Very-low-frequency electromagnetic detection device and method based on unmanned aerial vehicle

Abstract

The invention discloses a very-low-frequency electromagnetic detection device and method based on an unmanned aerial vehicle, and the device comprises a multi-rotor unmanned aerial vehicle flight platform which is configured to carry detection equipment and achieve ultra-low-altitude simulated flight; the pod type VLF electromagnetic measurement system comprises a light orthogonal three-coil sensor a and a light orthogonal three-coil sensor b, and each sensor is composed of three orthogonal air coils and used for receiving two very-low-frequency electromagnetic wave signals with different frequencies at the same time. Ground manual or manned aviation platforms are not needed, the unmanned aerial vehicle is more efficient, convenient and low in cost, personnel safety risk hidden dangers are avoided, the unmanned aerial vehicle is suitable for areas such as forests, marshes, deserts and gobi where complex terrains or manpower cannot reach, ultra-low-altitude ground-imitated flight measurement can be achieved by adopting the light multi-rotor unmanned aerial platform, and the unmanned aerial vehicle is closer to a detected target object; and the detection precision and the resolution ratio can be obviously improved.

Description

Technical Field

[0001] The present invention relates to the field of exploration technologies, and particularly to a very low frequency electromagnetic detection device and method based on an unmanned aerial vehicle platform. Background Art

[0002] In the prior art, the very low frequency electromagnetic method is a passive earth exploration technology that uses the electromagnetic waves emitted by military communication radio stations distributed globally as the field source. The emission frequency is generally 5 - 30 kHz. In areas with few emission radio stations, a customized transmitter can also be used for emission. The very low frequency electromagnetic method (VLF-EM) usually relies on ground-based manual or manned aerial platforms. The ground-based very low frequency method requires manual point-by-point measurement, which is difficult in complex terrain areas and may even be unable to reach some areas, resulting in sparse distribution of measurement data points, insufficient detection resolution, low operation efficiency, etc. At the same time, it is easily interfered by ground electromagnetic noise (such as power lines and industrial facilities), affecting data quality. Traditional manned aerial very low frequency methods require leasing or purchasing manned aircraft, with high operation costs. Manned aircraft are more strictly regulated by air traffic control, with poor flexibility. In complex terrain or bad weather conditions, the safety risk is relatively high. The flight altitude of manned aircraft is generally high, so the detection resolution is relatively low, and the electromagnetic interference of the manned aircraft itself is large, affecting the quality of very low frequency data acquisition. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a very low frequency electromagnetic detection device and method based on an unmanned aerial vehicle.

[0004] To solve the above technical problem, the present invention provides the following technical solutions:

[0005] A very low frequency electromagnetic detection device and method based on an unmanned aerial vehicle of the present invention includes:

[0006] A multi-rotor unmanned aerial vehicle flight platform configured to carry detection equipment and achieve ultra-low altitude terrain-following flight;

[0007] A pod-type VLF electromagnetic measurement system, including: a lightweight orthogonal three-coil sensor a and a lightweight orthogonal three-coil sensor b, each sensor being composed of three orthogonal air coils for simultaneously receiving very low frequency electromagnetic wave signals of two different frequencies;

[0008] A VLF data acquisition system, including a main control module, a sensor signal acquisition module, an A / D acquisition card, and a storage module, for controlling the operation of the sensors and recording magnetic field components, GPS data, attitude data, and environmental parameters;

[0009] A GPS navigation and positioning system for providing real-time position and altitude information;

[0010] It includes an attitude inertial navigation module, integrated in the data acquisition system, for obtaining the pitch angle, roll angle, yaw angle and three-axis motion parameters of the UAV.

[0011] A laser altimeter, installed at the bottom of the pod, for measuring the real-time relative height between the device and the ground.

[0012] As a preferred technical solution of the present invention, the multi-rotor UAV of the multi-rotor UAV flight platform is a six-rotor structure with a maximum payload of not less than 6 kg, supporting continuous cruise operation.

[0013] As a preferred technical solution of the present invention, the orthogonal three-coil sensor adopts a lightweight hollow structure, the weight of a single coil does not exceed 0.5 kg, and the coil diameter is 15 - 30 cm.

[0014] As a preferred technical solution of the present invention, the VLF data acquisition system supports simultaneously receiving two independent frequency signals in the range of 5 - 30 kHz, and synchronously records the UTC time, magnetic field strength, in-phase component and quadrature component.

[0015] The present invention also provides a very low frequency electromagnetic detection method based on a UAV, including the following steps:

[0016] (1) Survey network layout: Layout survey lines according to the trend of the target. The angle between the survey line direction and the target trend is not less than 60°, and the survey area extends outward by not less than 3 times the target depth.

[0017] (2) Radio station selection: Select a VLF transmitting radio station with the angle between the electromagnetic wave propagation direction and the target trend not exceeding 30°.

[0018] (3) Flight measurement: The UAV cruises at a height of 5 - 30 meters according to the preset KML route, and simultaneously collects VLF signals of two frequencies, and synchronously records the GPS coordinates, attitude parameters and relative height.

[0019] (4) Data processing: Use VLF2D software for two-dimensional inversion, including data filtering, construction of a uniform half-space initial model, forward simulation and least squares inversion iteration, and finally generate a resistivity profile.

[0020] As a preferred technical solution of the present invention, in the flight measurement step, the cruising speed of the UAV is 5 - 15 m / s, and the data sampling rate is not less than 10 Hz.

[0021] As a preferred technical solution of the present invention, the resistivity is calculated using the formula:

[0022]

[0023] Among them, ω is the angular frequency, μ0 is the magnetic permeability of vacuum, Hz is the vertical component of the magnetic field, and Hx is the horizontal component of the magnetic field.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. The present invention does not require ground personnel or manned aerial platforms, is more efficient, convenient and low-cost, avoids potential risks to personnel safety, and is applicable to areas with complex terrains or inaccessible forests, swamps, deserts, gobi, etc.

[0026] 2. The present invention adopts a lightweight multi-rotor unmanned flight platform, which can realize ultra-low altitude terrain-following flight measurement, getting closer to the detection target, and can significantly improve the detection accuracy and resolution.

[0027] 3. The present invention uses two independent lightweight orthogonal three-coil sensors to simultaneously receive VLF signals from two transmitting stations, effectively improving the data signal-to-noise ratio and the detection accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention, but do not constitute a limitation to the present invention. In the drawings:

[0029] Figure 1 : Schematic diagram of the overall structure of the detection device of the present invention;

[0030] Figure 2 : Cross-sectional view of the orthogonal three-coil sensor of the present invention;

[0031] Figure 3 : Flowchart of the detection method;

[0032] In the figure: 1. Multi-rotor UAV flight platform; 2. Pod-type VLF electromagnetic measurement system; 3. Lightweight orthogonal three-coil sensor a; 4. Lightweight orthogonal three-coil sensor b; 5. VLF data acquisition system; 6. GPS navigation and positioning antenna. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] The following describes the preferred embodiments of the present invention with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not used to limit the present invention.

[0034] Embodiment 1

[0035] As Figures 1-3 shown, the present invention provides a VLF electromagnetic detection device and method based on an unmanned aerial vehicle, including:

[0036] Multi-rotor UAV flight platform

[0037] Adopting a six-rotor structure, it is the DJI M600 with a maximum payload ≥ 6 kg, supporting continuous cruising operations, having the function of terrain-following flight, and a flight altitude of 5 - 30 meters.

[0038] Equipped with a redundant power system to ensure safe takeoff and landing in complex terrains.

[0039] Pod-type VLF electromagnetic measurement system

[0040] Dual orthogonal triple-coil sensors:

[0041] Two independent sensors, including a lightweight orthogonal triple-coil sensor a and a lightweight orthogonal triple-coil sensor b, each consisting of three lightweight orthogonal air coils with a diameter of 15 - 30 cm and a single weight ≤ 0.5 kg.

[0042] Support receiving two different frequency signals in the range of 5 - 30 kHz, 15 kHz and 25 kHz, without orientation required, reducing noise interference.

[0043] Data acquisition system:

[0044] The main control module uses an ARM processor to control the sensors to work, synchronously collecting magnetic field components (Hx, Hy, Hz), in-phase component (Real), quadrature component (Imag), magnetic field intensity (Total) and environmental parameters.

[0045] Integrated with an A / D acquisition card, using a 24-bit high-precision, storage module ≥ 128 GB solid-state storage and a GPS module with a positioning accuracy of ±0.1 meter.

[0046] Auxiliary system

[0047] Attitude and inertial navigation module: Built-in gyroscope, accelerometer and magnetometer, real-time output of pitch angle, roll angle, yaw angle and three-axis motion parameters.

[0048] Laser altimeter: Installed at the bottom of the pod, emitting laser vertically downward to measure the height from the ground with an accuracy of ±0.1 meter.

[0049] A VLF electromagnetic detection method based on an unmanned aerial vehicle, including the following steps:

[0050] Survey network planning

[0051] The included angle between the survey line direction and the target object trend ≥ 60°, and the survey area extends outward ≥ 3 times the target depth.

[0052] Imported into the UAV flight control system in KML format, with a preset flight altitude of 5 - 30 meters, speed of 5 - 15 m / s and sampling rate ≥ 10 Hz.

[0053] Radio selection

[0054] Select a VLF transmitting station where the angle between the electromagnetic wave propagation direction and the target object's trend is ≤ 30°. The NAA station in the United States at 17.8 kHz is selected to ensure the maximization of the secondary field signal intensity.

[0055] Flight measurement

[0056] The drone cruises along the preset route, synchronously recording GPS coordinates, attitude data, relative altitude, and dual-frequency VLF signals.

[0057] Adopt segmented operation. When the endurance of a single flight is insufficient, the drone automatically returns to base to replace the battery.

[0058] Data processing and interpretation

[0059] Preprocessing: Eliminate outliers, perform attitude correction, altitude compensation, and noise filtering.

[0060] Inversion modeling: Based on the VLF2D software, use the least squares method for iterative inversion. The number of iterations is ≥ 20 times, and the convergence accuracy is ≤ 0.01 to generate a two-dimensional resistivity profile.

[0061] Apparent resistivity calculation:

[0062]

[0063] Among them, ω = 2πf, μ0 = 4π × 10 -7 H / m.

[0064] Specifically during the experiment, for mineral resource exploration

[0065] Survey area conditions: A copper ore district in Yunnan, with rugged terrain and dense vegetation.

[0066] Device configuration: DJI M600 drone, with dual sensors receiving 15 kHz and 25 kHz signals respectively, flight altitude of 10 meters, and speed of 8 m / s.

[0067] Result: The inverted resistivity profile clearly shows the distribution of ore bodies within 30 meters underground, with a 92% coincidence rate with the borehole verification results.

[0068] Underwater target detection

[0069] Survey area conditions: Detection of an underwater pipeline in a certain section of the Yangtze River, with fast-flowing water.

[0070] Device improvement: Install a waterproof housing and change the laser altimeter to an ultrasonic depth finder.

[0071] Result: Successfully locate the metal pipeline at a depth of 5 meters underwater, with a burial depth error < 0.5 meters.

[0072] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An ultra-low frequency electromagnetic detection device based on a drone, characterized in that, Including: A multi-rotor UAV flight platform (1), configured to carry detection equipment and achieve ultra-low altitude terrain-following flight; A pod-type VLF electromagnetic measurement system (2), including: a lightweight orthogonal three-coil sensor a (3) and a lightweight orthogonal three-coil sensor b (4), each sensor being composed of three orthogonal air coils, for simultaneously receiving very low frequency electromagnetic wave signals of two different frequencies; A VLF data acquisition system (5), containing a main control module, a sensor signal acquisition module, an A / D acquisition card and a storage module, for controlling the operation of the sensors and recording magnetic field components, GPS data, attitude data and environmental parameters; A GPS navigation and positioning system (6), for providing real-time position and altitude information; Among them, it includes an attitude inertial navigation module, integrated in the data acquisition system, for obtaining the pitch angle, roll angle, yaw angle and three-axis motion parameters of the UAV; A laser altimeter, installed at the bottom of the pod, for measuring the real-time relative height between the device and the ground.

2. The VLF electromagnetic detection device based on an unmanned aerial vehicle according to claim 1, characterized in that The multi-rotor UAV of the multi-rotor UAV flight platform (1) is a six-rotor structure with a maximum payload of not less than 6 kg, supporting continuous cruise operation.

3. The very low frequency electromagnetic detection device based on an unmanned aerial vehicle according to claim 1, characterized in that, The orthogonal three-coil sensor adopts a lightweight hollow structure, with the weight of a single coil not exceeding 0.5 kg and the coil diameter being 15 - 30 cm.

4. The VLF electromagnetic detection device based on a drone according to claim 1, characterized in that, The VLF data acquisition system (5) supports simultaneously receiving two independent frequency signals in the range of 5 - 30 kHz, and synchronously recording UTC time, magnetic field intensity, in-phase component and quadrature component.

5. A VLF electromagnetic detection method based on an unmanned aerial vehicle according to claim 1, characterized in that, Including the following steps: (1) Survey network layout: Layout survey lines according to the trend of the target object, with the angle between the survey line direction and the trend of the target object not less than 60°, and the survey area extending outward not less than 3 times the target depth; (2) Radio station selection: Select a VLF transmitting radio station with the angle between the electromagnetic wave propagation direction and the trend of the target object not exceeding 30°; (3) Flight measurement: The UAV cruises at a height of 5 - 30 meters according to a preset KML route, real-time collecting VLF signals of two frequencies, and synchronously recording GPS coordinates, attitude parameters and relative height; (4) Data processing: Perform two-dimensional inversion using VLF2D software, including data filtering, construction of a uniform half-space initial model, forward simulation and least squares inversion iteration, and finally generate a resistivity profile.

6. The VLF electromagnetic detection method based on an unmanned aerial vehicle according to claim 5, characterized in that, In the flight measurement step, the cruising speed of the UAV is 5 - 15 m / s, and the data sampling rate is not less than 10 Hz.

7. A very low frequency electromagnetic detection method based on an unmanned aerial vehicle according to claim 5, characterized in that, The resistivity calculation adopts the formula: Where, ω is the angular frequency, μ0 is the vacuum permeability, Hz is the vertical component of the magnetic field, and Hx is the horizontal component of the magnetic field.

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