A multispectral infrared imaging gas cloud concentration detection system and detection method

Abstract

This invention discloses a multispectral infrared imaging gas cloud concentration detection system and method, comprising a data acquisition and processing computer, a focal plane detector, a drive motor, a filter wheel, and an imaging lens. The detection system requires pre-calibration according to "different types of gas - different concentrations - different temperatures." During detection, two identical systems, system a and system b, placed perpendicular to the gas cloud to be measured, work together to acquire two infrared images of the gas cloud at mutually perpendicular angles. This allows the determination of the thickness of the gas cloud at different pixel locations in the two perpendicular directions, thus obtaining the actual average concentration of the gas cloud at different pixel locations. This invention, through response calibration under different concentrations and background temperature differences within a gas chamber of a specific length, obtains the relationship between gas cloud concentration, thickness, temperature difference with the background, and the response difference between the gas cloud and the background, achieving remote sensing of the spatial concentration distribution and diffusion area of ​​the target gas.

Description

Technical Field

[0001] This invention relates to a method for obtaining the concentration of a gas under test by infrared imaging gas telemetry, specifically to a multispectral infrared imaging gas cloud concentration detection system and method, belonging to the field of infrared imaging gas detection. Background Technology

[0002] Chemical gases are widely used in production and daily life as raw materials and products. Leaks of chemical gases can cause serious safety accidents and harm the environment. Rapid gas detection during the production, storage, and transportation of chemical gases can promptly identify safety hazards, accurately locate gas leak points and the concentration distribution and diffusion trend of leaked gases in space, and take effective measures to avoid casualties and property damage.

[0003] Gas sensors, a type of chemical sensor, are components or devices that convert information such as gas composition and concentration into electrical signals such as potential, resistance, and current. Gas sensors are mainly classified into semiconductor, contact combustion, and electrochemical types. These methods are often based on chemical reactions and physical properties, calculating gas concentration by measuring the changes in the physical properties of the medium caused by the interaction between the analyte and the measurement medium.

[0004] Laser gas detection, based on the selective absorption of light by gas molecules at specific wavelengths, offers advantages such as high detection speed and the ability to detect low concentrations. Direct laser absorption detection measures the attenuation of a laser beam of a specific wavelength through a certain length of gas, thereby calculating the concentration of the gas to be detected. Tunable laser absorption spectroscopy utilizes the wavelength tuning characteristics of semiconductor lasers to obtain the gas absorption spectrum within the tuning range. After being modulated, the laser beam passes through the gas and is incident on the detector; the concentration of the target gas is proportional to the intensity of the harmonic signal of the high-frequency modulation signal.

[0005] Infrared imaging gas detection utilizes infrared gas images to identify the type and concentration of target gases at a distance, displaying the spatial distribution of gas clouds against the background. This enables long-distance, non-contact detection during safe production and hazardous chemical accident rescue. Infrared imaging gas detection technology is based on the principle of gas molecules absorbing infrared radiation of specific wavelengths. The absorption of background infrared radiation by the gas leakage and diffusion area causes a change in the infrared radiation of the gas area compared to the background, thus enabling gas identification. To obtain a gas image with clear contrast, a certain temperature difference is required between the gas and the background. This temperature difference typically depends on the gas concentration and the sensitivity of the infrared camera. When the temperature difference between the gas cloud and the background is small, direct imaging with an infrared camera may not be able to identify the gas cloud.

[0006] Patent CN 110914670 A discloses a gas imaging system and method. The infrared camera system includes a filter that blocks IR radiation outside a specific wavelength range. This infrared imaging device is used to detect the presence of gas. However, a single filter can only detect one type of gas, and the imaging system and method can only be used to detect the presence of a target gas in the field of view, but cannot obtain gas concentration information.

[0007] Patent CN 106017676 A discloses an infrared imaging spectral measurement system based on a graded-gradient filter. The system uses a detector module to receive infrared images, and a filter wheel composed of graded-gradient filters to disperse infrared radiation, thereby achieving infrared imaging and detection of multiple gases. However, currently, graded-gradient filters operate primarily in the visible light band, making it difficult to achieve continuous filtering in the infrared band. Therefore, this infrared imaging system cannot detect the concentration of gas clouds.

[0008] The main shortcomings of existing technologies are:

[0009] (1) Gas sensors are contact gas detection. Fixed-point online monitoring systems can only detect gas at fixed locations. Handheld detection is less efficient for large-scale detection and is difficult to quickly detect leaks and gas diffusion areas.

[0010] (2) Laser gas detection can only perform single-point detection, which is inefficient for large-scale detection. For laser gas telemetry systems, the laser diffuse reflection signal is used as the detection signal. The echo signal energy is weak, requiring a large receiving aperture, resulting in a large system size and complex optical path.

[0011] (3) Infrared imaging gas telemetry can directly observe the distribution area of ​​gas, but it can usually only detect the relative concentration of gas and it is difficult to obtain the actual concentration of gas cloud. Summary of the Invention

[0012] The technical problem to be solved by the present invention is to overcome the above-mentioned shortcomings and provide a multispectral infrared imaging gas cloud concentration detection system and detection method, which can remotely measure the accurate spatial concentration distribution and diffusion area of ​​target gas.

[0013] The technical solution of the present invention:

[0014] A multispectral infrared imaging gas cloud concentration detection system comprises a data acquisition and processing computer, a focal plane detector, a drive motor, a filter wheel, and an imaging mirror; wherein:

[0015] The focal plane detector and imaging mirror are arranged sequentially along the optical path of the gas cloud; the filter wheel is located between the focal plane detector and the imaging mirror, and the drive motor is used to drive the filter wheel to rotate; the data acquisition and processing computer is used to acquire images from the focal plane detector and analyze and process the acquired infrared images.

[0016] The focal plane detector is either a cooled focal plane detector or an uncooled focal plane detector; the drive motor is a small stepper drive motor; multiple narrowband filters corresponding to different types of gas absorption peaks are placed on the filter wheel, and the filters only transmit near the gas absorption peaks and cut off other bands.

[0017] The multispectral infrared imaging gas cloud concentration detection system of the present invention requires calibration. The calibration system consists of a data acquisition and processing computer, a focal plane detector, a drive motor, a filter wheel, an imaging mirror, a dual-cavity gas chamber, and a large area source blackbody. The focal plane detector, imaging mirror, dual-cavity gas chamber, and large area source blackbody are arranged sequentially along the same optical path. The filter wheel is located between the focal plane detector and the imaging mirror, and the drive motor drives the filter wheel to rotate. The dual-cavity gas chamber is located between the imaging mirror and the large area source blackbody. The data acquisition and processing computer is used to acquire images from the focal plane detector and analyze and process the acquired infrared images.

[0018] The dual-chamber system has a length of L1. Both chambers are evacuated. Based on the chamber volume, a certain amount of the test gas is filled into calibration chamber A, followed by nitrogen, to achieve a test gas concentration of C1. Reference chamber B is directly filled with nitrogen. The pressure in both chambers is atmospheric pressure. The chambers have no heating function; the gas temperature is allowed to reach ambient temperature after a certain period of stillness. The temperature of the blackbody is set to be higher than the ambient temperature by ΔT1, ΔT2, ΔT3, etc. Multiple narrow-band filters corresponding to different gas absorption peaks are placed on the filter wheel. These filters only transmit near the gas absorption peaks, cutting off other wavelengths. The filters are rotated to the filter corresponding to the gas to be calibrated, and infrared images are acquired at this point. The response difference between the infrared images of the calibration chamber A and the reference chamber B is calculated. By changing the concentration of gas A in the calibration chamber to C2, C3, C4, etc., and acquiring infrared images under different gas and ambient temperature differences ΔT1, ΔT2, ΔT3, etc., the response difference between the infrared images of region A in the calibration chamber and region B in the reference chamber is calculated to obtain the concentration calibration result. By changing the gas type and rotating the filter wheel to the corresponding filter, calibration can be performed on different gases, thus obtaining the concentration calibration results for different gases.

[0019] Multispectral infrared imaging gas concentration calibration systems require the detection of the temperature of the background and gas clouds to obtain the temperature difference between the clouds and the background. Infrared thermal imager temperature calibration technology establishes a curve between the imager's output response value and temperature based on the relationship between the temperature of a blackbody and the infrared thermal imager's response value. In practical applications, the detector's own temperature changes during operation, significantly affecting the detector's output signal. With increasing ambient temperature and infrared radiation absorption, a significant temperature drift occurs, affecting the infrared detector's response characteristics and consequently impacting temperature measurement accuracy. To obtain accurate temperatures, frequent temperature calibration and correction using a blackbody are necessary.

[0020] The calibration process of this invention for "different types of gases - different concentrations - different temperatures" includes:

[0021] a) The filter wheel stops at the position of filter a, and the transmission band of filter a corresponds to the absorption peak of gas a. The dual-chamber gas chamber is evacuated. Gas chamber A is filled with gas a at a concentration of C1, with nitrogen as the equilibrium gas. Gas chamber B is filled with nitrogen, and both chambers are maintained at one atmosphere. After a period of settling, until the gas temperature inside the chambers matches the ambient temperature, the blackbody temperature is set to be ΔT1 higher than the ambient temperature. The focal plane detector acquires the current infrared image, and the response difference between regions A and B in the infrared image is calculated as ΔDN. 111 ;

[0022] b) Set the temperature of the blackbody to be higher than the ambient temperature by ΔT2, ΔT3, ΔT4, ΔT5, ΔT6... respectively, and acquire infrared images at the current temperature. Calculate the response difference between region A and region B in the infrared image to obtain the response difference ΔDN between the infrared image of the gas cloud and the background at different background temperature differences for gas a at C1 concentration. 112 ΔDN 113 ΔDN 114 ΔDN 115 ΔDN 116 ...

[0023] c) The dual-chamber gas chambers are evacuated. Gas chamber A is filled with gas a at a concentration of C2, with nitrogen as the equilibrium gas. Gas chamber B is filled with nitrogen, and both chambers are maintained at one atmosphere. After a period of settling, once the gas temperature inside the chambers is equal to the ambient temperature, the blackbody temperature is set to be higher than the ambient temperature by ΔT1, ΔT2, ΔT3, ΔT4, ΔT5, ΔT6… The focal plane detector acquires the current infrared image, and the response difference ΔDN between regions A and B in the infrared image is calculated. 121 ΔDN 122 ΔDN 123 ΔDN 124 ΔDN 125 ΔDN 126...;

[0024] d) Change the concentration of gas a in the calibration chamber to C3, C4, C5... and acquire infrared images under different ambient temperature differences ΔT1, ΔT2, ΔT3... Calculate the response difference ΔDN between the infrared images of region A in the calibration chamber and region B in the reference chamber. 131 ,

[0025] ΔDN 132 ΔDN 133 ΔDN 141 ΔDN 142 ΔDN 143 ΔDN 151 ΔDN 152 ΔDN 153 ...;

[0026] e) The filter wheel stops at the position of filter b, and the transmission band of filter b corresponds to the absorption peak of gas b. The dual-chamber gas chamber is evacuated. Gas chamber A is filled with gas b at concentrations of C1, C2, C3… with nitrogen as the equilibrium gas. Gas chamber B is filled with nitrogen, and both chambers maintain one atmosphere of pressure. After a period of stillness, once the gas temperature inside the chamber is equal to the ambient temperature, the temperature of the blackbody is set to be ΔT1, ΔT2, ΔT3… higher than the ambient temperature. Infrared images are acquired at the current temperature, and the response difference between regions in chamber A and chamber B in the infrared image is calculated. This yields the response difference ΔDN between the infrared image of the gas cloud and the background at different background temperature differences of ΔT1, ΔT2, ΔT3… for gas b at concentrations of C1, C2, C3… 211 ΔDN 212 ΔDN 213 ΔDN 221 ΔDN 222 ΔDN 223 ΔDN 231 ΔDN 232 ΔDN 233 ...

[0027] f) The filter wheel has n filters, each with a transmission band corresponding to the absorption peak of a gas. The filter wheel stops at different filter positions. At filter n, gas n with different concentrations of C1, C2, C3... is filled into the dual-chamber gas chamber A. The temperature differences between the blackbody and the environment are set to ΔT1, ΔT2, ΔT3... for each gas concentration. Infrared images are acquired at the current temperature. The response difference between regions A and B in the infrared image is calculated to obtain the response difference ΔDN between the infrared image of the gas cloud and the background at different background temperature differences of ΔT1, ΔT2, ΔT3... for gas n at C1, C2, C3... concentrations. n11 ΔDN n12 ΔDNn13 ΔDN n21 ΔDN n22 ΔDN n23 ΔDN n31 ΔDN n32 ΔDN n33 ...

[0028] g) For each gas, the relationship between the gas concentration and temperature difference at different gas chamber thicknesses and the gas cloud and background response differences was obtained.

[0029] When detecting a gas cloud, the detection system of the present invention uses two identical systems, system a and system b, placed perpendicular to the gas cloud to be tested, to perform the detection together.

[0030] Based on the distance to the gas cloud and the field of view of the imaging lens, the actual thickness of the gas cloud in two mutually perpendicular directions can be calculated from the pixel area occupied by the gas cloud in the infrared image. Using the temperature difference between the gas cloud region and the background region, the response difference between the gas cloud region and the background region, and the thickness of the gas cloud, the actual concentration of each pixel in the two mutually perpendicular directions of the gas cloud can be obtained from the calibration data of the corresponding gas.

[0031] Furthermore, the detection system of the present invention is also equipped with a reflector that can cut into / out of the optical path, and the optical path of the reflector is at 45° to the optical path of the multispectral infrared imaging gas cloud concentration detection system. First, the reflector is cut into the optical path, and the radiation energy of a small blackbody placed on its side enters the focal plane detector. Different temperatures of the small blackbody are set, and the response values ​​of the high-temperature and low-temperature blackbody under different filters are obtained by rotating the filter wheel. According to the temperature calibration of the small blackbody, the temperature corresponding to different response values ​​under different filters is obtained. Then, the reflector is cut out of the optical path, and system a or system b directly detects the target gas cloud. According to the response value of the focal plane detector, the temperature of the gas cloud and the background area and the response difference are obtained. System a and system b, placed at 90° to the gas cloud, respectively acquire two infrared images of the gas cloud at mutually perpendicular angles.

[0032] Because the detector's temperature rises during operation, causing the response value to shift, the blackbody temperature is recalibrated every 30 minutes.

[0033] The gas cloud concentration detection process of the present invention includes:

[0034] (1) The multispectral infrared imaging gas detection system is equipped with a set of calibration blackbody. The blackbody is cut into and cut out the optical path by a reflector placed at 45°. The response of the detector is calibrated periodically, so that the temperature detection of gas clouds and background can be realized more accurately.

[0035] (2) Two sets of multispectral infrared imaging gas detection systems are placed vertically on the gas cloud to be measured, and the filter wheel is rotated to collect infrared images of the gas cloud and the background respectively.

[0036] (3) The type of gas can be determined by infrared images under different filter wheels. Only the clouds of the corresponding gas can be clearly imaged through the filter, while the clouds of other gases are less different from the background.

[0037] (4) The temperature difference between the gas cloud and the background and the response difference between the gas cloud and the background can be obtained through infrared images. By querying calibration data, the column concentration of the product of gas concentration and cloud thickness can be obtained.

[0038] (5) Given the distance between the multispectral infrared imaging gas detection device and the gas cloud and the field of view of the infrared imaging lens, the actual thickness of the gas cloud corresponding to each row of pixels can be obtained by the number of pixels occupied by the gas cloud on the infrared image, and thus the thickness of the gas cloud at different pixel positions in two vertical directions can be obtained.

[0039] (6) The obtained column concentration is divided by the actual thickness of the gas cloud in that direction to obtain the actual average concentration of the gas cloud at different pixel locations.

[0040] The working principle of this invention is as follows:

[0041] The principle of infrared imaging is that the focal plane absorbs infrared radiation, causing a change in its own temperature, which in turn causes a change in the thermistor value. The external signal processing circuit obtains the power of the infrared radiation by measuring the change in the thermistor value. The concentration, thickness, type of gas cloud, and the temperature difference between the gas cloud and the background all affect the imaging effect. For the same absorption band of a gas, the greater the gas concentration and thickness, the greater the absorbance, resulting in a clearer and more obvious image on the infrared detector. According to Lambert-Beer's law, the molar absorption coefficient of a gas is affected by the wavelength of the incident light. If the wavelength is within the spectral absorption range of the target gas, the stronger the absorption of infrared waves of that wavelength, and the clearer the target gas cloud during imaging. The greater the temperature difference between the gas and the background, the clearer the image of the target cloud and the more obvious the contrast of the cloud. Based on Lambert-Beer's law, the relative concentration of the gas is calculated from the real-time acquired infrared gas images, achieving quantitative detection. When a gas cloud appears in the field of view, the equivalent brightness temperature of the received spectral radiation is:

[0042] T(v)=T0(v)+Δ 2 T≈T0(v)+αcL×ΔT

[0043] Where: T0(v) is the equivalent brightness temperature of the background radiation; Δ 2 T is the brightness temperature spectral characteristic of the gas cloud, Δ 2T is related to the gas absorption coefficient α, cloud concentration c, cloud thickness L, and the temperature difference ΔT between the cloud and the background.

[0044] To determine the concentration of a gas cloud, it is necessary to obtain the received equivalent brightness temperature of the radiation and the background equivalent brightness temperature, as well as the gas absorption coefficient, gas thickness, and the temperature difference between the cloud and the background. The received equivalent brightness temperature of the radiation cannot be directly obtained, but the detector's response value is related to the received infrared radiation; the stronger the received infrared radiation energy, the larger the response value. By calibrating the response of the infrared imaging detector under different concentrations and background temperature differences within a gas chamber of a specific length, the relationship between the gas cloud concentration, gas cloud thickness, the temperature difference between the gas cloud and the background, and the response difference between the gas cloud and the background can be obtained.

[0045] The beneficial effects of this invention are:

[0046] This invention employs a dual-chamber gas chamber in front of a blackbody for concentration calibration, establishing the relationship between the difference in detector cloud and background response and gas concentration, gas type, gas thickness, and temperature difference between the cloud and background. Two vertically placed multispectral infrared imaging gas detection systems are used to calculate the thickness of the gas cloud in two directions based on the image size. A blackbody temperature calibration method is used to obtain the background temperature and the temperature of the gas cloud. Based on the detector's response to the gas cloud and background, and using the calibrated gas concentration data in front of the blackbody and the gas cloud thickness, the actual concentration distribution and diffusion trend of the gas cloud in two directions are obtained in real time. Narrow-band filter spectral dispersion allows for infrared imaging gas telemetry of various gases. After concentration calibration in the dual-chamber gas chamber in front of the blackbody, the two vertically placed infrared imaging gas detection systems can obtain the actual concentration and diffusion trend of the gas cloud. The vertically placed multispectral infrared imaging gas detection system obtains the size of the gas cloud in two directions, and through three-dimensional data inversion, a three-dimensional image of the gas cloud and its concentration distribution can be obtained. Attached Figure Description

[0047] Figure 1 Multispectral infrared imaging gas cloud concentration calibration system.

[0048] Figure 2 Gas calibration infrared image.

[0049] Figure 3 Concentration calibration.

[0050] Figure 4 Multispectral infrared imaging gas cloud concentration detection system.

[0051] Figure 5 Infrared image of a gas cloud.

[0052] In the figure: 1-Data acquisition and processing computer; 2-Focal plane detector; 3-Drive motor; 4-Filter wheel; 5-Imaging lens; 6-Dual-chamber gas chamber; 7-Large surface source blackbody; 8-Reflector; 9-Small surface source blackbody; 10-Gas cloud; 11-Background area. Detailed Implementation

[0053] like Figure 4 As shown, the multispectral infrared imaging gas cloud concentration detection system of the present invention consists of two identical systems, a and b. Systems a and b are set at mutually perpendicular angles to detect the gas cloud 10. Both systems a and b consist of a data acquisition and processing computer 1, a focal plane detector 2, a drive motor 3, a filter wheel 4, an imaging mirror 5, a reflector 8, and a small surface source blackbody 9; wherein:

[0054] The focal plane detector 2 and the imaging mirror 5 are arranged sequentially along the same optical path; the filter wheel 4 is located between the focal plane detector 2 and the imaging mirror 5, and the drive motor 3 is used to drive the filter wheel 4 to rotate; the reflector 8 is located behind the imaging mirror 5 and can enter / remove the optical path; the small surface source blackbody 9 is parallel to the optical path and can form a mutually perpendicular state with the imaging mirror 5 when the reflector 8 enters; the data acquisition and processing computer 1 is used to acquire the image of the focal plane detector 2 and analyze and process the acquired infrared image.

[0055] The focal plane detector 2 is a cooled focal plane detector with a 640×512 area array and an operating wavelength of 8-14μm; the drive motor 3 is a small stepper motor; the filter wheel 4 is a filter wheel with six narrowband filters (e.g., the first can be represented by filter a, the second by filter b, and so on, the sixth by filter f), and the transmission peaks of the filters are: 8.590μm, 10.347μm, 10.530μm, 10.567μm, and 10.567μm. The six filters are 10.744μm, 13.825μm, and 20nm at half maximum width, and are used to detect sulfur dioxide, butane, ethylene, sulfur hexafluoride, ammonia, and dichloromethane, respectively. Imaging lens 5 is an imaging lens with a field of view of 12°×9.6° and a light-transmitting aperture of 60mm. Dual-cavity gas chamber 6 is a dual-cavity gas chamber with a length of 1m and an inner diameter of 20cm for each of the two chambers. Large surface source blackbody 7 is a large surface source blackbody of 500mm×500mm.

[0056] A reflector 8, which can cut into / out of the optical path, is set up. The reflector 8 is a reflector with an 8-14μm high-reflectivity film coated on its surface, and its dimensions are 62mm × 86mm. The optical path of the reflector is at a 45° angle to the optical path of the multispectral infrared imaging gas cloud concentration detection system. The reflector 8 cuts into the optical path. The radiation energy of a small area source blackbody 9 placed on its side enters the focal plane detector 2. By setting different blackbody temperatures and rotating the filter wheel 4, the response values ​​of the high-temperature and low-temperature blackbody under different filters are obtained. Based on the temperature calibration of the small area source blackbody 9, the temperatures corresponding to different response values ​​under different filters are obtained.

[0057] The reflector 8 cuts out the optical path, and system a or system b directly detects the target gas cloud 10. Based on the response value of the focal plane detector 2, the temperature of the gas cloud 10 and the response difference between the background region 11 are obtained. System a and system b, placed at 90° to the gas cloud 10, respectively acquire two infrared images of the gas cloud 10 at mutually perpendicular angles, as shown below. Figure 5 (The left figure shows system a, and the right figure shows system b).

[0058] Based on the distance of the gas cloud 10 and the field of view of the imaging lens, the actual thickness of the gas cloud 10 in two mutually perpendicular directions can be calculated from the pixel area occupied by the gas cloud 10 in the infrared image. Based on the temperature difference between the gas cloud 10 region and the background region 11, the response difference between the gas cloud 10 region and the background region 11, and the thickness of the gas cloud 10, the actual concentration of each pixel in the two mutually perpendicular directions of the gas cloud 10 can be obtained from the calibration data of the corresponding gas.

[0059] The reflector 8 is a reflector with an 8-14μm high-reflectivity film coated on its surface, measuring 62mm × 86mm, and is placed at a 45° angle perpendicular to the optical path of the imaging lens; the small blackbody 9 is a 100mm × 100mm small blackbody. The reflector 8 is inserted into the optical path, and the temperatures of the small blackbody 9 are designed to be 10℃, 20℃, 30℃, 40℃, 50℃, and 60℃. By rotating the filter wheel 4, the responses of the blackbody at different temperatures after passing through different filters are collected, and the temperatures corresponding to the detector response values ​​under different filters are obtained.

[0060] After temperature calibration, reflector 8 cuts out the optical path, allowing the multispectral infrared imaging system to remotely measure the target gas concentration. Because the detector temperature rises during operation, causing a shift in the response value, temperature calibration is performed every 30 minutes.

[0061] Two multispectral infrared imaging gas detection systems are set up vertically to detect ammonia clouds. Assuming both devices are 100m away from the clouds, and the number of pixels occupied by the gas clouds in a certain row of the infrared image is 320 and 160 pixels respectively, the horizontal field of view of a single pixel is α.H =12° / 640 = 0.01875°, therefore the field of view for 320 pixels and 160 pixels is 6° and 3° respectively. The distance between the target cloud and the detection device is 100m, so the width of the cloud is 10.45m and 5.24m respectively. Based on the temperature difference between the target cloud and the background and the detector response difference, the gas concentration for a 1m thick cloud can be obtained according to calibration data. Dividing this by the target cloud thickness of 10.45m and 5.24m gives the actual concentration of the cloud. Since the number of pixels per row in the infrared image varies, resulting in different cloud widths, the actual concentration of the gas cloud at different pixel counts can be calculated.

[0062] Preferably, an infrared filter is added in front of the focal plane detector 2 to allow or block the infrared absorption peaks of the gas, thereby enabling the gas in the field of view to be distinguished without considering the gas and background temperature.

[0063] like Figure 1 As shown, the multispectral infrared imaging gas cloud concentration detection system of the present invention requires calibration. The calibration system consists of a data acquisition and processing computer 1, a focal plane detector 2, a drive motor 3, a filter wheel 4, an imaging mirror 5, a dual-cavity gas chamber 6, and a large area source blackbody 7. Specifically, the focal plane detector 2, the imaging mirror 5, and the large area source blackbody 7 are arranged sequentially along the same optical path; the filter wheel 4 is located between the focal plane detector 2 and the imaging mirror 5, and the drive motor 3 is used to drive the filter wheel 4 to rotate; the dual-cavity gas chamber 6 is located between the imaging mirror 5 and the large area source blackbody 7; the data acquisition and processing computer 1 is used to acquire images from the focal plane detector 2 and analyze and process the acquired infrared images.

[0064] The calibration method is as follows:

[0065] Calculations show that the volume of the double-chamber air chamber 6 is 31416 cm³. 3 Each chamber was filled with a volume of 31.416 cm³ at room temperature and pressure. 3 62.832cm 3 157.08cm 3 314.16cm 3 471.24cm 3 628.32cm 3 942.48cm 3 1256.24cm 3 The gas concentrations in the chambers are 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 3%, and 4%, respectively.

[0066] The temperature of the large area source blackbody 7 was set to be 1℃, 2℃, 3℃...20℃ higher than the ambient temperature. Infrared images of sulfur dioxide, butane, ethylene, sulfur hexafluoride, ammonia, and dichloromethane gases at different temperatures and concentrations were collected. Through data processing, the response difference of the detector in the gas cloud and background area at a gas thickness of 1m and concentrations of 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 3%, and 4% of sulfur dioxide, butane, ethylene, sulfur hexafluoride, ammonia, and dichloromethane gases at temperature differences of 1℃, 2℃, 3℃...20℃ can be obtained. This data is the gas calibration data under "different gas-concentration-temperature".

Claims

1. A multispectral infrared imaging gas cloud concentration detection system, characterized in that: The multispectral infrared imaging gas cloud concentration detection system consists of a data acquisition and processing computer (1), a focal plane detector (2), a drive motor (3), a filter wheel (4), and an imaging mirror (5); The focal plane detector (2) and the imaging mirror (5) are arranged sequentially along the optical path of the gas cloud (10); the filter wheel (4) is located between the focal plane detector (2) and the imaging mirror (5), and the drive motor (3) is used to drive the filter wheel (4) to rotate; the data acquisition and processing computer (1) is used to acquire the image of the focal plane detector (2) and analyze and process the acquired infrared image; the focal plane detector (2) is a cooled focal plane detector or an uncooled focal plane detector; the drive motor (3) is a small stepper drive motor; multiple narrowband filters corresponding to different types of gas absorption peaks are placed on the filter wheel (4), and the filters only transmit near the gas absorption peaks and cut off other bands; The multispectral infrared imaging gas cloud concentration detection system needs to be calibrated according to "different types of gas - different concentrations - different temperatures". The calibration system consists of a data acquisition and processing computer (1), a focal plane detector (2), a drive motor (3), a filter wheel (4), an imaging mirror (5), a dual-cavity gas chamber (6), and a large area source blackbody (7). Among them, the focal plane detector (2), the imaging mirror (5), the dual-cavity gas chamber (6), and the large area source blackbody (7) are arranged sequentially on the same optical path; the filter wheel (4) is located between the focal plane detector (2) and the imaging mirror (5), and the drive motor (3) is used to drive the filter wheel (4) to rotate; the dual-cavity gas chamber (6) is located between the imaging mirror (5) and the large area source blackbody (7); the data acquisition and processing computer (1) is used to acquire the image of the focal plane detector (2) and analyze and process the acquired infrared image; the dual-cavity gas chamber (6) is used to fill different gases and simulate different concentrations; the large area source blackbody (7) is used to simulate different background temperatures. When the multispectral infrared imaging gas cloud concentration detection system detects the gas cloud (10), it uses two identical systems, system a and system b, placed perpendicular to the gas cloud (10) to perform the detection. The system collects two infrared images of the gas cloud (10) at mutually perpendicular angles, thereby obtaining the thickness of the gas cloud at different pixel positions in the two vertical directions, and thus obtaining the actual average concentration of the gas cloud at different pixel positions.

2. The multispectral infrared imaging gas cloud concentration detection system according to claim 1, characterized in that: The length of the dual-chamber gas chamber (6) is L1. Both chambers are evacuated. According to the volume of the gas chamber, a certain amount of gas to be tested is filled into the calibrated gas chamber A, and then nitrogen is filled into it so that the concentration of the gas to be tested in the gas chamber is C1. Nitrogen is directly filled into the reference gas chamber B. The pressure of the two chambers is 1 atmosphere. The gas was allowed to stand still for a certain period of time until its temperature reached the ambient temperature. The temperature of the large surface source blackbody (7) was set to be higher than the ambient temperature. , , ...; Rotate the filter wheel (4) to the filter corresponding to the gas to be calibrated, collect the infrared image at this time, and calculate the response difference between the infrared images of the calibration gas chamber A area and the reference gas chamber B area; The concentration of gas A in the calibration chamber was changed to C2, C3, C4..., under different gas conditions and ambient temperature differences. , , ...Infrared images are acquired, and the response difference between the infrared images of the calibration chamber A region and the reference chamber B region is calculated to obtain the concentration calibration results.

3. The multispectral infrared imaging gas cloud concentration detection system according to claim 2, characterized in that, The calibration process includes: a) The filter wheel (4) stops at the position of filter a, and the transmission band of filter a corresponds to the absorption peak of gas a; the dual-chamber gas chamber (6) is evacuated, gas chamber A is filled with gas a with a concentration of C1, the equilibrium gas is nitrogen, and gas chamber B is filled with nitrogen. Both gas chambers maintain one atmosphere of pressure; after standing for a period of time, when the gas in the gas chamber is at the same temperature as the environment, the temperature of the large surface source blackbody (7) is set to be higher than the environment temperature. The focal plane detector (2) acquires the current infrared image and calculates the response difference between region A and region B of the infrared image. ; b) Set the temperature of the large surface source blackbody (7) to be higher than the ambient temperature. , , , , ...Acquire infrared images at the current temperature, calculate the response difference between region A and region B in the infrared image, and obtain the response difference between the infrared image of the gas cloud and the background at different ambient temperature differences for gas a at C1 concentration. , , , , ...; c) Evacuate the double-chamber gas chamber (6). Gas chamber A is filled with gas a of concentration C2, and the equilibrium gas is nitrogen. Gas chamber B is filled with nitrogen. Both gas chambers are kept at one atmosphere. After standing for a period of time, wait for the gas temperature in the gas chamber to be the same as the ambient temperature, and set the blackbody temperature to be higher than the ambient temperature. , , , , , ...The focal plane detector (2) acquires the current infrared image and calculates the response difference between region A and region B of the infrared image. , , , , , ...; d) Change the concentration of gas a in the calibration chamber to C3, C4, and C5. Temperature differences in different environments , , Infrared images were acquired, and the response difference between the infrared images of calibration chamber A and reference chamber B was calculated. , , , , , , , , ...; e) The filter wheel (4) stops at the position of filter b, and the transmission band of filter b corresponds to the absorption peak of gas b; the dual-chamber gas chamber (6) is evacuated, and gas chamber A is filled with C1, C2, and C3. Gas b is used as the equilibrium gas, and nitrogen is used in gas chamber B. Both gas chambers are maintained at one atmosphere of pressure. After standing for a period of time, once the gas temperature in the gas chambers is the same as the ambient temperature, the temperature of the blackbody is set to be higher than the ambient temperature. , , ...Acquire infrared images at the current temperature, calculate the response difference between region A and region B in the infrared image, and obtain the response of gas b at different concentrations of C1, C2, C3... , , ...the response difference between infrared images of gas clouds and the background under ambient temperature differences , , , , , , , , ...; f) The filter wheel (4) has n filters, and the transmission band of each filter corresponds to the absorption peak of a gas. The filter wheel (4) stops at different filter positions. At the position of filter n, gas n with different concentrations of C1, C2, C3... is filled into the gas chamber A. The temperature difference between the blackbody and the environment is set at each gas concentration. , , ...Acquire infrared images at the current temperature, calculate the response difference between region A and region B in the infrared image, and obtain the response of gas n at different concentrations of C1, C2, C3... , , ...the response difference between infrared images of gas clouds and the background under ambient temperature differences , , , , , , , , ...; g) For each gas, the relationship between the gas concentration and temperature difference at different gas chamber thicknesses and the difference between the gas cloud and the background response was obtained.

4. The multispectral infrared imaging gas cloud concentration detection system according to claim 3, characterized in that: By changing the type of gas, the filter wheel (4) rotates to the corresponding filter to calibrate different gases, thereby obtaining the concentration calibration results of different gases.

5. The multispectral infrared imaging gas cloud concentration detection system according to claim 1, characterized in that: The filter wheel (4) is a filter wheel with 6 narrow-band filters. The transmission peaks of the filters are 8.590 μm, 10.347 μm, 10.530 μm, 10.567 μm, 10.744 μm and 13.825 μm, respectively, and their half-width at half-maximum is 20 nm. The 6 filters are used to detect sulfur dioxide, butane, ethylene, sulfur hexafluoride, ammonia and dichloromethane, respectively.

6. The multispectral infrared imaging gas cloud concentration detection system according to claim 3, characterized in that, Calibration methods include: The dual-chamber air chamber (6) is a dual-chamber air chamber with a length of 1m and an inner diameter of 20cm for each chamber. Each chamber is filled with an air volume of 31.416cm³ at room temperature and pressure. 3 62.832cm 3 157.08cm 3 314.16cm 3 471.24cm 3 628.32cm 3 942.48cm 3 1256.24cm 3 If the gases are 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 3%, and 4%, respectively, then the concentrations of the gases in the chambers are 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 3%, and 4%. The temperature of the large surface source blackbody (7) is set to be 1℃, 2℃, 3℃...20℃ higher than the ambient temperature. Infrared images of sulfur dioxide, butane, ethylene, sulfur hexafluoride, ammonia and dichloromethane gas at different temperatures and concentrations are collected. Through data processing, the response difference of the detector in the gas cloud and background area can be obtained at a gas thickness of 1m with concentrations of 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 3%, and 4% for sulfur dioxide, butane, ethylene, sulfur hexafluoride, ammonia and dichloromethane gas at temperature differences of 1℃, 2℃, 3℃...20℃. This data is the gas calibration data under "different gas-concentration-temperature".

7. The multispectral infrared imaging gas cloud concentration detection system according to claim 1, characterized in that: A reflector (8) capable of cutting out / cutting into the optical path is also provided between the imaging mirror (5) and the gas cloud (10). The optical path of the reflector (8) is at 45° to the optical path of the multispectral infrared imaging gas cloud concentration detection system. During temperature calibration, the reflector (8) is first inserted into the optical path, and the radiation energy of the small black body (9) placed on its side enters the focal plane detector (2). Different temperatures of the small black body (9) are set, and the response values ​​of the high-temperature black body and the low-temperature black body under different filters are obtained by rotating the filter wheel (4). According to the temperature calibration of the small black body (9), the temperature corresponding to different response values ​​under different filters is obtained. After the temperature calibration is completed, the reflector (8) is cut out of the optical path.

8. The multispectral infrared imaging gas cloud concentration detection system according to claim 7, characterized in that: The imaging lens (5) is an imaging lens with a field of view of 12°×9.6° and a light-transmitting aperture of 60mm; The focal plane detector (2) is a cooled focal plane detector with a 640×512 array and a working wavelength of 8-14 μm. The large surface blackbody (7) is a 500mm×500mm large surface blackbody; The reflector (8) is a reflector with an 8-14μm high reflectivity film on its surface and a size of 62mm×86mm.

9. The multispectral infrared imaging gas cloud concentration detection system according to claim 7, characterized in that: The temperature calibration is performed every 30 minutes.

10. A method for detecting the concentration of gas clouds using multispectral infrared imaging, characterized in that, The multispectral infrared imaging gas cloud concentration detection system according to any one of claims 1-9, wherein the detection method comprises: (1) Two sets of multispectral infrared imaging gas detection systems a and b are placed vertically to the gas cloud to be tested, and the filter wheel (4) is rotated to collect infrared images of the gas cloud and the background respectively; (2) The type of gas can be determined by infrared images under different filter wheels. Only the clouds of the corresponding gas can be clearly imaged through the filter, while the clouds of other gases are very similar to the background. (3) The temperature difference between the gas cloud and the background and the response difference between the gas cloud and the background can be obtained through infrared images. By querying the calibration data, the column concentration of the product of gas concentration and cloud thickness can be obtained. (4) Given the distance between the multispectral infrared imaging gas detection device and the gas cloud and the field of view of the infrared imaging lens, the actual thickness of the gas cloud corresponding to each row of pixels can be obtained by the number of pixels occupied by the gas cloud on the infrared image, and thus the thickness of the gas cloud at different pixel positions in two vertical directions can be obtained. (5) Divide the obtained column concentration by the actual thickness of the gas cloud in that direction to obtain the actual average concentration of the gas cloud at different pixel locations.

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