Jökull - 01.01.2005, Side 157

The 2003 NW-Mýrdalsjökull Survey
The permanent stations were set to record data at
30 sec intervals with a 13◦ elevation mask. The Trim-
ble 5700 receivers were set to log continuously, while
the Trimble 4000 receiver was set to log six 1 hr files
spaced at 4 hr intervals each day (start times of 00, 04,
08, 12, 16, 20 h).
Figure 3. Semi-permanent GPS-station visit. The ab-
lation (lowering of surface) from April 22 to June 28
at this site was about 3 m. Pictured are Elín, Björn,
and Gísli Árni. – Ein af langtímamælistöðvunum.
Bráðnun (lækkun yfirborðs) frá 22. apríl til 28. júní
var um 3 m. Á myndinni eru Elín Helga Þórarinsdótt-
ir, Björn Oddsson og Gísli Árni Gíslason, sem eiga
miklar þakkir skyldar fyrir hjálpina.
The new Trimble 5700 receivers stopped record-
ing couple of days after being installed due to hard-
ware problems. The Trimble 4000 receiver also only
ran for a short time, perhaps due to power disrup-
tions from which they did not recover. On Thursday
September 18, 2003, we finally managed to retrieve
the instruments. The trip had been cancelled several
times, due to frequent low pressure fronts across the
south coast.
Radar measurements
A University of Washington radar system operating at
5 MHz was used. The distance between the transmit-
ting (T) and receiving (R) antennas was 15 m and data
was collected every 8 m along each survey line.
The data was band-passed between 3 and 7 MHz
(Figure 5). Ice thickness in the area ranges between
about 112 m to 304 m. The intensity of radar echoes
changed by a factor of 10 within the study area due to
changes in bed conditions, internal reflectors and/or
surface conditions (Matsouka et. al., submitted).
The strong reflector in the S-part of Figure 5 is
most likely from an ash layer from the Katla eruption
in 1918.
Figure 4. The semi-permanent GPS-station setup.
The solar-panels were used to charge the battery, and
the wooden framework was designed to slide up-and
down. – Uppsetning langtíma GPS-stöðva. Sólarsell-
urnar voru notaðar til að hlaða rafgeyminn og grind-
in var hönnuð þannig að hún fylgdi yfirborðinu.
Ablation measurements
The poles at the semi-permanent stations and wires
at other sites also served as ablation measurement
points. The wires had a weight attached to the end that
went into the drill hole and then froze. The difference
in the length of the wire between measurements thus
provides a measure of surface subsidence. Following
installation in April, measurements were made at ac-
cessible points in June and September.
JÖKULL No. 55, 2005 157