Jökull - 01.01.2012, Síða 136

E. Magnússon et al.
Figure 2. RES lines 1991–1993 (red), 2009 (blue), 2012 (orange), RES point survey 1998–2006 (purple dots)
and lake depth measurements 2006 (black dots). Green dots show points where thickness was estimated from a
derived relation between thickness and surface slope (Figure 3). The figure only shows ice thickness estimates
adopted in the making of the bedrock DEM (<20 m difference between the ice thickness obtained from our
simple relation and the ice thickness derived by subtracting the final bedrock DEM from the LiDAR surface
DEM). – Íssjármælilínur 1991–1993 (rauðar), 2009 (bláar), 2012 (appelsínugular), íssjármælipunktar 1998–
2006 (fjólubláir punktar) og dýptarmælingar á lónum 2006 (svartir punktar). Grænir punktar sýna staði þar
sem ísþykkt var áætluð út frá reynslusambandi yfirborðshalla og ísþykktar (3. mynd).
same antennae as used for the previous analogue sys-
tem, a similar receiver bandwidth is obtained. Data
are recorded digitally, making post-processing easier
compared to the analogue system. The final process-
ing steps are however essentially the same for both
systems and include digitizing the reflected bedrock
signal from a radargram showing distance along the
profile on the x-axis and the depth of the reflector
on the y-axis (Figure 4). This depth is derived from
the difference in travel time of the wave travelling
along the surface and the reflected wave. Geograph-
ical position and surface elevation are assigned to
134 JÖKULL No. 62, 2012