Multi-Spectral Transmission Atmospheric Extinction Coefficient Measurement Device and Calibration Method

Abstract

The present invention discloses a multi-spectral transmissive atmospheric extinction coefficient measuring device and a calibration method, including: a light source emitting unit and a detection and receiving unit. The light source emitting unit provides a stable and uniform radiation output that is approximately parallel, and includes an active light source assembly and a dark target assembly; the active light source assembly includes an active light source, a focusing and projection optical assembly, and a chopper; the dark target assembly includes a dark box; the active light source assembly is placed in the dark box; the active light source is a frequently operating light source, and the dark box serves for calibration. The detection and receiving unit detects and receives the signals emitted by the light source unit, and includes a telescope, a beam splitting prism, an optical camera, and a photodiode; the optical camera is used for measuring the radiance of the dark target and the sky background; the photodiode is used for measuring the radiation of the active light source, so as to realize the measurement of the multi-spectral atmospheric extinction coefficient on a regular basis. When the weather is fine and the visibility is greater than 30 km, the entire device is calibrated with the extinction coefficient calculated by observing the dark target and the surrounding sky background with the optical camera.

Description

Technical Field

[0001] The present invention relates to the technical field of atmospheric environment remote sensing, in particular to a multi-spectral transmission type atmospheric extinction coefficient measurement device and a calibration method. Background Art

[0002] The atmospheric extinction coefficient is directly related to parameters such as visibility and atmospheric transmittance, and has important application value in the field of atmospheric environment remote sensing. The atmospheric extinction coefficient is the ratio of the light flux lost by a parallel light beam emitted by an incandescent light source with a color temperature of 2700K when propagating through the atmosphere per unit distance. The atmospheric extinction coefficient is the sum of the scattering coefficient and absorption coefficient of atmospheric molecules and particles, including the scattering of air molecules, the absorption of ozone and water vapor molecules, and the absorption of uniformly mixed gas molecules such as oxygen and carbon dioxide. In the visible and near-infrared bands, the scattering of aerosol particles is the main factor of atmospheric extinction.

[0003] The Lambert-Beer law is the basic principle for measuring the atmospheric extinction coefficient. The proportion of light absorbed by a transparent medium is independent of the intensity of the incident light. Each equal-thickness layer of the medium absorbs the same proportion of light along the optical path. The radiation intensity transmitted through a homogeneous extinction medium decreases according to a simple exponential function. This law is the basic law of light absorption and is the theoretical basis for measuring the extinction coefficient by transmission. The extinction coefficient can be directly obtained. Therefore, theoretically, this measurement method has high accuracy. However, the transmission measurement has disadvantages such as a relatively high light source power, a large dynamic range of the detection system, and great difficulty in system calibration.

[0004] Indirect methods for measuring the extinction coefficient include forward scattering measurement and backward scattering measurement. Due to some assumptions, limited sampling space, etc., the accuracy of indirect measurement is not high. Therefore, this type of indirect measurement method has only been widely applied in scenarios where the accuracy requirement is not high.

[0005] According to the Lambert-Beer law, measuring the atmospheric extinction coefficient requires measuring the light intensity at the light source emission end and the light intensity at the detection and reception end, and the ratio of the two needs to be accurately obtained. Under the harsh field environment, the performance of the light source emission end and the detection and reception end will change over time. Therefore, regular system calibration is required. The conventional calibration method is to assume that the path extinction coefficients at the emission end and the reception end are zero under the condition of very high visibility (greater than 50 km), or to achieve system calibration by comparing and measuring with a mobile station (light source emission end / detection and reception end). However, these methods all have the disadvantages of low calibration accuracy or difficulty in implementation. Summary of the Invention

[0006] In order to overcome the defects in the above-mentioned prior art, one of the purposes of the present invention is to provide a multi-spectral transmission type atmospheric extinction coefficient measurement device with high calibration accuracy and easy implementation.

[0007] To achieve the above object, the present invention adopts the following technical solutions, including:

[0008] A multi-spectrum transmission type atmospheric extinction coefficient measuring device, including: a light source emission unit and a detection and reception unit. The light source emission unit is used to provide radiation output; the detection and reception unit is used to detect and receive the radiation signal of the light source emission unit. The light source emission unit includes: an active light source component and a dark target component.

[0009] The active light source component includes: an active light source, that is, an active target, and a focusing and projection optical component. The focusing and projection optical component is used to project the output beam of the active light source to infinity.

[0010] The dark target component includes: a dark box with a hollow cavity structure, that is, a dark target.

[0011] The active light source component is placed in the cavity of the dark box. An opening is provided on the dark box, and the opening is used for the beam output of the active light source component.

[0012] The detection and reception unit includes: a telescope, a beam splitting prism, an optical camera, and a photoelectric signal detection component, which are arranged in sequence along the light propagation direction. The telescope is used to receive the output beam of the light source emission unit and converge it to the beam splitting prism. The beam splitting prism is used to split the beam converged by the telescope and respectively inject it into the optical camera and the photoelectric signal detection component.

[0013] Preferably, the active light source adopts a halogen lamp. The focusing and projection optical component includes: a light source illumination lens, a condenser lens, and a projection lens, which are arranged in sequence along the light propagation direction. The condenser lens is located at the focal plane of the projection lens. Among them, the condenser lens magnifies and images the active light source on the projection lens, and the projection lens images the image formed by the condenser lens at infinity.

[0014] Preferably, the active light source component further includes a chopper, which is used to modulate the frequency of the active light source and perform chopping modulation on the active light source at a constant frequency within the range of 70HZ to 100HZ.

[0015] Preferably, the inner wall of the dark box is coated with an extinction coating, and the reflectivity of the extinction coating is less than 3%.

[0016] Preferably, the field of view area of the optical camera for the light source emission unit is larger than the opening size of the dark box.

[0017] Preferably, the photoelectric signal detection component uses the photovoltaic mode of a photodiode without bias voltage for photoelectric signal detection and uses lock-in amplification technology for digital signal processing.

[0018] The second object of the present invention is to provide a calibration method for a multi-spectrum transmissive atmospheric extinction coefficient measuring device, including the following steps:

[0019] S1. On a fine day, first calibrate the measuring device using the dark target method. Calculate the atmospheric extinction coefficient based on the count values of the dark target and the surrounding sky background observed by the optical camera, and obtain the atmospheric extinction coefficient α measured during calibration: 0 as:

[0020]

[0021] where r is the baseline distance, and DN 0,dark is the count value of the dark target observed by the optical camera, and DN 0,sky is the count value of the sky background observed by the optical camera;

[0022] S2. Use the atmospheric extinction coefficient α measured during calibration 0 to calibrate the measuring device, and obtain the atmospheric extinction coefficient α measured when the measuring device is working properly as:

[0023]

[0024] where DN is the count value of the active target observed by the optoelectronic signal detection component, and DN drak is the count value of the dark target observed by the optoelectronic signal detection component; DN 0 is the count value of the active target observed by the optical camera, and DN 0,drak is the count value of the dark target observed by the optical camera.

[0025] Preferably, before calibrating the measuring device in step S1, first perform relative radiometric calibration on the optical camera.

[0026] Preferably, use gray scale targets with reflectivities of more than two different values and uniformity better than 98% at the front end of the entrance pupil of the optical camera, i.e., the detection and receiving end, to perform relative radiometric calibration on the optical camera.

[0027] Preferably, the visibility on a fine day is greater than 30 km.

[0028] The advantages of the present invention are as follows:

[0029] (1) The active light source component of the atmospheric extinction coefficient measuring device of the present invention is built in a dark box, which not only improves the adaptability to the outdoor environment, but also can conveniently achieve high-precision calibration according to the observation values of the optical camera on a fine day.

[0030] (2) The active light source of the atmospheric extinction coefficient measuring device of the present invention adopts Köhler illumination optical design, which improves the light source uniformity and energy utilization rate. Multiple bands are measured alternately to obtain the extinction coefficients at different wavelengths, providing important parameters for the inversion of atmospheric aerosol types.

[0031] (3) The active light source of the atmospheric extinction coefficient measuring device of the present invention adopts chopping technology, and the detection and receiving end adopts lock-in amplification technology, effectively eliminating the measurement interference introduced by atmospheric turbulence and the like. Description of the Drawings

[0032] Figure 1 It is a schematic diagram of the composition principle of a multi-spectral transmission extinction coefficient measuring device.

[0033] Figure 2 It is a schematic diagram of the active light source assembly.

[0034] Figure 3 It is a schematic diagram of the focusing and projection optical assembly.

[0035] Figure 4 It is a schematic diagram of the dark target assembly.

[0036] Figure 5 It is a schematic diagram of the detection and receiving unit.

[0037] The reference numerals are as follows:

[0038] 1 - Light source emission unit, 2 - Detection and receiving unit, 11 - Active light source, 12 - Power supply,

[0039] 131 - Light source illumination lens, condenser lens, 133 - Projection lens, 14 - Stability monitoring radiometer,

[0040] 15 - Chopper, 16 - Dark box, 161 - Open target, 162 - Extinction diaphragm, 17 - Control module,

[0041] 171 - Filter wheel, 172 - Photodiode, 21 - Telescope, 22 - Beam splitter prism,

[0042] 23 - And optical camera, 24 - Photoelectric signal detection component. Detailed Embodiment

[0043] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0044] By Figure 1As shown in the figure, a multi-spectral transmission type atmospheric extinction coefficient measuring device includes: a light source emitting unit 1 and a detection and receiving unit 2.

[0045] The light source emitting unit 1 is used to provide a stable and uniform radiation output that is approximately parallel.

[0046] The light source emitting unit 1 includes: an active light source assembly, a dark target assembly, a support and protection assembly, and an attitude adjustment mechanism.

[0047] Consisting of Figure 1 and Figure 2 As shown in the figure, the active light source assembly includes: an active light source 11, i.e., an active target, a power supply 12, a focusing and projection optical assembly, a stability monitoring radiometer 14, and a chopper 15.

[0048] The active light source 11 uses a quartz halogen lamp, and the active light source 11 is a frequently operating light source.

[0049] The power supply 12 uses a highly stable DC power supply to supply power to the active light source 11.

[0050] The focusing and projection optical assembly is used to project the light beam emitted by the active light source 11 to infinity, adopting the optical design of Köhler illumination to improve the uniformity and energy utilization efficiency of the light beam emitted by the active light source 11.

[0051] The focusing and projection optical assembly includes: a light source illumination lens 131, a condenser lens 132, and a projection lens 133 arranged in sequence along the light propagation direction. Consisting of Figure 3 As shown in the figure, the condenser lens 132 magnifies and images the active light source 11 on the projection lens 133, and the projection lens 133 images the image of the condenser lens 132 at infinity. Among them, the distance between the light source illumination lens 131 and the condenser lens 132 is l1, the effective aperture of the condenser lens 132 is D1, the focal length of the projection lens 133 is f2, the condenser lens 132 is located at the focal plane of the projection lens 133, that is, the distance between the condenser lens 132 and the projection lens 133 is f2, and the effective aperture of the projection lens 133 is D2.

[0052] A folding mirror 18 and an eyepiece 181 corresponding to the folding mirror 18 are also provided between the condenser lens 132 and the projection lens 133.

[0053] The stability monitoring radiometer 14 is used to monitor the stability of the active light source 11.

[0054] The chopper 15 is used to modulate the frequency of the active light source 11, and the active light source 11 is chopped and modulated at a constant frequency within the range of 70HZ to 100HZ.

[0055] Consisting of Figure 2As shown, the active light source assembly further includes: a control module 17, a filter wheel 171 and a photodiode 172 disposed at the output end of the active light source 11; the control module 17 includes: a photoelectric signal detection card, a temperature acquisition card, a motor driver, a filter wheel driver, a microcomputer board, and a wireless communication terminal module.

[0056] As Figure 4 As shown, the dark target assembly includes: a dark box 16 with a hollow cavity structure, i.e., the dark target;

[0057] The active light source assembly is placed in the cavity of the dark box 16. The dark box 16 is provided with an opening 161, and the opening 161 is used for the beam output of the active light source assembly; the opening 161 faces north.

[0058] The inner wall of the dark box 16 is coated with an extinction coating, and the reflectivity of the extinction coating is less than 3%.

[0059] The dark box 16 is further provided with an extinction diaphragm 162 for eliminating stray light.

[0060] The dark target assembly further includes a blowing device, etc., and the blowing device is used to remove dust from the dark target assembly.

[0061] The dark target assembly is used to protect the active light source assembly and to calibrate the entire atmospheric extinction coefficient measuring device.

[0062] The support and protection assembly is an external facility of the light source emitting unit 1 and is used to support and protect the light source emitting unit 1.

[0063] The attitude adjustment mechanism is used to adjust the attitude of the active light source assembly, thereby adjusting the beam output direction of the active light source assembly.

[0064] The detection and reception unit 2 is used to detect and receive the radiation signal of the light source emitting unit 1,

[0065] As Figure 5 As shown, the detection and reception unit 2 includes: a telescope 21, a beam splitter prism 22, an optical camera 23, a photoelectric signal detection assembly 24, a pinhole diaphragm, etc. arranged in sequence along the light propagation direction.

[0066] The telescope 21 is used to receive and converge the output beam of the light source emitting unit 1.

[0067] The beam splitter prism 22 splits the output beam of the light source emitting unit 1 converged by the telescope 21 and respectively injects it into the optical camera 23 and the photoelectric signal detection assembly 24.

[0068] The field of view area of the optical camera 23 is larger than the opening size of the dark box 16; the optical camera 23 is used for measuring the radiance of dark targets, the surrounding sky background, and active targets, i.e., the active light source 11.

[0069] The optical camera 23 is also used to video monitor the light source emitting unit 1 to assist the attitude adjustment mechanism in adjustment.

[0070] The optoelectronic signal detection component 24 uses Si photodiodes for optoelectronic signal detection. Through the radiation measurement of active targets by Si photodiodes, the measurement of the multi-spectral atmospheric extinction coefficient is realized regularly.

[0071] The optoelectronic signal detection component 24 adopts the unbiased photovoltaic mode of Si photodiodes, with a dynamic range of more than 10 5 orders of magnitude. The response non-linearity calibration adopts the superposition method, and the digital signal processing adopts the lock-in amplification technology based on the cross-correlation theory. The reference signal with the same frequency and fixed phase relationship as the weak optical signal to be measured is used as the benchmark, and a series of multiplication operations and filtering processes are carried out to extract the useful signal.

[0072] In the present invention, a multi-spectral transmissive atmospheric extinction coefficient measurement device further includes: a control and data acquisition terminal unit, etc. The communication and data transmission between each unit adopt 4G / 5G wireless networks.

[0073] Since the atmospheric extinction coefficient measurement device may decay after being used in the field for a period of time, it needs to be calibrated regularly.

[0074] For the measurement device of the present invention, when the weather is fine, that is, when the visibility is greater than 30 km, the radiance of the dark target and the surrounding sky background observed by the optical camera is used, and the atmospheric extinction coefficient is calculated according to the Koschmieder law, that is, the atmospheric extinction coefficient is calculated by the target method, so as to calibrate the entire measurement device.

[0075] Since the calculation of the above atmospheric extinction coefficient is only related to the relative radiometric calibration of the optical camera, etc., before calibration, the optical camera is relatively radiometrically calibrated. Two or more gray-scale targets with different reflectivities and uniformity better than 98% are configured at the front end of the entrance pupil of the optical camera at the detection and receiving end. The relative radiometric calibration can be achieved by observing the gray-scale targets with different reflectivities and uniformity better than 98% configured at the detection end.

[0076] The calibration method is specifically as follows:

[0077] S1. When the weather is fine and the visibility is greater than 30 m, first calibrate the measuring device using the dark target method. Calculate the atmospheric extinction coefficient based on the count values of the dark target and the surrounding sky background observed by the optical camera 23, and obtain the atmospheric extinction coefficient α measured during calibration. 0 , specifically as follows:

[0078] The radiance L at the active target, which is at a distance r from the optical camera, r can be expressed as:

[0079] L r = L 0 * T r + L r,path (1)

[0080] where L 0 is the atmospheric path radiance near the optical camera, L 0 = 0, T r is the transmittance of the path, and L r,path is the atmospheric path radiance of the path.

[0081] Near the entrance pupil of the telescope, the contrast C of the dark target 0 is:

[0082]

[0083] where L 0,b is the radiance of the dark target measured by the optical camera near the telescope.

[0084] From formulas (1) and (2), it can be seen that at the active target, which is at a distance r from the optical camera, the contrast of the dark target is:

[0085]

[0086] where L r,b is the radiance of the dark target at the measurement baseline distance r, L 0,b is the radiance of the dark target near the measurement optical camera, L r,b = L 0,b * T r + L r,path ;

[0087] Since Therefore it can be obtained that:

[0088]

[0089] α 0 is the atmospheric extinction coefficient measured using the dark target method, that is, the atmospheric extinction coefficient measured during calibration; DN 0,dark is the count value of the dark target observed by the optical camera 23, DN0,sky It is the count value for the optical camera 23 to observe the sky background; r is the baseline distance, that is, the distance between the light source emission end and the detection and reception end;

[0090] S2. Using the atmospheric extinction coefficient α measured during calibration 0 Calibrate the measuring device. At this time, use the active light source method to measure the atmospheric extinction coefficient, and obtain the atmospheric extinction coefficient α measured when the measuring device is working properly, which is specifically as follows:

[0091] Assume that within a short period of time, the atmospheric extinction coefficient has not changed, then:

[0092]

[0093] Among them, I source is the light intensity of the active light source; S projection , S receiver are the areas of the projection lens and the telescope respectively; r is the baseline distance, that is, the distance between the light source emission end and the detection and reception end; DN 0 is the count value for the optical camera to observe the active target, and DN 0,drak is the count value for the optical camera to observe the dark target;

[0094] When observing with a Si photodiode,

[0095]

[0096] Among them, DN is the count value for the Si photodiode to observe the active target, and DN drak is the count value for the Si photodiode to observe the dark target;

[0097] According to formulas (5) and (6), the atmospheric extinction coefficient α measured when the measuring device is working properly can be obtained as:

[0098]

[0099] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. Multi - spectral transmission type atmospheric extinction coefficient measuring device, Comprising: A light source emission unit (1) and a detection and reception unit (2), wherein the light source emission unit (1) is used to provide radiation output; The detection and reception unit (2) is used to detect and receive the radiation signal of the light source emission unit (1); characterized in that, The light source emission unit (1) includes: an active light source assembly and a dark target assembly; The active light source assembly includes: an active light source (11) which is the active target, and a focusing and projection optical assembly; the focusing and projection optical assembly is used to project the outgoing light beam of the active light source (11) to infinity; The dark target assembly includes: a dark box (16) with a hollow cavity structure which is the dark target; The active light source assembly is placed in the cavity of the dark box (16); an opening (161) is provided on the dark box (16), and the opening (161) is used for the light beam output of the active light source assembly; The detection and reception unit (2) includes: a telescope (21), a beam - splitting prism (22), an optical camera (23), and a photoelectric signal detection assembly (24) arranged in sequence along the light propagation direction; the telescope (21) is used to receive and converge the output light beam of the light source emission unit (1) to the beam - splitting prism (22), and the beam - splitting prism (22) is used to split the light beam converged by the telescope (21) and respectively inject it into the optical camera (23) and the photoelectric signal detection assembly (24).

2. The multi - spectral transmission type atmospheric extinction coefficient measuring device according to claim 1, Characterized in that, The active light source (11) uses a halogen lamp; the focusing and projection optical assembly includes: a light source illumination lens (131), a condenser lens (132), and a projection lens (133) arranged in sequence along the light propagation direction; the condenser lens (132) is located at the focal plane of the projection lens (133); wherein, the condenser lens (132) magnifies and images the active light source (11) on the projection lens (133), and the projection lens (133) images the image formed by the condenser lens (132) at infinity.

3. The multi - spectral transmission type atmospheric extinction coefficient measuring device according to claim 1, Characterized in that, The active light source assembly further includes a chopper (15) for modulating the frequency of the active light source (11), and chopping - modulating the active light source (11) at a constant frequency within the range of 70HZ - 100HZ.

4. The multi - spectral transmission type atmospheric extinction coefficient measuring device according to claim 1, Characterized in that, The inner wall of the dark box (16) is coated with an extinction coating, and the reflectivity of the extinction coating is less than 3%.

5. The multi - spectral transmission type atmospheric extinction coefficient measuring device according to claim 1, Characterized in that, The field - of - view area of the optical camera (23) with respect to the light source emission unit (1) is larger than the opening size of the dark box (16).

6. The multi - spectral transmission type atmospheric extinction coefficient measuring device according to claim 1, Characterized in that, The photoelectric signal detection assembly (24) detects photoelectric signals in the photovoltaic mode of a photodiode without bias voltage, and uses lock - in amplification technology for digital signal processing.

7. A calibration method for a multi-spectral transmissive atmospheric extinction coefficient measurement device according to any one of claims 1 to 6, characterized in that, it includes the following steps: S1. When the weather is fine, first calibrate the measuring device using the dark target method. Calculate the atmospheric extinction coefficient based on the count values of the dark target and the surrounding sky background observed by the optical camera (23), and obtain the atmospheric extinction coefficient α measured during calibration. 0 It is: where r is the baseline distance, and DN 0,dark is the count value of the optical camera (23) observing the dark target, and DN 0,sky is the count value of the optical camera (23) observing the sky background; S2, using the atmospheric extinction coefficient α measured during calibration 0 Calibrate the measuring device to obtain the atmospheric extinction coefficient α measured when the measuring device is operating normally as follows: Among them, DN is the count value of the optoelectronic signal detection component (24) observing the active target, and DN drak is the count value of the optoelectronic signal detection component (24) observing the dark target; DN 0 is the count value of the optical camera (23) observing the active target, and DN 0,drak is the count value of the optical camera (23) observing the dark target.

8. The calibration method for a multi-spectral transmissive atmospheric extinction coefficient measurement device according to claim 7, characterized in that, before performing calibration on the measurement device in step S1, relative radiometric calibration is first performed on the optical camera.

9. The calibration method for a multi-spectral transmissive atmospheric extinction coefficient measurement device according to claim 8, characterized in that, at the front end of the entrance pupil of the detection and receiving end, i.e., the optical camera (23), gray scale targets with reflectivities of more than two different values and uniformities better than 98% are used to perform relative radiometric calibration on the optical camera.

10. A calibration method for a multi-spectral transmissive atmospheric extinction coefficient measurement device according to claim 7, characterized in that, the visibility on a fine day is greater than 30 km.

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