Method for calibrating and correcting spectrum of on-orbit grating spectrometer

Abstract

The invention relates to a method for calibrating and correcting the spectrum of an on-orbit grating spectrometer. The method comprises the following steps: step 1, accurately measuring the characteristics of a reference light source and modeling an initial light field; 2, simulating the depth of the light scattering process in the diffuse transmission plate; 3, comprehensively calculating the process of transmitting the light to the entrance pupil of the spectrograph; and 4, making and implementing a spectrum offset correction strategy. According to the method for calibrating and correcting the spectrum of the on-orbit grating spectrometer, a high-precision spectrum task can be completed, and the calibration precision is further improved. By utilizing the condition that the mercury lamp obliquely enters the diffuse projection plate of the spectrograph, theoretical analysis and spectrum calibration correction are carried out, and high-precision spectrum calibration can be completed through the analysis. According to the method for calibrating and correcting the spectrum of the on-orbit grating spectrometer, the precision and accuracy of spectrum measurement can be improved through accurate calculation and analysis, and solid technical support is provided for application of the spectrum technology in many fields.

Description

Technical Field

[0001] The invention relates to the technical field of spectrum calibration, and in particular to a method for spectrum calibration and correction of an on-orbit grating spectrometer. Background Art

[0002] At present, for the detection signal of the on-orbit spectrometer to be incident normally into the spectrometer channel, the calibration light source can only be placed at an angle and incident obliquely into the spectrometer channel, which will reduce the accuracy of spectral calibration. Spectral calibration refers to the process of determining the wavelength value corresponding to each channel of the spectrometer and the wavelength range and other parameters. Mercury lamps are usually used for on-orbit spectral calibration. Mercury lamps have the advantages of rich and characteristic spectral lines, high brightness, good wavelength accuracy, etc., and are widely used in the spectral calibration of on-orbit spectrometers. Spectral calibration is a key link in spectral measurement technology. However, the reference light source for spectral calibration can no longer be calibrated at normal incidence, but the light source is tilted to be incident on the grating spectrometer, which will reduce the accuracy of spectral calibration, resulting in the existing spectral calibration accuracy is not high enough, and the calibration accuracy in the ultraviolet, visible and infrared bands needs to be corrected. In the high-precision spectral calibration experiment, there are slight differences in the calibration results obtained by the tilted diffuse reflection plate spectral calibration and the direct irradiation spectral calibration. Therefore, the reference light source incident on the first element of the grating spectrometer, the ground glass, should be modeled using MIE scattering simulation, and the spectral shift caused by the oblique incidence of the reference light source should be corrected.

[0003] When using MIE scattering to model and analyze the diffuse projection plate, the rough surface of the frosted glass is not a perfect spherical particle. When modeling and analyzing, the calculation results can achieve a correction effect of 70-80% on the on-orbit spectral calibration. This method can only perform high-precision spectral calibration correction for spectral instruments that pass through diffuse projection plates or diffuse reflection plates, and has certain limitations. The closer the particles of the diffuse projection plate are to the micron size, the better the spectral calibration correction effect and the stronger the correction ability, so the correction effect will be affected by the particle size of the diffuse projection plate.

[0004] In summary, the current high-precision spectral calibration correction for spectrometers using diffuse projection or diffuse reflection panels has certain limitations in accuracy. The on-orbit spectrometer calibrated the visible band and found that the offset of the spectrum at 546.07nm in the visible band was 0.11nm. This method can only calibrate the spectrum to within ±0.05nm. Summary of the invention

[0005] The present invention aims to solve the technical problems in the prior art and provide a method for spectral calibration and correction of an on-orbit grating spectrometer.

[0006] In order to solve the above technical problems, the technical solutions of the present invention are as follows:

[0007] A method for spectral calibration and correction of an on-orbit grating spectrometer comprises the following steps:

[0008] Step 1: Accurately measure the characteristics of the reference light source and model the initial light field;

[0009] Step 2: In-depth simulation of the light scattering process in the diffuse transmission plate;

[0010] Step 3: Comprehensive calculation of the process of light transmission to the entrance pupil of the spectrometer;

[0011] Step 4: Spectral offset correction strategy formulation and implementation.

[0012] In the above technical solution, step one is specifically as follows:

[0013] Measure the reference light source, record the intensity values ​​of light at different wavelengths, and draw the spectral distribution curve;

[0014] Determine the polarization state of the light source and measure the parameters of the light source;

[0015] According to the measured light source parameters, an initial light field model of the reference light source is constructed and the parameters of the light field are set.

[0016] In the above technical solution, in step 1, the parameters of the light field include: propagation direction, initial light intensity distribution and polarization characteristics.

[0017] In the above technical solution, step 2 is specifically as follows:

[0018] Analyze the tiny particles in the diffuse transmission plate to obtain the physical characteristic parameters of the tiny particles;

[0019] Determine the material composition of the diffuse transmission plate;

[0020] Scattering parameters calculated based on MIE scattering theory;

[0021] Combining the geometric and physical properties of the diffuse transmission plate, the propagation process of light in the diffuse transmission plate is simulated.

[0022] In the above technical solution, in step 2, the specific process of simulating the propagation process of light in the diffuse transmission plate is:

[0023] Divide the diffuse transmission plate into many tiny units, and calculate the scattering, absorption and reflection of light passing through each unit in detail.

[0024] By gradually accumulating the effects of each unit, the distribution state of the light field after being scattered by the diffuse transmission plate is obtained.

[0025] In the above technical solution, step three is specifically as follows:

[0026] The scattered radiance on the rear surface of the diffuse transmission plate is mapped to the infinitesimal point of the slit, and then the spot area of ​​each transmission point on the target surface is calculated, and finally the precise energy distribution of the scattered light from the diffuse transmission plate to the entrance pupil of the spectrometer is derived.

[0027] In the above technical solution, step 4 is specifically as follows:

[0028] According to the irradiance at each height and the spectral broadening of its spectrometer, N columns of gridded slits corresponding to ideal Gaussian beams with different central wavelength values ​​and spectral broadening are added;

[0029] A Gaussian fit is performed on the added irradiance distribution to find the central wavelength, which is compared with the standard wavelength of the corresponding calibration light source to obtain the wavelength offset, thereby making a good correction for the spectral calibration.

[0030] The present invention has the following beneficial effects:

[0031] The method for spectral calibration and correction of an on-track grating spectrometer of the present invention can complete high-precision spectral tasks and further improve calibration accuracy. By utilizing the situation of different mercury lamp incident on the diffuse projection plate of the spectrometer, and performing theoretical analysis and spectral calibration correction, such analysis can complete high-precision spectral calibration.

[0032] The method for spectral calibration and correction of an on-orbit grating spectrometer of the present invention can improve the precision and accuracy of spectral measurement through precise calculation and analysis, and provides solid technical support for the application of spectral technology in many fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0034] Figure 1 Schematic diagram of high-precision spectral calibration and correction equipment.

[0035] Figure 2 This is a schematic diagram of the grating being projected onto the diffuse projection plate area through a certain point of the slit.

[0036] Figure 3 (a), (b), and (c) are schematic diagrams of slit irradiance distribution when the light source is incident at angles of 45°, 55°, and 65°, respectively.

[0037] Figure 4 Schematic diagram of Gaussian fitting of spectral data at normal incidence and 60° inclined incidence.

[0038] Figure 5 The present invention is a schematic flow chart of a method for spectral calibration and correction of an on-orbit grating spectrometer. DETAILED DESCRIPTION

[0039] The inventive concept of the present invention is:

[0040] The method for spectral calibration correction of an on-orbit grating spectrometer of the present invention fully considers the influence of the oblique incident diffuse projection plate on the high-precision spectral calibration, and effectively corrects the spectral calibration data of the on-orbit spectrometer.

[0041] In the calculation process, in order to accurately analyze the scattering of light by particles in the diffuse transmission plate, the method of the present invention for the calibration and correction of the spectrum of the on-track grating spectrometer introduces the MIE scattering theory. This theory can accurately describe the scattering phenomenon generated when light interacts with tiny particles, which is crucial for a deep understanding of the propagation characteristics of light in the diffuse transmission plate and provides an important theoretical basis for subsequent calculations.

[0042] Based on the MIE scattering theory and the principle of spectral energy transmission, the present invention's method for spectral calibration and correction of an on-orbit grating spectrometer calculates the energy distribution of light from a reference light source to the entrance pupil of the spectrometer after being scattered by a diffuse transmission plate. In this complex calculation process, the various energy conversion mechanisms involved in the transmission of light, such as absorption, scattering, and reflection, are fully considered, and the accuracy and reliability of the calculation results are ensured through rigorous mathematical models and precise parameter settings.

[0043] Since the energy distribution of the entrance pupil and the exit pupil of the spectrometer show an approximately linear relationship, in order to study the energy distribution more efficiently, the method of the present invention for the calibration and correction of the spectrum of the on-orbit grating spectrometer focuses the main analysis direction on the exit pupil energy. In order to grasp the distribution details of the exit pupil energy in detail, a grid processing method is adopted. The exit pupil surface is divided into many tiny grid units, and for each grid unit, a specific algorithm is used to calculate the irradiance according to its unique spatial position. Through this precise, unit-by-unit calculation method, the irradiance distribution information of different positions of the exit pupil can be obtained, and then the internal mechanism of the spectral position deviation phenomenon caused by the oblique incidence of the reference light source on the diffuse transmission plate can be deeply analyzed, and its cause-effect relationship and change law can be clarified.

[0044] The method of the present invention for spectral calibration and correction of an on-orbit grating spectrometer is centered on the precise analysis and calculation of exit pupil energy, providing a strong theoretical basis and rich data support for improving the accuracy of spectral calibration technology. Through in-depth mining and systematic analysis of these data, a practical solution can be provided to solve the problem of spectral offset caused by oblique incidence of light sources. This not only helps to break through the technical bottleneck of traditional spectral measurement equipment in dealing with such problems, but also significantly improves the measurement accuracy and reliability of spectral measurement equipment in various application scenarios, and provides a more scientific, accurate and stable technical foundation for subsequent spectral analysis, spectral calibration and other operations, thereby promoting further development and innovation in the entire field of spectral measurement technology.

[0045] When performing spectral calibration and correction, it is first necessary to clarify and determine the spectral calibration structure. This calibration structure covers multiple important components, including a reference light source, a diffuse transmission plate, and a spectrometer. There is a complex and subtle positional relationship between them, and these positional relationships play a decisive role in the entire spectral calibration and correction process. Through in-depth modeling and analysis of the positional relationship between them, the present invention can construct an accurate physical model that can describe the propagation path and energy distribution of light in the system. Specifically, according to the optical principles and the law of conservation of energy, combined with the position of the light source, the position of the diffuse transmission plate, and the position of the spectrometer, the irradiance distribution of the light source irradiating the surface of the diffuse transmission plate is calculated using accurate physical equations. In this calculation process, multiple factors such as the light intensity, propagation distance, and angle of the light source need to be considered. At the same time, the diffuse transmission plate should be regarded as an element with complex optical properties, and its absorption, reflection, and scattering of light need to be included in the calculation range.

[0046] The method for spectral calibration and correction of an on-orbit grating spectrometer of the present invention is described in detail below with reference to the accompanying drawings.

[0047] like Figure 5 As shown, the method for spectral calibration and correction of an on-orbit grating spectrometer of the present invention comprises the following steps:

[0048] Step 1: Accurately measure the characteristics of the reference light source and model the initial light field;

[0049] With the help of high-precision spectrometers and optical power meters, the reference light source is comprehensively and carefully measured. The intensity values ​​of light at different wavelengths are recorded in detail, and accurate spectral distribution curves are drawn. At the same time, a professional polarization meter is used to measure the polarization state of the light source, and a beam analyzer is used to accurately measure key parameters such as the divergence angle of the light source.

[0050] Based on the measured rich light source parameters, the initial light field model of the reference light source is constructed in advanced optical design software. During the modeling process, the propagation direction of the light field, the initial light intensity distribution, and the polarization characteristics are accurately set, thereby providing an accurate and reliable starting model for the subsequent calculation of light transmission in the entire system.

[0051] Step 2: In-depth simulation of the light scattering process in the diffuse transmission plate;

[0052] A high-precision particle size analyzer is used to comprehensively analyze the tiny particles in the diffuse transmission plate to obtain its particle size distribution range, average particle size, refractive index and other physical property parameters. At the same time, chemical analysis methods are used to determine the material composition of the diffuse transmission plate in order to more accurately calculate the interaction between light and the diffuse transmission plate.

[0053] The above parameters are input into professional calculation software developed based on MIE scattering theory or self-written efficient calculation program. Based on the core formula of MIE scattering theory, the program accurately calculates scattering parameters such as scattering cross section, absorption cross section and scattering phase function for particles of different particle sizes and refractive indices in the diffuse transmission plate and incident light of different wavelengths.

[0054] Based on the calculated scattering parameters, combined with the actual thickness of the diffuse transmission plate, particle concentration, spatial distribution and other geometric and physical characteristics, the propagation process of light in the diffuse transmission plate is simulated in detail. The diffuse transmission plate is divided into many tiny units, and the scattering, absorption and reflection of light passing through each unit are calculated in detail. By gradually accumulating the effects of each unit, the distribution state of the light field after scattering by the diffuse transmission plate is accurately obtained.

[0055] Step 3: Comprehensive calculation of the process of light transmission to the entrance pupil of the spectrometer;

[0056] In order to calculate the distribution of the radiation flux at the entrance pupil slit of the spectrometer, the reversibility of light propagation is considered and the grating vertices A, B, C, and D are irradiated. Figure 2 A, B, C, and D are the four vertices of the grating, and A', B', C', and D' are quadrilateral areas obtained by projecting a slit point onto the frosted glass. By calculation, the entrance pupil radiance distribution of the light that can be incident on the grating surface at the frosted glass can be obtained.

[0057] In order to more accurately calculate the energy distribution at the entrance pupil of the spectrometer, the present invention regards the slit as a two-dimensional grid composed of multiple infinitesimal transmission points. The projection of each transmission point on the scattering surface will form a specific area. The grating system projects the scattering surface through the vertex. The detected wavelength is different and the rotation angle of the grating is different. Therefore, quadrilaterals with multiple different areas are formed on the scattering surface. The radiant brightness of the scattered light in the quadrilateral area transmitted to the slit point can be calculated. By performing a projection on each point on the entrance pupil grid, the radiant brightness matrix at the entrance pupil can be obtained. In theoretical calculations, the present invention infinitesimally calculates the radiant brightness of the rear surface of the diffuse transmission plate and the slit, and then calculates the radiation flux from each slit point corresponding to an area on the rear surface of the diffuse transmission plate to the slit point.

[0058] In summary, the scattered radiance on the rear surface of the diffuse transmission plate is mapped to the micro-element point of the slit, and then the spot area of ​​each transmission point on the target surface is calculated, and finally the accurate energy distribution of the scattered light from the diffuse transmission plate to the entrance pupil of the spectrometer, that is, the slit, is derived. This method allows us to perform detailed energy distribution calculations at the entrance pupil of the spectrometer, ensuring accurate modeling of the spectrometer response.

[0059] Step 4: Spectral offset correction strategy formulation and implementation;

[0060] Different heights on the slit correspond to different diffraction wavelengths. The irradiance corresponding to different heights can be obtained from the previous steps. The radiant flux distribution of the spectral bandwidth at the exit slit is obtained by adding the irradiance of a row at the same height of the slit. The spectrum line will be broadened when passing through the spectrometer, and its waveform conforms to the Gaussian distribution.

[0061] Because each height of the exit slit corresponds to a wavelength, according to the irradiance at each height and the spectral broadening of its spectrometer, the ideal Gaussian beams corresponding to different central wavelength values ​​and spectral broadening of the gridded slits are added; Gaussian fitting is performed on the added irradiance distribution to find the central wavelength, which is compared with the standard wavelength of the corresponding calibration light source to obtain the wavelength offset, thereby making a good correction for the spectral calibration.

[0062] The method of the present invention is used to correct the remote sensing measurement data of the Fengyun-3 solar irradiance spectrometer, and a spectral calibration correction experiment is carried out with a double grating spectrometer. The calibration light source (mercury lamp) is incident at different angles to obtain the exact spectral position offset to complete the task of high-precision spectral calibration.

[0063] like Figure 1 As shown, the calibration light source is continuously tilted at an angle, and the distance from the center of the diffuse projection panel remains unchanged. By changing the angle, the spectral data is recorded, and the offset of the spectral position is determined by Gaussian fitting.

[0064] like Figure 2 As shown, the grating is projected onto the diffuse projection plate through a certain point of the slit. This area of ​​diffuse projection can reach the grating through a point of the slit. The irradiance of this point of the slit is recorded, and the slit is divided into M*N points. This method is used to obtain the irradiance distribution of the slit M*N.

[0065] Figure 3 To simulate the calculation results of the calculation part, when the light source is inclined at 45°, 55°, and 65°, the radiance distribution of the spectrometer entrance slit can be explained. It can be explained that the radiance of the spectrometer entrance slit is uneven due to the inclined incidence of the calibration light source, resulting in spectral drift. The larger the inclination angle, the more uneven the slit radiance and the larger the spectral drift. This can confirm that the frosted glass cannot be regarded as a simple Lambertian scattering and MIE scattering, but through the modified MIE scattering theory, the irregular spherical scatterer (ground glass) is modeled, the size of the spectral drift is discovered and corrected, so as to meet the requirements of on-track optical precision spectral calibration and ensure the accuracy of the spectral data.

[0066] Figure 4This is the experimental verification part. The experiment found that when the calibration light source is obliquely incident, the spectral signal will drift to a certain extent. According to the Gaussian fitting of the calibration light source, it is found that the normal incidence and oblique incidence do have similar trends to the results of theoretical calculations. Therefore, the experiment can verify the correctness of the theory and provide good experimental support for this method.

[0067] The method for spectral calibration and correction of an on-track grating spectrometer of the present invention can complete high-precision spectral tasks and further improve calibration accuracy. By utilizing the situation of different mercury lamp incident on the diffuse projection plate of the spectrometer, and performing theoretical analysis and spectral calibration correction, such analysis can complete high-precision spectral calibration.

[0068] The method for spectral calibration and correction of an on-orbit grating spectrometer of the present invention can improve the precision and accuracy of spectral measurement through precise calculation and analysis, and provides solid technical support for the application of spectral technology in many fields.

[0069] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for spectral calibration and correction of an on-orbit grating spectrometer, characterized in that: The following steps are involved: Step 1: Accurately measure the characteristics of the reference light source and model the initial light field; Step 2: In-depth simulation of the light scattering process in the diffuse transmission plate; Step 3: Comprehensive calculation of the process of light transmission to the entrance pupil of the spectrometer; Step 4: Spectral offset correction strategy formulation and implementation.

2. The method for spectral calibration and correction of an on-orbit grating spectrometer according to claim 1, characterized in that: Step 1 is as follows: Measure the reference light source, record the intensity values ​​of light at different wavelengths, and draw the spectral distribution curve; Determine the polarization state of the light source and measure the parameters of the light source; According to the measured light source parameters, an initial light field model of the reference light source is constructed and the parameters of the light field are set.

3. The method for spectral calibration and correction of an on-orbit grating spectrometer according to claim 2, characterized in that: In step 1, the parameters of the light field include: propagation direction, initial light intensity distribution, and polarization characteristics.

4. The method for spectral calibration and correction of an on-orbit grating spectrometer according to claim 1, characterized in that: Step 2 is as follows: Analyze the tiny particles in the diffuse transmission plate to obtain the physical characteristic parameters of the tiny particles; Determine the material composition of the diffuse transmission plate; Scattering parameters calculated based on MIE scattering theory; Combining the geometric and physical properties of the diffuse transmission plate, the propagation process of light in the diffuse transmission plate is simulated.

5. The method for spectral calibration and correction of an on-orbit grating spectrometer according to claim 4, characterized in that: In step 2, the specific process of simulating the propagation of light in the diffuse transmission plate is as follows: Divide the diffuse transmission plate into many tiny units, and calculate the scattering, absorption and reflection of light passing through each unit in detail. By gradually accumulating the effects of each unit, the distribution state of the light field after being scattered by the diffuse transmission plate is obtained.

6. The method for spectral calibration and correction of an on-orbit grating spectrometer according to claim 1, characterized in that: Step three is as follows: The scattered radiance on the rear surface of the diffuse transmission plate is mapped to the infinitesimal point of the slit, and then the spot area of ​​each transmission point on the target surface is calculated, and finally the precise energy distribution of the scattered light from the diffuse transmission plate to the entrance pupil of the spectrometer is derived.

7. The method for spectral calibration and correction of an on-orbit grating spectrometer according to claim 1, characterized in that: Step 4 is as follows: According to the irradiance at each height and the spectral broadening of its spectrometer, N columns of gridded slits corresponding to ideal Gaussian beams with different central wavelength values ​​and spectral broadening are added; A Gaussian fit is performed on the added irradiance distribution to find the central wavelength, which is compared with the standard wavelength of the corresponding calibration light source to obtain the wavelength offset, thereby making a good correction for the spectral calibration.

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