Geology Reference
In-Depth Information
(a)
(b)
-5
-10
-15
-20
Thin ice
-25
HH
HV
VV
-30
-35
0
30
60
Ice thickness (cm)
90
120
150
(c)
(d)
3.0
150
2.5
120
2.0
90
1. 5
60
1. 0
30
0.5
0.0
0
0
30
60
Ice thickness (cm)
90
120
150
0
30
60
90
120
150
Observed ice thickness (cm)
Figure 10.38 (a) L‐band airborne polarimetric SAR data from the Sea of Okhotsk in 1997 SAR image; (b) back-
scattering coefficient versus ice thickness; (c) co‐polarization ratio versus ice thickness, and (d) observed versus
estimated thickness [adapted from Nakamura et al ., 2005].
When it reaches the underside of the sea ice, it generates
eddy currents in the seawater. These currents induce a
secondary EM field, which returns through the sea ice
cover and can be measured by the receiving coil. The
strength of the secondary EM field is related to the dis-
tance from the receiving coil to the ice‐water interface
(the conductive surface). If the height of the transmit-
ting coil above the snow‐ice surface is known, then the
ice thickness (including the depth of possible snow
cover) can be determined. That height can be obtained
using a laser altimeter. Transmitting and receiving coils,
a laser altimeter, a geographic positioning system, a
0 and surface roughness.
The correlation coefficient is 0.70; significant at 99%
level in this case.
regression equation between
hh
10.4.5. Helicopter‐Borne Electromagnetic Sensor
Sea ice has a very low electrical conductivity (0-50
mS/m) compared to seawater (2400-2700 mS/m), which
is a very good conductor. If a low‐frequency EM gener-
ated by a transmitting coil strikes a sea ice surface, it
should penetrate the ice volume almost unaffected.
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