Time-Domain Electromagnetic Sounding

The electrical structure of the earth can be studied effectively to depths of 3-5 km using a time-domain electromagnetic sounding method. In the method, an electromagnetic field is generated by passing a current step with an amplitude of several hundred amperes through a grounded wire 1-2 km in length. Then, the magnetic induction is detected and recorded at distances of 10-12 km. Experience with several thousand such soundings has shown them to provide accurate information on the electrical structure of the subsurface.