Patent ID: 12216216

In the figures:1—supporting rod I,2—supporting rod II,3—transmitting wireframe,4—receiving wireframe I,5—transmitting and receiving system,51—dual-channel simultaneous data acquisition module,6—receiving wireframe II,7—anti-torsion rope,8—unmanned aerial vehicle,9—geological body.

DETAILED DESCRIPTION

The present disclosure will now be further described with reference to the accompanying drawings and examples, but is not to be construed as limiting the disclosure in any way, and any variations or modifications thereof based on the teachings of the present disclosure are intended to be within the scope of the present disclosure.

As shown inFIGS.1to4, a low-altitude frequency domain electromagnetic detection device of the present disclosure includes a supporting rod I1, a supporting rod II2, a transmitting wireframe3, a receiving wireframe I4, a transmitting and receiving system5, a receiving wireframe II6, wherein the supporting rods I1and II2are non-magnetic rigid rods, the transmitting wireframe3, the receiving wireframe I4and the receiving wireframe II6are rectangular frames and wound with a plurality of turns of enameled wires, the number of turns and diameters of the enameled wires of the receiving wireframe I4and the receiving wireframe II6are the same, the transmitting wireframe3, the receiving wireframe I4, the transmitting and receiving system5and the receiving wireframe II6are respectively fixedly connected with the supporting rod I1and the supporting rod II2at intervals in sequence along the extending direction of the supporting rod I1, and two sides of a frame composed of the supporting rod I1and the supporting rod II2are respectively connected with an unmanned aerial vehicle8through non-magnetic anti-torsion ropes7;

the transmitting and receiving system5includes a main control module, a storage module, a sine wave generation module, an altimeter module, a GNSS module, a dual-channel synchronous data acquisition module51, the transmitting wireframe3is in signal connection with the sine wave generation module, the receiving wireframe I4and the receiving wireframe II6are in signal connection with the dual-channel synchronous data acquisition module51, respectively, the sine wave generation module, the altimeter module, the GNSS module and the dual-channel synchronous data acquisition module51are in signal connection with the main control module, respectively, and the main control module controls the sine wave generation module and receives data of the altimeter module, the GNSS module and the dual-channel synchronous data acquisition module51and records the data in the storage module.

The transmitting wireframe3, the receiving wireframe I4and/or the receiving wireframe II6are provided with a non-magnetic rigid housing, the enameled wires are fixedly arranged inside the non-magnetic rigid housing; the number of turns of the enameled wires of the receiving wireframe I4is 8-12 times the number of turns of the enameled wires of the transmitting wireframe3.

The center-to-center distance from the transmitting wireframe3to the receiving wireframe II6is at least 4 times the center-to-center distance from the transmitting wireframe3to the receiving wireframe I4.

The dual-channel synchronous data acquisition module51includes an A/D analog-to-digital conversion module and an MCU digital acquisition controller, and an input terminal of the A/D analog-to-digital conversion module is in signal connection with the receiving wireframe I4and the receiving wireframe II6respectively for converting an analog signal of induced electromotive force of the receiving wireframe into a digital signal; an input terminal and an output terminal of the MCU digital acquisition controller are in signal connection with the A/D analog-to-digital conversion module and the main control module respectively for controlling the A/D analog-to-digital conversion module and transmitting digital signal data to the main control module.

As shown inFIG.4, the transmitting and receiving system5is further provided with an adjustable analog signal amplification module, the receiving wireframe II6is in signal connection with an input terminal of the adjustable analog signal amplification module, an output terminal of the adjustable analog signal amplification module is in signal connection with the dual-channel synchronous data acquisition module51.

A control terminal of the adjustable analog signal amplification module is in signal connection with the main control module.

The supporting rod I1and the supporting rod II2are parallel and of equal length to each other, and two sides of the frame composed of the supporting rod I1and the supporting rod II2are connected with the unmanned aerial vehicle8through four symmetrical anti-torsion ropes7, respectively.

The supporting rods11and II2are carbon fiber round rods, rigid plastic round rods or non-magnetic titanium alloy rods.

The frame composed of the supporting rod I1and the supporting rod II2is not less than 5 m apart from a foot stand of the unmanned aerial vehicle8.

The main control module further performs Fast Fourier Transform on received time series data acquired by the receiving wireframe I4and the receiving wireframe II6in seconds to convert the data into an amplitude corresponding to an operating frequency, the normalized secondary field PPM calculation is subsequently performed, and the position coordinate data acquired by the GNSS module and the flight height data acquired by the altimeter module at the same time are collated with the normalized secondary field PPM data, and recorded in the storage module.

The normalized secondary field PPM calculation is performed by using an equation (15), an equation (16) and an equation (17):

V⁢22=n⁢V⁢2-V⁢1n-1,(15)V⁢21=V⁢2-V⁢22=V⁢2-nV⁢2-V⁢1n-1,(16)PPM=V⁢22V⁢21,(17)

wherein: V1is the induced electromotive force of the receiving wireframe I4, V2is the induced electromotive force of the receiving wireframe II6, V21, V22are the primary field and secondary field induced electromotive forces of the receiving wireframe II6, respectively, and the unit is V; n is the calibration factor of the receiving wireframe I4and the receiving wireframe II6.

The main control module collates the data by taking the second as the unit and integrates the position coordinate data and the flight height data acquired at the same time with the normalized secondary field PPM data at the same time to form the time-based time data.

The unmanned aerial vehicle8is a multi-rotor unmanned aerial vehicle, a fixed wing unmanned aerial vehicle or an unmanned airship.

The main control module is a PC, a PLC, a single board computer or an industrial computer.

The anti-torsion rope7is a non-metallic rope.

The sine wave generation module is an existing arbitrary sine wave generator which can meet the electromagnetic detection frequency range, the altimeter module is an ultrasonic range finder, the GNSS module is an existing arbitrary GNSS antenna and a GNSS host, and the dual-channel synchronous data acquisition module51is an existing arbitrary high-precision analog-digital dual-channel synchronous data acquisition module.

A power supply battery is fixed between the supporting rod I1and the supporting rod II2, and the power supply battery is connected to the power supply terminal of the transmitting and receiving system5.

As shown inFIGS.1to4, the electromagnetic detection method of the present disclosure based on the low-altitude frequency domain electromagnetic detection device includes the following steps:

A. Equipment assembly: a transmitting wireframe3, a receiving wireframe I4, a transmitting and receiving system5, and a receiving wireframe II6are fixed in sequence at intervals between a supporting rod I1and a supporting rod II2which are parallel to form a fixed frame structure, the receiving wireframe I4and the receiving wireframe II6are enabled in signal connection with the dual-channel synchronous data acquisition module51, respectively and the sine wave generation module, the altimeter module, the GNSS module and the dual-channel synchronous data acquisition module51are in signal connection with the main module, respectively, and then the fixed frame structure is suspended below the unmanned aerial vehicle8with a plurality of non-magnetic anti-torsion ropes7;

B. Coefficient calibration: the unmanned aerial vehicle8is controlled to take off to a height above the effective depth detection capability of the receiving wireframe I4, then the sine wave generation module is controlled to generate signals and electromagnetic waves are transmitted through the transmitting wireframe3, the induced electromotive forces V1, V2of the receiving wireframe I4and the receiving wireframe II6are read by the main control module, then a calibration factor n=V1/V2is calculated, and an amplification factor of the adjustable analog signal amplification module is adjusted to n;

C. Data acquisition: the unmanned aerial vehicle8is controlled to perform operations according to a designed course, the main control module of the transmitting and receiving system5controls the sine wave generation module and electromagnetic waves are transmitted through the transmitting wireframe3, the data of the altimeter module, the GNSS module and the dual-channel synchronous data acquisition module51are received synchronously, the position coordinates, the flight height and the induced electromotive force time series data of the receiving wireframe I4and the receiving wireframe II6are recorded in the storage module in real time; and

D. Normalized secondary field calculation: Fast Fourier Transform is performed on the received time series data acquired by the receiving wireframe I4and the receiving wireframe II6to convert the data into an amplitude corresponding to an operating frequency by the main control module, normalized secondary field PPM calculation is performed subsequently, and the position coordinate data acquired by the GNSS module and the flight height data acquired by the altimeter module at the corresponding time is collated with the normalized secondary field PPM data, and the data is recorded in the storage module.

In the step A, an adjustable analog signal amplification module is provided between the receiving wireframe II6and the dual-channel synchronous data acquisition module51, and input and output terminals of the adjustable analog signal amplification module are respectively in signal connection with the receiving wireframe II6and the dual-channel synchronous data acquisition module51.

In the step D, the normalized secondary field PPM calculation is performed by using an equation (15), an equation (16) and an equation (17):

V⁢22=n⁢V⁢2-V⁢1n-1,(15)V⁢21=V⁢2-V⁢22=V⁢2-nV⁢2-V⁢1n-1,(16)PPM=V⁢22V⁢21,(17)

wherein: V1is the induced electromotive force of the receiving wireframe I4, V2is the induced electromotive force of the receiving wireframe II6, V21, V22are the primary field and secondary field induced electromotive forces of the receiving wireframe II6, respectively, and the unit is V; n is the calibration factor of the receiving wireframe I4and the receiving wireframe II6.

The present disclosure further includes a qualitative judgment step, wherein the qualitative judgment is to use the position coordinates, the flight height and the PPM data recorded in the storage module to qualitatively judge an abnormal geological body with resistivity difference: according to the flight altitude and the PPM data, the apparent resistivity is obtained by using the nomogram searching method, and an average value of the apparent resistivity recorded for consecutive 10 s is taken as the background apparent resistivity, when the apparent resistivity is higher than 130% of the average value of the apparent resistivity, the geological body is qualitatively judged as a high-resistivity abnormal geological body; when the apparent resistivity is lower than 50% of the average value of the apparent resistivity, the geological body is qualitatively judged as a low-resistivity abnormal geological body; when the apparent resistivity is in the range from being higher than 50% of the average value of the apparent resistivity to being lower than 130% of the average value of the apparent resistivity, the geological body is judged as a normal geological body.

In the data acquisition step, the sine wave generation module has an emission period of 102 to 104 Hz; the sampling frequency of the receiving wireframe I4and the receiving wireframe II6is more than 5 times the frequency generated by the sine wave generation module; the altimeter module is an ultrasonic range finder or an infrared laser range finder and measures at a frequency greater than 10 Hz.

Example 1

As shown inFIGS.1to4, the airborne survey process is as follows:

1. The transmitting wireframe3, the receiving wireframe I4, the transmitting and receiving system5, and the receiving wireframe II6are fixed in sequence at intervals between the supporting rod I1and the supporting rod II2which are parallel to form a fixed frame structure (the supporting rods I1and II2are carbon fiber round rods having an outer diameter of 20 mm and a length of 5 m), the receiving wireframe I4and the receiving wireframe II6are enabled in signal connection with the dual-channel synchronous data acquisition module51of the transmitting and receiving system5, respectively. The adjustable analog signal amplification module is arranged between the receiving wireframe II6and the dual-channel synchronous data acquisition module51, the sine wave generation module, the altimeter module, the GNSS module and the dual-channel synchronous data acquisition module51are respectively in signal connection with the main control module, then the fixed frame structure is suspended horizontally below the agricultural multi-rotor unmanned aerial vehicle (i.e. the unmanned aerial vehicle8) having a load capacity of more than 15 kg with a plurality of non-magnetic anti-torsion ropes7, and the distance from the transmitting wireframe3to the foot stand of the unmanned aerial vehicle8is 5 m; wherein, the transmitting wireframe3is wound with 100 turns of enameled wires of φ1.2 mm to form a frame shape of 600 mm×400 mm, the receiving wireframe I4and the receiving wireframe II6are each wound with 1000 turns of enameled wires of φ0.35 mm to form a frame shape of 600 mm×400 mm, and then each of the enameled wires is fixed in the non-magnetic rigid housing.

2. The multi-rotor unmanned aerial vehicle is controlled to take off to a height (e.g., greater than 50 meters) above the effective depth detection capability of the receiving wireframe I4, then the sine wave generation module is controlled to generate signals and electromagnetic waves are transmitted through the transmitting wireframe3, the induced electromotive forces V1, V2of the receiving wireframe I4and the receiving wireframe II6are read by the main control module, then a calibration factor n=V1/V2is automatically calculated by the main control module, and then the main control module adjusts an amplification factor of the adjustable analog signal amplification module to n.

As shown inFIG.3, the induced electromotive force reading of the receiving wireframe I4is V1, including a primary field V11and a secondary field V12, with the relationship as follows:

V⁢1=V⁢11+V⁢12,(11)

the induced electromotive force reading of the receiving wireframe II6is V2, including a primary field V21and a secondary field V22, with the relationship as follows:

V⁢2=V⁢21+V⁢22,(12)

when the multi-rotor unmanned aerial vehicle takes off to a height above the effective depth detection capability of the receiving wireframe I4, the magnitude of the secondary field can be neglected and it is assumed that only the primary field generated by the transmitting wireframe is contained in the received induced electromotive force. At this point:

V⁢11=nV⁢21,(13)

wherein, n is the scaling factor for the two groups of receiving wireframes.

3. The multi-rotor unmanned aerial vehicle performs operations according to a designed course, the main control module of the transmitting and receiving system5controls the sine wave generation module and electromagnetic waves with varying field strengths and frequencies are transmitted through the transmitting wireframe3, the data of the altimeter module, the GNSS module and the dual-channel synchronous data acquisition module51are synchronously received, and the position coordinates, the flight height and the induced electromotive force time series data of the receiving wireframe I4and the receiving wireframe II6are recorded in the storage module in real time.

As shown inFIG.3, in the low-altitude flight probe operation, it is considered that the induced electromotive forces caused by the geological body received by the receiving wireframe I4and the receiving wireframe II6are approximately equal, then:

nV⁢2-V⁢1=nvV⁢22-V⁢12≈(n-1)⁢V⁢22(14)

4. The main control module performs Fast Fourier Transform on received time series data acquired by the receiving wireframe I4and the receiving wireframe II6to convert the data into an amplitude corresponding to an operating frequency, the normalized secondary field PPM calculation is subsequently performed, and the position coordinate data acquired by the GNSS module and the flight height data acquired by the altimeter module at the corresponding time are collated with the normalized secondary field PPM data, and recorded in the storage module. Wherein, the normalized secondary field PPM calculation is performed by using an equation (15), an equation (16) and an equation (17):

V⁢22=n⁢V⁢2-V⁢1n-1,(15)V⁢21=V⁢2-V⁢22=V⁢2-nV⁢2-V⁢1n-1,(16)PPM=V⁢22V⁢21,(17)

wherein: V1is the induced electromotive force of the receiving wireframe I4, V2is the induced electromotive force of the receiving wireframe II6, V21, V22are the primary field and secondary field induced electromotive forces of the receiving wireframe II6, respectively, and the unit is V; n is the calibration factor of the receiving wireframe I4and the receiving wireframe II6.

5. After the airborne survey is completed, the abnormal geological body with the resistivity difference is qualitatively judged by reading the data in the storage module of the transmitting and receiving system5, and using the position coordinates, the flight altitude and the PPM data: according to the flight altitude and the PPM data, the apparent resistivity is obtained by using the nomogram searching method (Wu Chengping, Wang Weiping, Hu Xiangyun, et al. APPARENT RESISTIVITY CONVERSION AND APPLICATION OF FREQUENCY DOMAIN HELICOPTER AERIAL ELECTROMAGNETIC METHOD [J]. GEOPHYSICALS & CHEMICAL EXPLORATION, 2009, 33 (04): 427-430 +435.), and an average value of the apparent resistivity recorded for consecutive 10 s is taken as the background apparent resistivity, when the apparent resistivity is higher than 130% of the average value of the apparent resistivity, the geological body is qualitatively judged as a high-resistivity abnormal geological body; when the apparent resistivity is lower than 50% of the average value of the apparent resistivity, the geological body is qualitatively judged as a low-resistivity abnormal geological body; when the apparent resistivity is in the range from being higher than 50% of the average value of the apparent resistivity to being lower than 130% of the average value of the apparent resistivity, the geological body is judged as a normal geological body.

While preferred embodiments of the present disclosure are described above, the scope of protection of the present disclosure is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present disclosure disclosed herein should be covered by the present disclosure. Therefore, the protection scope of the present disclosure should be subject to the protection scope of the claims.