Air-ground collaborative excitation integrated time-frequency receiving airborne electromagnetic detection system and method

Abstract

The present invention discloses an air-ground collaborative excitation integrated time-frequency receiving airborne electromagnetic detection system and method, belonging to the technical field of airborne geophysical exploration. The electromagnetic detection system of the present invention includes a time-frequency receiver, a helicopter airborne time-domain transmitter, a time-frequency receiving coil, and a ground frequency-domain transmitter; the electromagnetic detection method of the present invention emits time-domain pulses in the air by the helicopter and emits frequency-domain continuous waves on the ground, and the two are synchronously excited and received entirely by air, and based on the frequency point separation and data decoupling technology, the helicopter airborne time-domain electromagnetic data and the air-ground frequency-domain electromagnetic data are obtained in one flight. The electromagnetic detection system of the present invention combines the high-resolution imaging ability of helicopter airborne time-domain electromagnetic for shallow depths of hundreds of meters with the strong penetration characteristics of air-ground frequency-domain electromagnetic for deep depths, and is particularly suitable for large-scale resource exploration under complex surface conditions such as mountainous areas and water areas, and it can achieve refined exploration of shallow geological structures while taking into account the detection of deep geological structures.

Description

Technical Field

[0001] The present invention relates to the technical field of airborne geophysical exploration, and specifically to an air-ground collaborative excitation integrated time-frequency receiving airborne electromagnetic detection system and method. This transient electromagnetic detection system emits time-domain pulses through a helicopter airborne electromagnetic emission system and emits 2 n pseudo-random continuous waves through a ground frequency-domain emission system, and both are excited simultaneously and the entire airborne electromagnetic is received, which can achieve refined shallow geological structures while taking into account the detection of large-depth geological structures. Background Art

[0002] The detection depth of traditional all-airborne helicopter airborne time-domain electromagnetic systems is only in the hundreds of meters but has high resolution. The detection depth of semi-airborne frequency-domain or time-domain electromagnetic detection with ground emission and airborne reception is deeper but the overall resolution is poor. Therefore, an all-airborne helicopter airborne time-domain electromagnetic system and a semi-airborne frequency-domain or time-domain electromagnetic detection system are combined to conduct electromagnetic detection on the same survey area, so as to be able to refine shallow stratum data while maintaining a large detection depth range. If the two electromagnetic detection systems work simultaneously, for the received electromagnetic signals, they are mutual interference sources, making it difficult to separate the electromagnetic signals from each other. Therefore, most of the existing combined schemes of helicopter airborne electromagnetic method and ground-air electromagnetic method are time-sharing excitation, and separate flight detections need to be carried out on the data of each system, with low efficiency and poor spatio-temporal matching of the data. The following are some documents of the prior art.

[0003] CN202210596682.1 discloses a mixed-field source electromagnetic detection system, which needs to carry two types of coils, namely an airborne high-sensitivity small-bandwidth coil and an airborne low-sensitivity large-bandwidth coil respectively. Since it cannot achieve one-time flight detection and receive ground electrical source and airborne magnetic source data simultaneously, its detection cost and detection efficiency cannot be optimized.

[0004] CN201711067239.0 discloses an airborne mixed-field source coded electromagnetic detection system, whose helicopter platform simultaneously carries high-frequency transmitting and receiving antennas, and low-frequency transmitting and receiving antennas. The time-domain and frequency-domain combined transmission is realized on the helicopter platform. The time-domain transient electromagnetic detection system detects deep geological bodies, and the low-frequency pseudo-random emission system is responsible for shallow geological bodies. However, due to the limitation of helicopter power supply for the excitation source, its detection depth is still in the hundreds of meters, depending on the helicopter airborne time-domain electromagnetic system with load.

[0005] CN200810050865.3 discloses a combined field source emission device for mixed-field source electromagnetic method, whose goal is to emit field source signals that can switch between electrical sources and magnetic sources in a set of equipment. It is designed for ground emission sources and cannot be integrated into a helicopter airborne electromagnetic detection system due to the power limitation of the helicopter.

[0006] CN200810143301.4 discloses a combined field source artificial source frequency domain electromagnetic sounding method, which is a combination of low / middle / high frequency transmitters and low / middle / high frequency receivers. By means of a combined current excitation signal composed of different main frequencies and different powers, all frequency geoelectric response information of different frequency groups is received simultaneously at one time. However, this method is a frequency domain ground electromagnetic detection method and cannot achieve rapid geological detection in complex terrain areas. Summary of the Invention

[0007] In order to solve the above problems, the present invention provides an air-ground collaborative excitation integrated time-frequency receiving airborne electromagnetic detection system and method, which realizes both shallow high-resolution of helicopter time domain electromagnetic method and large-depth detection of air-ground frequency domain electromagnetic method in one flight through the methods of full reception of ground frequency domain electromagnetic electrical source response and airborne time domain electromagnetic magnetic source response, frequency point separation and electromagnetic response decoupling. On the basis of a flexible and maneuverable helicopter platform, the present invention combines the shallow layer high-resolution advantage of helicopter airborne time domain electromagnetic detection and the large-depth advantage of helicopter air-ground frequency domain electromagnetic detection, and realizes extremely efficient rapid, large-scale and all-round electromagnetic exploration adaptable to harsh geological conditions.

[0008] In order to achieve the above object, the solution provided by the present invention is as follows:

[0009] An air-ground collaborative excitation integrated time-frequency receiving airborne electromagnetic detection system, comprising a helicopter mounting device and a ground device. Among them, the helicopter mounting device includes in-cabin equipment and a suspended device suspended under the helicopter by a suspension rope, and the suspended device is electrically connected to the in-cabin equipment through a cable;

[0010] The suspended device includes:

[0011] A helicopter airborne time domain electromagnetic transmitting coil;

[0012] A helicopter airborne time domain electromagnetic compensation coil electrically connected to the helicopter airborne time domain transmitting coil;

[0013] An attitude sensor installed on the helicopter airborne time domain electromagnetic transmitting coil;

[0014] A time-frequency receiving coil fixed on a horizontal cross-tension rope;

[0015] A preamplifier fixed on the suspension rope and electrically connected to the time-frequency receiving coil;

[0016] The in-cabin equipment includes:

[0017] A helicopter airborne time domain transmitter electrically connected to the helicopter airborne time domain electromagnetic transmitting coil, which is used to generate a bipolar pulse current in the helicopter airborne time domain electromagnetic transmitting coil as a magnetic source;

[0018] A time-frequency receiver for collecting the induced voltage signal amplified by a preamplifier from a time-frequency receiving coil and other auxiliary information;

[0019] A radar altimeter for obtaining the height information of the helicopter from the ground and transmitting the height information from the ground to the time-frequency receiver;

[0020] A GPS device for obtaining the GPS information of the helicopter and transmitting the GPS information to the time-frequency receiver;

[0021] The ground device includes:

[0022] Two grounding electrodes inserted into the ground;

[0023] A ground frequency domain transmitter electrically connected to the grounding electrodes for generating a 2 n pseudo-random continuous wave current in the two grounding electrodes; the ground frequency domain transmitter and the two grounding electrodes are located on the same straight line;

[0024] A ground station for obtaining the three-component magnetic field data of the natural field, the ground station including a three-component receiving sensor and a supporting acquisition device;

[0025] Wherein, the helicopter airborne time domain transmitter and the ground frequency domain transmitter are simultaneously excited, and the minimum frequency difference between the two sets of frequency points of the time domain electromagnetic excitation fundamental frequency and its odd harmonics of the helicopter airborne time domain transmitter and the 2 n pseudo-random all excitation frequency points of the ground frequency domain transmitter is greater than 0.

[0026] As a specific embodiment of the present invention, the X and Y components in the three-component sensor in the ground station are respectively parallel to the geomagnetic north-south direction and the east-west direction, and the Z component is completely perpendicular to the geoid.

[0027] As a specific embodiment of the present invention, the relative height difference between the equipment in the cabin and the suspended equipment is 30 meters to 50 meters.

[0028] An air-ground collaborative excitation integrated time-frequency receiving airborne electromagnetic detection method includes the following steps:

[0029] S1. Arrange a ground frequency domain transmitter, grounding electrodes and a ground station according to the location of the survey area, and set the survey line; determine the time domain electromagnetic excitation fundamental frequency f 0 of the helicopter airborne time domain transmitter and the 2 n pseudo-random excitation fundamental frequency f 1 of the ground frequency domain transmitter;

[0030] Determine the time domain electromagnetic excitation fundamental frequency f 0 and 2 n pseudo-random excitation fundamental frequency fThe rules of 1 are as follows:

[0031] Maximize the fundamental frequency of time-domain electromagnetic excitation and its odd harmonics, and the minimum frequency difference between the two sets of frequency points of all pseudo-random excitation frequency points is used as the optimization objective to determine each excitation fundamental frequency. Its objective function is as follows: n Pseudo-random all excitation frequency points, the minimum frequency difference between the two sets of frequency points is the optimization target, determine each excitation fundamental frequency, and its objective function is the following formula:

[0032] ;

[0033] ;

[0034] N 0 represents the order of the time-domain electromagnetic excitation harmonic; n Represents 2 n Pseudo-random order;

[0035] Or, maximize the odd and even harmonics of the time-domain electromagnetic excitation fundamental frequency, and the minimum frequency difference between the two sets of frequency points of all pseudo-random excitation frequency points is used as the optimization objective to determine each excitation fundamental frequency. Its objective function is as follows: n Pseudo-random all excitation frequency points, the minimum frequency difference between the two sets of frequency points is the optimization target, determine each excitation fundamental frequency, and its objective function is the following formula:

[0036] ;

[0037] ;

[0038] When solving the above objective function, it is found that under the above two conditions, the two excitation fundamental frequencies and the maximized minimum frequency difference respectively satisfy specific relationships. Therefore, the specific relationships can be used to determine each excitation fundamental frequency, thereby reducing the calculation amount. Therefore, as a specific implementation manner of the present invention,

[0039] When determining each excitation fundamental frequency with the minimum frequency difference between the two sets of frequency points of all pseudo-random excitation frequency points by maximizing the fundamental frequency of time-domain electromagnetic excitation and its odd harmonics, the two excitation fundamental frequencies satisfy the following relationship: n Pseudo-random all excitation frequency points, the minimum frequency difference between the two sets of frequency points is the optimization target, determine each excitation fundamental frequency, and the two excitation fundamental frequencies satisfy the following relationship:

[0040] ;

[0041] In the formula, m Is any non-negative integer. At this time, the maximized minimum frequency difference obtained is: ;

[0042] When determining each excitation fundamental frequency with the minimum frequency difference between the two sets of frequency points of all pseudo-random excitation frequency points by maximizing the odd and even harmonics of the time-domain electromagnetic excitation fundamental frequency, the two excitation fundamental frequencies satisfy the following relationship: n Pseudo-random all excitation frequency points, the minimum frequency difference between the two sets of frequency points is the optimization target, determine each excitation fundamental frequency, and the two excitation fundamental frequencies satisfy the following relationship:

[0043] ;

[0044] At this time, the obtained maximum minimized frequency difference is: ;

[0045] In this step, the waveform of the helicopter airborne time-domain transmitter can select appropriate bipolar triangular wave or bipolar trapezoidal wave pulses according to relevant geological data information; when arranging the grounding electrodes, the distance between the poles and the geographical location are determined according to the survey area range to ensure that the outermost end of the survey area is within the action range of the frequency-domain excitation field; the ground station should be set near the survey area and away from human interference; the survey lines should be designed with equal horizontal intervals within the survey area according to the detection resolution, and reciprocating lines should be set in key areas.

[0046] S2. Start the equipment, including using the ground power supply to turn on the hoisting equipment;

[0047] This step includes starting the ground station and collecting the three-component magnetic field data of the natural field; according to the determined 2 n pseudo-random excitation frequency f 1. Start the ground frequency-domain transmitter; when using the ground power supply to turn on the time-frequency receiver and the radar altimeter, the GPS equipment (including its auxiliary system), and start the helicopter airborne time-domain transmitter according to the determined time-domain electromagnetic excitation fundamental frequency f 0 and the waveform, and turn on the attitude sensor located on the helicopter airborne time-domain electromagnetic emission coil; after connecting the helicopter power supply, disconnect the ground power supply;

[0048] S3. The helicopter flies along the survey line under the condition of keeping the hoisting equipment 30 meters to 200 meters above the ground. During the flight, the helicopter airborne time-domain transmitter and the ground frequency-domain transmitter are excited simultaneously. The time-frequency receiver collects electromagnetic data, the radar altimeter obtains the helicopter's height information above the ground, and the GPS equipment obtains the helicopter's GPS information, and the height information above the ground and the GPS information are bound to the electromagnetic data through time stamps;

[0049] In this step, the electromagnetic data collected by the time-frequency receiver is the time-domain magnetic source electromagnetic response signal excited in the air and the frequency-domain electrical source electromagnetic response signal excited on the ground, which are induced by the time-frequency receiving coil and pre-amplified by a low-noise preamplifier.

[0050] S4. After the flight, collect the data of the time-frequency receiver, the attitude sensor and the ground station, and split the collected data according to the survey line, and align the electromagnetic data with the geographical location;

[0051] S5. Data processing: Based on the time-domain electromagnetic excitation fundamental frequency and its odd harmonic frequencies and 2 nPseudo-random excitation frequency points, the helicopter airborne time-domain electromagnetic trace data obtained by performing equal-amplitude comb filtering or other filtering on the electromagnetic data after the processing of step S4 and then performing trace extraction, and the ground-air frequency-domain frequency point data obtained by fast Fourier transform or quadrature phase-locking are used to complete data decoupling;

[0052] S6. Inversion imaging: According to the ground-air frequency-domain electromagnetic inversion imaging method, the ground-air frequency-domain frequency point data and the ground station signal are used to calculate the apparent resistivity to obtain the apparent resistivity information ρ of the exploration area 频 ; According to the helicopter airborne electromagnetic inversion imaging method, the helicopter airborne time-domain electromagnetic trace data is used to calculate the resistivity to obtain the resistivity information ρ of the exploration area 时 .

[0053] Advantageous effects: The present invention first proposes an airborne electromagnetic detection system with "simultaneous excitation of helicopter airborne time-domain pulses and ground-air frequency-domain continuous waves, and integrated airborne time-frequency reception by helicopter in the air" under the collaborative excitation of ground and air, and proposes a time-frequency signal decoupling method supporting this airborne electromagnetic detection system. By separately setting the frequency points of time-frequency excitation and screening the frequencies of electromagnetic data, the data aliasing problem in simultaneous integrated reception is solved. Generally speaking, based on the high mobility of the helicopter platform, the present invention constructs a set of electromagnetic exploration systems with full terrain coverage and high efficiency by integrating the high-resolution imaging ability of airborne time-domain electromagnetic for shallow depths of hundreds of meters and the strong penetration characteristics of ground-air frequency-domain electromagnetic for deep depths. It is particularly suitable for large-scale resource exploration under complex surface conditions such as mountains and waters. Compared with other electromagnetic time-frequency excitation methods using ground sources, it can achieve the effect of refined shallow detection while taking into account large detection depths. Compared with separately performing flight detections using ground-air frequency-domain electromagnetic and airborne time-domain electromagnetic, its detection cost is low and detection efficiency is high. Description of the Drawings

[0054] Figure 1 is a schematic diagram of the airborne electromagnetic detection system with collaborative excitation of ground and air and integrated time-frequency reception of the present invention;

[0055] Figure 2 is a schematic diagram of the frequency point data of the 7th-order 2 pseudo-random frequency-domain electromagnetic with a fundamental frequency of 8.4 Hz after data decoupling in Example 2 n ;

[0056] Figure 3 is a schematic diagram of the trace data of the time-domain electromagnetic with a fundamental frequency of 25 Hz after data decoupling in Example 2;

[0057] Figure 4 is a schematic diagram of the frequency point data of the 7th-order 2 pseudo-random frequency-domain electromagnetic with a fundamental frequency of 7.5 Hz after data decoupling in Example 3 n ;

[0058] Figure 5It is a schematic diagram of the trace data of the 75Hz fundamental frequency time-domain electromagnetic after data decoupling in Embodiment 3;

[0059] In the figure, helicopter 1; time-frequency receiver 2; radar altimeter 3; GPS device 4; helicopter airborne time-domain transmitter 5; time-frequency receiving coil 6; helicopter airborne time-domain electromagnetic transmitting coil 7; helicopter airborne time-domain compensation coil 8; preamplifier 9; attitude sensor 10; ground frequency-domain transmitter 11; grounding electrode 12; ground station 13. Specific implementation mode

[0060] The present invention will be further described in detail below in conjunction with the embodiments and the accompanying drawings, but the implementation modes of the present invention are not limited thereto.

[0061] Embodiment 1: Please refer to Figure 1 , which shows a schematic diagram of a specific structure of the air-ground collaborative excitation integrated time-frequency receiving airborne electromagnetic detection system of the present invention. The air-ground collaborative excitation integrated time-frequency receiving airborne electromagnetic detection system of the present invention includes a helicopter mounting device and a ground device. Among them, the ground device is arranged on the ground, and the helicopter mounting device flies with the helicopter 1. The helicopter mounting device further includes in-cabin equipment and suspended equipment, and the suspended equipment is structurally connected to the helicopter 1 through a suspension rope and electrically connected through a cable, and the relative height between the two is 30 meters to 50 meters.

[0062] The suspended equipment includes a helicopter airborne time-domain electromagnetic transmitting coil 7, a helicopter airborne time-domain electromagnetic compensation coil 8, an attitude sensor 10, a time-frequency receiving coil 6 and a preamplifier 9. Among them, the helicopter airborne time-domain electromagnetic compensation coil 8 is electrically connected to the helicopter airborne time-domain electromagnetic transmitting coil 7; the attitude sensor 10 is installed on the helicopter airborne time-domain electromagnetic transmitting coil 7; the time-frequency receiving coil 6 is a flexible time-frequency receiving coil and is fixed on a horizontal cross-tension rope; the preamplifier 9 uses a low-noise preamplifier and is fixed on the suspension rope and electrically connected to the time-frequency receiving coil 6.

[0063] The in-cabin equipment includes a helicopter airborne time-domain transmitter 5, a time-frequency receiver 2, a radar altimeter 3 and a GPS device 4. Among them, the helicopter airborne time-domain transmitter 5 is electrically connected to the helicopter airborne time-domain electromagnetic transmitting coil 7 and is used to generate a bipolar pulse current in the helicopter airborne time-domain electromagnetic transmitting coil 7; the time-frequency receiver 2 is used to collect the induced voltage signal amplified by the preamplifier 9 from the time-frequency receiving coil 6 and other auxiliary information; the radar altimeter 3 is used to obtain the height information of the helicopter 1 from the ground and transmit this information to the time-frequency receiver 2; the GPS device 4 is used to obtain the GPS information of the helicopter 1 and transmit this information to the time-frequency receiver 2.

[0064] The ground device includes a ground frequency domain transmitter 11, two grounding electrodes 12, and a ground station 13. Among them, the two grounding electrodes 12 are connected to both ends of the cable and inserted into the soil. The cable is electrically connected to the ground frequency domain transmitter 11, and the two grounding electrodes 12 and the cable are on a straight line. The ground frequency domain transmitter is used to generate 2 n pseudo-random continuous wave current in the two grounding electrodes; the ground station 13 includes a three-component receiving sensor and a supporting acquisition device, which is used to obtain the three-component magnetic field data of the natural field. The X and Y components in the three-component sensor are parallel to the geomagnetic north-south direction and the east-west direction respectively, and the Z component is completely perpendicular to the geoid. The airborne helicopter time domain transmitter 5 and the ground frequency domain transmitter 11 are excited simultaneously, and the fundamental frequency of the time domain electromagnetic excitation of the helicopter airborne time domain transmitter and its odd harmonics, and the 2 n pseudo-random all excitation frequency points. The minimum frequency difference between these two groups of frequency points is greater than 0.

[0065] Embodiment 2: An air-ground collaborative excitation integrated time-frequency receiving airborne electromagnetic detection method, including the following steps:

[0066] S1. Arrange a ground frequency domain transmitter, grounding electrodes, and a ground station according to the location of the survey area, and set the survey line; determine the fundamental frequency of the time domain electromagnetic excitation of the helicopter airborne time domain transmitter f 0 and the 2 n pseudo-random excitation fundamental frequency f 1 of the ground frequency domain transmitter.

[0067] Specifically, after selecting the fundamental frequency of the time domain electromagnetic excitation of 25 Hz and the 2 n pseudo-random sequence excitation fundamental frequency in the range of 5 Hz to 10 Hz and its order is 7, with the minimum frequency difference between the fundamental frequency of the time domain electromagnetic excitation and its odd harmonics, and the 2 n pseudo-random all excitation frequency points as the optimization target (step size is 0.1 Hz), select the 2 n pseudo-random sequence fundamental frequency of 8.4 Hz. According to the geological data information, set the triangular current waveform of the time domain electromagnetic excitation, and the peak value of the excitation current is 500 A. Arrange 30 mutually parallel horizontal survey lines at intervals of 100 m. The two grounding electrode points are located at the edge of the exploration area, with a straight-line distance of 3 km, and the ground frequency domain transmitter is placed in the middle position between the two grounding poles. The ground station is arranged 2 km northeast of the survey area, far from high-voltage wires and factories. Calibrate the three-component sensor, align the X / Y components with the geomagnetic north / south and east / west directions respectively, and the verticality error of the Z component < 0.5°;

[0068] S2. Start the equipment, including starting the ground station, and collect the three-component magnetic field data of the natural field; according to the determined 2 n pseudo-random excitation frequency f1. Start the ground frequency-domain transmitter; when using the ground power supply, turn on the time-frequency receiver, radar altimeter, and GPS device (including its auxiliary system), and according to the determined fundamental frequency of electromagnetic excitation in the time domain f 0. Start the time-domain transmitter with the waveform; turn on the attitude sensor on the helicopter's airborne time-domain electromagnetic emission coil;

[0069] S3. The helicopter flies along the survey line under the condition of keeping the height of the suspended equipment 30 meters to 150 meters above the ground. During the flight, the helicopter's airborne time-domain transmitter and the ground frequency-domain transmitter are simultaneously excited. The time-frequency receiver collects electromagnetic data (including the helicopter's airborne time-domain electromagnetic response signal and the ground-air frequency-domain electromagnetic response signal) at a sampling rate of 192 kHz. The radar altimeter obtains the helicopter's height information above the ground, and the GPS device obtains the helicopter's GPS information. Moreover, the height information above the ground and the GPS information are bound to the electromagnetic data through timestamps;

[0070] S4. After the flight, turn off the helicopter's airborne time-domain transmitter and the ground frequency-domain transmitter; use the ground power supply to take out the data in the time-frequency receiver, take out the attitude sensor data, and end the ground station acquisition work after saving the three-component magnetic field data of the ground station. Intercept the collected data according to the survey line, GPS data points, and the planned survey line position coordinate points, and align the geographical positions of the electromagnetic data with the GPS information through timestamps;

[0071] S5. Data processing: Based on the fundamental frequency of electromagnetic excitation in the time domain and its odd harmonic frequencies and 2 n pseudo-random excitation frequency points, the electromagnetic data processed in step S4 is processed by equal-amplitude comb filtering and then decimated to obtain the helicopter's airborne time-domain electromagnetic decimated data, and the ground-air frequency-domain frequency point data is obtained by fast Fourier transform, completing the decoupling of the electromagnetic data. After decoupling, the ground-air frequency-domain frequency point data is as Figure 2 shown. Its frequency point curves are smooth, the relationship between frequency points is clear, and the response amplitude magnitudes are close; after decoupling, the helicopter's airborne time-domain electromagnetic decimated data is as Figure 3 shown. Each time trace curve is smooth, the relationship between traces is significant, and there is no overlap of trace curves;

[0072] S6. Inversion imaging: According to the ground-air frequency-domain electromagnetic inversion imaging method, calculate the apparent resistivity of the exploration area ρ 频 by calculating the apparent resistivity of the ground-air frequency-domain frequency point data and the ground station signal; according to the helicopter's airborne electromagnetic inversion imaging method, calculate the resistivity information ρ 时 of the exploration area by calculating the resistivity of the helicopter's airborne time-domain electromagnetic decimated data;

[0073] S7. Data Interpretation: Combine the constructed metallogenic geological model with the inversion imaging to delineate the electromagnetic anomaly area, and combine geological data such as strata, structures, and geochemical analysis within the anomaly area to optimize the target area and achieve effective exploration of mineral resources.

[0074] Example 3: The steps are the same as those in Example 2, except that some parameters are different. The specific differences are as follows:

[0075] In step S1, after selecting the fundamental frequency of time-domain electromagnetic excitation as 75 Hz and the fundamental frequency of the 2 n pseudo-random sequence is in the range of 5 Hz to 10 Hz and its order is 7, and to maximize the odd and even harmonics of the fundamental frequency of time-domain electromagnetic excitation and the 2 n minimum frequency difference of these two groups of frequency points of all excitation frequency points of the pseudo-random sequence is taken as the optimization objective (step size is 0.5 Hz), and the fundamental frequency of the 2 n pseudo-random sequence is 7.5 Hz. According to the geological data information, set the trapezoidal current waveform of time-domain electromagnetic excitation, and the peak value of the excitation current is 400 A. Arrange 50 mutually parallel horizontal survey lines at 100 m intervals. The two electrode points are located at the edge of the exploration area, with a straight-line distance of 5 km, and the ground frequency-domain transmitter is placed at the middle position between the two pole points. The ground station is arranged 1.5 km northeast of the survey area, far away from high-voltage wires and factories, and the calibration three-component sensor X / Y is aligned with the geomagnetic north-south / east-west directions respectively, and the verticality error of the Z component is < 0.5°.

[0076] In step S3, the helicopter flies along the survey line under the condition of keeping the height of the suspended equipment 30 m to 100 m above the ground.

[0077] In step S5, the decoupled ground-air frequency-domain electromagnetic data of each frequency point is as Figure 4 shown, and the curves of each frequency point are smooth and the relationships between frequency points are clear; the decoupled helicopter airborne time-domain electromagnetic trace data is as Figure 5 shown, and the curves of each time trace are smooth and the relationships between traces are significant.

[0078] The above is only the preferred specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed in the embodiments of the present invention should be covered by the protection scope of the present invention.

Claims

1. An air-ground collaborative excitation integrated time-frequency receiving airborne electromagnetic detection system, characterized in that, It includes a helicopter mounting device and a ground device. Among them, the helicopter mounting device includes in-cabin equipment and a suspended load device suspended under the helicopter by a suspension rope. The suspended load device is electrically connected to the in-cabin equipment via a cable. The suspended load device includes: A helicopter airborne time-domain electromagnetic emission coil; A helicopter airborne time-domain electromagnetic compensation coil electrically connected to the helicopter airborne time-domain electromagnetic emission coil; An attitude sensor installed on the helicopter airborne time-domain electromagnetic emission coil; A time-frequency receiving coil fixed on a horizontal cross-tension rope; A preamplifier fixed on the suspension rope and electrically connected to the time-frequency receiving coil; The in-cabin equipment includes: A helicopter airborne time-domain transmitter electrically connected to the helicopter airborne time-domain emission coil, which is used to generate a bipolar pulse current in the helicopter airborne time-domain emission coil; A time-frequency receiver, which is used to collect the induced voltage signal amplified by the preamplifier from the time-frequency receiving coil and other auxiliary information; A radar altimeter, which is used to obtain the helicopter's height above the ground information and transmit the height above the ground information to the time-frequency receiver; A GPS device, which is used to obtain the helicopter's GPS information and transmit the GPS information to the time-frequency receiver; The ground device includes: Two grounding electrodes inserted into the ground; A ground frequency domain transmitter electrically connected to the grounding electrode, configured to generate 2 n pseudo-random continuous wave currents in the two grounding electrodes; the ground frequency domain transmitter and the two grounding electrodes are located on the same straight line; A ground station, which is used to obtain the three-component magnetic field data of the natural field. The ground station includes a three-component receiving sensor and a supporting acquisition device; Among them, the helicopter airborne time-domain transmitter and the ground frequency-domain transmitter are excited simultaneously, and the minimum frequency difference between the time-domain electromagnetic excitation fundamental frequency and its odd harmonics of the helicopter airborne time-domain transmitter and the 2 n pseudo-random all excitation frequency points of these two groups of frequency points is greater than 0.

2. The airborne electromagnetic detection system for integrated time-frequency reception with air-ground collaborative excitation according to claim 1, wherein The relative height difference between the in-cabin equipment and the suspended load device is 30 meters to 50 meters.

3. The airborne electromagnetic detection system for time-frequency reception with integrated air-ground collaborative excitation according to claim 1, wherein The X and Y components in the three-component receiving sensor are parallel to the geomagnetic north-south direction and the east-west direction respectively, and the Z component is completely perpendicular to the geoid.

4. An air-ground collaborative excitation integrated time-frequency receiving airborne electromagnetic detection method, which uses the air-ground collaborative excitation integrated time-frequency receiving airborne electromagnetic detection system described in any one of claims 1 to 3 for detection, and is characterized in that, It includes the following steps: S1. Arrange the ground frequency domain transmitter, grounding electrode and ground station according to the location of the survey area, and set the survey line; determine the time domain electromagnetic excitation fundamental frequency of the helicopter airborne time domain transmitter f 0 and the 2 of the ground frequency domain transmitter n pseudo-random excitation fundamental frequency f 1; Determine the fundamental frequency of electromagnetic excitation in the time domain f 0 and the 2 n Fundamental frequency of pseudo-random excitation f The rule for 1 is as follows: Maximize the fundamental frequency of time-domain electromagnetic excitation and its odd harmonics, and the minimum frequency difference between two sets of frequency points of all pseudo-random excitation frequency points is taken as the optimization goal to determine each excitation fundamental frequency; or, maximize the odd and even harmonics of the fundamental frequency of time-domain electromagnetic excitation, and the minimum frequency difference between two sets of frequency points of all pseudo-random excitation frequency points is taken as the optimization goal to determine each excitation fundamental frequency; n Maximize the fundamental frequency of time-domain electromagnetic excitation and its odd harmonics, and the minimum frequency difference between two sets of frequency points of all pseudo-random excitation frequency points is taken as the optimization goal to determine each excitation fundamental frequency; or, maximize the odd and even harmonics of the fundamental frequency of time-domain electromagnetic excitation, and the minimum frequency difference between two sets of frequency points of all pseudo-random excitation frequency points is taken as the optimization goal to determine each excitation fundamental frequency; n Maximize the fundamental frequency of time-domain electromagnetic excitation and its odd harmonics, and the minimum frequency difference between two sets of frequency points of all pseudo-random excitation frequency points is taken as the optimization goal to determine each excitation fundamental frequency; S2. Start the equipment, including turning on the suspended load device using the ground power supply; S3. The helicopter flies along the survey line under the condition that the suspended load device is 30 meters to 200 meters above the ground. During the flight, the helicopter airborne time-domain transmitter and the ground frequency-domain transmitter are simultaneously excited. The time-frequency receiver collects electromagnetic data, the radar altimeter obtains the helicopter's height above the ground information, the GPS device obtains the helicopter's GPS information, and the height above the ground information and the GPS information are bound to the electromagnetic data through time stamps; S4. After the flight ends, collect the data of the time-frequency receiver, the attitude sensor and the ground station, split the collected data according to the survey line, and align the electromagnetic data with the geographical location. S5. Data processing: Based on the fundamental frequency of time-domain electromagnetic excitation and its odd harmonic frequencies, and the n n pseudo-random excitation frequency points, the helicopter airborne time-domain electromagnetic trace data obtained by decimating the electromagnetic data processed in step S4 after processing through an equal-amplitude comb filter or other filters, and the ground-air frequency-domain frequency point data obtained through fast Fourier transform or quadrature phase-locking are used to complete data decoupling; S6. Inversion imaging: According to the electromagnetic inversion imaging method in the ground-air frequency domain, calculate the apparent resistivity of the exploration area ρ by calculating the apparent resistivity of the ground-air frequency domain frequency point data and the ground station signal. 频 According to the helicopter airborne electromagnetic inversion imaging method, calculate the resistivity of the exploration area ρ by calculating the resistivity of the helicopter airborne time domain electromagnetic extraction channel data. 时 .

5. The air-ground coordinated excitation integrated time-frequency receiving airborne electromagnetic detection method according to claim 4 is characterized in that: The determination of the fundamental frequency of time-domain electromagnetic excitation f 0 and 2 n The fundamental frequency of pseudo-random excitation f The rule of 1 is simplified to: the fundamental frequency of time-domain electromagnetic excitation f 0 and 2 n The fundamental frequency of pseudo-random excitation f 1 satisfies the following relational expression: or ; wherein, m is any non-negative integer.

Images