A deep-sea hydrothermal sulfide anisotropy detection system and method

Abstract

The present application relates to marine electromagnetic exploration technology and is a system and method for detecting anisotropy of deep-sea hydrothermal sulfides. The system comprises: a transmitting system comprising an X-axis coil with its normal located on the X-axis, a Y-axis coil with its normal located on the Y-axis, and a Z-axis coil with its normal located on the Z-axis, forming an orthogonal structure; a three-component synchronous receiving system comprising a three-axis receiving coil located in a seabed hole, which continuously collects magnetic field intensity, polarization direction, and three-dimensional spatial coordinates at each receiving node; a three-axis synchronous control system employing multi-frequency orthogonal current signals with a phase difference of 90°; and a processor that performs spectrum analysis on the signals received by the three-component synchronous receiving system, calculates the anisotropic response ratios for each polarization direction in the horizontal plane based on the complex amplitude response, and determines the dominant principal axis direction of the conductivity anisotropy based on the anisotropic response ratios. The present application implements full-angle scanning excitation, significantly improving the detection capability of anisotropic structures of hydrothermal sulfides.

Description

Technical Field

[0001] The present application relates to marine electromagnetic exploration technology, and specifically to a deep-sea hydrothermal sulfide anisotropy detection system and method. Background Art

[0002] Deep-sea hydrothermal sulfides, a key reservoir of deep-sea mineral resources, are rich in a variety of mineral metals. Their significant electrical anisotropy (resistivity anisotropy coefficients of up to 3-5 times) poses a technical challenge to traditional marine controlled-source electromagnetic methods. Currently available detection methods face technical limitations in detecting anisotropic targets: single-axis transmitting systems with fixed polarization directions struggle to achieve full-space electromagnetic field vector coverage and exhibit low sensitivity to anisotropic targets such as hydrothermal sulfides. In complex deep-sea terrain, single-axis transmitting systems cannot dynamically adjust polarization directions to compensate for detection blind spots, making it difficult to identify the complex electrical structure of hydrothermal sulfides. This leads to the risk of multiple solutions in three-dimensional electrical structure inversion. For example, Chinese Patent Publication No. CN115419403A utilizes high-voltage DC energy storage and shock wave conversion technology to achieve high-power downhole excitation, but it lacks the ability to generate a dynamically rotating polarization field, resulting in inaccurate identification of the anisotropic principal axis of layered conductive targets. Summary of the Invention

[0003] The embodiment of the present application provides a deep-sea hydrothermal sulfide anisotropy detection system to solve the problems of insufficient anisotropy detection capability and difficulty in identifying the complex electrical structure of hydrothermal sulfides in the traditional single-axis controlled source electromagnetic method in deep-sea hydrothermal sulfide exploration.

[0004] The present application also provides a method for detecting anisotropy of deep-sea hydrothermal sulfides.

[0005] According to a first aspect of the present application, an embodiment provides a deep-sea hydrothermal sulfide anisotropy detection system, comprising:

[0006] The transmitting system includes an X-axis coil whose normal direction is located on the X-axis, a Y-axis coil whose normal direction is located on the Y-axis, and a Z-axis coil whose normal direction is located on the Z-axis, forming an orthogonal structure;

[0007] The three-component synchronous receiving system includes a three-axis receiving coil located in the seabed hole, which moves at a spacing less than one-tenth of the skin depth and continuously collects magnetic field strength, polarization direction, and three-dimensional spatial coordinates at each receiving node;

[0008] The three-axis synchronous control system uses multi-frequency orthogonal current signals with a phase difference of 90 degrees and dynamically adjusts the current amplitude to control the X-axis coil and Y-axis coil to generate a circularly polarized electromagnetic field with controllable rotation direction in the horizontal plane, and to pass a constant current into the Z-axis coil.

[0009] The processor performs spectrum analysis on the signal received by the three-component synchronous receiving system, determines the frequency of the received signal, and extracts the complex amplitude response of each polarization direction on the frequency, calculates the anisotropic response ratio of each polarization direction in the horizontal plane based on the complex amplitude response, and determines the dominant principal axis direction of the conductivity anisotropy based on the anisotropic response ratio.

[0010] Furthermore, the Z-axis coil forms an independent detection channel, and the minimum effective current flowing into the Z-axis coil is calculated according to the minimum field strength required by the target layer.

[0011] Furthermore, the multi-frequency orthogonal current signal is:

[0012] ,

[0013] ,

[0014] in, is the transmission frequency of the multi-frequency orthogonal current signal, is the emission current, is the X-axis coil emission current amplitude, is the Y-axis coil transmitting current amplitude.

[0015] Furthermore, the processor calculates anisotropic response ratios in each polarization direction in the horizontal plane based on the complex amplitude response, including:

[0016] Calculate the modulus of the induced magnetic flux density in different polarization directions based on the complex amplitude response;

[0017] The ratio of the modulus of the induced magnetic flux density in different polarization directions of the three-axis receiving coil at the receiving node to the minimum modulus of the induced magnetic flux density in all polarization directions of the three-axis receiving coil at the same receiving node is calculated to obtain the anisotropic response ratio.

[0018] Furthermore, the transmitting system is arranged above the area to be measured and the three-component synchronous receiving system.

[0019] According to a second aspect of the present application, a method for detecting anisotropy of deep-sea hydrothermal sulfides is provided, the method comprising:

[0020] A multi-frequency orthogonal current signal with a phase difference of 90° is passed through the X-axis coil and the Y-axis coil. The current amplitude is dynamically adjusted to control the X-axis coil and the Y-axis coil to generate a circularly polarized electromagnetic field with controllable rotation direction in the horizontal plane. A constant current is passed through the Z-axis coil. The X-axis coil, the Y-axis coil, and the Z-axis coil form an orthogonal structure.

[0021] The three-axis receiving coil located in the seabed hole moves at a spacing less than one-tenth of the skin depth and continuously collects magnetic field strength, polarization direction, and three-dimensional spatial coordinates at each receiving node;

[0022] The data collected by the three-axis receiving coil is subjected to spectrum analysis to determine the received signal frequency, and the complex amplitude response of each polarization direction on the frequency is extracted. The anisotropic response ratio of each polarization direction in the horizontal plane is calculated based on the complex amplitude response, and the dominant principal axis direction of the conductivity anisotropy is determined based on the anisotropic response ratio.

[0023] Furthermore, the Z-axis coil forms an independent detection channel, and the minimum effective current flowing into the Z-axis coil is calculated according to the minimum field strength required by the target layer.

[0024] Furthermore, the multi-frequency orthogonal current signal is:

[0025] ,

[0026] ,

[0027] in, is the transmission frequency of the multi-frequency orthogonal current signal, is the emission current, is the X-axis coil emission current amplitude, The Y-axis coil transmits the current amplitude

[0028] Furthermore, the anisotropic response ratios in each polarization direction in the horizontal plane are calculated based on the complex amplitude response, including:

[0029] Calculate the modulus of the induced magnetic flux density in different polarization directions based on the complex amplitude response;

[0030] The ratio of the modulus of the induced magnetic flux density in different polarization directions of the three-axis receiving coil at the receiving node to the minimum modulus of the induced magnetic flux density in all polarization directions of the three-axis receiving coil at the same receiving node is calculated to obtain the anisotropic response ratio.

[0031] Furthermore, when it is detected that the anisotropic response ratio is greater than 1.3, it is determined that an anisotropic target exists.

[0032] Compared with the prior art, the embodiments of the present application have at least the following beneficial effects:

[0033] This application uses three-axis dynamic polarization modulation technology (circularly polarized rotating magnetic fields of the X-axis coil and Y-axis coil and constant current excitation of the Z-axis coil to achieve full-angle scanning excitation, significantly improving the detection capability of anisotropic structures of hydrothermal sulfides. Based on the anisotropic response ratio, the main axis direction and spatial distribution of the ore body are quantified, solving the bottleneck of traditional single-axis linear polarization field in identifying complex electrical structures, and providing a high-precision detection method for deep-sea resource assessment. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A structural block diagram of a deep-sea hydrothermal sulfide anisotropy detection system provided in an embodiment of the present application;

[0035] Figure 2 A schematic diagram of the position and structure of a launch system of a deep-sea hydrothermal sulfide anisotropy detection system during detection provided in an embodiment of the present application;

[0036] Figure 3 A schematic diagram of a circularly polarized electromagnetic field provided in an embodiment of the present application;

[0037] Figure 4 Schematic diagram of the change of magnetic flux density under different polarization directions at a receiving node at a depth of 6 meters provided in an embodiment of the present application (a) and a schematic diagram of the change of anisotropic response ratio (b);

[0038] Figure 5 This is the maximum value of the anisotropic response ratio of each receiving node position provided in the embodiment of the present application. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0040] In this application, the target detection area is located in the deep sea, with the horizontal plane as the interface, the medium above the horizontal plane is medium I, and the medium below the horizontal plane is medium II.

[0041] This application mainly constructs a transmitting system of three-axis orthogonal transmitting coils, and realizes a multi-frequency composite transmitting mode by independently controlling the current parameters of the three-axis coils: establishing a dynamic circular polarization transmitting mode of the X / Y-axis coils, combined with the depth adaptation transmitting mode of the Z-axis coil to form a three-dimensional rotating polarization electromagnetic field; collecting multi-component magnetic field response data of the target area through electromagnetic sensing movement in the seabed hole; finally, calculating the anisotropic response ratio parameters based on the received magnetic field analysis, and determining the direction of the main axis of conductivity anisotropy.

[0042] See also Figure 1 The structural block diagram of a deep-sea hydrothermal sulfide anisotropy detection system is shown in FIG. Figure 2 The figure shows the position and structure of the launch system of a deep-sea hydrothermal sulfide anisotropy detection system during detection. The present application discloses a deep-sea hydrothermal sulfide anisotropy detection system, comprising:

[0043] A transmitting system, a three-component synchronous receiving system, a three-axis synchronous control system and a processor, wherein: the transmitting system includes an X-axis coil whose normal is located on the X-axis, a Y-axis coil whose normal is located on the Y-axis and a Z-axis coil whose normal is located on the Z-axis to form an orthogonal structure; the X-axis coil, the Y-axis coil and the Z-axis coil are multi-turn coils, which can be square or circular. For ease of understanding, a rectangular coordinate system is established. The X-axis coil refers to a normal vector perpendicular to the plane of the X-axis coil and parallel to the X-axis. The Y-axis coil refers to a normal vector perpendicular to the plane of the Y-axis coil and parallel to the Y-axis. The plane where the Z-axis coil is located is parallel to the horizontal plane, and the normal vector is parallel to the Z-axis. Usually, the X-axis coil, the Y-axis coil and the Z-axis coil are set to the same size. The X-axis coil, the Y-axis coil and the Z-axis coil can use Helmholtz coils.

[0044] The three-component synchronous receiving system includes a three-axis receiving coil located in the seabed hole, which moves at a spacing less than one-tenth of the skin depth and continuously collects magnetic field strength, polarization direction, and three-dimensional spatial coordinates at each receiving node;

[0045] The three-component synchronous receiving system includes sensors with three orthogonal receiving coils for measuring physical quantities in the X, Y, and Z directions. Synchronization ensures simultaneous signal acquisition across the three channels through clock synchronization or GPS timing. The triaxial receiving coils can be housed in a waterproof housing and carried into the seabed borehole via a suspension or other portable structure. The speed of movement can be controlled by a motor. The skin depth, defined as the depth at which the amplitude of an electromagnetic wave propagating through a conductive medium decays to 1 / e of its initial value, can be calculated using the skin depth formula. The term "moving at intervals less than one-tenth of the skin depth" refers to the use of multiple receiving nodes, with spacing between them less than one-tenth of the skin depth. The triaxial receiving coils stop at each receiving node and collect data.

[0046] For example: the three-component synchronous receiving system moves along the vertical channel (seabed hole) at a spacing of 0.5m, and the receiving nodes are set in the depth range of 0-10m (the depth interval of each receiving node is 0.5m). The modulus value of the induced magnetic flux density in different polarization directions is recorded at each receiving node, and the polarization direction and the node position coordinates of the receiving coil at each moment are recorded to form a multi-dimensional electromagnetic field response data set covering the target detection area.

[0047] The three-axis synchronous control system uses multi-frequency orthogonal current signals with a 90° phase difference. It dynamically adjusts the current amplitude to control the X- and Y-axis coils to generate a circularly polarized electromagnetic field with controllable rotation direction in the horizontal plane, while also supplying a constant current to the Z-axis coil. The current amplitude in the X- and Y-axis coils varies sinusoidally over time, maintaining the same frequency and a 90° phase difference. A circularly polarized electromagnetic field refers to a circular trajectory traced by the endpoints of the electromagnetic field vector over time in a plane perpendicular to the direction of propagation. Circular polarization can be categorized as right-handed circular polarization or left-handed circular polarization, depending on the direction of rotation of the electromagnetic field vector.

[0048] The three-axis synchronous control system can control a multi-frequency current source to provide the same current source for the X-axis coil, the Y-axis coil and the Z-axis coil, including a three-channel current source with an output current range of ±20A and a frequency range of 0.1Hz-20kHz.

[0049] See also Figure 3 The schematic diagram of the circularly polarized electromagnetic field is shown. When the polarization direction When the magnetic field direction is ;when When the magnetic field direction is Polarization direction When the magnetic field direction is , polarization direction When the magnetic field direction is , polarization direction When the magnetic field direction is , polarization direction When the magnetic field direction is , polarization direction When the magnetic field direction is , polarization direction When the magnetic field direction is , and so on, that is, when the polarization direction exist The magnetic field changes with the direction within the plane, such as shown.

[0050] The processor performs spectrum analysis on the signal received by the three-component synchronous receiving system, determines the frequency of the received signal, and extracts the complex amplitude response of each polarization direction on the frequency. Based on the complex amplitude response, the anisotropic response ratio of each polarization direction in the horizontal plane is calculated, and the dominant axis direction of the conductivity anisotropy is determined based on the anisotropic response ratio. Spectral analysis can convert the time domain signal into the frequency domain signal through fast Fourier transform, thereby obtaining the spectrum of the signal, and obtaining the received signal frequency from the spectrum. The complex amplitude response refers to the amplitude and phase information of the signal. Extracting the complex amplitude response of each polarization direction on the frequency refers to The amplitude and phase information of the signal in the polarization direction within the range.

[0051] Conductivity anisotropy means that the conductivity in different directions is different. Determining the dominant axis direction of conductivity anisotropy is used to characterize the layered structure and spatial distribution characteristics of hydrothermal sulfide ore bodies.

[0052] In one embodiment, the Z-axis coil forms an independent detection channel. The minimum effective current flowing into the Z-axis coil is calculated based on the minimum field strength required for the target layer. Based on the skin depth and dielectric conductivity characteristics of the target layer, the minimum field strength required is inferred through the electromagnetic wave attenuation model, and the effective current is calculated for excitation to ensure that the electromagnetic field effectively penetrates into the deep target layer. Specifically, the minimum effective current Calculated by the following formula:

[0053] ,

[0054] in, is the sensitivity of the receiving device (i.e., minimum field strength), is the maximum transmit and receive distance, is the target layer burial depth, is the skin depth, is the vacuum permeability, is the number of turns of the Z-axis coil, is the Z-axis coil transmission frequency, is the Z-axis coil geometry factor, is the system efficiency factor.

[0055] In one embodiment, a three-axis synchronous control system generates multi-frequency orthogonal current signals with a phase difference of 90° in the X-axis coil and the Y-axis coil. The multi-frequency orthogonal current signals are:

[0056] ,

[0057] ,

[0058] in, is the transmission frequency of the multi-frequency orthogonal current signal, is the X-axis coil emission current amplitude, is the Y-axis coil emission current amplitude, is the emission current.

[0059] In one embodiment, the processor calculates the anisotropic response ratio in each polarization direction in the horizontal plane according to the complex amplitude response, including:

[0060] Calculate the modulus of the induced magnetic flux density in different polarization directions based on the complex amplitude response;

[0061] The ratio of the modulus of the induced magnetic flux density in different polarization directions of the three-axis receiving coil at the receiving node to the minimum modulus of the induced magnetic flux density in all polarization directions of the three-axis receiving coil at the same receiving node is calculated to obtain the anisotropic response ratio.

[0062] The anisotropic response ratio is:

[0063] ,

[0064] in, It is the minimum value of the modulus of the induced magnetic flux density in all polarization directions of the triaxial receiving coil at a certain receiving node. is the modulus of the induced magnetic flux density of the three-axis receiving coil in different polarization directions at the receiving node , is the anisotropic response ratio, and the distribution curve of the anisotropic response ratio is calculated. When the maximum value is obtained, the corresponding polarization direction That is, the principal axis direction of the conductivity tensor at the receiving node. When the anisotropic response ratio is detected to be greater than 1.3, it is determined that an anisotropic target exists.

[0065] For example, Figure 4 (a) Different polarization directions at the receiving node 6m depth The change of magnetic flux density under Figure 4 (b) Changes in the anisotropic response ratio. The minimum value of the magnetic flux density is 134.4 nT, which occurs at = 180°; the maximum value is 187.7 nT, which occurs at = 90°. The maximum anisotropic response ratio is calculated to be 1.40, corresponding to the magnetic field direction =90°, which is the direction of the anisotropy principal axis at the receiving node at a depth of 6 meters.

[0066] like Figure 5 The figure shows the maximum value of the anisotropic response ratio at each receiving node position, from seabed basalt (isotropic medium) to sulfide anomaly (anisotropic medium) on the seabed. When the anisotropic response ratio is detected to be greater than 1.3, an anisotropic target is determined to exist.

[0067] The present invention provides a method for detecting anisotropy of deep-sea hydrothermal sulfides, comprising:

[0068] A multi-frequency orthogonal current signal with a phase difference of 90° is passed through the X-axis coil and the Y-axis coil. The current amplitude is dynamically adjusted to control the X-axis coil and the Y-axis coil to generate a circularly polarized electromagnetic field with controllable rotation direction in the horizontal plane. A constant current is passed through the Z-axis coil. The X-axis coil, the Y-axis coil, and the Z-axis coil form an orthogonal structure.

[0069] The three-axis receiving coil located in the seabed hole moves at a spacing less than one-tenth of the skin depth and continuously collects magnetic field strength, polarization direction, and three-dimensional spatial coordinates at each receiving node;

[0070] The data collected by the three-axis receiving coil is subjected to spectrum analysis to determine the received signal frequency, and the complex amplitude response of each polarization direction on the frequency is extracted. The anisotropic response ratio of each polarization direction in the horizontal plane is calculated based on the complex amplitude response, and the dominant principal axis direction of the conductivity anisotropy is determined based on the anisotropic response ratio.

[0071] In one embodiment, the Z-axis coil forms an independent detection channel, and the minimum effective current flowing into the Z-axis coil is calculated based on the minimum field strength required by the target layer.

[0072] In one embodiment, the multi-frequency orthogonal current signal is:

[0073] ,

[0074] ,

[0075] in, is the transmission frequency of the multi-frequency orthogonal current signal, is the emission current, is the X-axis coil emission current amplitude, The Y-axis coil transmits the current amplitude

[0076] In one embodiment, calculating the anisotropic response ratio in each polarization direction in the horizontal plane based on the complex amplitude response includes:

[0077] Calculate the modulus of the induced magnetic flux density in different polarization directions based on the complex amplitude response;

[0078] The ratio of the modulus of the induced magnetic flux density in different polarization directions of the three-axis receiving coil at the receiving node to the minimum modulus of the induced magnetic flux density in all polarization directions of the three-axis receiving coil at the same receiving node is calculated to obtain the anisotropic response ratio.

[0079] In one embodiment, when it is detected that the anisotropic response ratio is greater than 1.3, it is determined that an anisotropic target exists.

[0080] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A deep-sea hydrothermal sulfide anisotropy detection system, characterized in that: include: The transmitting system includes an X-axis coil whose normal direction is located on the X-axis, a Y-axis coil whose normal direction is located on the Y-axis, and a Z-axis coil whose normal direction is located on the Z-axis, forming an orthogonal structure; The three-component synchronous receiving system includes a three-axis receiving coil located in the seabed hole, which moves at a spacing less than one-tenth of the skin depth and continuously collects magnetic field strength, polarization direction, and three-dimensional spatial coordinates at each receiving node; The three-axis synchronous control system uses multi-frequency orthogonal current signals with a phase difference of 90 degrees and dynamically adjusts the current amplitude to control the X-axis coil and Y-axis coil to generate a circularly polarized electromagnetic field with controllable rotation direction in the horizontal plane, and to pass a constant current into the Z-axis coil. The processor performs spectrum analysis on the signal received by the three-component synchronous receiving system, determines the frequency of the received signal, and extracts the complex amplitude response of each polarization direction on the frequency, calculates the anisotropic response ratio of each polarization direction in the horizontal plane based on the complex amplitude response, and determines the dominant principal axis direction of the conductivity anisotropy based on the anisotropic response ratio.

2. The deep-sea hydrothermal sulfide anisotropy detection system according to claim 1, characterized in that: The Z-axis coil forms an independent detection channel, and the minimum effective current flowing into the Z-axis coil is calculated according to the minimum field strength required by the target layer.

3. The deep-sea hydrothermal sulfide anisotropy detection system according to claim 1, characterized in that: The multi-frequency orthogonal current signal is: ， ， in, is the transmission frequency of the multi-frequency orthogonal current signal, is the emission current, is the X-axis coil emission current amplitude, is the Y-axis coil transmitting current amplitude.

4. The deep-sea hydrothermal sulfide anisotropy detection system according to claim 1, characterized in that: The processor calculates the anisotropic response ratio for each polarization direction in the horizontal plane based on the complex amplitude response, including: Calculate the modulus of the induced magnetic flux density in different polarization directions based on the complex amplitude response; The ratio of the modulus of the induced magnetic flux density in different polarization directions of the three-axis receiving coil at the receiving node to the minimum modulus of the induced magnetic flux density in all polarization directions of the three-axis receiving coil at the same receiving node is calculated to obtain the anisotropic response ratio.

5. The deep-sea hydrothermal sulfide anisotropy detection system according to claim 1, characterized in that: The transmitting system is arranged above the area to be measured and the three-component synchronous receiving system.

6. A method for detecting anisotropy of deep-sea hydrothermal sulfides, characterized in that: The method comprises: A multi-frequency orthogonal current signal with a phase difference of 90° is passed through the X-axis coil and the Y-axis coil. The current amplitude is dynamically adjusted to control the X-axis coil and the Y-axis coil to generate a circularly polarized electromagnetic field with controllable rotation direction in the horizontal plane. A constant current is passed through the Z-axis coil. The X-axis coil, the Y-axis coil, and the Z-axis coil form an orthogonal structure. The three-axis receiving coil located in the seabed hole moves at a spacing less than one-tenth of the skin depth and continuously collects magnetic field strength, polarization direction, and three-dimensional spatial coordinates at each receiving node; The data collected by the three-axis receiving coil are spectrally analyzed to determine the received signal frequency, and the complex amplitude response of each polarization direction on the frequency is extracted. The anisotropic response ratio of each polarization direction in the horizontal plane is calculated based on the complex amplitude response, and the dominant principal axis direction of the conductivity anisotropy is determined based on the anisotropic response ratio.

7. The method for detecting anisotropy of deep-sea hydrothermal sulfides according to claim 6, characterized in that: The Z-axis coil forms an independent detection channel, and the minimum effective current flowing into the Z-axis coil is calculated according to the minimum field strength required by the target layer.

8. The method for detecting anisotropy of deep-sea hydrothermal sulfides according to claim 6, wherein: The multi-frequency orthogonal current signal is: ， ， in, is the transmission frequency of the multi-frequency orthogonal current signal, is the emission current, is the X-axis coil emission current amplitude, is the Y-axis coil transmitting current amplitude.

9. The method for detecting anisotropy of deep-sea hydrothermal sulfides according to claim 6, wherein: The anisotropic response ratios for each polarization direction in the horizontal plane are calculated based on the complex amplitude response, including: Calculate the modulus of the induced magnetic flux density in different polarization directions based on the complex amplitude response; The ratio of the modulus of the induced magnetic flux density in different polarization directions of the three-axis receiving coil at the receiving node to the minimum modulus of the induced magnetic flux density in all polarization directions of the three-axis receiving coil at the same receiving node is calculated to obtain the anisotropic response ratio.

10. The method for detecting anisotropy of deep-sea hydrothermal sulfides according to claim 6, characterized in that: When the anisotropic response ratio is detected to be greater than 1.3, it is determined that an anisotropic target exists.

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