CN118091767A - Coding method and detection method for ground space-time frequency electromagnetic synchronous pulse excitation sequence - Google Patents
Coding method and detection method for ground space-time frequency electromagnetic synchronous pulse excitation sequence Download PDFInfo
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Abstract
The invention belongs to the field of detection of a ground-air electromagnetic method, in particular to a coding method and a detection method of a ground-air time-frequency electromagnetic synchronous pulse excitation sequence, wherein the coding method comprises the following steps: constructing a multi-frequency pseudo-random signal of the time-frequency synchronous excitation pulse and constructing a bipolar square wave signal of the time-frequency synchronous excitation pulse; the method comprises the steps of carrying out segmentation interception coding on a time-frequency synchronous excitation pulse, and corresponding a frequency domain signal corresponding to a multi-frequency pseudo-random signal and a time domain signal corresponding to a bipolar square wave signal to the segmentation interception coding; and fusing configuration parameters required by the frequency domain signal and the time domain signal into the segmentation interception code, wherein the configuration parameters comprise a time domain excitation pulse width, a sequence turn-off observation window length, a ns-level delay system clock and a system frequency. Realizing time-frequency synchronous excitation by constructing time-frequency composite pulses, and obtaining the complete transient response and steady state response of the earth; the accurate excitation of the underground target body is realized. The problem of the detection blind area of time-frequency domain ground-air electromagnetism is solved.
Description
Technical Field
The invention belongs to the field of ground-air electromagnetic method detection, and particularly relates to a coding method and a detection method of a ground-air time-frequency electromagnetic synchronous pulse excitation sequence.
Background
In the field of geophysical prospecting, the earth-air electromagnetic method is another novel electromagnetic detection means besides the ground electromagnetic method and the aviation electromagnetic method, is not limited by terrain on the basis of keeping the detection depth and the detection precision, and can be used for rapidly detecting areas with complex earth surface conditions in a non-contact and large depth.
In high-precision ground-air electromagnetic detection application, the traditional detection method utilizes two sets of independent systems of a time domain and a frequency domain to perform joint detection, namely, a long-distance line source is paved on the ground, a time domain method is adopted in a near source region, and a frequency domain method is adopted in a far source region.
At present, two sets of independent systems of a time domain and a frequency domain are commonly utilized for joint detection, namely, a long-distance line source is paved on the ground, a time domain method is adopted in a near-distance area, and a frequency domain method is adopted in a far-distance area.
Disclosure of Invention
The invention aims to solve the technical problem of providing a coding method of a ground space time frequency electromagnetic synchronous pulse excitation sequence, which realizes time frequency synchronous excitation by constructing a time frequency composite pulse and obtains a complete transient response and steady state response of the ground; thereby realizing the accurate excitation of the underground target body. The problem of the empty electromagnetism in time-frequency domain ground detection blind area is solved to promote detection efficiency.
The invention also provides a detection method of the control signal generated by adopting the encoding method of the ground space-time frequency electromagnetic synchronous pulse excitation sequence.
The invention is realized in such a way that a method for encoding a ground space-time frequency electromagnetic synchronous pulse excitation sequence comprises the following steps:
constructing a multi-frequency pseudo-random signal of the time-frequency synchronous excitation pulse and constructing a bipolar square wave signal of the time-frequency synchronous excitation pulse;
The method comprises the steps of carrying out segmentation interception coding on a time-frequency synchronous excitation pulse, and corresponding a frequency domain signal corresponding to a multi-frequency pseudo-random signal and a time domain signal corresponding to a bipolar square wave signal to the segmentation interception coding;
And fusing configuration parameters required by the frequency domain signal and the time domain signal into the segmentation interception code, wherein the configuration parameters comprise a time domain excitation pulse width, a sequence turn-off observation window length, a ns-level delay system clock and a system frequency.
Further, the multi-frequency pseudo-random signal for constructing the time-frequency synchronous excitation pulse specifically comprises:
Constructing a periodic sequence by self-closing addition of a three-element set consisting of 1,0 and 1, and normalizing functions of the three-element set Expressed as period/>Is a continuous square wave signal of:
，
Wherein n represents the number of the pseudo-random transmitting frequency points, the value range is all positive integers, k represents the marks of the square waves on the time axis, and the value is as follows: 0, ±1, ±2, ±3 … n; t represents any time within the duration of the transmission, Representing period as/>Is a sign of a square wave signal;
multi-frequency excitation response by self-closing addition using signal spectral superposition The addition group element is [ -1,0,1], the mathematical expression: /(I)Wherein/>Representing a pseudo-random waveform function with n frequency points, wherein i is from 1 to n;
The iterative pulse code for obtaining the waveforms with five, seven or more odd frequency components is as follows:
，
Wherein, Represents an element "/>" 1Representing a pseudo-random waveform function having n+2 frequency bins;
The time domain expression of the multi-frequency pseudo-random signal in the in-phase or anti-phase frequency domain observation window is as follows: Wherein m represents the number of pseudo-random encoding step transitions,/> Representing the first position on the time axis where a step occurs,/>Representing the position on the time axis where the mth step occurs, T F represents the duration of a single in-phase or anti-phase pseudorandom waveform, A represents the voltage amplitude,/>For the time domain representation of a multi-frequency pseudorandom signal within an in-phase or anti-phase frequency domain observation window,/>Representing the position on the time axis where the m-1 st step occurs.
Further, constructing a bipolar square wave signal of the time-frequency synchronous excitation pulse, which specifically comprises the following steps:
setting a waveform emission initial time Emission current intensity is/>Bipolar square wave signal/>Expressed as: /(I)Where w is the pulse width,/>Representing the transmission period of the time domain waveform, t being any time within the transmission duration,/>A step function having a function value of 1 when t is equal to or greater than 0 and a function value of 0 when t < 0;
Setting the emission period of the time domain waveform to be endless, and obtaining bipolar square wave amplitude-frequency characteristics as follows:
wherein/> Is any frequency in the frequency spectrum.
Further, segment interception encoding is performed on the time-frequency synchronous excitation pulse, including:
Dividing a transmission period of a time-frequency synchronous excitation pulse, namely, a transmission period comprising time domain and frequency domain transmission information into four parts: an anti-phase time domain observation window T-, an in-phase time domain observation window T+, an anti-phase frequency domain observation window F-, and an in-phase frequency domain observation window F+.
Further, the method for mapping the frequency domain signal corresponding to the multi-frequency pseudo-random signal and the time domain signal corresponding to the bipolar square wave signal into the segment truncation coding comprises the following steps: the reverse phase time domain observation window T-, the in-phase time domain observation window T+ appears when the high level or the low level is stepped to 0 voltage, the step is used as the start of the reverse phase time domain observation window T-or the in-phase time domain observation window T+ and is continued until the next step signal appears; the inverse frequency domain observation window F-and the in-phase frequency domain observation window F + remain consistent with the multi-frequency pseudorandom signal duration.
Further, the frequency domain signal corresponding to the multi-frequency pseudo-random signal and the time domain signal corresponding to the bipolar square wave signal are corresponding to the segmentation interception code, and the method further comprises the steps of synthesizing the frequency domain signal and the time domain signal to obtain a synthesized waveform, wherein the synthesizing comprises the following steps:
The first step: adding a section of waveform with duration voltage of 0 behind the frequency domain signal corresponding to the multi-frequency pseudo-random signal, and forming a time domain signal by the voltage step at the tail end of the frequency domain signal to 0 and the subsequent continuous 0 voltage waveform, wherein the time domain signal is used as a synthesized waveform of the first step;
And a second step of: the synthesized waveform of the first step is phase shifted 180 degrees to form a phase shifted waveform, and then the end time of the synthesized waveform of the first step is taken as the start time of the phase shifted waveform.
Further, the time-frequency synchronous excitation pulse obtained by encoding the encoding method is used for controlling a system to generate a control signal, and the method comprises the following steps:
S1: the peripheral crystal is used as a reference clock for controlling a Field Programmable Gate Array (FPGA) in a system, and the frequency of the reference clock is a fixed frequency, which is called a system clock;
S2: based on a system clock, an inversion time domain observation window T-, an in-phase time domain observation window T+ and an inversion frequency domain observation window F-and an in-phase frequency domain observation window F+ are designed, wherein a part of a waveform with 1 is the inversion frequency domain observation window F-and the in-phase frequency domain observation window F+, a part of the waveform with 0 is the inversion time domain observation window T-, the in-phase time domain observation window T+, and the generated waveform is called time-frequency composite pulse gating;
S3: performing one-time AND logic operation on the time-frequency composite pulse gating and the system clock to obtain waveforms of clock signals only when the reverse phase frequency domain observation window F-and the in-phase frequency domain observation window F+ appear, which are called reference clocks;
S4: based on a reference clock, constructing a waveform sequence of a frequency domain signal with an in-phase frequency domain observation window F+ and a time domain signal with an anti-phase time domain observation window T-, wherein the step moment of the time domain signal appears at the end of the frequency domain signal and is called unipolar in-phase pulse;
s5: taking the reverse logic of the unipolar in-phase pulse to obtain a unipolar reverse phase pulse;
s6: according to the time-frequency composite pulse gating in the step S2, bipolar in-phase gating is obtained, and bipolar reverse phase gating is obtained after inversion;
S7: performing AND logic on the bipolar in-phase gating and the bipolar inversion gating obtained in the step S6 and the unipolar in-phase pulse and the unipolar inversion pulse respectively to obtain a bipolar in-phase pulse and a bipolar inversion pulse respectively;
S8: and performing OR logic on the bipolar in-phase pulse and the bipolar anti-phase pulse to obtain a bipolar in-phase composite pulse, taking the inverse to obtain a bipolar anti-phase composite pulse, and taking the obtained bipolar in-phase composite pulse and the bipolar anti-phase composite pulse as control signals of the H full bridge driving circuit.
A detection method of a control signal generated by adopting a ground space-time frequency electromagnetic synchronous pulse excitation sequence coding method comprises the following steps:
Configuring parameters of a control system in a transmitter, including a time domain parameter configuration and a frequency domain rate parameter configuration, wherein the time domain parameter configuration includes: selecting the length of a current turn-off acquisition window; the frequency domain rate parameter configuration comprises reference frequency and transmission frequency point selection;
The obtained bipolar in-phase composite pulse and bipolar anti-phase composite pulse are used as control signals of an H full-bridge driving circuit to be transmitted, and when the transmission is started, a control system enters a circulation state until the transmission is stopped; and after the transmission state is ended, re-entering a parameter configuration state, and waiting for the next transmission parameter configuration.
Compared with the prior art, the invention has the beneficial effects that:
The method completes the synchronous excitation of the time frequency domain of single multi-frequency points by designing the time frequency composite pulse sequence based on the frequency modulation technology. The method solves the problem of limitation of detection areas of the traditional single method, realizes non-blind area full coverage detection from a near zone to a far zone, and further plays the advantages of a ground-air electromagnetic method.
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FIG. 1 is a flowchart of a method for encoding a geospatial time-frequency electromagnetic synchronization pulse excitation sequence provided by an embodiment of the present invention;
FIG. 2 is a waveform of a ternary prime pulse code transmission provided by an embodiment of the present invention;
FIG. 3 is a waveform of a three-frequency excitation pulse transmission provided by an embodiment of the present invention;
FIG. 4 is a time-frequency composite pulse waveform based on a frequency modulation method according to an embodiment of the present invention;
FIG. 5 is a three-frequency point time-frequency synchronization pulse time sequence code provided by an embodiment of the present invention;
Fig. 6 is a schematic diagram of a time-frequency composite pulse emission control system according to an embodiment of the present invention;
fig. 7 is a graph showing the actual measurement effect of the encoding method of the geospatial time-frequency electromagnetic synchronous pulse excitation sequence according to the embodiment of the present invention, where (a) and (b) are the results of the conventional detection method and the time-frequency synchronous detection method, respectively.
Detailed Description
The present invention will be described in further detail with reference to the following examples in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Referring to fig. 1, a method for encoding a geospatial space-time frequency electromagnetic synchronous pulse excitation sequence according to an embodiment of the present invention includes:
constructing a multi-frequency pseudo-random signal of the time-frequency synchronous excitation pulse and constructing a bipolar square wave signal of the time-frequency synchronous excitation pulse;
The method comprises the steps of carrying out segmentation interception coding on a time-frequency synchronous excitation pulse, and corresponding a frequency domain signal corresponding to a multi-frequency pseudo-random signal and a time domain signal corresponding to a bipolar square wave signal to the segmentation interception coding;
And fusing configuration parameters required by the frequency domain signal and the time domain signal into the segmentation interception code, wherein the configuration parameters comprise a time domain excitation pulse width, a sequence turn-off observation window length, a ns-level delay system clock and a system frequency.
The method for constructing the multi-frequency pseudo-random signal of the time-frequency synchronous excitation pulse specifically comprises the following steps:
The periodic sequence is constructed by self-closing addition of a set of three elements consisting of 1,0, -1, and pulses are emitted by three elements consisting of 1,0, -1, as shown in fig. 2. Normalization function of three-element set Expressed as period/>Is a continuous square wave signal of:
Wherein n represents the number of pseudo-random transmitting frequency points, the following n is the same meaning, the value range is all positive integers, k represents the marks of the square wave on the time axis, and the value is: 0, ±1, ±2, ±3 … n; t represents any time within the transmission duration,/> Representing period as/>Is a sign of a square wave signal;
multi-frequency excitation response by self-closing addition using signal spectral superposition The addition group element is [ -1,0,1], the mathematical expression:
wherein/> Representing a pseudo-random waveform function with n frequency points, wherein i is from 1 to n;
The iterative pulse coding method comprises the steps of obtaining waveforms with five, seven and more odd frequency components by utilizing a waveform coding rule with three frequency components, wherein the iterative pulse coding method comprises the following steps:
，
Wherein, Represents an element "/>" 1A pseudo-random waveform function with n+2 frequency points is shown, taking three frequency points as an example, the excitation pulse emission waveform is shown in fig. 3, and the normalized pulse amplitude changes along with the clock period, so that the width of the clock period and the normalized pulse amplitude are from {111} to {/>}, {1}, And {/>Variations in the excitation pulse transmit waveform is generated from the pulse encoded transmit waveform of figure 2, wherein the transmit pulse is generated from a reference clock, the voltage amplitude of the transmit pulse is derived from/>To/>Three frequency bins of 1, 0 and-1 are generated.
The time domain expression of the multi-frequency pseudo-random signal in the in-phase or anti-phase frequency domain observation window is as follows: Wherein m represents the number of pseudo-random encoding step transitions,/> Representing the first position on the time axis where a step occurs,/>Representing the position on the time axis where the mth step occurs, T F represents the duration of a single in-phase or anti-phase pseudorandom waveform, A represents the voltage amplitude,/>For the time domain representation of a multi-frequency pseudorandom signal within an in-phase or anti-phase frequency domain observation window,/>Representing the position on the time axis where the m-1 st step occurs.
The method for constructing the bipolar square wave signal of the time-frequency synchronous excitation pulse specifically comprises the following steps: the ideal single-period universal time domain expression of the transmitting waveform is expressed by using a step function, and the initial time of waveform transmitting is setEmission current intensity is/>Bipolar square wave signal/>Expressed as:
，
Where w is the pulse width of the pulses, Representing the transmission period of the time domain waveform, t being any time within the transmission duration,/>A step function having a function value of 1 when t is equal to or greater than 0 and a function value of 0 when t < 0;
Setting the emission period of the time domain waveform to infinity The obtained bipolar square wave amplitude-frequency characteristics are as follows: wherein/> Is any frequency in the frequency spectrum.
The method comprises the steps of carrying out sectional interception coding on the time-frequency synchronous excitation pulse, and corresponding to a frequency domain signal corresponding to a multi-frequency pseudo-random signal and a time domain signal corresponding to a bipolar square wave signal, to the sectional interception coding, wherein the method specifically comprises the following steps:
segment interception encoding is carried out on the time-frequency synchronous excitation pulse:
The waveforms encoded in one embodiment are shown in fig. 4, where the transmission period of one time-frequency synchronous excitation pulse includes both time domain and frequency domain transmission information. The method is divided into four parts: an anti-phase time domain observation window T-, an in-phase time domain observation window T+, an anti-phase frequency domain observation window F-, and an in-phase frequency domain observation window F+.
The method comprises the steps of correspondingly receiving frequency domain signals corresponding to the multi-frequency pseudo-random signals and time domain signals corresponding to the bipolar square wave signals into the segmentation interception codes, and further comprising the following steps: the reverse phase time domain observation window T-, the in-phase time domain observation window T+ appears when the high level or the low level is stepped to 0 voltage, the step is used as the start of the reverse phase time domain observation window T-or the in-phase time domain observation window T+ and is continued until the next step signal appears; the inverse frequency domain observation window F-and the in-phase frequency domain observation window F + remain consistent with the multi-frequency pseudorandom signal duration.
Two different signals then need to be synthesized together, the synthesis process comprising:
The first step: adding a section of waveform with duration voltage of 0 behind the frequency domain signal corresponding to the multi-frequency pseudo-random signal, and forming a time domain signal by the voltage step at the tail end of the frequency domain signal to 0 and the subsequent continuous 0 voltage waveform, wherein the time domain signal is used as a synthesized waveform of the first step;
And a second step of: the synthesized waveform of the first step is phase shifted 180 degrees to form a phase shifted waveform, and then the end time of the synthesized waveform of the first step is taken as the start time of the phase shifted waveform.
The required time-frequency synchronous excitation pulse is obtained by the coding method, and the waveform coded by the coding method is realized by hardware according to binary program voice in combination with a control system in application. An application of the three-frequency-point pulse timing coding is illustrated as an example, as shown in fig. 5. Pulse coding accuracy all refers to system clockProcessing is performed so that the pulse emission width and the time domain observation window length are minimally adjusted to accuracy/>. The system frequency is selected to be 32.768 MHz, 3 times frequency is multiplied to 98.304 MHz through a PLL (Phase-locked loop), and the frequency points commonly used in a frequency domain electromagnetic method are covered. The method specifically comprises the following steps:
S1: the reference clock of the field programmable gate array FPGA of the control system is generated by the peripheral crystal oscillator, which is a fixed frequency, referred to herein as the "system clock", see the system clock in fig. 5;
S2: based on a system clock, a time domain and frequency domain observation window is designed according to a code inversion time domain observation window T-, an in-phase time domain observation window T+, an inversion frequency domain observation window F-and an in-phase frequency domain observation window F+ by segmentation, wherein a part of a waveform which is 1 is the in-phase/inversion frequency domain observation window, a part of the waveform which is 0 is the in-phase/inversion time domain observation window, and the generated waveform is called time-frequency composite pulse gating;
S3: performing one-time AND logic operation on the time-frequency composite pulse gating and the system clock to obtain waveforms of clock signals only when the reverse phase frequency domain observation window F-and the in-phase frequency domain observation window F+ appear, wherein the waveforms of the clock signals are called as reference clocks;
S4: based on the reference clock, a waveform sequence of a frequency domain signal in an in-phase frequency domain observation window and a time domain signal of an anti-phase time domain observation window T-is constructed (the step moment of the time domain occurs at the end of the in-phase frequency domain), and the waveform is called a unipolar in-phase pulse;
S5: taking the 'unipolar in-phase pulse' to be 'inverse' logic to obtain 'unipolar reverse pulse';
S6: waveforms in which only the same phase current occurs during the transmit duration are referred to as unipolar; waveforms in which opposite phase currents occur during the transmit duration are referred to as bipolar; because the waveforms need to construct two groups of bipolar waveforms, namely a group of frequency domain waveforms with opposite phases and a group of time domain waveforms with opposite phases, the time-frequency composite pulse gating appearing in the step S2 needs to be further subdivided, so that the bipolar in-phase gating is obtained firstly, and then the bipolar reverse phase gating is obtained after the reverse phase gating;
S7: performing AND logic on the bipolar in-phase gating and the bipolar inversion gating obtained in the step S6 and the unipolar in-phase pulse and the unipolar inversion pulse respectively to obtain the bipolar in-phase pulse and the bipolar inversion pulse;
s8: the "bipolar in-phase pulse" and the "bipolar reverse pulse" are processed as OR logic to obtain the "bipolar in-phase composite pulse", and the "reverse" is taken to obtain the "bipolar reverse composite pulse", so that the control signal obtained as the H full bridge driving circuit is output to the H full bridge driving circuit, and the obtained voltage waveform result is shown in figure 4.
In one embodiment of the present invention, a control system architecture is provided, as shown in fig. 6. Comprising the following steps:
The main control module is used for controlling and generating a synchronous pulse excitation sequence;
A serial communication bus for data exchange;
The display and operation interface is used for man-machine interaction and parameter configuration;
and other peripheral modules are used for clock synchronization, delay reduction, voltage stabilization and other functions.
The main control module adopts a Cyclone IV processor (the model is EP4CE6E 2217) to receive instructions from an ARM processor (the model is STM32F103VET 6) to generate various parameters of pulse, and the ARM processor is totally called ADVANCED RISC MACHINE; the display and operation interface is realized by an LCD display module, and the LCD is totally called a Liquid CRYSTAL DISPLAY, LCD display module, a mechanical key and an industrial rocker to realize man-machine interaction; the Cyclone IV processor realizes the receiving and transmitting synchronization through the GPS time service module, realizes ns-level delay time sequence in cooperation with the constant-temperature crystal oscillator, provides reference clocks for the two processors through the two passive crystal oscillators, and realizes real-time state inquiry through the fault checking module; each regulated power supply of the control system converts input voltage into working voltage of each module through a low dropout linear regulator (low dropout regulator, LDO), and the working voltage is respectively 3.3V regulated and supplied to the ARM processor, 2.5V regulated and 1.2V regulated and supplied to the Cyclone IV processor. And the main control module controls the H full-bridge driving circuit to output waveforms according to the control signals.
The control system needs to perform system parameter configuration, comprising two parts of time domain parameter configuration and frequency domain parameter configuration, wherein the time domain parameter configuration is mainly the current turn-off acquisition window length selection and is divided into: 10 ms, 20 ms, 40 ms, and 80 ms; the frequency domain frequency parameter configuration comprises reference frequency and transmission frequency point selection, the frequency domain frequency reference frequency selection range is 0.01171875 Hz-2048 Hz, and the transmission frequency point selection comprises single frequency point, three frequency points, five frequency points, seven frequency points and the like. After the configuration of each parameter is completed, generating a time-frequency composite pulse code to wait for transmitting. When transmission is started, the system enters a loop state until transmission is stopped. And after the system finishes the transmitting state, the system reenters the system parameter configuration state and waits for the next transmitting parameter configuration.
The invention also provides a detection method of the control signal generated by the encoding method of the ground space-time frequency electromagnetic synchronous pulse excitation sequence, which comprises the following steps:
Configuring parameters of a control system in a transmitter, including a time domain parameter configuration and a frequency domain rate parameter configuration, wherein the time domain parameter configuration includes: selecting the length of a current turn-off acquisition window; the frequency domain rate parameter configuration comprises reference frequency and transmission frequency point selection;
The obtained bipolar in-phase composite pulse and bipolar anti-phase composite pulse are used as control signals of an H full-bridge driving circuit to be transmitted, and when the transmission is started, a control system enters a circulation state until the transmission is stopped; and after the transmission state is ended, re-entering a parameter configuration state, and waiting for the next transmission parameter configuration.
In the field detection, a high-power transmitter is arranged on the ground to face underground to transmit the time-frequency electromagnetic synchronous pulse excitation sequence, and a receiver is mounted on an aerial flight platform such as an unmanned plane, an airship and the like to collect the reflected electromagnetic field signals. On the basis of keeping the detection depth and the detection precision, the method is not limited by terrain, and can be used for rapidly detecting the area with complex surface conditions in a non-contact and large depth.
By the application of the embodiment, the ground-air electromagnetic detection instrument equipment is used for carrying out high-efficiency and fine detection on the investigation and detection of the empty water in the new coal mine at the eastern part of the double-duck mountain coal basin in friendship county of Heilongjiang province. The whole newly installed coal mine area is distributed in a strip shape, and the north-south span exceeds 4000 m. If a traditional time domain or frequency domain electromagnetic detection system is adopted, the signal-to-noise ratio of the acquired data in the transition region between the near source and the far source is difficult to ensure; if multiple sources are deployed to combat the problem of low signal to noise ratio, construction efficiency is greatly reduced and the area of land crop damage is increased, thereby increasing the economic loss incurred by green claims.
The control system parameters are configured to: the time domain transmitting frequency selects 12.5 Hz, and the frequency domain transmitting frequency selects three frequency points. In other configuration aspects, the electrical source length is 2000 m, the transmitting current is 25A, the receiving coil area is 2160 m 2, the sampling frequency is 156 kHz, the maximum transmitting voltage is 900V, the unmanned aerial vehicle navigational speed is 6 m/s, and the flying height is 45 m.
Fig. 7 is a slice diagram of the measured apparent resistivity of the new installation zone 8# coal seam, and fig. 7 (a) and 7 (b) are graphs of the results of the conventional detection method and the time-frequency synchronous detection method, respectively, wherein the method adopts a ground-space time domain method for processing and explaining in the range from north to south 2000 m, and adopts a ground-space frequency domain method for processing and explaining in the range from 2000 m to 4000 m, so that the detection dead zone in the frequency domain data processing range and the detection result in the known mining water accumulation zone can be detected, wherein the method can be seen that the underground water outlet point is more obvious and the detection dead zone is not generated.
Compared with the traditional detection method, the waveform coded by the method is used for detection, has the technical advantages of higher sensitivity, wider frequency band range, stronger noise resistance, larger dynamic range and the like, and improves the recognition degree of abnormal bodies in a near zone and a far zone compared with the traditional detection method. Meanwhile, the detection blind zone which is caused by the fact that the traditional detection method cannot acquire high signal-to-noise ratio data in the transition area can be eliminated. Through the verification of the drilling result, the mining space water is reserved in the transition area, and the measured result is identical with the actual data. In summary, the result obtained by using the pulse coding and control system of the space-time-frequency electromagnetic synchronous pulse excitation sequence of the invention is more accurate than that obtained by using the traditional space-time electromagnetic detection system.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention.
Claims (8)
1. The method for encoding the ground space-time frequency electromagnetic synchronous pulse excitation sequence is characterized by comprising the following steps of:
constructing a multi-frequency pseudo-random signal of the time-frequency synchronous excitation pulse and constructing a bipolar square wave signal of the time-frequency synchronous excitation pulse;
The method comprises the steps of carrying out segmentation interception coding on a time-frequency synchronous excitation pulse, and corresponding a frequency domain signal corresponding to a multi-frequency pseudo-random signal and a time domain signal corresponding to a bipolar square wave signal to the segmentation interception coding;
And fusing configuration parameters required by the frequency domain signal and the time domain signal into the segmentation interception code, wherein the configuration parameters comprise a time domain excitation pulse width, a sequence turn-off observation window length, a ns-level delay system clock and a system frequency.
2. The method for encoding a geospatial time-frequency electromagnetic synchronous pulse excitation sequence according to claim 1, wherein the constructing a multi-frequency pseudo-random signal of time-frequency synchronous excitation pulses specifically comprises:
Constructing a periodic sequence by self-closing addition of a three-element set consisting of 1,0 and 1, and normalizing functions of the three-element set Expressed as period/>Is a continuous square wave signal of:
，
Wherein n represents the number of the pseudo-random transmitting frequency points, the value range is all positive integers, k represents the marks of the square waves on the time axis, and the value is as follows: 0, ±1, ±2, ±3 … n; t represents any time within the duration of the transmission, Representing period as/>Is a sign of a square wave signal;
multi-frequency excitation response by self-closing addition using signal spectral superposition The addition group element is [ -1,0,1], the mathematical expression: /(I)Wherein/>Representing a pseudo-random waveform function with n frequency points, wherein i is from 1 to n;
The iterative pulse code for obtaining the waveforms with five, seven or more odd frequency components is as follows:
，
Wherein, Represents an element "/>" 1Representing a pseudo-random waveform function having n+2 frequency bins;
The time domain expression of the multi-frequency pseudo-random signal in the in-phase or anti-phase frequency domain observation window is as follows: Wherein m represents the number of pseudo-random encoding step transitions,/> Representing the first position on the time axis where a step occurs,/>Representing the position on the time axis where the mth step occurs, T F represents the duration of a single in-phase or anti-phase pseudorandom waveform, A represents the voltage amplitude,/>For the time domain representation of a multi-frequency pseudorandom signal within an in-phase or anti-phase frequency domain observation window,/>Representing the position on the time axis where the m-1 st step occurs.
3. The method for encoding the geospatial time-frequency electromagnetic synchronous pulse excitation sequence according to claim 1, wherein the step of constructing a bipolar square wave signal of time-frequency synchronous excitation pulses comprises the following steps:
setting a waveform emission initial time Emission current intensity is/>Bipolar square wave signal/>Expressed as: Where w is the pulse width,/> Representing the transmission period of the time domain waveform, t being any time within the transmission duration,/>A step function having a function value of 1 when t is equal to or greater than 0 and a function value of 0 when t < 0;
Setting the emission period of the time domain waveform to be endless, and obtaining bipolar square wave amplitude-frequency characteristics as follows:
wherein/> Is any frequency in the frequency spectrum.
4. The method for encoding the geospatial time-frequency electromagnetic synchronous pulse excitation sequence according to claim 1, wherein the step of performing segment interception encoding on the time-frequency synchronous excitation pulse comprises the steps of:
Dividing a transmission period of a time-frequency synchronous excitation pulse, namely, a transmission period comprising time domain and frequency domain transmission information into four parts: an anti-phase time domain observation window T-, an in-phase time domain observation window T+, an anti-phase frequency domain observation window F-, and an in-phase frequency domain observation window F+.
5. The method for encoding a geospatial time-frequency electromagnetic synchronization pulse excitation sequence according to claim 4, wherein the step of mapping the frequency domain signal corresponding to the multi-frequency pseudo-random signal and the time domain signal corresponding to the bipolar square wave signal into the segment truncation encoding comprises: the reverse phase time domain observation window T-, the in-phase time domain observation window T+ appears when the high level or the low level is stepped to 0 voltage, the step is used as the start of the reverse phase time domain observation window T-or the in-phase time domain observation window T+ and is continued until the next step signal appears; the inverse frequency domain observation window F-and the in-phase frequency domain observation window F + remain consistent with the multi-frequency pseudorandom signal duration.
6. The method for encoding a geospatial time-frequency electromagnetic synchronous pulse excitation sequence according to claim 5, wherein the frequency domain signal corresponding to the multi-frequency pseudo-random signal and the time domain signal corresponding to the bipolar square wave signal are corresponding to the segment interception code, and further comprising synthesizing the frequency domain signal and the time domain signal to obtain a synthesized waveform, the synthesizing comprising:
The first step: adding a section of waveform with duration voltage of 0 behind the frequency domain signal corresponding to the multi-frequency pseudo-random signal, and forming a time domain signal by the voltage step at the tail end of the frequency domain signal to 0 and the subsequent continuous 0 voltage waveform, wherein the time domain signal is used as a synthesized waveform of the first step;
And a second step of: the synthesized waveform of the first step is phase shifted 180 degrees to form a phase shifted waveform, and then the end time of the synthesized waveform of the first step is taken as the start time of the phase shifted waveform.
7. The method for encoding a geospatial time-frequency electromagnetic synchronous pulse excitation sequence according to claim 6, wherein the time-frequency synchronous excitation pulse encoded by the encoding method is used for a control system to generate a control signal, and the method comprises the following steps:
S1: the peripheral crystal is used as a reference clock for controlling a Field Programmable Gate Array (FPGA) in a system, and the frequency of the reference clock is a fixed frequency, which is called a system clock;
S2: based on a system clock, an inversion time domain observation window T-, an in-phase time domain observation window T+ and an inversion frequency domain observation window F-and an in-phase frequency domain observation window F+ are designed, wherein a part of a waveform with 1 is the inversion frequency domain observation window F-and the in-phase frequency domain observation window F+, a part of the waveform with 0 is the inversion time domain observation window T-, the in-phase time domain observation window T+, and the generated waveform is called time-frequency composite pulse gating;
S3: performing one-time AND logic operation on the time-frequency composite pulse gating and the system clock to obtain waveforms of clock signals only when the reverse phase frequency domain observation window F-and the in-phase frequency domain observation window F+ appear, which are called reference clocks;
S4: based on a reference clock, constructing a waveform sequence of a frequency domain signal with an in-phase frequency domain observation window F+ and a time domain signal with an anti-phase time domain observation window T-, wherein the step moment of the time domain signal appears at the end of the frequency domain signal and is called unipolar in-phase pulse;
s5: taking the reverse logic of the unipolar in-phase pulse to obtain a unipolar reverse phase pulse;
s6: according to the time-frequency composite pulse gating in the step S2, bipolar in-phase gating is obtained, and bipolar reverse phase gating is obtained after inversion;
S7: performing AND logic on the bipolar in-phase gating and the bipolar inversion gating obtained in the step S6 and the unipolar in-phase pulse and the unipolar inversion pulse respectively to obtain a bipolar in-phase pulse and a bipolar inversion pulse respectively;
S8: and performing OR logic on the bipolar in-phase pulse and the bipolar anti-phase pulse to obtain a bipolar in-phase composite pulse, taking the inverse to obtain a bipolar anti-phase composite pulse, and taking the obtained bipolar in-phase composite pulse and the bipolar anti-phase composite pulse as control signals of the H full bridge driving circuit.
8. A method for detecting a control signal generated by the method for encoding a geospatial time-frequency electromagnetic synchronization pulse excitation sequence according to claim 7, comprising:
Configuring parameters of a control system in a transmitter, including a time domain parameter configuration and a frequency domain rate parameter configuration, wherein the time domain parameter configuration includes: selecting the length of a current turn-off acquisition window; the frequency domain rate parameter configuration comprises reference frequency and transmission frequency point selection;
The obtained bipolar in-phase composite pulse and bipolar anti-phase composite pulse are used as control signals of an H full-bridge driving circuit to be transmitted, and when the transmission is started, a control system enters a circulation state until the transmission is stopped; and after the transmission state is ended, re-entering a parameter configuration state, and waiting for the next transmission parameter configuration.
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