, with peaks at 26 m. These results show that the citizen science kinematic GPS data can provide high-resolution data necessary for the validation of satellite altimetry, with the added benefit of potential direct sampling properties of the surface and firn. Linking up with citizen-science expeditions is a beneficial way of providing cost-effective satellite validations and may also have a societal impact by involving more people in the climate monitoring of ice sheets.
Highlights
The launch of the European National Space Institute (Space) Agency’s (ESA’s) first European remote sensing satellite (ERS-1) in 1991 made the Greenland ice-sheet-wide monitoring of the surface-elevation change possible
From the statistics of the different inter-comparisons given in Table 1, it is evident that ΔHOIB has fewer data points than CryoSat-2 despite having a much higher sampling frequency
This is partly because most of the Operation IceBridge data are near the coast, leaving few overlapping areas with Arctic Trucks, while CryoSat-2 has a larger coverage
Summary
The launch of the European Space Agency’s (ESA’s) first European remote sensing satellite (ERS-1) in 1991 made the Greenland ice-sheet-wide monitoring of the surface-elevation change possible. Satellite altimeters have provided an unbroken record of changes in ice-sheet surface elevation (Forsberg et al 2017; Shepherd et al 2018 Sørensen et al 2018a). This 30-year record from ERS-1, ERS-2, Envisat, ICESat, CryoSat-2, and the latest ICESat-2 satellites will continue into the future with the commissioning of the Sentinel-3 satellite series by the European Commission (Seitz et al 2010).
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