C. Haas, EVALUATION OF SHIP-BASED ELECTROMAGNETIC-INDUCTIVE THICKNESS MEASUREMENTS OF SUMMER SEA-ICE IN THE BELLINGSHAUSEN AND AMUNDSEN SEAS, ANTARCTICA, Cold regions science and technology, 27(1), 1998, pp. 1-16
The accuracy of electromagnetic-inductive (EM) sea-ice thickness measu
rements performed from a moving icebreaker is evaluated. Ice thickness
distributions and ridge statistics are derived. In the Bellingshausen
Sea the ice was moderately deformed with mean and modal ice thickness
es of 1.3 and 0.9 m, respectively. In contrast, the heavily deformed i
ce in the Amundsen Sea had mean thicknesses between 2.3 and 3.1 m, wit
h modes between 1.6 and 2.7 m. By means of the measured apparent elect
rical conductivity on ice of known thickness, the conductivity of the
perennial summer ice was found to be significant and could not be negl
ected in the calibration of EM measurements. The high conductivity is
mainly due to the widespread occurrence of seawater-filled gaps close
to the ice surface. The system, consisting of commercially available i
nstruments, yielded reliable mean thickness estimates. This is shown b
y comparison with drill-hole measurements and visual observations. How
ever, the thickness profiles appear highly low-pass filtered compared
to their surface height profile determined with a laser altimeter. Thu
s the system possesses a limited lateral resolution such that the thic
kness of single pressure ridges cannot be resolved. This is only in pa
rt attributed to the trade-off between increasing instrument height an
d decreasing lateral resolution of EM measurements. The low resolution
is mainly due to the particular EM instrument, as its sensitivity is
highly reduced if used far above the water surface, and it has a compa
ratively long time constant of 1 s. Additionally, the water-filled gap
in the ice generally reduces the sensitivity of the measured apparent
conductivity to ice thickness changes. (C) 1998 Elsevier Science B.V.