CN103576205B - Air-ground transient electromagnetic exploration method based on composite magnetic source technology - Google Patents

Abstract

The invention discloses a kind of air-ground transient electromagnetic exploration method based on composite magnetic source technology, the method proposes air-ground transient electromagnetic exploration engineering based on combination source technology first, specifically 4,6 or 8 magnetic source of equally spaced layout on a big circumference on the ground centered by exploration targets region, in the unmanned plane collection of survey area overhead by the induced electromotive force transient response under each combination source forcing.Due to the fact that used combination source is multi-source and is symmetrical, therefore the problems such as uncertain are explained in the response results amplitude difference position big, local non-homogeneous body greatly reducing the nearly far field point using stationary source to be brought, the multi-angle observation information about subsurface anomaly body can be obtained, reduce the impact of inverting multi-solution, it is achieved efficient, high-resolution, the large area of complex region and the exploration of the big degree of depth.

Description

Ground-space transient electromagnetic survey method based on combined magnetic source technology

technical field

The invention relates to a ground-air transient electromagnetic prospecting method based on combined source emission and UAV reception, belonging to the category of geophysical electromagnetic prospecting methods.

Background technique:

The transient electromagnetic method is a traditional electromagnetic prospecting method for ore and water exploration. The transmitting loop is arranged on the ground to supply the current pulse signal, and the receiving coil is also arranged on the ground to receive the vertically induced electromotive force transient signal. Then, according to the observation data, the underground electrical structure is inverted and interpreted to achieve the purpose of geological exploration. This method has low work efficiency and even cannot work in areas with complex terrain and difficult ground geophysical prospecting. Therefore, people thought of applying airborne transient electromagnetic survey technology to realize large-area and long-distance geophysical prospecting work. There are two methods of aviation transient electromagnetic methods, which use fixed-wing as the platform and helicopter as the platform. The former has fast operation speed, large emission magnetic moment, and relatively large exploration depth. The latter has high spatial resolution and relatively small exploration depth. . Since this method requires airborne transmitters, receivers, hosts, power supplies and other equipment, the exploration depth of aviation transient electromagnetics is very limited. The exploration depth of fixed-wing aviation transient electromagnetics is generally 400-800 meters. Electromagnetic exploration depth is generally about 300 meters. It can be seen from the above that none of the existing transient electromagnetic survey methods can achieve high-efficiency, high-resolution, large-area and deep-depth exploration in complex areas.

Contents of the invention

The object of the present invention is to provide a ground-space transient electromagnetic prospecting method based on combined magnetic source technology, which can realize high-efficiency, high-resolution, large-area and deep-depth prospecting in areas with complex surface environments.

The ground-space transient electromagnetic survey method based on the combined magnetic source technology provided by the present invention includes arranging a magnetic source on the ground that emits a periodic bipolar current pulse signal, and using a coil to receive an induced electromotive force transient signal. The magnetic source There are 4, 6 or 8, and they are evenly spaced on a circle on the ground centered on the exploration target area, and each magnetic source can be regarded as a vertical magnetic dipole source; the receiving coil is carried on the UAV, and no one The aircraft flies above the survey target area to collect the induced electromotive force transient response data under the excitation of various combined sources. The combined source refers to the excitation source composed of several or all magnetic sources symmetrically distributed.

The above-mentioned unmanned aerial vehicle flies along the parallel route above the survey area in an end-to-end round-trip manner. After the measurement of one combined source is completed, the excitation signal of another combined source is changed, and the round-trip flight is carried out under the new combined excitation source signal. Measure on the fly until all combined sources are measured.

The above-mentioned magnetic sources are 4, assuming that the labels of each source are A, B, C, D in turn, the first flight measurement under the excitation of the combined source labeled A and C is carried out; The flight measurement under the excitation of the combined source; the third flight measurement under the excitation of the combined source marked as A, B, C, and D is carried out, and finally the measurement data of the three combined sources are obtained.

The above-mentioned magnetic sources are 6, and the labels of each source are set as A, B, C, D, E, F in turn, and the flight measurement under the excitation of the combined source marked as A, C, E is carried out for the first time; The flight measurement under the excitation of the combined source marked as B, D, F; the third flight measurement under the excitation of the combined source marked as A, B, C, D, E, F, and finally the measurement of the three combined sources data.

The above-mentioned magnetic sources are 8, assuming that the labels of each source are A, B, C, D, E, F, G, and H in turn, and the first flight under the excitation of the combined sources labeled A, C, E, and G is carried out. Measurements; second in-flight measurement under combined source excitation marked B, D, F, H; third time under combined source excitation marked A, B, C, D, E, F, G, H Finally, the measurement data of the three combined sources are obtained.

In the present invention, a plurality of magnetic sources are arranged on the ground to emit pulsed current signals, and a receiving coil is used to measure the three-component induced electromotive force response signal in the air, and the drone can fly and measure efficiently in the air. Since the exploration area is in the central area of multiple magnetic sources, each magnetic source can be regarded as a vertical magnetic dipole. At the same time, since multiple magnetic sources are arranged on the ground, the intensity of the observation data is relatively large, and the signal-to-noise ratio is also relatively high. higher. In the traditional ground transient electromagnetic method, if you want to do area exploration, if you use the method of moving source, such as the center loop or overlapping loop method, you need to collect point by point on the ground network measuring points, terrain fluctuations or surface environment If it is bad, not only the workload is heavy, but also the work efficiency is low and even the work cannot be carried out; if the fixed loop device is used, when the offset distance of the measuring point is large, the transient electromagnetic response amplitude of the fixed loop source with an excitation source is relatively small. Small. In addition, if there is a local inhomogeneity located near or below the emission source, similar to the field source copying effect of the ground CSAMT method, the response data in the outer observation area will be affected by the local inhomogeneity. When a traditional excitation source is used for exploration, the inhomogeneity near the source will affect a large area, which will have a very adverse effect on the delineation of underground anomalies. Using combined source excitation technology, the excitation source is arranged on a large approximate circle around the exploration target area, which will not only increase the response signal strength of the exploration area, increase the exploration depth, but also weaken the influence of local inhomogeneous bodies on the response data of the entire area. influences. Another advantage of the combined source excitation technology is that multiple acquisition data of different combined sources can be obtained, so as to obtain multi-angle observation information about underground anomalies and reduce the influence of inversion multi-solution. Therefore, the method of the present invention can overcome many difficulties faced in the exploration of large areas, and realize the exploration of complex areas with high efficiency, high resolution, large area and large depth.

The following uses a simple three-layer medium model combined source-UAV ground-air transient electromagnetic response as an example to perform simulation calculations to further explain the specific effects of the present invention.

Assume that the layer resistivity of the three-layer model is 100, 20 and 100 ohm-meters, and the layer thickness is 300 meters. Each magnetic source laid on the ground is a vertical magnetic dipole (Vertical Magnetic Dipole, VMD) source with the same parameters, the magnetic moment is 1Am ² , and they are placed at different points on a circle on the ground. The receiving coil is 1 m ² and its height is 100 m. Assuming that the transmitting signal is a step pulse, the transient response of the induced electromotive force at 32 time points after power-off is measured.

Comparing the response results of the distribution of five combined emitters, the first one is a vertical magnetic dipole emitter located at (-2000,0,0)m, the second is also a VMD emitter located at (2000 ,0,0)m, the third type is that 2 VMD emission sources are located at (-2000,0,0)m and (2000,0,0)m respectively, the fourth type is that 4 VMD emission sources are located at (-2000,0,0)m, (2000,0,0)m, (0,-2000,0)m, (0,2000,0)m, the fifth type is 8 VMD emission sources, they The positions of the eight points on the circle with the origin of the ground coordinates as the center and a radius of 2000m, among which the first source is located at (2000,0,0)m, and the positions of the other sources and the origin are in the same positive x direction The angles are 45 degrees, 90 degrees, 135 degrees, 180 degrees, 225 degrees, 270 degrees and 315 degrees.

Figures 1 to 5 are the distribution diagrams of the three component responses on the flight surface (z=-100m) under the excitation of five combined sources at 4.32ms after power failure. Observing each figure, it can be known that when only one excitation source is used, the distribution of the response has directionality, and the farther away from the excitation source, the smaller the response amplitude. When combined source excitation is used, the exploration target area gradually becomes uniform. The more symmetrically distributed excitation sources in the combined source, the more uniform the response distribution in the central area and the larger the response range, which is more beneficial to the exploration of underground structures. Fig. 6 is a comparative diagram of the z-component transient curves of corresponding points (0, 0, -100) m above the flight surface at the center of the exploration area under five combined sources. It can be seen from the figure that when there is one source, the response is consistent regardless of whether it is arranged on the left or right of the exploration area; when multiple sources are combined, the transient response form is consistent. bigger.

Figure 7 shows the z-component response profile curves on the flight survey line at three time points y=0m. It can be seen that when the traditional ground single source is excited, the profile response curves at each instant decay monotonously toward the far source. However, when the symmetrical combination source of the present invention is used for excitation, the central part of each instantaneous profile curve becomes relatively smooth, which is convenient for detection.

From the above simulation results, it can be seen that the combined source with symmetrical distribution can overcome the problem of far-source attenuation of single source, enhance the signal-to-noise ratio of data, reduce the influence of multiple solutions in inversion, and improve the reliability of interpretation results. In addition, the multi-measurement technology of multi-source combination can obtain multi-angle detection information, and the ability to distinguish local targets is also stronger.

The present invention will be further described below in conjunction with drawings and embodiments.

Description of drawings

Figure 1 is the three-component response distribution of the first excitation source (a left source) at 4.32ms on the receiving height plane, where Figures a~c are the distribution diagrams of the induced electromotive force responses of the x, y, and z components respectively.

Figure 2 is the three-component response distribution of the second excitation source (a right source) at 4.32ms on the receiving height plane, where Figures a~c are the distribution diagrams of the induced electromotive force responses of the x, y, and z components respectively.

Figure 3 is the three-component response distribution of the third excitation source (left and right sources) at 4.32ms on the receiving height plane, where Figures a~c are the distribution diagrams of the induced electromotive force responses of the x, y, and z components respectively.

Figure 4 is the three-component response distribution of the fourth excitation source (up, down, left, and right) at 4.32 ms on the receiving height plane, where Figures a to c are the distributions of the x, y, and z component induced electromotive force responses.

Figure 5 is the distribution of the three-component response at 4.32 ms on the receiving height plane of the fifth excitation source (8 sources equally spaced on the circumference), where Figures a to c are the distributions of the induced electromotive force responses of the x, y, and z components respectively picture.

Figure 6 is a comparison chart of Vz component transient response curves at (0, 0, -100) m under five emission sources.

Figure 7 is the z-component response profile curves on the flight survey line at three time points y=0m.

Figure 8 is a distribution diagram of four magnetic sources on the ground.

Figure 9 is a schematic diagram of the flight path of the drone.

Figure 10 is a distribution diagram of six magnetic sources on the ground.

Figure 11 is a distribution diagram of 8 magnetic sources on the ground.

detailed description

During the implementation of the present invention, at first it is necessary to determine the radius of the circle where the magnetic source is located, the number that the magnetic source adopts, the emission pulse waveform, the sampling time sequence, the flight height, the flight route, etc., and then carry out data collection. Below, respectively use 4 sources, 6 sources and 8 sources for illustration.

Example 1

There are 4 magnetic sources, all of which are vertical magnetic dipole sources with the same parameters. Let the labels of each source be A, B, C, and D in turn, as shown in Figure 8. The combination of labels A and C is performed for the first time The flight measurement under the source excitation; the second flight measurement under the combined source excitation marked as B and D; the third time the flight measurement under the combined source excitation marked as A, B, C, D, and finally three Measurement data from a combination of sources.

The UAV carries a three-component receiving coil and flies along the route shown in Figure 9 over the survey target area. Fly route 2 in the opposite direction, and then return along route 3, and so on, after flying all the routes, the measurement of a combined source is completed. Then, go back along the original route to carry out the flight measurement of the next combination source until all the combination sources are measured.

After the data collection is completed, data processing, inversion interpretation and other work are carried out according to the workflow of ground-space transient electromagnetic.

Example 2

There are 6 magnetic sources, all of which are vertical magnetic dipole sources with the same parameters. Let the labels of each source be A, B, C, D, E, and F in turn, as shown in Figure 10. The first time the label is A The flight measurement under the combined source excitation of , C, E; the second flight measurement under the combined source excitation marked as B, D, F; the third time is marked as A, B, C, D, E, F Finally, the measurement data of the three combined sources are obtained.

The flight route of the unmanned aerial vehicle is identical with embodiment 1. After the data collection is completed, data processing, inversion interpretation and other work are carried out according to the workflow of ground-space transient electromagnetic.

Example 3

There are 8 magnetic sources, all of which are vertical magnetic dipole sources with the same parameters, and the marks of each source are A, B, C, D, E, F, G, H in turn, as shown in Figure 11, the first Take the in-flight measurements excited by the combined sources marked A, C, E, G; the second time make the in-flight measurements excited by the combined sources marked B, D, F, H; the third time make all 8 combined sources The flight measurement under the excitation finally obtains the measurement data of the three combined sources.

The flight route of the unmanned aerial vehicle is identical with embodiment 1. After the data collection is completed, data processing, inversion interpretation and other work are carried out according to the workflow of ground-space transient electromagnetic.

Claims (4)

1. air-ground transient electromagnetic exploration method based on composite magnetic source technology, including arranging on the ground Launch the magnetic source of periodic bipolar current pulse signal, receive induced electromotive force transition letter with coil Number, it is characterised in that: described magnetic source is 4,6 or 8, and each magnetic source is evenly spaced to be distributed in On a circumference centered by exploration targets region；Receiving coil is loaded on unmanned plane, and unmanned plane exists Exploration targets overlying regions flies along the route being parallel to each other by end to end reciprocating manner, gathers each Plant the induced electromotive force transient response data under combination source forcing, after a kind of combination source is measured, change Another kind of combination source forcing signal, the flight under shuttle flight carries out new combination of stimulation source signal again Measuring, till all combination sources are all measured, described combination source refers to by symmetrical several Or the driving source that all magnetic source is constituted.

The air-ground transient electromagnetic side of reconnoitring based on composite magnetic source technology the most according to claim 1 Method, it is characterised in that: magnetic source is 4, if the labelling in each source is followed successively by A, B, C, D, It is marked for the first time as the flight measurement under the combination source forcing of A, C；Second time be marked into B, Flight measurement under the combination source forcing of D；Third time is marked the combination source into A, B, C, D Flight measurement under Ji Li, finally gives the measurement data in three kinds of combination sources.

The air-ground transient electromagnetic side of reconnoitring based on composite magnetic source technology the most according to claim 1 Method, it is characterised in that: magnetic source is 6, if the labelling in each source be followed successively by A, B, C, D, E, F, is marked for the first time as the flight measurement under the combination source forcing of A, C, E；Second time is carried out It is labeled as the flight measurement under the combination source forcing of B, D, F；Third time be marked into A, B, C, Flight measurement under the combination source forcing of D, E, F, finally gives the measurement data in three kinds of combination sources.

The air-ground transient electromagnetic side of reconnoitring based on composite magnetic source technology the most according to claim 1 Method, it is characterised in that: magnetic source is 8, if the labelling in each source be followed successively by A, B, C, D, E, F, G, H, be marked for the first time as the flight measurement under the combination source forcing of A, C, E, G； Second time is marked as the flight measurement under the combination source forcing of B, D, F, H；Third time is carried out It is labeled as the flight measurement under the combination source forcing of A, B, C, D, E, F, G, H, finally gives The measurement data in three kinds of combination sources.