An optical path system for a NO2 imaging detector

Abstract

This invention discloses an optical path system for a NO2 imaging detector. The detector's optical path imaging system is an optomechanical system that utilizes a beam splitter to perform parallel non-dispersive imaging in the visible band, enabling visualized remote sensing of the location and status of pollutant gas emissions or leaks. The detector's optical path imaging system comprises four sub-optical paths with no moving parts, resulting in fast imaging speed and reliable operation. By sharing a front-end optical path for simultaneous imaging measurement, emission source image localization, and error correction, the system's size and weight are reduced, and subsequent image processing and concentration calculation are facilitated. It offers numerous advantages, including visualization, high spatiotemporal resolution, and low cost.

Description

Technical Field

[0001] This invention belongs to the field of optical telemetry and correction technology, specifically relating to an optical path system for an NO2 imaging detector, which is used to receive solar scattered radiation through a telescope and transmit it to a subsequent camera imaging detection mechanism after beam splitting. Background Technology

[0002] To address air pollution, accurate and timely access to regional air pollution information is crucial. NO2 monitoring is a vital component of air pollution control. NO2 imaging detectors acquire two-dimensional distribution maps of NO2 gas by detecting visible light radiation penetrating the gas, meeting the requirements for analyzing pollution emissions and variations. They must also eliminate or correct interference from other gases and minimize measurement errors caused by the optical path itself. Key technologies include variable field of view and high temporal resolution imaging. The optical system must possess both good spatial imaging quality and imaging speed to achieve the required spatial and temporal resolution. It also needs to have positioning and correction capabilities for the optical path and meet system requirements regarding size, weight, structure, cost, and reliability.

[0003] The concentration gradient of NO2 pollutant emissions often exhibits characteristics of small spatial range and rapid speed, posing challenges to monitoring. Traditional point source monitoring is insufficient to meet the needs of observing its dynamic changes, while some current optical remote sensing systems have drawbacks such as complex measurement optical paths, large size, high cost, and typically low temporal resolution. Summary of the Invention

[0004] To address the urgent need for rapid imaging, location, and monitoring of NO2 atmospheric pollutants emitted from pollution sources, and to achieve high temporal resolution full-frame imaging of emission distributions such as plumes from pollution sources, this invention provides an optical path system for an NO2 imaging detector. This system is an optical and mechanical system that can receive solar scattered light radiation through a telescope and simultaneously achieve imaging of four sub-optical paths after beam splitting. This solves the problems of current systems being too large, complex in structure, high in cost, and low in temporal resolution.

[0005] To solve the above problems, the solution of the present invention is as follows:

[0006] An optical path system for an NO2 imaging detector, the imaging detector system comprising: a main optical path: an incident optical path of scattered sunlight; two branch optical paths: a positioning and correction optical path and a measurement optical path; and four sub-optical paths: a positioning and detection optical path, a correction and measurement optical path, a first sub-measurement optical path, and a second sub-measurement optical path;

[0007] The solar scattered light incident main optical path is a telescope, collimator, and beam splitter optical path, which is sequentially equipped with a telescope collimator group, an exit aperture, and a first beam splitter; the positioning and correction optical path is equipped with a second beam splitter; the measurement optical path is equipped with a first filter and a third beam splitter; the positioning and detection optical path is equipped with a first camera; the correction and measurement optical path is equipped with a second filter, a third gas cell unit, and a second camera; the first sub-measurement optical path is equipped with a first gas cell unit and a third camera; and the second sub-measurement optical path is equipped with a second gas cell unit and a fourth camera.

[0008] In this system, the solar scattered light from the target area enters the imaging detector system through the collimating lens group. After collimation, it is incident on the first beam splitter through the exit aperture and split into two different beams. One beam enters the positioning and correction optical path, and after passing through the second beam splitter, it is split into two beams again. One beam reaches the first camera for imaging, and the other beam passes through the second filter and the third gas cell unit before being imaged on the second camera. The other beam exiting from the first beam splitter enters the measurement optical path, passes through the first filter, and reaches the third beam splitter, where it is split into two beams again. One beam passes through the first gas cell unit and is imaged on the third camera, while the other beam passes through the second gas cell unit and is finally imaged on the fourth camera.

[0009] Furthermore, the telescope collimating lens group is composed of multiple spherical and aspherical lenses with adjustable focal length, the aperture of the exit aperture is adjustable, and the first beam splitter is a flat beam splitter with a beam splitting ratio of 50:50.

[0010] Furthermore, the second beam splitter is a flat beam splitter with a beam splitting ratio of 50:50.

[0011] Furthermore, the first filter is a bandpass filter with a center wavelength of 436nm, a half-width at half-maximum of 10nm, a cutoff frequency of 426nm and 446nm, and a transmittance greater than 85% in the range of 433-439nm. The third beam splitter 6 is a flat beam splitter with a splitting ratio of 50:50.

[0012] Furthermore, the second filter is a bandpass filter with a center wavelength of 600nm and a half-width at half-maximum of 10nm; the third gas cell unit is a quartz glass cell with an internal vacuum; and the second camera is a monochrome CMOS camera.

[0013] Furthermore, the first gas cell unit is a quartz glass cell, which contains NO2 gas with a concentration greater than 1×10⁻⁶. 18 molec / cm 2 The third camera mentioned is a monochrome CMOS camera.

[0014] Furthermore, the second gas cell unit is a quartz glass cell with an internal vacuum, and the fourth camera is a monochrome CMOS camera.

[0015] Furthermore, the first camera is a color CMOS camera.

[0016] Furthermore, the positioning detection optical path and the correction measurement optical path share the front positioning correction optical path, the first sub-measurement optical path and the second sub-measurement optical path share the front measurement optical path, and the positioning correction optical path and the measurement optical path share the frontmost solar scattered light incident optical path.

[0017] As can be seen from the above technical solution, this invention simultaneously achieves imaging along four sub-optical paths using three beam splitters. The positioning and detection optical path can locate the NO2 distribution position using the image and the measurement optical path results, and perform localized magnification for focused detection based on the orientation. The image obtained by the calibration measurement optical path can be used to correct and eliminate interference from smoke, dust, and water vapor. The images measured by the first and second sub-measurement optical paths are combined to calculate the NO2 concentration and distribution in the target area and complete flat-field correction. All cameras used are high-speed CMOS cameras, which offer high temporal resolution, good cost-effectiveness, adjustable integration time, short response time, and high signal-to-noise ratio.

[0018] The beneficial effects of this invention are:

[0019] 1. By utilizing three beam splitters to simultaneously achieve imaging along four sub-optical paths, this system meets the requirements for visually monitoring the location and status of pollutant gas emissions or leaks. Its short length allows for a smaller system size, while also increasing instrument flexibility, facilitating movement and mounting on various platforms. The use of fixed optics with no moving parts enhances its anti-interference capabilities and reliability.

[0020] 2. By adding several beam splitters and filters to the optical path, the optical paths for measurement, positioning and correction can be shared, which reduces the number of parts, simplifies the system structure, and reduces the overall size and weight. It can simultaneously realize imaging measurement, emission source image positioning and error correction, and no additional image registration is required in the later stage.

[0021] 3. It features no dispersive elements, resulting in high radiative energy utilization and excellent imaging quality. High-speed CMOS detectors ensure both temporal resolution and signal-to-noise ratio. The overall system cost is low, making it economical. Attached Figure Description

[0022] Figure 1 This is a diagram showing the optical path system components and optical path diagram of the NO2 imaging detector of the present invention. Detailed Implementation

[0023] See Figure 1A lightweight, low-cost, high-temporal-resolution NO2 imaging detector optical path system is provided, comprising multiple imaging measurement optical systems, including:

[0024] Main optical path: Incident optical path A for sunlight scattered light;

[0025] Two branch optical paths: positioning and calibration optical path B, and measurement optical path C;

[0026] And four sub-optical paths: positioning detection optical path D, calibration measurement optical path E, first sub-measurement optical path F, and second sub-measurement optical path G;

[0027] Among them, the main incident optical path A of the solar scattered light is a telescope, collimating and beam splitting optical path, which is provided with a telescope collimating lens group 1, an exit beam 2 and a first beam splitter 3 in sequence.

[0028] The positioning and correction optical path B is equipped with a second beam splitter 4;

[0029] The measurement optical path C is equipped with a first filter 5 and a third beam splitter 6;

[0030] The positioning and detection optical path D is equipped with a first camera 7;

[0031] The calibration measurement optical path E is equipped with a second filter 8, a third gas cell unit 9, and a second camera 10;

[0032] The first sub-measurement optical path F is provided with a first gas cell unit 11 and a third camera 12;

[0033] The second sub-measurement optical path G is provided with a second gas cell unit 13 and a fourth camera 14;

[0034] In this system, solar scattered light from the target area enters the imaging detector system through the collimating lens group 1. After collimation, it passes through the exit aperture 2 and is incident on the first beam splitter 3, where it is split into two different beams. One beam enters the positioning correction optical path B, and after passing through the second beam splitter 4, it is split into two beams again: one beam reaches the first camera 7 for imaging, and the other beam passes through the second filter 8 and the third gas cell unit 9 before being imaged on the second camera 10. The color image formed by the beam reaching the first camera 7 can provide the observer with an image of the target area. Then, based on the NO2 detection results, the field of view can be adjusted to magnify the location of pollution for focused measurement. The second filter 8 is a narrowband filter. After the incident light passes through the second filter 8, the transmitted light in this band reaches the second camera 10, and the resulting image can be used to remove interference from smoke, water vapor, etc., on NO2 measurement. Another beam of light emitted from the first beam splitter 3 enters the measurement optical path C, passes through the first filter 5, and reaches the third beam splitter 6, where it is split into two beams again: one beam passes through the first gas cell unit 11 and is imaged on the third camera 12, while the other beam passes through the second gas cell unit 13 and is finally imaged on the fourth camera 14. The first filter 5 is a narrowband filter, the first gas cell unit 11 is a quartz glass cell containing NO2 gas, and the second gas cell unit 13 is a quartz glass cell with an internal vacuum. By comparing the transmitted light passing through the second gas cell unit 13 and the transmitted light passing through the first gas cell unit 11 after filtering by the first filter 5, the concentration of NO2 gas in the atmosphere of the target area can be deduced.

[0035] The positioning detection optical path D and the correction measurement optical path E share the positioning correction optical path B in front, the first sub-measurement optical path F and the second sub-measurement optical path G share the measurement optical path C in front, while the positioning correction optical path B and the measurement optical path C share the foremost solar scattered light incident optical path A.

[0036] Four sub-optical paths can be imaged simultaneously using three beam splitters.

[0037] By combining the images obtained from the first and second sub-measurement optical paths, the NO2 concentration and distribution in the target area can be calculated, and flat-field correction can be performed. Imaging is performed on the polluted area and the adjacent clean atmospheric background. The measurement principle is based on the Lambert-Beer absorption law: when light passes through the atmosphere, light energy is absorbed by gases in the atmosphere, thus weakening the light intensity in a certain wavelength band. The transmitted light intensity and absorbance conform to the Lambert-Beer law, and the concentration of a certain gas in the atmosphere can be measured by the degree of light intensity reduction within a certain wavelength range. A filter is used to select wavelength bands where NO2 absorption is strong and other gases absorption is relatively weak. Let I1 and I be the signals measured after the beam passes through the NO2 gas cell and the vacuum gas cell, respectively, and let a be the logarithmic ratio of I1 and I. When the concentration of the measured gas increases, more incident light is absorbed, the light signal decreases, I decreases, I1 / I increases, and a increases accordingly; conversely, when the concentration of the measured gas decreases, the absorption of incident light is less, I increases, I1 / I decreases, and a decreases accordingly. It can be seen that a changes monotonically with the change in the concentration of the measured gas. Experimental testing revealed a linear relationship between the concentration of the target NO2 gas and a, with a proportionality coefficient k. This relationship and the k value can be obtained using calibration methods. This relationship and k value enable quantitative detection of NO2 distribution. In actual measurements, even with identical optical setups, the detectors of the two sub-optical path cameras may exhibit slightly different pixel response inhomogeneities. To reduce errors, flat-field correction is necessary, which can be achieved by subtracting a background value. Images were taken against a clean sky background near the NO2 emission point. The signal values ​​obtained from the two sub-optical path camera modules were I... 1ref and I ref Similarly, take I 1ref and I ref Using the logarithmic ratio as a background value can effectively reduce the impact of non-uniformity.

[0038] The image obtained by calibrating the measurement optical path can be used to correct and eliminate the interference of smoke and water vapor. NO2 absorption is weaker in the wavelength band of the beam after passing through the filter, while the absorption of smoke and water vapor is approximately constant relative to the wavelength band of the measurement optical path beam. Therefore, the beam absorption information measured by this optical path can be used to subtract the influence of smoke and water vapor on NO2 imaging measurements.

[0039] The positioning detection optical path can locate the distribution location of NO2 by combining the acquired image with the quantitative test results of the measurement optical path, and perform local magnification for focused detection based on the orientation. Specifically, based on the acquired color image information and the NO2 emission distribution measured by the measurement optical path, the focal length and direction of the front zoom lens are adjusted to magnify the NO2 emission area, thereby achieving the purpose of focusing on observing the NO2 emission or leakage points of interest.

Claims

1. An optical path system for a NO2 imaging detector, characterized in that, The optical path system of the imaging detector includes: Main optical path: Incident optical path of solar scattered light (A); Two branch optical paths: positioning and correction optical path (B), and measurement optical path (C); And four sub-optical paths: positioning detection optical path (D), calibration measurement optical path (E), first sub-measurement optical path (F), and second sub-measurement optical path (G); The main incident light path (A) of the solar scattered light is a telescope, collimating and beam splitting light path, which is provided with a telescope collimating lens group (1), an exit beam diaphragm (2) and a first beam splitter (3) in sequence. The positioning and correction optical path (B) is provided with a second beam splitter (4); The measurement optical path (C) is provided with a first filter (5) and a third beam splitter (6); The positioning and detection optical path (D) is equipped with a first camera (7); The calibration measurement optical path (E) is equipped with a second filter (8), a third gas cell unit (9), and a second camera (10); The first sub-measurement optical path (F) is provided with a first gas cell unit (11) and a third camera (12); The second sub-measurement optical path (G) is provided with a second gas cell unit (13) and a fourth camera (14); In this system, the sunlight scattered from the target area enters the imaging detector system through the collimating lens group (1), and after collimation, it is incident on the first beam splitter (3) through the exit aperture (2) and split into two different beams: one beam enters the positioning correction optical path (B), and after passing through the second beam splitter (4), it is split into two beams again: one beam reaches the first camera (7) for imaging, and the other beam passes through the second filter (8) and the third gas cell unit (9) and is then imaged on the second camera (10); the other beam emitted from the first beam splitter (3) enters the measurement optical path (C), passes through the first filter (5) and reaches the third beam splitter (6), and is split into two beams again: one beam passes through the first gas cell unit (11) and is imaged on the third camera (12), and the other beam passes through the second gas cell unit (13) and is finally imaged on the fourth camera (14).

2. The optical path system of a NO2 imaging detector according to claim 1, characterized in that, The collimating lens group (1) consists of multiple spherical and aspherical lenses with adjustable focal length. The aperture of the exit aperture (2) is adjustable. The first beam splitter (3) is a flat beam splitter with a beam splitting ratio of 50:

50.

3. The optical path system of a NO2 imaging detector according to claim 1, characterized in that, The second beam splitter (4) is a flat beam splitter with a beam splitting ratio of 50:

50.

4. The optical path system of a NO2 imaging detector according to claim 1, characterized in that, The first filter (5) is a bandpass filter with a center wavelength of 436nm, a half-width of 10nm, a cutoff frequency of 426nm and 446nm, and a transmittance of more than 85% in the range of 433-439nm. The third beam splitter (6) is a flat beam splitter with a beam splitting ratio of 50:

50.

5. The optical path system of a NO2 imaging detector according to claim 1, characterized in that, The second filter (8) is a bandpass filter with a center wavelength of 600nm and a half-width at half-maximum of 10nm. The third gas cell unit (9) is a quartz glass cell with an internal vacuum. The second camera (10) is a monochrome CMOS camera.

6. The optical path system of a NO2 imaging detector according to claim 1, characterized in that, The first gas cell unit (11) is a quartz glass cell that contains NO2 gas with a concentration greater than 1×10⁻⁶. 18 molec / cm 2 The third camera (12) is a monochrome CMOS camera.

7. The optical path system of a NO2 imaging detector according to claim 1, characterized in that, The second gas pool unit (13) is a quartz glass pool with an internal vacuum, and the fourth camera (14) is a monochrome CMOS camera.

8. The optical path system of a NO2 imaging detector according to claim 1, characterized in that, The first camera (7) is a color CMOS camera.

9. The optical path system of a NO2 imaging detector according to claim 1, characterized in that, The positioning detection optical path (D) and the calibration measurement optical path (E) share the positioning calibration optical path (B) in front, the first sub-measurement optical path (F) and the second sub-measurement optical path (G) share the measurement optical path (C) in front, and the positioning calibration optical path (B) and the measurement optical path (C) share the foremost solar scattered light incident optical path (A).

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