CN100487493C - Magnetotelluric impedance measuring method - Google Patents
Magnetotelluric impedance measuring method Download PDFInfo
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- CN100487493C CN100487493C CNB200610078739XA CN200610078739A CN100487493C CN 100487493 C CN100487493 C CN 100487493C CN B200610078739X A CNB200610078739X A CN B200610078739XA CN 200610078739 A CN200610078739 A CN 200610078739A CN 100487493 C CN100487493 C CN 100487493C
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Abstract
This invention relates to magnetotelluric survey data signal processing technology. It is a magnetotelluric impedance measurement method. Step: the signal acquisition by the least square method magnetotelluric impedance, and consulate frequency of the electric field and magnetic field signal coherent signal, when more than 75 percent of coherent measurement frequency and impedance in the 0.7-1 phase in the rate of broadband not within the 175-180, magnetotelluric impedance calculation and the results recorded or graphical format. Otherwise, a robust method magnetotelluric impedance type of interference or under the time domain or frequency domain using wavelet automatic threshold pressure on the magnetotelluric method noise signal noise filtering pressure, the invention is conducive to raising magnetotelluric data accuracy and reliability to avoid the man-made factor of magnetotelluric impedance calculation of the impact and relevance of a single judge by MT data quality in near-field presence made an error.
Description
Technical field
The invention belongs to geophysical exploration technology, be specifically related to the magneto-electrotelluric survey signal data and handle, is a kind of magnetotelluric impedance measuring method.
Background technology
The method of geophysical survey magneto-electrotelluric survey, normally by mt (MT) electric field or magnetic field sensor image data, the electric field of output or field signal enter A/D change-over circuit output digital signal by filtering and amplifying circuit, through processing such as filtering, sampling, gain corrections, the impedance of output MT calculated signals mt, and result of calculation shown with graphics mode, be used for reflecting the situation of exploration targets.
Obtain reliable MT measurement data, the MT impedance computation is crucial.Because the MT method adopts natural electromagnetic field signal as field source, two orthogonal electric field components and magnetic-field component that the MT method is measured are subjected to various interference inevitably.In the MT impedance computation, with field signal as input signal, with electric field signal as output signal.Transport function when the MT impedance computation is equivalent to ask for two output signal responses of two input signal excitations (quadrature field) (orthogonal electric field).Impedance computation method the earliest is a least square method, the noise Gaussian distributed of this method hypothesis MT signal.But above-mentioned hypothesis is disturbing bigger situation to be difficult to satisfy, and flying spot appears in the MT measurement result constantly.At above-mentioned situation, Sutarno and Vozoff have proposed robust (Robust) method (the D.Sutarno and K.Vozoff of mt impedance in 1991, Phase-smoothed robust M-estimation of magnetotelluricimpedance functions, Geophysics, v56, n12, p.1999-2007,1991).Egbert and Livelybrooks had further developed robust method (Gary D.Egbert and Dean W.Livelybrooks afterwards, Single station magnetotelluric impedance estimation:Coherence weighting and the regression M-estimate, Geophysics, V61, n4, p964-970,1996.).Robust method has 2 shortcomings: one, during MT signal noise Gaussian distributed, robust method result of calculation is not optimum, is suboptimum; Two, calculated amount is big, computing time than least square fado several times.On the other hand, when interference was very big, robust method was also powerless.Because it is not flying spot that the robust computing method requires to have at least in all measurement data the point more than 50%, could obtain reliable measurement result.In these cases, the MT signal of measuring is carried out filtering, up-and-coming a kind of data processing method when just having become interference very big.Yet the MT signal is a random signal, all exists with random signal on the whole frequency of measuring, and is unfeasible with common filtering method.Because disturb the same random signal that shows as with the MT signal.In order to address the above problem, Trad and Travassos proposed in 2000 with interference (the Daniel 0.Trad and JandryM.Travassos in the small echo threshold values filter method compacting MT magnetic signal, Wavelet filtering of magnetotelluric data, Geophysics, V65, n2, P482-491,2000.).Concrete grammar is after with wavelet transformation the MT signal being carried out multiple dimensioned decomposition, the wavelet decomposition result on one or more yardsticks to be adopted threshold values filtering.Said method also has three shortcomings, the one, the big probability that occurs that disturbs was very little during MT measured, and the measurement data more than 90% just can meet the demands with Robust Estimation method or Least Square in Processing, adopts little wave pressure to make an uproar in these cases, not only waste computing time, and can filter useful signal.Because which kind of method filtering no matter the MT signal distributions on whole measurement frequency range, adopt, all can impact useful signal.The 2nd, determine that the threshold values of threshold values filtering does not have computable foundation, determine the threshold values size by people's experience after just being divided into many levels, human factor is very big, and application has difficulties in practice.The 3rd, calculated amount is big, is tens of times of least square method required time.
In addition, be the degree of coherence of electric field signal and field signal to MT quality of data basis for estimation at present.
With the field signal is input signal, and electric field signal is an output signal, the degree of coherence in electric field and magnetic field
Be defined as follows:
In the formula, Φ
Xy(z), Φ
Xx(z) and Φ
Yy(z) represent cross-power spectrum, field signal auto-power spectrum and the electric field signal auto-power spectrum of electric field and field signal respectively.
Usually, degree of coherence is near 1, and the expression quality of data is good, and degree of coherence is near 0, and the expression quality of data is poor.Yet when electric field signal and field signal were subjected to the homology near-field interference, degree of coherence equaled 1 substantially, only utilized degree of coherence to come the judgment data quality to obtain wrong result sometimes.For example, near transformer station, city and mine, its interference often is presented as strong homology near-field interference, and at this moment degree of coherence utilizes degree of coherence to select data will cause the strong jamming data to be retained, thereby causes the poorest MT impedance measurements near 1.
Summary of the invention
The object of the invention is to provide a kind of result who overcomes the single MT impedance measurement technique of present employing that the deviation shortcoming is arranged, can be according to the type and the quality of data of mt signal interference, determine MT impedance measurement step, can improve a kind of magnetotelluric impedance measuring method of the speed of MT impedance computation.
The present invention adopts following technical scheme:
Magnetotelluric impedance measuring method adopts usual way to gather electric field or magnetic field data, is converted to digital signal by filtering with after amplifying, and adopts following steps:
1) adopt least square method to calculate the mt impedance to the signal of gathering, and calculating frequency electric field signal and field signal degree of coherence, when measure more than 75% the frequency degree of coherence be 0.7-1 and impedance in phase place all be not 175-180 degree in wide frequency ranges, carry out step 4), otherwise carry out step 2);
2) adopt the robust method to calculate the mt impedance, calculate electric field signal and field signal degree of coherence, if measure the frequency degree of coherence more than 75% and be 0.7-1 and impedance in phase place all be not that 175-180 degree carry out step 4) in wide frequency ranges, otherwise carry out step 3);
3) adopting the small echo threshold values to press the method for making an uproar that the mt signal is carried out filtering according to interference type automatically in time domain or frequency field presses and makes an uproar, utilize the robust method to calculate the mt impedance again;
4) calculate mt impedance and show with outcome record or with graphics mode.
Described small echo threshold values presses the method for making an uproar when having fixed frequency to disturb, and then carries out small echo threshold values pressure in frequency field and makes an uproar.
Described small echo threshold values is pressed and is made an uproar method when instantaneous interference is arranged, and presses in time domain and makes an uproar.
Described wide frequency ranges is by a plurality of frequency impedance phases being arranged continuously greater than 175 degree.
The present invention has realized mt impedance computation result optimal, has avoided sub-optimal result and error result to occur.Help improving the measuring accuracy and the reliability of magnetotelluric data.In the magnetotelluric noise Gaussian distributed, or interference ratio hour, and computing velocity is calculated fast several times than robust method.When Robust Estimation is failed, adopt the compacting of small echo threshold method to disturb automatically, more effective than single Robust Estimation.Avoided of the influence of artificial factor to the mt impedance computation.By whether having a plurality of frequency impedance phases to discern near-field interference continuously, avoided the single employing degree of correlation to judge this shortcoming of misjudgment when the MT quality of data exists in the near field greater than 175 degree.
Description of drawings
Fig. 1 is a process flow diagram of the present invention.
Fig. 2 is a quality of data A+E process flow diagram of the present invention.
Embodiment
The present invention combines in that least square method, robust method and little wave pressure are made an uproar, and substep is realized the calculating of MT impedance, obtains optimal result.
The present invention adopts usual way to gather electric field or magnetic field data, is converted to digital signal by filtering with after amplifying, and step is:
1) adopt least square method to calculate the mt impedance to the signal of gathering, and calculating frequency electric field signal and field signal degree of coherence, when measure more than 75% the frequency degree of coherence be 0.7-1 and impedance in phase place all be not 175-180 degree in wide frequency ranges, then export the MT impedance data, finish the anti-computation process of MT, otherwise;
2) adopt the robust method to calculate the mt impedance, calculate electric field signal and field signal degree of coherence, if measure the frequency degree of coherence more than 75% and be 0.7-1 and impedance in phase place all be not 175-180 degree in wide frequency ranges then export the MT impedance data, finish the anti-computation process of MT, otherwise;
3) adopting the small echo threshold values to press the method for making an uproar that the mt signal is carried out filtering according to interference type automatically in time domain or frequency field presses and makes an uproar, utilize the robust method to calculate the mt impedance again; Calculate the mt impedance and show with outcome record or with graphics mode,
Described small echo threshold values presses the method for making an uproar when having fixed frequency to disturb, and then carries out small echo threshold values pressure in frequency field and makes an uproar.
Described small echo threshold values is pressed and is made an uproar method when instantaneous interference is arranged, and presses in time domain and makes an uproar.
Described wide frequency ranges is by a plurality of frequency impedance phases being arranged continuously greater than 175 degree.
Now realize MT impedance computation basic process in conjunction with Figure of description 1 explanation the present invention.
＜1〉input MT time domain data: from MT time domain data file, read the MT time series;＜2〉MT impedance least square method impedance computation: the MT data to input are carried out least square method MT impedance computation;＜3〉judge MT impedance data quality, if the quality of data meets the requirements, execution in step＜10 successively then〉and step＜11, otherwise execution in step＜4;＜4〉the MT data are carried out robust method MT impedance computation;＜5〉judge MT impedance data quality, if the quality of data meets the requirements, execution in step＜10 successively then〉and step＜11, otherwise execution in step＜6;＜6〉the MT data are carried out the denoising of small echo threshold method;＜7〉the MT data are carried out robust method MT impedance computation;＜8〉judge MT impedance data quality,, execution in step＜10 successively then if the quality of data meets the requirements〉and step＜11, otherwise execution in step＜9 successively and step＜11;＜9〉confirm that the MT quality of data is undesirable, and the report analysis result;＜10〉output MT impedance data;＜11〉finish MT impedance computation process.
The present invention judges that to the MT quality of data also the mt impedance by direct analytical calculation comes the judgment data quality except the degree of coherence of foundation electric field signal and field signal.
When having the homology near-field interference, the mt impedance shows as: impedance phase is spent near 180 in wider frequency.Utilize These characteristics, can judge whether to exist the homology near-field interference, and then judge the MT quality of data.
Now, the method for judging the MT quality of data is described in conjunction with Figure of description 2.
＜1〉input MT frequency domain data and MT impedance data;＜2〉utilize the MT frequency domain data to calculate the degree of correlation of electric field signal and field signal;＜3〉judge whether the degree of correlation surpasses 15% of total frequency less than 0.7 frequency, if be very, execution in step＜6 successively then〉and step＜7, otherwise carry out next step;＜4〉judge impedance phase continuously greater than the frequencies of 175 degree whether less than total frequency 15%, if condition does not satisfy, execution in step＜6 successively then〉and step＜7, otherwise carry out next step;＜5〉make the MT quality of data and reach requirement judgement, execution in step＜7 then 〉;＜6〉make the undesirable judgement of the MT quality of data, execution in step＜7 then 〉;＜7〉output MT quality of data judged result.
Judge the MT quality of data by said method, avoided the independent use degree of correlation can't discern this shortcoming of near-field interference.
The present invention can realize on V5-2000 magnetotelluric data collector.
Claims (2)
1, a kind of magnetotelluric impedance measuring method adopts usual way to gather electric field or magnetic field data, is converted to digital signal by filtering with after amplifying, and it is characterized in that also adopting following steps:
1) adopt least square method to calculate the mt impedance to the signal of gathering, and calculating frequency electric field signal and field signal degree of coherence, when measure more than 75% the frequency degree of coherence be 0.7-1 and impedance in phase place all be not 175-180 degree in wide frequency ranges, carry out step 4), otherwise carry out step 2);
2) adopt the robust method to calculate the mt impedance, calculate electric field signal and field signal degree of coherence, if measure the frequency degree of coherence more than 75% and be 0.7-1 and impedance in phase place all be not that 175-180 degree carry out step 4) in wide frequency ranges, otherwise carry out step 3), described wide frequency ranges is a plurality of frequency impedance phases to be arranged continuously greater than 175 degree;
3) adopting the small echo threshold values to press the method for making an uproar that the mt signal is carried out filtering according to interference type automatically in time domain or frequency field presses and makes an uproar, utilize the robust method to calculate the mt impedance again;
4) calculate mt impedance and show with outcome record or with graphics mode.
2, a kind of magnetotelluric impedance measuring method according to claim 1 is characterized in that: described small echo threshold values presses the method for making an uproar when having fixed frequency to disturb, and then carries out small echo threshold values pressure in frequency field and makes an uproar; When instantaneous interference is arranged, then press and make an uproar in time domain.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN102944901A (en) * | 2012-11-30 | 2013-02-27 | 中国船舶重工集团公司第七二二研究所 | Magnetotelluric impedance estimating method |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN101556340B (en) * | 2008-04-10 | 2011-08-03 | 中国石油集团东方地球物理勘探有限责任公司 | Three-dimensional small surface element magnetotelluric continuous array data acquisition method |
| CN101858988B (en) * | 2009-04-08 | 2012-08-15 | 中国石油天然气集团公司 | Magneto-electrotelluric signal collection method and device |
| CN103389514B (en) * | 2013-07-18 | 2016-04-20 | 中国科学院地质与地球物理研究所 | A kind of mt denoising device and mt denoising method |
| CN105866852B (en) * | 2016-04-01 | 2017-10-13 | 西南科技大学 | It is a kind of remote with reference to mt impedance computation method based on correlation detection |
| CN110133737B (en) | 2019-06-26 | 2020-03-06 | 中国科学院地质与地球物理研究所 | Electromagnetism prediction method for blind mine |
| CN111273367B (en) * | 2020-03-11 | 2021-01-08 | 中南大学 | Method for estimating earth electromagnetic impedance |
| CN111736226B (en) * | 2020-06-30 | 2021-06-11 | 吉林大学 | Method and system for determining magnetotelluric time domain impedance |
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| US4686476A (en) * | 1981-11-23 | 1987-08-11 | Mobil Oil Corporation | Plotting of magnetotelluric impedance to determine structure and resistivity variation of anomalies |
| US4811220A (en) * | 1984-05-31 | 1989-03-07 | Mceuen Robert B | Method for visual display and analysis of subsurface rock properties and structure utilizing colored magnetotelluric transfer functions |
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| US4686476A (en) * | 1981-11-23 | 1987-08-11 | Mobil Oil Corporation | Plotting of magnetotelluric impedance to determine structure and resistivity variation of anomalies |
| US4811220A (en) * | 1984-05-31 | 1989-03-07 | Mceuen Robert B | Method for visual display and analysis of subsurface rock properties and structure utilizing colored magnetotelluric transfer functions |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN102944901A (en) * | 2012-11-30 | 2013-02-27 | 中国船舶重工集团公司第七二二研究所 | Magnetotelluric impedance estimating method |
| CN102944901B (en) * | 2012-11-30 | 2015-10-14 | 中国船舶重工集团公司第七二二研究所 | A kind of mt impedance estimation method |
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