Patent ID: 6911823

Claim:
A method for characterizing a target metal object in ground, comprising: (a) characterizing the ground at two distinct sinusoidal frequencies of interrogation; (b) characterizing the target metal object in the ground at said two frequencies: (c) characterizing a plurality of reference metal objects apart from the ground at said two frequencies; (d1) computing a respective first number for each of said reference metal objects using the characterizations of said steps (a) and (c); (d2) computing a second number for the target, metal object using the characterization of step (b); (e) comparing said first and second numbers; and (f) characterizing the target metal object with the result of the comparison of said step (e), wherein the characterizing step (a) provides for determining at least the ratios (Y 1 ground/Y 2 ground) and (X 1 ground/X 2 ground), where X 1 ground, Y 1 ground are reactive and resistive components of the response of the ground to interrogation at a first of said two frequencies, where X 2 ground, Y 2 ground are reactive and resistive components of the response of the ground to interrogation at a second of said two frequencies, wherein the characterizing step (c) provides for determining at least the ratios, for each of the objects, (X 1 object/X 2 object), (Y 1 object/Y 2 object), and (Y 2 object/X 2 object), where X 1 object, Y 1 object are reactive and resistive components of the response of one of the objects to interrogation apart from the ground at said first frequency, where X 2 object, Y 2 object are reactive and resistive components of the response of said one of the objects to interrogation apart from the ground at said second frequency, and wherein said first number is proportional to: tan −1 [(Y 2 object/X 2 object)·[(Y 1 ground/Y 2 ground)−(Y 1 object/Y 2 object)]/[(X 1 ground/X 2 ground)−(X 1 object/X 2 object)]].