Millimeter wave radar-based goaf coal spontaneous combustion high-temperature point detection system and method

Abstract

The invention discloses a millimeter wave radar-based goaf coal spontaneous combustion high-temperature point detection system and method, and the system obtains goaf echo data through a millimeter wave radar scanning unit, and reconstructs a three-dimensional space structure through a data collection and processing unit. The temperature inversion unit inverts the radiation brightness temperature into the physical temperature based on the principle of an active microwave radiometer and a coal rock dielectric constant-temperature sensitivity model, a three-dimensional temperature field distribution diagram is generated, and finally high-temperature point identification and alarm are achieved through the high-temperature identification and early warning unit. According to the invention, the defects of the existing contact-type, indirect-type and superficial detection technologies are overcome, remote, non-contact, high-precision and three-dimensional visual detection and positioning of hidden fire sources in the goaf are realized, and an effective technical means is provided for early prevention and treatment of coal mine fires.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of mine safety and disaster prevention, and particularly relates to a goaf coal spontaneous combustion high-temperature point detection system and method based on a millimeter wave radar. BACKGROUND

[0002] Coal is the main energy source in China, and its consumption accounts for more than 50% of the total primary energy consumption. However, coal mine safety production is restricted by various disasters, among which goaf coal spontaneous combustion is particularly prominent. According to statistics, more than 50% of coal mines in China have the risk of coal spontaneous combustion. With the increase of mining depth, the gas pressure and content increase significantly, and the ground temperature rises, leading to a general increase in coal temperature, and coal spontaneous combustion occurs more and more frequently. Goaf coal spontaneous combustion has become one of the main causes of mine fires, gas explosions and other major accidents, and seriously threatens the safety of miners and wastes coal resources.

[0003] Goaf coal spontaneous combustion is a complex dynamic evolution process influenced by multiple factors and multiple field coupling, and has the characteristics of regional concealment, complex influencing factors, and nonlinear data. It is difficult to accurately identify and accurately predict in the early stage, and timely and accurate mastery of the goaf coal spontaneous combustion high-temperature point is the key to preventing and controlling goaf coal spontaneous combustion and its composite disasters. However, the existing detection methods for goaf coal spontaneous combustion high-temperature points still have defects such as difficult deployment, delayed early warning, and inability to accurately detect internal heat sources, and have great limitations.

[0004] For example, contact detection technology (such as temperature sensors and distributed optical fibers) needs to be deployed deep into the dangerous goaf, and has problems such as high cost, easy damage, limited monitoring range (point or line), and cannot realize large-scale surface scanning, which is prone to missed detection.

[0005] Indirect detection technology (such as gas analysis method) indirectly infers the fire condition by detecting the concentration of marker gas, which has serious lag, and the gas migration is greatly affected by ventilation, making it difficult to accurately locate the heat source.

[0006] The shallow detection technology (such as infrared thermal imaging method) has very poor penetration ability and cannot detect the internal heat source of the goaf blocked by gangue and coal pillars, and is limited to surface temperature detection.

[0007] Traditional geophysical methods (such as ground penetrating radar method, resistivity method, and magnetic method) are mainly sensitive to medium structure or water, and lack specificity and sensitivity to changes in physical parameters caused by temperature. For example, the literature (Research and Prospect on Identification and Detection Technology of Goaf Coal Spontaneous Combustion High-temperature Point - Deng Jun et al.) in Coal Science and Technology, Vol. 49, No. 2, points out that the resistivity method is easily disturbed by ground stray current, the magnetic method is only suitable for goafs containing magnetic minerals, and both methods have depth limitations and geological interference problems when dealing with deep heat sources.

[0008] It can be seen that the prior art lacks an effective means capable of non-contact, long-distance, high-precision and multi-dimensional temperature field detection inside the hidden goaf. SUMMARY

[0009] The present application aims to overcome the deficiencies of the prior art and provide a goaf coal spontaneous combustion high-temperature point detection system and method based on a millimeter wave radar, which realizes early warning.

[0010] To achieve the above-mentioned purpose, the present application adopts the following technical solutions: The goaf coal spontaneous combustion high-temperature point detection system based on a millimeter wave radar comprises a millimeter wave radar scanning unit, a data acquisition and processing unit, a temperature inversion unit and a high-temperature identification and warning unit. The millimeter wave radar scanning unit is arranged in one or more detection points facing the goaf, and is used to emit millimeter wave signals to the goaf and receive echo signals. The data acquisition and processing unit is connected with the millimeter wave radar scanning unit, and is used to acquire and process the echo signals and reconstruct a three-dimensional spatial structure diagram of the goaf through a distance-angle joint imaging algorithm. The temperature inversion unit is connected with the data acquisition and processing unit, and is used to extract the radiation brightness temperature value of each spatial resolution unit from the echo signals and invert the radiation brightness temperature value into a physical temperature value according to a preset permittivity-temperature sensitivity model, and then generate a three-dimensional temperature field distribution diagram of the goaf. The high-temperature identification and warning unit is connected with the temperature inversion unit, and is used to identify a high-temperature abnormal area exceeding a preset threshold according to the three-dimensional temperature field distribution diagram and generate a warning information.

[0011] Preferably, the millimeter wave radar scanning unit is a frequency-modulated continuous wave radar system, and adopts a one-transmitting and multiple-receiving or multiple-transmitting and multiple-receiving antenna configuration, and the working frequency is located in the W band or a higher frequency band.

[0012] Preferably, the distance-angle joint imaging algorithm comprises a MIMO-SAR algorithm.

[0013] Preferably, the permittivity-temperature sensitivity model is a mathematical model for describing the relationship between the real part and the imaginary part of the permittivity of the coal rock medium and the temperature, which is established in advance by measuring the coal rock samples of the target mining area, and the function form is: ε(T) = f(T); wherein ε is the complex permittivity, and T is the physical temperature. The model on which the temperature inversion unit performs temperature inversion is: T = f(T_B, epsilon'(T), epsilon''(T), theta); wherein, T is a physical temperature value, T_B is a radiation brightness temperature value, epsilon'(T) and epsilon''(T) are respectively a real part and an imaginary part of a dielectric constant of a coal rock medium, and theta is a radar wave incidence angle.

[0014] Preferably, the system further comprises a display unit for fusedly displaying the three-dimensional space structure diagram and the three-dimensional temperature field distribution diagram.

[0015] The application discloses a goaf coal spontaneous combustion high-temperature point detection method based on a millimeter wave radar. Step S1: system deployment and scanning; a millimeter wave radar scanning unit is deployed at a detection point facing a goaf, and the millimeter wave radar scanning unit is used to scan a target goaf to obtain original echo data; Step S2: three-dimensional space structure reconstruction; the original echo data is processed, and a synthetic aperture radar or a beam forming technology is used for imaging to obtain a three-dimensional space structure image of the goaf; Step S3: temperature inversion; a radiation brightness temperature value of each space resolution unit is extracted from the calibrated echo signal, and the radiation brightness temperature value is inverted into a physical temperature value based on a dielectric constant-temperature sensitivity model; Step S4: temperature field analysis and high-temperature point identification; the inverted physical temperature value is synthesized into a three-dimensional temperature field distribution diagram of the goaf, and a high-temperature abnormal area is identified; Step S5: early warning and output; the spatial position, temperature and range information of the high-temperature abnormal area are output, and early warning is given when the temperature is over the limit.

[0016] Preferably, in the step S2, a MIMO-SAR algorithm is used for three-dimensional space structure reconstruction.

[0017] Preferably, in the step S3, the dielectric constant-temperature sensitivity model is a dielectric constant-temperature corresponding relationship database established by laboratory measurement of a target mine coal sample, and the function form is: epsilon(T) = f(T); wherein, epsilon is a complex dielectric constant, and T is a physical temperature; The model on which the temperature inversion unit performs temperature inversion is: T = f(T_B, epsilon'(T), epsilon''(T), theta); wherein, T is a physical temperature value, T_B is a radiation brightness temperature value, epsilon'(T) and epsilon''(T) are respectively a real part and an imaginary part of a dielectric constant of a coal rock medium, and theta is a radar wave incidence angle.

[0018] Preferably, in the step S4, the generated three-dimensional temperature field distribution diagram is fusedly displayed with the three-dimensional space structure diagram obtained in the step S2.

[0019] Preferably, in said step S3, the temperature inversion comprises the following operations; In the millimeter wave band, the Planck blackbody radiation law can be simplified as Rayleigh-Jeans approximation:

[0020] where: : radiance, unit is W·m - ²·sr - ¹·Hz - ¹, represents the power of radiation per unit area, unit solid angle, unit frequency; k: Boltzmann constant (1.38×10 23J / K); λ: operating wavelength (m); : brightness temperature, unit is Kelvin (K).

[0021] For real-world objects (gray bodies), its brightness temperature is equal to its physical temperature T multiplied by the emissivity e, that is =e T, the emissivity e is between 0 and 1, depending on the material, surface roughness and observation frequency of the object.

[0022] The conversion step from the original signal to the brightness temperature value is as follows: Step 1: from the original voltage signal to the received power (V→ ) The antenna of the radar or radiometer receives the signal and outputs a voltage V, which is processed through the receiver chain (including low-noise amplifier, mixer, filter, intermediate frequency amplifier, etc.) and finally digitized.

[0023] System calibration: In order to accurately convert the voltage value to power value, the entire receiver system needs to be absolutely calibrated, usually using two reference sources with known brightness temperature: “Hot” reference source: usually a load resistor, whose physical temperature is accurately measured (such as by thermocouple), and its brightness temperature is considered equal to the physical temperature (high emissivity).

[0024] “Cold” reference source: usually a liquid nitrogen load (about 77K) or a cold air pointing (cosmic background radiation about 2.7K).

[0025] Calibration equation: by measuring the voltage values Vhot and Vcold output by the two reference sources, a linear conversion relationship can be established:

[0026] where G is the gain of the system and N is the noise power of the system. G and N can be solved by two reference points. Thus, for any target measurement, the corresponding received power can be calculated.

[0027] Step 2: From received power to radiance brightness For a typical passive millimeter-wave radiometer, the relationship between the received power and the radiance brightness of the observed scene can be simplified as:

[0028] where: Ae: the effective receiving area of the antenna (m²); Ω: the beam solid angle of the antenna (sr); Δf: the bandwidth of the receiver (Hz); the factor 1 / 2 is because the antenna usually only receives one polarization (such as vertical or horizontal), while natural radiation is non-polarized, and the energy is equally divided on two orthogonal polarizations.

[0029] Since the product of the antenna parameters and Ω satisfies , the above formula can be further simplified.

[0030] Step 3: From radiance brightness to brightness temperature Substitute the above formulas directly into the modified Rayleigh-Jones formula:

[0031] Thus, we get the brightness temperature value :

[0032] Pack all the system parameters (G, N, , Ω, Δf, λ, etc.) into a "calibration coefficient" or model, so that the system can directly output the corresponding brightness temperature value for each pixel or each beam pointing.

[0033] Compared with the prior art, the present application has the following significant advantages: 1) Non-contact, long-distance and high safety: overcomes the layout problem of contact detection, can operate in a safe area tens to hundreds of meters away, greatly guarantees personnel safety.

[0034] ​​​​​2) Strong penetration and internal detection capability: millimeter wave has a certain penetration ability for dry coal rock, which can "see through" the surface barrier and directly detect the internal heat source of the goaf, solving the bottleneck that infrared technology cannot detect internal heat sources, and realizing real early warning.

[0035] 3) High spatial resolution and accurate three-dimensional positioning: high-precision spatial positioning is realized, which can accurately indicate the three-dimensional coordinates of high-temperature points and provide accurate target points for directional management.

[0036] 4) Surface detection and full-area coverage: Through scanning, the temperature information of the entire goaf section can be obtained at one time, forming a temperature field cloud map, which avoids the risk of missing detection of point sensors.

[0037] The present application creatively combines millimeter wave radar imaging and temperature sensitivity of dielectric constant, which belong to different fields, and realizes integrated detection of structure and temperature field for the first time, realizes remote, non-contact, surface scanning detection of the internal temperature field of the goaf, accurately locates the high-temperature abnormal area, provides scientific basis for early warning and accurate management of coal spontaneous combustion, has good penetration, anti-interference performance, and is suitable for continuous measurement in mine operation environment. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 is a schematic diagram of the detection point arrangement structure of the present application.

[0039] Figure 2 is a schematic diagram of the system framework and data flow of the present application.

[0040] Figure 3 is a method flowchart of the present application.

[0041] Figure 4 is a three-dimensional space structure and temperature field fusion diagram of the goaf detected and displayed by the present application. DETAILED DESCRIPTION

[0042] The present application will be further described as follows in combination with the drawings: In the process of stoping operation, the working face B and the goaf A are often connected (see FIG. 1). Figure 1 There is still a certain amount of coal in the goaf A, which will bring air into the goaf A when the working face B is mined, and then induce the risk of coal spontaneous combustion. Therefore, the high-temperature points in the goaf A need to be detected and warned to reduce the risk of spontaneous combustion and timely contain the expansion of the influence.

[0043] Referring to FIG. 2, Figure 1 and 2The application discloses a goaf coal spontaneous combustion high-temperature point detection system based on a millimeter wave radar.

[0044] The millimeter wave radar scanning unit is a frequency-modulated continuous wave radar system, adopts an antenna configuration of one transmitter and multiple receivers or multiple transmitters and multiple receivers, and has a working frequency in a W wave band (75-110 GHz) or a higher frequency band; the millimeter wave radar scanning unit emits signals to a goaf and receives echoes by using the strong penetration and high resolution characteristics of millimeter waves.

[0045] The data acquisition and processing unit is used for acquiring radar echo data and reconstructing a three-dimensional space structure diagram of the goaf by a joint range-angle high-resolution imaging algorithm (such as a MIMO-SAR algorithm), so as to clearly display the spatial distribution of residual coal, collapsed gangue and the like.

[0046] The temperature inversion unit extracts the radiation brightness temperature value of each space resolution unit from the echoes based on the principle of an active microwave radiometer.

[0047] The model is used to accurately invert the radiation brightness temperature value into a physical temperature value, so as to generate a three-dimensional temperature field distribution diagram of the goaf, which is a core innovative point of the application.

[0048] The high-temperature identification and early warning unit is used for receiving three-dimensional temperature field data, setting multiple temperature threshold values, calculating the position, area, highest temperature and other parameters, automatically identifying and marking a high-temperature abnormal area, and triggering an alarm when the temperature is over the limit.

[0049] The display unit is used for providing a man-machine interactive interface, fusing the display of the three-dimensional space structure diagram and the three-dimensional temperature field distribution diagram, and realizing the visual and accurate positioning of the high-temperature point. Figure 4 In the display unit, the physical temperature values of the resolution units are marked by different colors according to different temperature threshold values, for example, red represents a high heat source, and in turn, orange, yellow, green and blue correspond to different temperatures in descending order, and meanwhile, a space position coordinate system is established, so that the area formed by the resolution units exceeding the high-temperature threshold value can be quickly positioned and investigated.

[0050] On the basis of the above system, the goaf coal spontaneous combustion high temperature point detection method based on millimeter wave radar is executed, including the following steps, see the attached Figure 3 : Step S1: system layout and scanning; Deploy millimeter wave radar at the detection point facing the goaf, and scan the target goaf to obtain raw echo data.

[0051] Step S2: three-dimensional space structure reconstruction; Process the raw echo data, and use synthetic aperture radar or beam forming technology for imaging to obtain a three-dimensional space structure image of the goaf; wherein the three-dimensional space structure reconstruction is performed using the MIMO-SAR algorithm.

[0052] Step S3: temperature inversion; Extract the radiation brightness temperature value of each spatial resolution unit from the calibrated echo signal, and based on the permittivity-temperature sensitivity model, invert the radiation brightness temperature value into a physical temperature value; the permittivity-temperature sensitivity model is a corresponding relationship database between permittivity and temperature established by laboratory measurement of target mine coal samples.

[0053] Specifically, the permittivity-temperature sensitivity model is a corresponding relationship database between permittivity and temperature established by laboratory measurement of target mine coal samples, and its function form is: ε(T) = f(T); wherein ε is the complex permittivity, and T is the physical temperature; The model on which the temperature inversion unit performs temperature inversion is: T = f(T_B, ε'(T), ε"(T), θ); wherein T is the physical temperature value, T_B is the radiation brightness temperature value, ε'(T) and ε"(T) are the real part and the imaginary part of the coal rock medium permittivity respectively, and θ is the radar wave incidence angle; Wherein, the construction steps of the permittivity-temperature sensitivity model are: Obtain multiple sets of historical data of the permittivity of coal rock medium and the temperature of the measurement point of the goaf at different temperatures, and construct a sample data set based on the historical data of the permittivity of the coal rock medium and the temperature of the measurement point, wherein the permittivity of the coal rock medium is taken as the input data, and the temperature of the measurement point is taken as the target output; Construct a long short-term memory network prediction model, and train and iterate, verify the long short-term memory network prediction model based on the sample data set to obtain the permittivity-temperature sensitivity model; Obtain the permittivity data of the target mine coal sample in the coal mine, and the permittivity-temperature sensitivity model generates the corresponding measurement point temperature value according to the input permittivity data of the target mine coal sample, that is, the function relationship between the real part ε'(T) and the imaginary part ε"(T) of the coal rock permittivity and the physical temperature T.

[0054] The temperature inversion step is: Based on the principle of active microwave radiometer, according to the corresponding relationship between the dielectric constant of the gas at different temperatures and the millimeter wave, the radiation brightness temperature value of each spatial resolution unit is extracted from the calibrated echo signal, and the physical temperature value of each resolution unit is calculated through the model T = f(T_B, ε'(T), ε"(T), θ) relied on by temperature inversion; For example: In the millimeter wave band, the Planck blackbody radiation law can be simplified as Rayleigh-Jones approximation:

[0055] Among them: : Radiant intensity, unit is W·m - ²·sr - ¹·Hz - ¹, indicates the power of radiation per unit area, unit solid angle, unit frequency; k: Boltzmann constant (1.38×10 23J / K); λ: Working wavelength (m); : Brightness temperature, unit is Kelvin (K).

[0056] For real-world objects (gray bodies), its brightness temperature is equal to its physical temperature T multiplied by the emissivity e, that is =e T, the emissivity e is between 0 and 1, which depends on the material, surface roughness and observation frequency of the object.

[0057] The conversion step from the original signal to the brightness temperature value is as follows: Step 1: From the original voltage signal to the received power (V→ ) The antenna of the radar or radiometer receives the signal and outputs a voltage V, which is processed through the receiver chain (including low-noise amplifier, mixer, filter, intermediate frequency amplifier, etc.), and finally digitized.

[0058] System calibration: In order to accurately convert the voltage value to power value, the entire receiver system needs to be absolutely calibrated, usually using two reference sources with known brightness temperature: “Hot” reference source: usually a load resistor, whose physical temperature is accurately measured (such as through a thermocouple), and its brightness temperature is considered equal to the physical temperature (high emissivity).

[0059] “Cold” reference source: usually a liquid nitrogen load (about 77K) or a cold air (cosmic background radiation about 2.7K).

[0060] Calibration equation: By measuring the voltage values Vhot and Vcold output by the two reference sources, a linear conversion relationship can be established:

[0061] where G is the gain of the system and N is the noise power of the system. G and N can be solved by the two reference points. Thus, for any target measurement voltage , its corresponding received power can be calculated.

[0062] Step 2: From received power to radiance brightness ( → ) For a typical passive millimeter wave radiometer, the relationship between the received power and the radiance brightness of the observed scene can be simplified as:

[0063] where: Ae: effective receiving area of the antenna (m²); Ω: beam solid angle of the antenna (sr); Δf: receiver bandwidth (Hz); factor 1 / 2 is because the antenna usually only receives one polarization (such as vertical or horizontal), and the natural radiation is non-polarized, evenly divided on two orthogonal polarizations.

[0064] Since the product of the antenna parameters and Ω satisfies , the above formula can be further simplified.

[0065] Step 3: From radiance brightness to brightness temperature ( → ) Substitute the above formulas directly into the modified Rayleigh-Jones formula:

[0066] Thus, we get the brightness temperature value :

[0067] Pack all the system parameters (G, N, , Ω, Δf, λ, etc.) into a "calibration coefficient" or model, so that the system can directly output the corresponding brightness temperature value for each pixel or each beam pointing.

[0068] Step S4: Temperature field analysis and high-temperature point identification; synthesize the inverted physical temperature values ​​into a three-dimensional temperature field distribution map of the goaf, and identify the high-temperature anomaly areas (a set of high-temperature resolution units) within it, based on a preset temperature threshold (e.g., 70). ° C, 150 ° C, 300 ° (C, etc.) to determine the coal spontaneous combustion process and obtain the distinguishing unit of the spontaneous combustion zone boundary; Step S5: Warning and Output; Output the spatial location, temperature and range information of the high temperature abnormal area, and issue a warning when the temperature exceeds the limit.

[0069] Finally, the three-dimensional temperature field distribution map generated in step 4 is fused and displayed with the three-dimensional spatial structure map obtained in step S2. See appendix. Figure 4 In this system, different colors are used to mark the physical temperature value of each resolution unit according to different temperature thresholds. For example, red represents a high heat source, and orange, yellow, green, and blue correspond to different decreasing temperatures. Simultaneously, a spatial coordinate system is established to enable rapid location and investigation of areas composed of resolution units exceeding the high temperature threshold. For example, Figure 4 There is an elliptical high-temperature area on the top side of the rear of the goaf, with the highest temperature at the center reaching 215°C. ° C. This area is automatically marked in red by the system and an audible and visual alarm is triggered.

[0070] This invention is based on an active-passive composite mode of millimeter-wave radar. High-temperature point detection primarily relies on passive radiation observation, while when the actively emitted beam illuminates a high-temperature target, the target not only reflects radar waves but also enhances its own thermal radiation. The processing requires separating the active scattering component (carrying range and shape information) and the passive radiation component (carrying temperature information) from the total received signal. The processing model for the passive radiation component is identical to that described above. The active scattering component can be used for precise positioning and auxiliary identification, while temperature information is mainly retrieved from the passive component.

[0071] Treatment and verification after the discovery of the high-temperature point: Based on the precise coordinates provided by the detection, the construction team drilled a directional borehole to the center of the high-temperature area for grouting and nitrogen injection. A week later, a follow-up measurement showed that the temperature in the area had dropped below 40°C, and the CO concentration had also decreased significantly, verifying the accuracy of the detection results obtained using this invention.

[0072] The above preferred embodiments should be regarded as illustrative examples of the embodiments of the present application. Any technical deductions, substitutions, improvements, etc. that are similar to or based on the present application should be considered within the scope of protection of this patent.

Claims

1. A high-temperature detection system for spontaneous combustion of coal in goaf areas based on millimeter-wave radar, characterized in that, include: Millimeter-wave radar scanning unit, data acquisition and processing unit, temperature inversion unit, high-temperature identification and early warning unit; The millimeter-wave radar scanning unit is deployed at one or more detection points facing the goaf area, and is used to transmit millimeter-wave signals to the goaf area and receive its echo signals. The data acquisition and processing unit is connected to the millimeter-wave radar scanning unit. It is used to acquire and process the echo signal and reconstruct a three-dimensional spatial structure map of the goaf area through a range-angle joint imaging algorithm. The temperature inversion unit is connected to the data acquisition and processing unit. It is used to extract the radiation brightness temperature value of each spatial resolution unit from the echo signal, and invert the radiation brightness temperature value into a physical temperature value according to the preset dielectric constant-temperature sensitivity model, thereby generating a three-dimensional temperature field distribution map of the goaf. The high temperature identification and early warning unit is connected to the temperature inversion unit. It is used to identify high temperature anomaly areas exceeding a preset threshold based on the three-dimensional temperature field distribution map and generate early warning information.

2. The high-temperature detection system for spontaneous combustion of coal in goaf areas based on millimeter-wave radar according to claim 1, characterized in that: The millimeter-wave radar scanning unit is a frequency-modulated continuous wave radar system, and adopts a one-transmit-multiple-receiver or multiple-transmit-multiple-receiver antenna configuration, with its operating frequency located in the W-band or higher frequency band.

3. The high-temperature detection system for spontaneous combustion of coal in goaf areas based on millimeter-wave radar according to claim 1, characterized in that: The range-angle joint imaging algorithm includes the MIMO-SAR algorithm.

4. The high-temperature detection system for spontaneous combustion of coal in goaf areas based on millimeter-wave radar according to claim 1, characterized in that: The dielectric constant-temperature sensitivity model is a mathematical model pre-established by measuring coal and rock samples from the target mining area to describe the relationship between the real and imaginary parts of the dielectric constant of the coal and rock medium and temperature. Its functional form is: ε(T) = f(T); where ε is the complex dielectric constant and T is the physical temperature. The temperature inversion unit performs temperature inversion based on the following model: T = f(T_B, ε'(T), ε"(T), θ); where T is the physical temperature value, T_B is the radiation brightness temperature value, ε'(T) and ε"(T) are the real and imaginary parts of the dielectric constant of the coal and rock medium, respectively, and θ is the radar wave incident angle.

5. The high-temperature detection system for spontaneous combustion of coal in goaf areas based on millimeter-wave radar according to claim 1, characterized in that: It also includes a display unit for merging and displaying the three-dimensional spatial structure diagram and the three-dimensional temperature field distribution diagram.

6. A method for detecting high-temperature points of spontaneous combustion of coal in goaf areas based on millimeter-wave radar, characterized in that, Includes the following steps: Step S1: System deployment and scanning; deploy millimeter-wave radar scanning units at the detection points facing the goaf, and scan the target goaf using the millimeter-wave radar scanning units to obtain raw echo data; Step S2: Three-dimensional spatial structure reconstruction; The original echo data is processed and imaged using synthetic aperture radar or beamforming technology to obtain a three-dimensional spatial structure image of the goaf area. Step S3: Temperature Inversion; Extract the radiative brightness temperature value of each spatially resolved cell from the calibrated echo signal, and invert the radiative brightness temperature value into a physical temperature value based on the dielectric constant-temperature sensitivity model. Step S4: Temperature field analysis and high temperature point identification; synthesize the physical temperature values ​​obtained from the inversion into a three-dimensional temperature field distribution map of the goaf, and identify the high temperature anomaly areas within it; Step S5: Warning and Output; Output the spatial location, temperature and range information of the high temperature abnormal area, and issue a warning when the temperature exceeds the limit.

7. The method for detecting high-temperature points of spontaneous combustion of coal in goaf areas based on millimeter-wave radar according to claim 6, characterized in that: In step S2, the MIMO-SAR algorithm is used to reconstruct the three-dimensional spatial structure.

8. The method for detecting high-temperature points of spontaneous combustion of coal in goaf areas based on millimeter-wave radar according to claim 6, characterized in that: In step S3, the dielectric constant-temperature sensitivity model is a database of the correspondence between dielectric constant and temperature established by measuring coal samples from the target mining area in the laboratory. Its functional form is: ε(T) = f(T); where ε is the complex dielectric constant and T is the physical temperature. The temperature inversion unit performs temperature inversion based on the following model: T = f(T_B, ε'(T), ε"(T), θ); where T is the physical temperature value, T_B is the radiation brightness temperature value, ε'(T) and ε"(T) are the real and imaginary parts of the dielectric constant of the coal and rock medium, respectively, and θ is the radar wave incident angle.

9. The method for detecting high-temperature points of spontaneous combustion of coal in goaf areas based on millimeter-wave radar according to claim 6, characterized in that: In step S4, the generated three-dimensional temperature field distribution map is fused and displayed with the three-dimensional spatial structure map obtained in step S2.

10. The method for detecting high-temperature points of spontaneous combustion of coal in goaf areas based on millimeter-wave radar according to claim 6, characterized in that: In step S3, the temperature inversion includes the following operations; In the millimeter-wave band, Planck's blackbody radiation law can be simplified to the Rayleigh-Jeans approximation: in: Radiance, measured in W·m - ²·sr - ¹·Hz - ¹ represents the power radiated per unit area, unit solid angle, and unit frequency; k: Boltzmann constant (1.38 × 10⁻⁶). 23J / K); λ: operating wavelength (m); Brightness temperature, measured in Kelvin (K). For real-world objects (gray bodies), their brightness temperature It equals its physical temperature T multiplied by its emissivity e, that is =e T, the emissivity e is between 0 and 1, depending on the material of the object, the surface roughness and the observation frequency; The conversion steps from the original signal to the brightness temperature value are as follows: Step 1: From raw voltage signal to received power (V→) ) When a radar or radiometer antenna receives a signal, it outputs a voltage V. This voltage passes through the receiver link (including a low-noise amplifier, mixer, filter, intermediate frequency amplifier, etc.) and is eventually digitized. System calibration: In order to accurately convert voltage values ​​into power values, the entire receiver system needs to be absolutely calibrated, typically using two reference sources with known brightness temperatures. "Thermal" reference source: usually a load resistor whose physical temperature is precisely measured (e.g., via a thermocouple) and whose brightness temperature is considered equal to its physical temperature (high emissivity). "Cold" reference sources: usually liquid nitrogen load (about 77K) or pointing to cold space (cosmic background radiation about 2.7K). Calibration equation: By measuring the voltage values ​​Vhot and Vcold output from these two reference sources, a linear conversion relationship can be established: Where G is the system gain and N is the system noise power, G and N can be solved using two reference points. Thus, the voltage measured for any target... The corresponding received power can be calculated from these. ; Step 2: From Received Power to Radiance ( → ) For a typical passive millimeter-wave radiometer, the received power Radiance of the observation scene The relationship between them can be simplified as follows: Where: Ae: effective receiving area of ​​the antenna (m²); Ω: beam solid angle of the antenna (sr); Δf: receiver bandwidth (Hz); the factor 1 / 2 is because antennas typically receive only one polarization (such as vertical or horizontal), while natural radiation is non-polarized, with energy evenly distributed across two orthogonal polarizations; due to antenna parameters The product of Ω satisfies The above formula can be further simplified; Step 3: From radiance to brightness temperature ( → ) Substituting the above equations directly into the transformed Rayleigh-Jeans formula: Thus, we obtained the brightness temperature value. : All the above system parameters (G, N, ... (e.g., Ω, Δf, λ, etc.) are packaged into a "calibration coefficient" or model, allowing the system to directly output the brightness temperature value corresponding to each pixel or each beam pointing. .

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