Jökull - 01.01.2012, Síða 116

A. Schomacker et al.
Table 1. Overview of the aerial photographs and DEMs used in this study. – Tafla 1. Yfirlit yfir loftmyndir og
hæðarlíkön sem notuð voru í þessari rannsókn.
Date of Images Flying altitude DEM grid cell Total RMS Remarks
photography recorded by (m a.s.l.) size (m) triangulation
residual (m)
1938 Geodetic Institute, Low – – Oblique images,
Denmark cover upper part of glacier.
29.08.1945 USAAF 7010 – – Poor image quality.
09.08.1960 USAAF – – –
13.08.1960 – 3965 3, 5, 10 1.8
13.09.1975 Landmælingar Íslands 5725 – –
10.09.1978 Landmælingar Íslands 5815 – –
22.08.1980 Landmælingar Íslands 6705 – –
04.09.1984 Landmælingar Íslands 5486 – –
31.08.1990 Landmælingar Íslands 5486 – – Partly cloudy.
14.08.1996 Landmælingar Íslands 5486 3, 5, 10 1.3 Partly cloudy.
2001 Loftmyndir ehf 3555 3, 5, 10 4.4
11.08.2004 Loftmyndir ehf 3625 3, 5, 10 3.6
2007 Samsýn ehf. – – – Only orthophotographs.
29.08.2009 Loftmyndir ehf. 3475 – –
July/Aug. 2010 Icelandic Meteorological Office – 5 < 1 LiDAR
ences, University of Iceland). The LiDAR-derived
DEM of Sólheimajökull has a spatial resolution of
5 m, and was included in the DEM time series analy-
sis in this study. No aerial photographs were obtained
during the airborne LiDAR campaign.
The time-series of DEMs were handled and an-
alyzed in ArcGIS 10. Differences between individ-
ual models provide a quantification of the surface
elevation change (erosion/deposition and ice thin-
ning/thickening). All DEMs were resampled to 10 m
grids when calculating the difference-DEMs in order
to minimize noise from small-scale changes and un-
evenly aligned pixels. This approach gives a valuable
insight into changes in glacier margins and forefields
(e.g. Nuth et al., 2007; Schomacker and Kjær, 2007;
Schomacker, 2008; Abermann et al., 2011).
Geomorphological mapping
Orthorectified aerial photographs and visualizations
of the DEMs were exported to ArcGIS 9.3 for geo-
morphological mapping. Along with the mapping in
ArcGIS, images were inspected in stereo on the digi-
tal photogrammetrical workstation. We aimed to iden-
tify and map glacial landforms to give an overview of
the valley and the modern glacier forefield. The ge-
omorphological map was verified and completed dur-
ing field work in 2007–2009.
Sedimentological logging
In order to decipher the genesis of landforms and their
stratigraphical context, river-cut geological sections
along the main river, Jökulsá á Sólheimasandi, were
investigated. For stratigraphical purposes, sections
were logged using the data chart of Krüger and Kjær
(1999). Exposed sections in landforms were docu-
mented by photography and sketched.
Dating
Organic material is rarely encountered in the river-
cut sections along Jökulsá á Sólheimasandi. However,
two samples of vegetation buried by glacial sediments
were recovered and submitted for AMS 14C dating
at the Ångström laboratory in Uppsala, Sweden. 14C
ages were calibrated to calendar years using OxCal v.
4.1.7. These age determinations provide a maximum
age for landforms on the surface of the sampling lo-
cality.
We also sampled three large boulders on lat-
eral moraine crests and one site with glacially stri-
ated bedrock for Cosmogenic Exposure Dating (CED)
114 JÖKULL No. 62, 2012