Patent ID: 7034539

Claim:
An underground exploration apparatus comprising: an oscillator capable of selecting among two or more fundamental oscillation frequencies; a voltage-current converter for converting a voltage signal generated by the oscillator into current; a pair of electrodes placed on or buried in the ground apart from each other in order to conduct a high frequency current supplied by the voltage-current converter through the ground; a measuring unit for measuring a high frequency voltage generated between both ends of the electrodes to detect an impedance between two points of the electrodes; a retention unit for holding a value of the impedance outputted from the measuring unit for each oscillation frequency; a computing unit for calculating a difference between impedances held by the retention unit to obtain an impedance difference resulting from different oscillation frequencies; and a judging unit for detecting and judging a large change in impedance between the two points of the electrodes within a short time by at least one of the frequencies, based on the impedance difference calculated by the computing unit.