PURPOSE:To simply execute measurement with high accuracy by using a commercial signal which has been brought to frequency control with high accuracy as a signal source, stacking it in a time area by utilizing its periodicity and bringing its result to fast Fourier transform. CONSTITUTION:When a commercial frequency signal flowing to a transmission line is used as a signal source, an electric field and a magnetic field existing in a natural environment are detected by a measuring instrument 2. On the other hand, a signal synchronized with the commercial frequency signal is generated by a synchronizing signal generating circuit 1, and a detected signal is synchronized with a synchronizing signal and brought to sampling by a sampling circuit 3. Measuring data which has been extracted in such a way is added in an adding circuit 4 in a time area. Since said signal has been brought to sampling in synchronism with the commercial frequency signal by the sampling circuit 3, only an electromagnetic field of the commercial frequency increases in proportion to the number of times of stacking. On the other hand, an electromagnetic field in other natural environment does not increase in propor tion to the number of times of stacking since it has no relation to its period, and as a result, only the commercial frequency electromagnetic field is emphasized, and an S/N is improved.

Data processing method and device for probing underground specific resistance

PURPOSE:To enable the detection of a plurality of underground structures, by selecting an important point after calculating specific resistance distribution over an entire investigating region, and performing measurement and data analysis according to a five- component multi-frequency band receiving type MI investigation system. CONSTITUTION:Two-component ELF band receiving type MT investigation 1 is conducted over an entire investigating region to fabricate a specific resistance distribution drawing 2 and an important point is selected to perform the determination 3 of a five- component multi-frequency band receiving type MT investigation point. The wave forms of three magnetic field components and two electric field components are measured with respect to ultra-low frequency due to pulsation of geomagnetism, ultra-low frequency due to thunder discharge and ultra-low frequency transmitted from an omega station and five-component multi-frequency band receiving type MT investigation 4 while a specific resistance columnar drawing 5 is obtained by laminar structure analysis due to an electronic calculator and the estimation 6 of an underground structure is performed and apparent specific resistance distribution 7 in analyzed cross-sectional area due to model calculation and an actual one are compared to perform the desired interpretation 8 of an underground structure.

Underground structure investigation system

PURPOSE: To simply execute measurement with high accuracy by deriving an underground specific resistance from a ratio of an electric field component and a magnetic field component of the sum of a primary electromagnetic field radiated from a transmission line and a secondary electromagnetic field generated by a current induced under the ground by the primary electromagnetic field. CONSTITUTION: Two pieces of potential electrodes 121, 122 are embedded under the ground at a prescribed internal, usually at an interval of about 20W30m, and also, an earth electrode 13 is embedded. Subsequently, an induction coil 11 is placed so as to be orthogonal to a transmission line. A measuring instrument body 101 amplifies detecting signals from the induction coil 11 and an electric field sensor 12 by amplifiers 21, 22, respectively, and also, 50Hz or 60Hz and its higher harmonic component are extracted by filters 31, 32 and applied to a data processor 4. The data processor 4 brings an obtained signal to high speed Fourier transform and detects intensity of an electric field and a magnetic field to each frequency, and from a ratio of the electric field and the magnetic field, an underground specific resistance is calculated, and outputted by an output device 5 consisting of a printer, etc. COPYRIGHT: (C)1989,JPO&Japio

Underground probing method and device utilizing commercial frequency signal

PURPOSE:To analyze an underground structure two-dimensionally, by providing a device, which receives a very low frequency band and an ultra low frequency band, and a noise eliminating filter which eliminates the noise due to a commercial power source and comparing an apparent specific resistance value with a model calculation result value. CONSTITUTION:Very low frequency electromagnetic waves, which are propagated by the Schumann resonance phenomenon or the like and exist naturally, and ultra low frequency electromagnetic waves transmitted from an omega station are used, and the magnetic field is measured by an inductance coil 11, and the electric field is measured by electrodes 12 and 12. The coil 11 has about 50,000 turns, and electrodes 12 and 12 are about several tens meters apart from each other. A band eliminating filter 2 is installed for the purpose of eliminating the noise due to the commercial frequency. An apparent specific resistance value for every frequency is obtained on a basis of measured numeric values and is compared with the calculation result value of a layered structure model by a preliminarily programmed computer, and next, the specific resistance is changed in the depth direction and the horizontal direction, and the underground structure is analyzed two-dimensionally similarly.

Mogi Tooru

Papers

Probing and analyzing method and device for underground structure