Image Processing Reference
In-Depth Information
Figure3.17 Radar image of Wadi Kufra, Libya. (CourtesyofNASA)
1970s and discovered regions of ice that had what appeared to be very flat, smooth
terrain underneath, which was consistent with the radar signature one would expect
to see from liquid water under the ice. Seismic data and satellite imagery later
confirmed the existence of the lake and its full extent. 10 Imaging through the
ice is possible only in the microwave band of the electromagnetic spectrum, as
shorter wavelengths of light are highly absorbed. Microwaves travel through the
ice of Antarctica and reflect off the material underneath, mapping the topology of
whatever lies beneath; it is as though the ice were removed completely. Figure 3.18
shows a 6-cm-wavelength microwave image of the lake taken byRadarsat, a
Canadian satellite equipped with imaging radar that flies in a circumpolar orbit,
enabling it to scan both the Arctic and Antarctic regions. The image is made of
multiple rectangular images that are overlaid. The images are from theswaths
defined by the orbital path of the satellite. Note the rough terrain surrounding the
lake; this is the mountainous topology of the rock beneath the ice sheet. The lake's
“surface” appears smooth, since we cannot see the rock beneath the lake, which is
effectively shielded by the reflective properties of the liquid water.
10 Oliver Morton, “Ice Station Vostok,”Wired8(4), 121-146 (April 2000).
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