CN103091717A - Electromagnetic prospecting method capable of achieving self-synchronizing frequency conversion of receiving and sending - Google Patents
Electromagnetic prospecting method capable of achieving self-synchronizing frequency conversion of receiving and sending Download PDFInfo
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Abstract
Disclosed is an electromagnetic prospecting method capable of achieving self-synchronizing frequency conversion of receiving and sending. A sending machine provides a current signal serving as an artificial excitation source and with certain frequency and capacity for the ground through a sending electrode. The frequency of the sent current signal switches automatically according to a preset 'time-frequency table'. A receiving machine synchronously receives a magnetotelluric response according to the same 'time-frequency table' as the sending machine. Uncorrelated noise is removed with relevant detecting methods, a magnetotelluric response containing geoelectrical resistivity information is obtained, and finally distribution of geoelectrical resistivity is worked out.
Description
Technical field
The present invention relates to a kind of New Geophysical Exploration, particularly the electromagnetic exploration method of frequency field.
Background technology
The exploration of controllable source frequency domain electromagnetic methods is the important means of geophysical survey.The principle of controllable source frequency domain electromagnetic methods is in conduction property and the electromagnetic frequency used of underground penetration depth and underground medium, close relationship to be arranged according to electromagnetic signal.The electromagnetic wave of high frequency penetrates more shallow, reflection shallow-layer information; The electromagnetic wave of low frequency penetrates deeply, understands underground deep information.The controllable source frequency domain electro-prospecting is having application very widely aspect the resource explorations such as the underground metal mineral reserves of searching, geologic hazard detection, distribution of water resources, coal, oil gas.
Frequency domain electro-prospecting relatively more commonly used mainly contains at present: traditional frequency conversion method, odd harmonic method, double frequency current method, controllable source audio-frequency magnetotelluric magnetic method, Pseudorandom method, multifrequency constant amplitude method etc.The traditional frequency conversion method need to successively change frequency, the power supply of frequency and measurement one by one, and measuring speed is slow, inefficiency, the relatively low deficiency that waits of accuracy of observation.For overcoming the problem of this frequency conversion observation, realize the light, efficient, anti-interference of prospecting instrument, the controllable source prospecting constantly develops, and receiving/transmission method is constantly brought forth new ideas, and has developed the method for exploration such as Harmonic Method, dual-frequency method, Sequence pseudo random approach, multifrequency constant amplitude power supply synchronization.Harmonic Method is progressive to some extent compared with early stage frequency variation method, can once power and carry out the measurement of a plurality of frequency harmonics, decay and harmonic frequency skewness yet Harmonic Method harmonic wave intensity overtone order is inversely proportional to; Dual-frequency method is synthetic with the electric current of two kinds of frequencies, feeds simultaneously undergroundly, and the disposable signal that receives simultaneously two kinds of frequencies has improved the deficiency of early stage frequency variation method to a certain extent, compares with the odd harmonic method, and its two frequency content intensity are fully equal.
In order to realize the electromagnetic exploration method of new development, current controllable source electromagnetic survey Instrument Development trend is: utilize Signal coding and simultaneous techniques to realize that the multiple-frequency signal transmitting-receiving is strict synchronous; Gather when utilizing broadband analog channel, high-speed data acquisition and large capacity storage to realize the broadband multiple-frequency signal; Utilize the modern digital signal to process to image data and realize signal extraction anti-interference, high s/n ratio.
Such as pseudorandom observation method and multifrequency constant amplitude power supply technique are to utilize transmitter to contain simultaneously the resultant current of a plurality of main frequency compositions to underground emission, receiver receives the earth response of these frequency signals simultaneously, thereby realizes that once observation just can be extracted the response of a plurality of different frequencies.
But also to the design and the higher requirement that realizes proposing of prospecting instrument, there is larger difficulty in practical engineering application to the electromagnetic survey development trend:
At first, the low-band signal in electromagnetic spectrum is mainly used in electromagnetic survey, and in this frequency range, has a large amount of interference, particularly industrial noise.And the multiple-frequency signal receiver needs the analog channel in broadband.The broadband passband allows larger external noise enter receiver, and signal to noise ratio (S/N ratio) is low, and the decrease resolution to useful signal of analogue-to-digital converters (ADC) has increased nonlinear distortion, has reduced the effect that follow-up signal is processed.
Secondly, in order to realize the direct collection to broadband signal, need to adopt high-speed ADC, again in order to take into account the dynamic range of receiving system, often adopt low-speed highly precise ADC in low-frequency range.High-speed data acquisition needs corresponding high speed data transfer and mass data storage, has increased the complexity of system.
At last, in order to process the mass data of collection, for extracting high-quality measuring-signal from disturbing, need complicated Processing Algorithm and high performance process computer.Reduced the real-time that signal is processed.The field engineer can not in time and get information about measurement result, can not in time according to circumstances correct the measurement problem, has reduced field engineer's participation, has reduced the result of use of instrument.
Summary of the invention
In order to overcome above-mentioned existing methodical deficiency, the present invention proposes a kind of electromagnetic exploration method of receiving and dispatching the automatic synchronization frequency conversion.
The present invention adopts " T/F table " to realize that automatic transceiving is synchronous with frequently, according to predetermined " T/F table ", at different time sections sending and receiving different frequency signals." T/F table " can be set flexibly according to the needs of exploration.Detection system of the present invention adopts receiver to synchronize with transmitter with the frequency receiving frequency signals, realizes receiving the frequency translation of signal with multiplier, in conjunction with bandpass filter, realizes the bandpass filter of any centre frequency, the filtering out-of-band noise.Receiver is realized utmost point filtering also by real-time correlation detection technology to the signal of current frequency, the characteristics that have anti-interference, high efficient and flexible, easily realize.
The present invention utilize transmitter according to " T/F table " in the schedule time to the current signal of underground infeed preset frequency as the artificial excitation source, adopt the synchronous MAGNETOTELLURIC RESPONSE ON with frequently receiving the position of receiver, remove noise through analog filtering and digital signal processing method, obtain the spectral response of the earth, calculate the Ka Ni electricalresistivityρ of Asian TV Station
s, impedance phase
The geophysical informations such as Apparent complex resistivity.The present invention provides new thinking and method for the high efficient and flexible of electromagnetic surveying, anti-interference, high resolution detection depth.
The step of the inventive method is as follows:
(1) transmitter is according to " T/F table " current signal in the schedule time to underground infeed preset frequency, with this current signal as the artificial excitation source;
(2) receiver in tens of kilometer range, receives the electromagnetic response information of the earth at distance artificial excitation field source number meter;
(3) realize synchronous same frequency by GPS/ Big Dipper time service locating module between sending and receiving, and record transmitting-receiving positional information;
(4) receiver after pre-filtering is amplified, is moved by multiplier sensor signal, then is passed through bandpass filter filtering out-of-band noise with signal frequency;
(5) filtered signal is converted to digital signal through analogue-to-digital converters, and recycling digital correlation detection algorithm is removed uncorrelated noise, extracts MAGNETOTELLURIC RESPONSE ON;
(6) MAGNETOTELLURIC RESPONSE ON by the step 5) gained calculates the Ka Ni electricalresistivityρ of Asian TV Station
sAnd impedance phase
Described MAGNETOTELLURIC RESPONSE ON is the function of geoelectrical resistivity, transmitting-receiving distance and frequency.According to the theory of magnetotelluric sounding method (MT), by the MAGNETOTELLURIC RESPONSE ON computer card Buddhist nun electricalresistivityρ of Asian TV Station
sAnd impedance phase
Etc. relevant geophysical information.
Receiver utilizes multiplier that optional frequency is moved fixed frequency according to the feature of signal spectrum, then adopts the method for bandpass filter filtering out-of-band noise out-of-band noise to be:
According to following formula:
ω wherein
nBe signal frequency, A
nBe signal amplitude,
Be signal phase, ω
LSignal frequency for the local frequency synthesizer generation of receiver; Obtain from following formula, the signal multiplication of two frequencies obtains the signal of two other frequency, that is: ω
n-ω
LAnd ω
n+ ω
LSignal after multiplying each other has passed through the bandpass filter filtering of rear class
, keep
, keep the information that contains original signal amplitude and phase place in item.
Receiver realizes that according to frequency current in " T/F table " filtering is non-with undesired signal frequently with frequently detecting; As follows with the principle that frequently detects: the signal r (t) of reception is expressed as:
Wherein, E
nFor being submerged in the useful signal amplitude in noise, n (t) is noise; Because transmitting-receiving is same frequently synchronous according to " T/F table ", so the relevant reference signal of current signal conduct that adopts transmitter to send: s (t)=I
nSin ω
nT, wherein, I
nBe the amplitude of transmitter current, ω
nBe signal frequency; Through following correlation computations, can get:
Wherein, ω
nBe signal frequency,
Be signal phase, T is for receiving the duration of signal, and s (t) is transmitted signal, as reference signal.Uncorrelated due to signal and noise,
Item levels off to zero, makes the noise of reception suppressed.
According to " T/F table ", sometime the section in, the signal spectrum concentration of energy of single-frequency signals.The different time periods sends the signal of different frequency, from whole launch time, can think multiple-frequency signal." T/F table " be set with very large dirigibility, can be according to actual needs, send the signal that high resolution frequency, frequency distribute arbitrarily.
Signal frequency and duration require to set flexibly according to exploration, in detection according to concrete needs, selected N signal frequency and Transmission Time Interval, formulate the T/F table, transmitter is by meta-frequency meter emission this moment, after often sending one group of N frequency, circulation emission again, be a cycle period launch time of one group of N frequency.N is integer, and the value of N is decided according to the actual requirements, and span is between 1-255.Receiver can begin to receive at any time, as long as accepted a cycle period, just can obtain the MAGNETOTELLURIC RESPONSE ON that needs.For improving signal quality, also can increase the reception duration, receive a plurality of cycle periods.This circulation sends, and the working method that random time begins to receive is that multicast is provided convenience, and field survey efficient is provided.
The present invention has adopted the transmitting-receiving automatic frequency-conversion method of " T/F table ", and sends by " T/F table " circulation, and receiver any time begins to receive, and the measurement that has improved early stage frequency variation method is slow, the characteristics of poor efficiency.
The present invention adopts transmitter and receiver according to " T/F table " synchronous transmitting-receiving.In section sometime, the signal that transmitter sends is the signal of single-frequency, the signal spectrum concentration of energy; And transmitter sends the signal of different frequency in the different time periods, from whole launch time, can think multiple-frequency signal again.The bandpass filter that receiver adopts multiplier to be fixed centre frequency realizes the bandpass filter of any centre frequency, simplified circuit design, realize filtering, the filtering out-of-band noise, compare the broadband multifrequency receiving/transmission methods such as pseudorandom, multifrequency constant amplitude, reduce the industrial noise impact, had higher signal to noise ratio (S/N ratio).
" T/F table " in the present invention can explore needs according to reality, and frequency and frequency interval are set in frequency range flexibly, and frequency that can be intensive when needing distributes and improves stratigraphic resolution.
The present invention adopts the real-time digital correlation detection technology, further suppresses noise and improves signal to noise ratio (S/N ratio), extracts useful information, and antijamming capability is strong.Real time signal processing is compared the broadband multifrequency receiver to the direct collection of broadband signal, has reduced the demand to high speed data transfer and mass data storage, has reduced the complexity of detection system design.
Description of drawings
Fig. 1 electromagnetic prospecting system block diagram of the present invention;
Fig. 2 the present invention " T/F table " schematic diagram;
Fig. 3 transmitter composition frame chart of the present invention;
Fig. 4 transmitter power supply unit of the present invention connection layout;
Fig. 5 transmitter power part of the present invention schematic diagram;
The sinusoidal waveform oscillogram that Fig. 6 the present invention sends according to " T/F table ";
Pulse width modulating technology (SPWM) schematic diagram of the sinusoidal output of Fig. 7 the present invention;
The square-wave waveform that Fig. 8 the present invention sends according to " T/F table ";
Fig. 9 receiver structure composition frame chart of the present invention;
Multiplier frequency translation schematic diagram in Figure 10 receiver of the present invention.
Embodiment
The present invention will be further described below in conjunction with the drawings and specific embodiments.
The autosynchronous variable-frequency electromagnetic exploration system of described transmitting-receiving block diagram as shown in Figure 1.The exploration system of using the inventive method mainly comprises transmitter and receiver.Transmitter feeds the current signal of certain frequency and size to the earth by sender electrode, as the artificial excitation source, the current signal frequency of transmission automaticallyes switch according to default " T/F table ".Receiver synchronously receives MAGNETOTELLURIC RESPONSE ON according to " the T/F table " identical with transmitter, through related detecting method, filtering noise, obtains the MAGNETOTELLURIC RESPONSE ON that includes geoelectrical resistivity information of high s/n ratio.
The principle of coherent detection filtering noise is as follows:
The signal r (t) that receives can be expressed as:
Wherein, E
nFor being submerged in the useful signal amplitude in noise, n (t) is noise.Because transmitting-receiving is with frequently synchronous, so the relevant reference signal of the current signal of available transmission conduct: s (t)=I according to " T/F table "
nSin ω
nT, I
nBe the amplitude of transmitter current, ω
nBe signal frequency.Do following correlation computations, can get:
Wherein, ω
nBe signal frequency,
Be signal phase, T is for receiving the duration of signal, and s (t) be transmitted signal, is used as reference signal, uncorrelated due to signal and noise,
Level off to zero, make the noise of reception suppressed, realize jamproof purpose.
MAGNETOTELLURIC RESPONSE ON is the function of geoelectrical resistivity, transmitting-receiving distance and frequency.Can obtain geophysical parameters information under different investigation depth conditions according to the earth frequency response characteristic.
Described " T/F table " as shown in Figure 2, in detection, according to concrete actual conditions and needs, as geologic condition, on-the-spot disturb size and to the requirement of stratigraphic resolution, selected N signal frequency and duration, formulation T/F table.Transmitter is by meta-frequency meter emission this moment, and after often sending one group of N frequency, circulation is launched again, and be a cycle period launch time of one group of N frequency.N is integer, and the value of N is decided according to the actual requirements, and span is between 1-255.Receiver can begin to receive at any time, as long as accepted a cycle period, just can obtain the complete MAGNETOTELLURIC RESPONSE ON that needs.Transmitter is realized synchronous with exploration frequently with receiver by identical " T/F table ".Transmitter and receiver realize that by the GPS/ Big Dipper time service locating module in machine correct time synchronizes.The frequency range of the current signal that transmitter sends is 0.01Hz ~ 100kHz, covers very low frequency (VLF) (VLF), ultra-low frequency (ULF), extremely low frequency (ELF), ultralow frequency (SLF) frequency range.
Described transmitter theory diagram as shown in Figure 3.Described transmitter comprises processor, power supply unit, synchronous control unit, clock unit, GPS/ Big Dipper time service positioning unit, Direct Digital Frequency Synthesizers, transmission current detecting unit, output waveform generating unit, isolation drive unit, inversion full-bridge, and output filter circuit.Wherein isolation drive, inversion full-bridge, output filter circuit form the power output part of transmitter; Processor except power output part, power supply unit, synchronous control unit, clock unit, GPS/ Big Dipper time service positioning unit, Direct Digital Frequency Synthesizers, transmission current detecting unit, and the output waveform generating unit is the master controller part of transmitter.
Described power supply unit comprises low-voltage power supply and high voltage supply two parts.As shown in Figure 4, external power source such as accumulator, 220V civil power or generator are connected to power supply unit.Power supply unit is realized rectification, filtering, having regulation of blood pressure, current-limiting protection function.The low-voltage power supply of power supply unit and high voltage supply two parts are low-voltage and the high voltage of stable output respectively, and wherein low-voltage power supply part output LOW voltage to the power end of master controller, partly powers for master controller; High voltage supply part output HIGH voltage is powered to power output part to the power end of power output part.GPS/ Big Dipper positioning unit is connected with processor by serial ports; Clock unit is connected to the processor port, and high precision frequency square wave is provided; Processor is connected with Direct Digital Frequency Synthesizers by control interface, controlled frequency compositor output high resolution frequency signal; Direct Digital Frequency Synthesizers realizes high-resolution frequency signal.Clock unit provides high precision clock, according to predetermined " T/F table " to underground transmission current signal.The temporal information of using GPS/ Big Dipper time service positioning unit and clock unit to provide in transmitter.GPS/ Big Dipper time service positioning unit provides precise time and pulse per second (PPS), but easily is disturbed, and the situation of signal occurs not having.Can provide by clock unit to address this problem, when there is no GPS/ Big Dipper signal, adopt the clock unit in transmitter to realize punctual function.Clock unit is generally realized with the rubidium clock of high stable constant-temperature crystal oscillator or small size.Synchronous control unit is searched " T/F table ", to the current signal of underground transmission certain frequency according to the high precision clock that GPS/ Big Dipper time service unit and clock unit provide.When transmitter need to be exported square wave, the output of Direct Digital frequency synthesis unit was directly connected to the isolation drive unit.When transmitter needed sine wave output, the high resolution frequency of Direct Digital frequency synthesis unit output was transported to the output waveform generating unit as the reference frequency.The output waveform generating unit utilizes sine pulse midth modification (SPWM) to produce the pulsed modulation waveform, outputs to the isolation drive unit, drives the inversion full-bridge.
The power output part of transmitter as shown in Figure 5.By the master controller of transmitter partly synthetic Waveform Input to the isolation drive unit, the inversion full-bridge that is formed by high-power semiconductor switch by the isolation drive unit drives, the output terminal of inversion full-bridge is connected to output filter circuit, by output filter circuit filtering higher harmonic current, then send to the earth by electrode.Be in series with sampling resistor in the transmission loop of power stage, the transmission current detecting unit of master controller part is sampled and detects the voltage at sampling resistor two ends.
The waveform sine wave as shown in Figure 6 that described transmitter sends, the present invention adopts width modulation (PWM) inverter circuit to add output filter circuit and realizes the output of highly efficient power sinusoidal signal.The output waveform of inversion full-bridge by output filter circuit, can obtain sinusoidal output waveform as shown in Figure 7.Switching device in the PWM inverter circuit adopts the high power semi-conductor power electronic devices, as insulated gate bipolar transistor (IGBT) or power field effect pipe (Power MOSFET).
Described transmitter for more simply design, is exported replacement for the sinusoidal signal of a certain frequency is also available with square wave frequently in actual applications.Output waveform as shown in Figure 8, because square wave can resolve into first-harmonic and harmonic wave thereof.The first-harmonic of square wave is considered as the sine output of equivalence, adopts the mode that sends square wave, more easily the transmitter of designing high-power.
The waveform of the current signal that transmitter sends is sine wave, square wave or other cyclical signals, frequency range 0.001Hz ~ 100kHz, and frequency resolution is high.Described current signal has covered very low frequency (VLF) (VLF), ultra-low frequency (ULF), extremely low frequency (ELF), the frequency ranges such as ultralow frequency (SLF).
The composition structure of described receiver as shown in Figure 9.Described receiver comprises electric-field sensor, magnetic field sensor, prime filter amplification circuit, multiplier, Direct Digital Frequency Synthesizers (DDS), bandpass filtering amplifying circuit, analogue-to-digital converters (ADC), primary processor, clock unit, GPS/ Big Dipper time service positioning unit, and synchronous control unit.Electric-field sensor is comprised of two electrodes that insert the earth, is used for measuring the horizontal component of telluric electricity field, and magnetic field sensor is the induction type magnetic field sensor, and electric-field sensor and magnetic field sensor are connected to the prime filter amplification circuit; Two multiplication input signals of multiplier are the signal of prime filter amplification circuit output and the output signal of Direct Digital Frequency Synthesizers (DDS), the output signal of multiplier is delivered to the bandpass filtering amplifying circuit, is input to afterwards analogue-to-digital converters (ADC) again; Primary processor connecting analog-digital quantizer (ADC), collection signal.The prime filter amplification circuit adopts programmable amplifier, and primary processor is by the gain multiple of gain control making foot control prime filter amplification circuit processed; Primary processor is controlled Direct Digital Frequency Synthesizers (DDS) by the DDS control interface and is produced the high resolution frequency signal; GPS/ Big Dipper time service positioning unit is connected with primary processor by serial ports; GPS/ Big Dipper time service positioning unit and clock unit are connected to the primary processor port, are used for providing split-second precision, give transmitting-receiving synchronous with frequently providing safeguard.
Electric-field sensor in receiver and magnetic field sensor pick up the electromagnetic response signal of the earth, the electromagnetic signal that receives is faint and contain larger noise, by the electromagnetic response signal of prime filter amplification circuit amplification sensor input, and outer noise and the interior power frequency of band of filtered signal bandwidth disturbed.The prime filter amplification circuit selects the low noise device of low distortion to realize amplification and the filtering of signal.After prime filter amplification circuit filter and amplification, be input to multiplier and bandwidth-limited circuit by the signal of sensor input.The current frequency of the Time dependent multiplier local signal that synchronous control unit basis " T/F table " and clock unit and GPS/ Big Dipper time service positioning unit provide, thereby the centre frequency of decision bandpass filter.
The present invention adopts the multiplication converter technique to realize moving of signal frequency, and signal frequency is moved on fixing low frequency, has simplified the processing of multiple-frequency signal.The schematic diagram that multiplier is realized frequency translation as shown in figure 10.
Receiver of the present invention utilizes multiplier that optional frequency is moved fixed frequency according to the feature of signal spectrum, then adopts the method for bandpass filter filtering out-of-band noise out-of-band noise to be:
According to following formula:
ω wherein
nBe signal frequency, A
nBe signal amplitude,
Be signal phase, ω
LSignal frequency for the local frequency synthesizer generation of receiver.
Can see that from following formula the signal multiplication of two frequencies obtains the signal of two other frequency, ω
n-ω
LAnd ω
n+ ω
LSignal after multiplying each other has passed through the dead center frequency filter filtering of rear class
, keep
, can see keeping the information that item contains original signal amplitude and phase place.This multiplication frequency conversion can transform to frequency signal arbitrarily on the frequency of appointment and the information of preserving original signal.By this conversion, the signal frequency conversion of different frequency needs only to a certain fixed frequency the processing that a passage can be realized different frequency signals, has greatly simplified the design of filtering and amplifying circuit.Carry out analog-digital conversion by analogue-to-digital converters (ADC) afterwards, analogue-to-digital converters (ADC) can adopt the analogue-to-digital converters of the S-D type of high precision, high resolving power, great dynamic range.Digital signal after analog-digital conversion adopts the digital correlation detection algorithm by primary processor, remove uncorrelated noise, extract MAGNETOTELLURIC RESPONSE ON, according to the theory of magnetotelluric sounding method (MT), by the MAGNETOTELLURIC RESPONSE ON computer card Buddhist nun electricalresistivityρ s of Asian TV Station and impedance phase
Etc. relevant geophysical information.
Claims (5)
1. electromagnetic exploration method of receiving and dispatching the automatic synchronization frequency conversion, it is characterized in that, described method is: by transmitter according to " T/F table " in the schedule time to the current signal of underground infeed preset frequency as the artificial excitation source, adopt the synchronous MAGNETOTELLURIC RESPONSE ON with frequently receiving the position of receiver, remove noise through analog filtering and digital signal processing method, obtain the spectral response of the earth, then calculate geophysical information.
2. the electromagnetic exploration method of transmitting-receiving automatic synchronization according to claim 1 frequency conversion, is characterized in that, described method step is as follows:
1) transmitter is according to " T/F table " current signal in the schedule time to underground infeed preset frequency, with this current signal as the artificial excitation source;
2) receiver in tens of kilometer range, receives the electromagnetic response information of the earth at distance artificial excitation field source number meter;
3) realize synchronous same frequency by GPS/ Big Dipper time service locating module between sending and receiving, and record transmitting-receiving positional information;
4) receiver after pre-filtering is amplified, is moved by multiplier sensor signal, then is passed through bandpass filter filtering out-of-band noise with signal frequency;
5) filtered signal is converted to digital signal through analogue-to-digital converters, and recycling digital correlation detection algorithm is removed uncorrelated noise, extracts MAGNETOTELLURIC RESPONSE ON;
6) MAGNETOTELLURIC RESPONSE ON by the step 5) gained calculates the Ka Ni electricalresistivityρ of Asian TV Station
sAnd impedance phase
3. the electromagnetic exploration method of transmitting-receiving automatic synchronization according to claim 2 frequency conversion is characterized in that: in described step 3), receiver realizes that according to frequency current in " T/F table " filtering is non-with undesired signal frequently with frequently detecting; As follows with the principle that frequently detects: the signal r (t) of reception is expressed as:
Wherein, E
nFor being submerged in the useful signal amplitude in noise, n (t) is noise; Because transmitting-receiving is same frequently synchronous according to " T/F table ", so the relevant reference signal of current signal conduct that adopts transmitter to send: s (t)=I
nSin ω
nT, wherein, I
nBe the amplitude of transmitter current, ω
nBe signal frequency; Through following correlation computations, can get:
Wherein, ω
nBe signal frequency,
Be signal phase, T is for receiving the duration of signal, and s (t) is transmitted signal, as reference signal; Uncorrelated due to signal and noise,
Item levels off to zero, makes the noise of reception suppressed.
4. the surface em method of exploration of transmitting-receiving automatic synchronization according to claim 2 frequency conversion, it is characterized in that: in described step 4), receiver is according to the feature of signal spectrum, utilize multiplier that optional frequency is moved fixed frequency, then adopt the method for bandpass filter filtering out-of-band noise out-of-band noise to be;
According to following formula:
ω wherein
nBe signal frequency, A
nBe signal amplitude,
Be signal phase, ω
LSignal frequency for the local frequency synthesizer generation of receiver; Obtain from following formula, the signal multiplication of two frequencies obtains the signal of two other frequency, that is: ω
n-ω
LAnd ω
n+ ω
LSignal after multiplying each other has passed through the bandpass filter filtering of rear class
, keep
, keep the information that contains original signal amplitude and phase place in item.
5. the electromagnetic exploration method of transmitting-receiving automatic synchronization according to claim 1 and 2 frequency conversion, it is characterized in that, signal frequency in described " T/F table " and duration require to set N signal frequency and emission duration according to exploration, formulate by " T/F table ", described transmitter is by described T/F table " send; after often sending one group of N frequency, circulation sends again, and the emission duration of one group of N frequency is a cycle period; Receiver begins to receive at any time; Be a cycle period launch time of one group of N frequency, and N is integer; The span of N is between 1-255.The frequency range of the current signal that described transmitter sends is 0.01Hz ~ 100kHz.
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| CN104375191A (en) * | 2014-12-08 | 2015-02-25 | 中国石油天然气集团公司 | Magnetotelluric data acquisition system and method |
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