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observed ice topography. These drag coef
cients are then used to illustrate the
effects on Ekman pumping when only the spatial variations of the oceanic drag are
considered.
2 Data and Methods
The data used for this study were collected by helicopter
flights over the Arctic
Ocean during a campaign with the ice breaker RV Polarstern in summer 2011. The
map with the tracks along which the data have been collected is shown in Fig.
1
.
During the campaign, two different types of data have been collected: sea-ice
surface elevation pro
fl
les using a laser altimeter and sea-ice thickness using the
so-called EM-bird. The laser altimeter pro
les are collected using a Riegel LD90-
3100HS that was introduced in 2001. This instrument has a wavelength of 905 nm,
a sampling frequency of 100 Hz and an accuracy of
±
1.5 cm. The point spacing is
about 30
les recorded by the laser altimeter show an altitude
variation due to the surface roughness of the ice and a variation at a lower frequency
due to the movement of the helicopter. In order to remove this movement, a
combination of low and high pass
-
40 cm. The pro
filters is used (Hibler
1972
).
The EM-bird is a device to measure the sea-ice thickness directly using elec-
tromagnetic induction (Haas
2004
; Haas et al.
2009
). The EM-bird contains two
coils for transmission and receptions of electromagnetic
fields and can measure the
distance between the instrument and the ice-ocean interface by using the electro-
magnetic
field generated by induction in the conductive sea water. In addition, a
Fig. 1 Map of the Arctic
Ocean with the location of the
laser altimeter and EM-bird
measurements. The red circle
encloses the measurements
taken in the area that in the
present study is referred to as
the Central Arctic
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