By Sainan Sun
The inland of Antarctica is covered by thick ice of up to 4000 meters, which is accumulated over thousands of year. During this long term, ice is compressed in layers and we can get historical climate information from these layers.
Therefore, the internal structure and ice properties, as well as the basal properties are of glaciological and climatological interest. Ice-radar is a very useful tool for the study of glaciers and ice sheets. Nowadays, ice-radar is widely used in the study of Antarctica.
Radio-echo sounding techniques are based on the propagation of electromagnetic wave through the ice. A radar system contains the wave generator, the transmitting antenna and the receiving antenna.
The transmitter sends a pulse downwards and it is partially reflected at discontinuities and travels back to the surface, where the signals are detected by the receiver.
The radio-wave propagation through ice and the intensity of the radar-wave reflection are controlled by the permittivity and conductivity, which is in turn determined by ice properties such as density, acidity and anisotropy of the crystal fabric.
The radar systems for glaciology study can be operated directly on the glacier surface or from a helicopter or aeroplane (Figure). The advantage of surface based radar system is less power loss, while airborne radar measurements cover larger areas.
For different observations, choice of radar frequency should be made considering the radar resolution and wave penetration. The radar resolution increases with frequency, while wave penetration decreases with frequency.
Therefore, high-frequency radars (e.g. 800 MHz) for high-resolution are often implemented to study the shallow snow layer; mid-frequency radars (e.g. 200 MHz) are implemented in the investigation of the firn layer; and low-frequency radars (< 25 MHz) for the study of the deep solid ice and the ice-bedrock interface.
The observed datasets are then processed to reconstruct the internal layers and the basal layer. Finally, we can get the profile of the observed region as below.