A high detail benchmark dataset of mid-1980's ice margin positions for all Greenland ice masses
Abstract
We introduce the first complete high resolution aerophotogrammetric map of Greenland ice masses, including both the ice sheet and all local glaciers and ice caps (GIC). This PROMICE (Programme for Monitoring of the Greenland Ice Sheet) product is based on 1:150.000 scale vertical aerial photographs acquired between 1978 and 1987. The flight campaigns covered N and most of NE Greenland in 1978, E and SE Greenland in 1981, all of the west coast from 60°N to 87°N in 1985, and the remaining part of NE Greenland in 1987. Over the following decades, 1:100,000 and 1:250,000 scale topographic maps were produced by GEUS (Geological Survey of Denmark and Greenland), formerly GGU (Greenland Geological Survey) and by KMS (Danish National Survey and Cadastre). KMS also surveyed the vast majority of geodetic ground control points used for aerotriangulation. We manually edited the vector polygons from these topographic maps to correct issues related to debris covered ice, medial moraines, supraglacial lakes and ice contact lakes. The local ice masses in topological contact with the ice sheet but clearly independent in their ablation and accumulation areas were separated from the ice sheet by manually digitizing ice divides based on surface topography, resulting in all polygons belonging to one of the 'disconnected ice mass', 'local ice mass' or 'ice sheet' classes. The total glacierized area of the ice sheet and GIC in the 1980's was 1,804,638 km2 ± 27,268 km2 and the GIC alone covered 88,083 ± 1,240 km2. This GIC extent is significantly larger than most previously reported estimates, and it is in line with the area of 89,273 ± 2,767 km2 found independently by Rastner et al. (The Cryosphere Discuss., in review) using 1999-2002 30 m Landsat 7 imagery for ice masses with 'no or weak connection' to the ice sheet. It is not possible to assess glacier change by comparing these two aggregate totals because they are indistinguishable within the reported uncertainties, and also because the splitting of ice masses essentially independent but in topological contact with the ice sheet includes a degree of subjectivity. However, terminus positions and individual ice masses can easily be compared between the two datasets. A third dataset, the GIMP 15 m ice cover grid based on 1999-2001 panchromatic Landsat 7 scenes (Howat & Negrete, in prep.) has recently become available. It offers a level of detail closer to the PROMICE map, and we discuss several cases of marked frontal changes, particularly at marine terminating glaciers, and detection of glacier surge events. The mid-1980's PROMICE glacier outlines provide a regionally-synchronous benchmark of ice margin positions from before the widespread availability of high resolution satellite imagery, and with a higher detail than the products currently being released based on pre-SLC failure Landsat 7.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.C13H..07C
- Keywords:
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- 0720 CRYOSPHERE / Glaciers;
- 0726 CRYOSPHERE / Ice sheets;
- 0758 CRYOSPHERE / Remote sensing;
- 0772 CRYOSPHERE / Distribution