Full-irradiation aviation electromagnetic observation method

Abstract

The invention discloses a full-irradiation aviation electromagnetic observation method. The method comprises the following steps: S1, scanning survey line topographic data of a target survey area; s2, dynamically controlling postures of a transmitting coil and a receiving coil based on the survey line topographic data in the S1, and collecting electromagnetic data of a target survey area; and S3, processing the electromagnetic data collected in the step S2, and carrying out random cross gradient constraint inversion to obtain geological structure information of the underground target in the target measurement area. The detection effect of an aviation electromagnetic method in a steep fluctuating environment is remarkably improved for mineral resources, engineering geophysical prospecting and hydrogeological prospecting in a complex terrain area through a full-irradiation aviation electromagnetic observation system in a complex fluctuating terrain and an isotropic resistivity cross constraint inversion method. According to the method, the interference of topographic factors on electromagnetic signals is effectively reduced, and the limitation of insufficient signal coverage in complex topographies in a traditional method is overcome, so that the data processing precision is improved, and richer underground information is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of geophysical electromagnetic prospecting, in particular to a full-illumination airborne electromagnetic observation method. BACKGROUND

[0002] With the increasing depletion of easily exploitable shallow mineral resources in China, the demand for mineral exploration is gradually extending to complex terrain areas, such as mountainous areas, deserts and other areas that are difficult to cover by traditional ground exploration. Airborne electromagnetic method (AEM) has become an important technical means for prospecting in these areas due to its high efficiency, rapid coverage of large areas and strong adaptability. Compared with ground electromagnetic method, airborne electromagnetic method does not require direct contact with the ground and can complete large-scale geological data collection in a short time, especially suitable for finding clues in complex environments such as mountains and deserts. Therefore, this technology has been widely applied in the field of resource exploration.

[0003] Traditional airborne electromagnetic exploration systems can be divided into time domain and frequency domain according to the characteristics of the transmitted electromagnetic signal, or into fixed-wing and helicopter according to the airborne platform. However, regardless of the observation system, significant limitations are exposed in complex terrain. First, in traditional airborne electromagnetic systems, the transmitting coil and the receiving coil are usually installed at a fixed angle on the helicopter pod. In flat or small undulating terrain, this design can make the electromagnetic signal approximately vertically incident to the ground, thereby ensuring good penetration depth and data quality. However, in complex terrain (such as steep mountainous areas), the surface slope changes dramatically, and the fixed coil cannot adjust its attitude according to the terrain, resulting in the signal incident angle deviating from the vertical direction. This non-vertical incidence reduces the signal penetration efficiency, increases the scattering and noise of the reflected signal, and ultimately affects the detection accuracy and the reliability of the underground electrical imaging. Second, in time-domain airborne electromagnetic method, the helicopter will fly a certain distance within the measurement window, and the terrain within this distance may change significantly. For example, in steep mountainous areas, the rapid changes in height and slope make the data collected by the fixed coil mixed with signal responses under multiple terrain conditions. This mixing effect introduces data variability, making subsequent processing and interpretation complex, and even may mask key underground anomaly features, reducing the recognition rate of prospecting clues. Due to the inability of the signal to maintain the best incident angle with the ground at all times, the electromagnetic field penetration depth of the traditional method is limited in complex terrain, especially when detecting deep ore bodies. At the same time, signal attenuation and noise increase caused by non-vertical incidence further weaken the system's ability to distinguish small or low-contrast targets. This has become a major bottleneck for traditional technology in the context of increasingly scarce resources and the trend of exploration targets towards deep and concealed ore bodies.

[0004] The problems of the full airborne electromagnetic observation system are caused by the fixed coil design and the poor adaptability to the terrain changes, resulting in the decline of the detection effect and the difficulty in meeting the high-precision requirements of the current exploration.

[0005] Application content

[0006] The purpose of the present application is to provide a full irradiation airborne electromagnetic observation method, and the specific technical solutions are as follows:

[0007] A full irradiation airborne electromagnetic observation method, comprising: S1, scanning the survey line terrain data of the target survey area; S2, dynamically controlling the attitude of the transmitting coil and the receiving coil based on the survey line terrain data in S1, collecting electromagnetic data of the target survey area; S3, processing the electromagnetic data collected in S2 and randomly cross gradient constraint inversion, obtaining the geological structure information of the underground target of the target survey area.

[0008] The scanning of the survey line terrain data of the target survey area in S1 comprises: S1.1, collecting the latitude, longitude and altitude data in the target survey area; S1.2, dividing the target survey area into multiple survey sections according to the sampling interval of the speed and time domain signal collected in S1.1; S1.3, calculating the terrain angle of each survey section based on the altitude difference and horizontal distance in the survey section in 1.2, forming a segmented survey line terrain data. Repeat steps S1.1 to S1.3 at different heights to obtain survey line terrain data at different heights.

[0009] The dynamic control of the attitude of the transmitting coil and the receiving coil in S2 comprises: S2.1, controlling the angle of the transmitting coil based on the terrain angle of each survey section in S1.3, for making the electromagnetic wave emitted by the coil always vertically incident to the ground; S2.2, controlling the angle of the receiving coil according to different detection requirements, for capturing underground response signals in different directions.

[0010] S3 comprises: S3.1, processing the electromagnetic data collected in S2 to obtain three-component electromagnetic information at different receiving coil angles and different receiving heights; S3.2, based on the three-component electromagnetic information obtained at different coil angles and different receiving heights in S3.1, using the electromagnetic wave propagation characteristics at different angles and heights to perform inversion, obtaining accurate underground geological information.

[0011] The calculation of the terrain angle of each survey section in S1.3 comprises:

[0012] S1.31, calculating the horizontal distance, specifically, for the adjacent two points P i and P i+1 in the survey section, the horizontal distance d i can be calculated through the latitude and longitude coordinates, wherein:

[0013] The latitude difference is converted into distance: Δlat=lati+1 -lat i ,

[0014] Convert the longitude difference into distance: Dlon = lon i+1 -lon i , which needs to be multiplied by the cosine factor cos(lat i ),

[0015] Horizontal distance:

[0016]

[0017] S1.32, elevation difference calculation, specifically, the elevation difference h i is the absolute difference of the elevations of the two points:

[0018] h i = |alt i+1 -alt i |;

[0019] S1.33, terrain angle calculation, specifically, the terrain angle a i is calculated by the ratio of the elevation difference to the horizontal distance:

[0020]

[0021] Therefore:

[0022]

[0023] The processing of the collected electromagnetic data in S3.1 includes data error correction caused by the receiving coil posture, airborne platform noise suppression, and error correction caused by the offset of the pod angle, which is used to obtain information of geological bodies from different perspectives and improve the analysis ability of underground structures.

[0024] The inversion in S3.2 includes:

[0025] S3.21, based on the three-component electromagnetic information obtained at different receiving coil angles and different receiving heights obtained in S3.1, each data is inverted separately, and the objective function of inversion is:

[0026]

[0027] wherein, is the observation data objective function, which is in the form of:

[0028]

[0029] d obs is the single-component combined observation data, d 正演 is the forward operator, is the data covariance matrix, T * is the complex conjugate, is the objective function of the model prior constraint condition, λ m is the model item regularization parameter, which is in the form of:

[0030]

[0031] m is the current resistivity model, m0 is the prior model, is the model covariance matrix;

[0032] S3.22, when each iteration is carried out to the 4th time, the objective function adds the isotropic resistivity constraint term, and the objective function becomes:

[0033]

[0034] Wherein, μ cg is the model cross-gradient regularization parameter, and the added is the objective function of the model cross-gradient term, which is in the form of:

[0035]

[0036] m is the current inversion resistivity model, m 约束 is the combined isotropic resistivity constraint model.

[0037] The present application has the beneficial effects that through the full-illumination airborne electromagnetic observation system under complex terrain and the isotropic resistivity cross-constraint inversion method, the detection effect of the airborne electromagnetic method in the steep and undulating environment is significantly improved for the mineral resources, engineering geophysical prospecting and hydrogeological exploration in the complex terrain area. The system acquires the terrain data of the survey line by pre-scanning, and dynamically controls the posture of the transmitting and receiving coils based on the data, realizes the segmented electromagnetic signal transmission and reception, and avoids the signal loss or attenuation caused by terrain shielding. This method effectively reduces the interference of terrain factors on the electromagnetic signal, overcomes the limitation of insufficient signal coverage in the traditional method in complex terrain, thereby improving the processing accuracy of the data and obtaining more rich underground information. And through the random cross-gradient constraint inversion method, better inversion effect is obtained. The full-illumination airborne electromagnetic observation method and the random cross-gradient constraint inversion method under complex terrain show better detection ability than the traditional airborne electromagnetic method in dealing with signal interference in complex steep terrain, provide strong data support for accurate identification and positioning of deep resources, and provide key technical support for resource potential evaluation and development scheme optimization.

[0038] Drawings of the specification

[0039] Figure 1 is the full-illumination airborne electromagnetic observation process schematic diagram of the present application;

[0040] Figure 2 Fig. 1 is a schematic diagram of the overall observation system in the present application;

[0041] Figure 3 Fig. 2 is a schematic diagram of the segmented terrain data in the present application;

[0042] Figure 4 Fig. 3 is a schematic diagram of the variation of the angle of the receiving coil with the terrain in the present application;

[0043] Figure 5 Fig. 4 is a schematic diagram of the multiple angles of the receiving coil in the present application;

[0044] Figure 6 Fig. 5 is a schematic diagram of the multiple receiving heights in the present application;

[0045] Figure 7 Fig. 6 is a schematic diagram of the terrain survey line model in the present application;

[0046] Figure 8 Fig. 7 is a schematic diagram of the full-illumination observation operation in the present application;

[0047] Figure 9 Fig. 8 is a schematic diagram of the observation according to the preset survey line and the preset angle in the present application;

[0048] Figure 10 Fig. 9 is a schematic diagram of the inversion constraint relationship in the present application. Embodiments

[0049] To make the objects, technical solutions and advantages of the present application clearer, further detailed description will be given below with reference to the embodiments and the accompanying drawings. It should be understood that the description is only exemplary and is not intended to limit the scope of the present application. In addition, in the following description, the description of the known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present application.

[0050] As shown in Fig. 1, a full-illumination airborne electromagnetic observation method comprises the following steps: Figure 1

[0051] As shown in Fig. 2, S1, scanning the survey line terrain data of the target survey area, specifically comprising: Figures 2-3

[0052] S1.1, collecting the latitude, longitude and altitude data in the target survey area.

[0053] S1.2, dividing the target survey area into multiple survey segments according to the sampling interval of the speed and time domain signal collected in S1.1.

[0054] S1.3, calculating the terrain angle of each survey segment based on the altitude difference and horizontal distance in the survey segment in 1.2, and forming segmented survey line terrain data.

[0055] ​​Repeat steps S1.1 to S1.3 at different altitudes to obtain topographic data for survey lines at different altitudes.

[0056] The calculation of the terrain angle for each measurement segment in S1.3 includes:

[0057] S1.31 Calculate the horizontal distance. Specifically, for two adjacent points P within the measured segment... i and P i+1 Horizontal distance d i It can be calculated using latitude and longitude coordinates, where:

[0058] Latitude difference converted to distance: Δlat = lat i+1 -lat i ,

[0059] Longitude difference converted to distance: Δlon = lon i+1 -lon i It needs to be multiplied by the cosine factor cos(lat) at the latitude. i ),

[0060] Horizontal distance:

[0061]

[0062] S1.32, Altitude difference calculation, specifically, altitude difference h i The absolute difference in elevation between two points:

[0063] h i =|alt i+1 -alt i |;

[0064] S1.33, Calculation of terrain angle, specifically, terrain angle α i Calculated by the ratio of elevation difference to horizontal distance:

[0065]

[0066] therefore:

[0067]

[0068] like Figures 4-6 As shown, S2 dynamically controls the attitude of the transmitting and receiving coils based on the topographic data of the survey line in S1 to collect electromagnetic data of the target survey area. Specifically, this includes:

[0069] S2.1, Based on the terrain angle of each measurement segment in S1.3, control the angle of the transmitting coil to ensure that the electromagnetic waves emitted by the coil are always incident perpendicularly on the ground surface.

[0070] S2.2, control the angle of the receiving coil according to different detection requirements, for capturing underground response signals in different directions.

[0071] S3, process the electromagnetic data collected in S2 and perform stochastic cross-gradient constrained inversion to obtain the geological structure information of the underground target in the target survey area. Specifically, it includes:

[0072] S3.1, process the electromagnetic data collected in S2 to obtain three-component electromagnetic information under different receiving coil angles and different receiving heights. Specifically, it includes data error correction caused by receiving coil posture, airborne platform noise suppression, and error correction caused by pod angle deviation, which is used to obtain information of geological bodies from different perspectives and improve the analysis ability of underground structure.

[0073] S3.2, based on the three-component electromagnetic information obtained in S3.1 under different receiving coil angles and different receiving heights, use the electromagnetic wave propagation characteristics of different angles and heights to perform inversion to obtain accurate underground geological information. Specifically, it includes:

[0074] S3.21, based on the three-component electromagnetic information obtained in S3.1 under different receiving coil angles and different receiving heights, each data is inverted separately, and the objective function of inversion is:

[0075]

[0076] wherein, is the observation data objective function, which is in the form of:

[0077]

[0078] d obs is the single-component combined observation data, d 正演 is the forward operator, is the data covariance matrix, T * is the complex conjugate, is the model prior constraint condition objective function, λ m is the model term regularization parameter, which is in the form of:

[0079]

[0080] m is the current resistivity model, m0 is the prior model, is the model covariance matrix;

[0081] S3.22, when each iteration is performed to the 4th time, the objective function adds an isotropic resistivity constraint term, and the objective function becomes:

[0082]

[0083] wherein, μ cg is a model cross-gradient regularization parameter, increasing is the objective function of the model cross-gradient term, which is in the form of:

[0084]

[0085] m is a current inversion resistivity model, m 约束 is a combined isotropic resistivity constraint model.

[0086] The mineral resources, engineering geophysical prospecting and hydrogeological exploration under complex undulating terrain are faced with the problems of terrain shielding and signal distortion, especially in steep mountains, the traditional time-domain airborne electromagnetic method is difficult to ensure full coverage and vertical incidence of signals, resulting in significant decline in detection effect. Based on this practical demand, the present application proposes a full irradiation airborne electromagnetic observation system under complex undulating terrain, which can effectively overcome the interference of terrain undulation on electromagnetic signals and improve the exploration accuracy and reliability.

[0087] The system obtains the corresponding relationship between latitude, longitude and altitude by pre-scanning the terrain data of the survey line, and dynamically adjusts the posture of the transmitting and receiving coils based on this, realizing segmented signal transmission and reception. This design ensures that electromagnetic waves are fully and uniformly irradiated to all target areas in the survey area, avoiding signal loss or attenuation caused by terrain shielding. By keeping the coil angle consistent in each flight section and independently collecting signals, electromagnetic anomaly signals of different depths and regions can be captured more clearly, and the complexity of the superposition of terrain factors and geological signals can be effectively separated, thereby significantly improving the data processing accuracy. And a random cross-gradient constraint method is used to invert the full irradiation observation data, which describes the underground anomaly shape from multiple angle responses, optimizes the stability of the inversion while ensuring the accuracy of the inversion.

[0088] Compared with the traditional method, the full irradiation method exhibits excellent detection capability in complex terrain environment, not only improves the signal coverage and spatial resolution, but also accurately restores the electrical structure of the underground medium through advanced inversion algorithm, so that the identification and positioning of deep resources are more accurate and reliable. This provides strong technical support for resource exploration in complex terrain areas such as southwest China.

[0089] In order to make the present application easier to be understood, further description will be made in combination with specific application schemes.

[0090] First, a survey line model is established in a complex terrain environment, and the terrain model is displayed in a two-dimensional plan view. Through this step, the idea of the present application can be preliminarily verified, and it is ensured that the system can effectively transmit and receive electromagnetic signals under complex terrain. In a certain area, a terrain model with different undulations is established, and through analysis of the model, it is found that the terrain has a large height difference and a complex slope. Based on this, different heights of survey lines are designed, which are l1, l2 and l3, as shown in Figure 7 It can be verified by the terrain data that under the complex terrain, the system can dynamically adjust the coil posture to ensure that the electromagnetic wave is vertically incident.

[0091] By combining the terrain data and the coil posture control model, an angle relationship model between the transmitting coil and the receiving coil is established. Based on the height difference and the horizontal distance of the terrain, the tilt angle of the transmitting coil is accurately calculated, and the posture of the receiving coil is flexibly adjusted according to the detection requirements.

[0092] According to the above angle relationship model between the transmitting coil and the receiving coil, a coil posture preset control method is further formulated, which can automatically adjust the coil posture according to the terrain change. This method controls the tilt angle of the transmitting coil and the receiving coil to ensure full irradiation coverage of the electromagnetic wave, and optimizes the receiving effect under different detection heights and angles. As shown in Figure 8 .

[0093] As shown in Figure 9 , according to the designed observation route and the preset coil posture, the unmanned aerial vehicle flies along the survey lines l1, l2 and l3 for the ground simulation, the transmitting coil changes the posture and the incident angle according to the pre-scanned terrain data, and the receiving coil angle θ rx1 , θ rx2 , θ rx3 can be selected according to the detection requirements, and three-component B x , B y , B z data under different angles are received. Through flexible combination of flight height, transmitting coil angle and receiving coil angle, on-demand observation is realized to obtain different data for better characterization of complex terrain irregular anomaly body characteristics.

[0094] Multi-angle, multi-height and multi-component airborne electromagnetic information processing, and signal fusion technology is used to improve the accuracy and resolution of the signal. The three-component electromagnetic data under different angles and heights are processed, such as data error correction caused by receiving coil posture, airborne platform noise suppression, and error correction caused by pod angle deviation. We can obtain information of geological bodies from different perspectives to improve the analysis ability of underground structures. In the test area, by adjusting the flight height and scanning angle, more clear underground anomaly data than traditional methods can be obtained.

[0095] like Figure 10 As shown, a stochastic cross-gradient constraint inversion is finally performed to obtain the geological structure information of the underground target. A comprehensive analysis of the electromagnetic inversion results can provide accurate reference data for subsequent geological exploration and mineral resource detection. For the three flight altitude survey lines l1, l2, and l3 (corresponding to flight altitudes from smallest to largest as h1, h2, and h3), the three receiving coil angles θ... rx1 θ rx2 θ rx3 The three components B below x B y B z The data was inverted using the same resistivity cross-constraint inversion method. For 27 data points at three flight altitudes and three receiving coil angles, the data is numbered as follows: Data 1 (l1, θ) rx1 B x ), data 2(l1, θ rx1 B y ), data 3(l1, θ rx1 B z ), data 4(l1, θ rx2 B x ), data 5(l1, θ rx2 B y ), data 6(l1, θ rx2 B z ...data 27(l3, θ) rx3 B z The process involves first performing inversion individually, then performing pairwise constrained inversions on the fourth iteration, and then continuing with individual inversions. This continues until the inversion stopping condition is met, ultimately yielding the isotropic resistivity model mtotal. This mutual isotropic resistivity stochastic cross-gradient constrained inversion better characterizes the directional features of anomalies in complex terrain, eliminating false information caused by terrain undulations and single-parameter inversions.

Claims

1. A full-illumination airborne electromagnetic survey method, characterized by, The method comprises the following steps: S1, scanning the survey line topographic data of the target survey area; S2, dynamically controlling the attitude of the transmitting coil and the receiving coil based on the survey line topographic data in S1, and collecting electromagnetic data of the target survey area; S3, processing the electromagnetic data collected in S2 and performing random cross-gradient constraint inversion to obtain the geological structure information of the underground target in the target survey area.

2. The full-bore airborne electromagnetic survey method of claim 1, wherein, The survey line topographic data of the target survey area in S1 comprises: S1.1, collecting latitude, longitude and altitude data in the target survey area; S1.2, dividing the target survey area into multiple survey sections according to the sampling interval of the speed and time domain signal collected in S1.1; S1.3, calculating the topographic angle of each survey section based on the altitude difference and horizontal distance in the survey section in S1.2 to form segmented survey line topographic data.

3. The full-borehole electromagnetic survey method of claim 2, wherein, The steps of S1.1 to S1.3 are repeated at different heights to obtain survey line topographic data at different heights.

4. The full-borehole electromagnetic survey method of claim 3, wherein, The dynamic control of the attitude of the transmitting coil and the receiving coil in S2 comprises: S2.1, controlling the angle of the transmitting coil based on the topographic angle of each survey section in S1.3, so that the electromagnetic wave emitted by the coil is always vertically incident to the ground surface; S2.2, controlling the angle of the receiving coil according to different detection requirements, so as to capture underground response signals in different directions.

5. The full-bore airborne electromagnetic survey method of claim 4, wherein, S3 comprises: S3.1, processing the electromagnetic data collected in S2 to obtain three-component electromagnetic information at different receiving coil angles and different receiving heights; S3.2, based on the three-component electromagnetic information obtained in S3.1 at different receiving coil angles and different receiving heights, using the electromagnetic wave propagation characteristics at different angles and heights to perform inversion to obtain accurate underground geological information.

6. The method of claim 2, wherein the full-bore airborne electromagnetic survey is performed using a frequency domain system. The calculation of the topographic angle of each survey section in S1.3 comprises: S1.31, calculate horizontal distance, in particular for two adjacent points P i and P i+1 within a measurement section, the horizontal distance d i may be calculated from the latitude and longitude coordinates, wherein: Latitude difference converted to distance: Δlat = lat i+1 - lat i , Convert the longitude difference to distance: Dlon = lon i+1 -lon i , multiplied by the cosine factor at the latitude, cos(lat i ), horizontal distance: S1.32, elevation difference calculation, in particular, elevation difference h i is the absolute difference of the two point elevations: h i =|alt i+1 -alt i |; S1.33, terrain angle calculation, in particular, terrain angle a i By the ratio of the height difference and the horizontal distance: Therefore:

7. The method of claim 5, wherein the full-bore airborne electromagnetic survey is performed using a frequency domain system. The processing of the collected electromagnetic data in S3.1 comprises: data error correction caused by the attitude of the receiving coil, airborne platform noise suppression, and error correction caused by the angle deviation of the pod, which is used to obtain information of the geological body from different perspectives and improve the analysis ability of the underground structure.

8. The full-bore airborne electromagnetic survey method of claim 7, wherein, The inversion in S3.2 comprises: S3.21, based on the three-component electromagnetic information obtained in S3.1 at different receiving coil angles and different receiving heights, each kind of data is inverted separately, and the objective function of the inversion is: wherein is the observed data objective function, which has the form: d obs is the single-component combined observation data, d 正演 is the forward operator, is the data covariance matrix, T * is the complex conjugate, is the objective function of the model prior constraint condition, λ m is the model term regularization parameter, which is in the form of: m is the current resistivity model, m0is the prior model, is the model covariance matrix; S3.22, when the iteration is performed to the 4th time, the objective function adds the isotropic resistivity constraint term, and the objective function becomes: where μ cg is a model cross-gradient regularization parameter, increasing the is the objective function of the model cross-gradient term, which is of the form: m is the current resistivity model, m 约束 is the combined isotropic resistivity constraint model.

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