|
Definition:
|
A radar, usually a pulsed system with one transmitting and one receiving antenna, operating at a frequency suitable for imaging the subsurface. In glaciology, low frequencies (2220 mhz) are suitable for ice thickness measurements whereas higher frequencies of several hundred mhz are suitable for snow thickness measurements, including detection of the current summer surface and older Annual layering (see radar method). Higher frequencies yield better resolution but may not allow very deep penetration; lower frequencies exhibit the reverse properties. Choice of frequency is therefore paramount. Radar imaging of the subsurface relies on accurate determination of the two-way travel time of the radar wave, which depends on the density. Reflections are caused by contrasts in the (complex) relative dielectric constant at interfaces between layers. Illustrative values of the real part of the relative dielectric constant, at frequencies used by ground-penetrating radars, are 1 for air, ~3.15 for pure ice, ~10 for bedrock and 88 for water at 0
|