ERSC 3V93 Lecture 50: Seismic Methods v2 II
6 May 2016
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Document Summary
Radio detection and ranging radar" technology developed in wwii. 1950"s accidental discovery of ice penetrating capabilities by us air force in greenland. 1970"s airborne radar used to measure thickness of polar ice sheets. 1980"s georadar" adapted for imaging near surface. 90"s space borne radar used extensively e. g. srtm. Measure two-way travel time of pulsed radio signals reflected at geologic boundaries with contrasting electrical properties (permittivity) near-vertical incidence. Em radiation exists at frequencies from 1 hz (atmospheric micropulsations) to x-rays at 1024. Hz (x-rays), gpr uses range: 10 mhz 1 ghz wavelengths 0. 1 - 100 metres. Em waves consist electrical field (ex) and a magnetic field (my) oriented at right angles to direction of wave propagation both travel at speed of light (c = 3 x 108 ms-1) Electromagnetic induction current passed through coil produces a electromagnetic field magnetic moved in coil produces electric current (emf)
