Patent ID: 7095357
Filing Date: 2006-08-22
Classification: G01S,G01V,H01Q

Abstract:
1. A method for transmitting an electromagnetic signal or pulse to and through an earth formation and recovering from the return signal or pulse, select frequencies that are strongly coupled to the earth at aircraft heights or on the surface of the earth and at the same time penetrate to great depths of the order of tens of thousands of feet or more including the steps of: (a) disposing capacitor plates having a largest dimension L either in direct contact with the earth formation or elevated a height Z above the earth formation to form an earth capacitor comprising the plate assembly, the air or space between the plates and the earth if Z>0 and the region in the earth formation either in direct contact with the plates or separated from the plates by the height, Z>0, whereupon returning frequencies are selected that in the earth formation are electrically coupled or for each frequency up to the highest selected frequency, where KoZ<1 and Ko is the wave number in air, (b) applying a short voltage or current pulse via a transformer with core magnetic flux adjusted for enhanced radiation at lower frequencies <500 KHZ, across the capacitor plates from a pulse generator to transmit electromagnetic radiation into the earth formation, where for each returning lower frequency component of the electromagnetic radiation, the largest dimension L is small such that Re(KL)<1 and KoZ<1, where Re(K) is the positive wave number in the earth formation of said lower frequency component and Ko is the positive wave number in air of each returning lower frequency component at all frequencies present <1 MHZ and indeed very much less than 1 MHZ, (c) detecting electromagnetic radiation that has propagated through the earth formation in response to application of the short voltage or current pulse, and (d) processing only frequency components of the desired electromagnetic radiation, in a select lower frequency window, in the broad frequency continuum <1 MHZ which lower frequencies have propagated into the earth formation to penetration depth very much greater than of the order of several tens of thousands of feet to detect the electrical properties, that is, the reconstituted pulse amplitude as a function of time is transformed into the magnitude of the relative dielectric and the conductivity as a function of depth using a model for a system of vertically traveling up-going and down-going waves and Maxwell's Equations to deduce said electrical properties with an iterative process.