A method for spectral calibration and correction of on-orbit grating spectrometer

Abstract

The present invention relates to a method for spectral calibration and correction of an on-orbit grating spectrometer, comprising the following steps: Step 1: Accurate measurement of reference light source characteristics and initial light field modeling; Step 2: In-depth simulation of the light scattering process in a diffuse transmission plate; Step 3: Comprehensive calculation of the process of light transmission to the entrance pupil of the spectrometer; Step 4: Development and implementation of a spectral offset correction strategy. The method for spectral calibration and correction of an on-orbit grating spectrometer of the present invention can complete high-precision spectral tasks and further improve the calibration accuracy. By utilizing the conditions of mercury lamps with different inclinations incident on the diffuse transmission plate of the spectrometer, and performing theoretical analysis and spectral calibration correction, such analysis can complete high-precision spectral calibration. 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 provide solid technical support for the application of spectral technology in many fields.

Description

Technical Field

[0001] The present 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] Currently, for on-orbit spectrometers with normal incidence detection signals entering the spectrometer channels, the calibration light source can only be tilted and incident at an angle, which reduces the accuracy of spectral calibration. Spectral calibration is the process of determining parameters such as the wavelength value and wavelength range corresponding to each spectrometer channel. Mercury lamps are commonly used for on-orbit spectral calibration. Mercury lamps offer advantages such as rich and distinct spectral lines, high brightness, and excellent wavelength accuracy, making them widely used for spectral calibration of on-orbit spectrometers. Spectral calibration is a key step in spectral measurement technology. However, the reference light source for spectral calibration can no longer be calibrated at normal incidence. Instead, the light source is tilted into the grating spectrometer, which reduces the accuracy of spectral calibration. This results in insufficient accuracy for existing spectral calibration, and calibration accuracy in the ultraviolet, visible, and infrared bands requires correction. In high-precision spectral calibration experiments, slight differences were observed between spectral calibration using a tilted diffuse reflector plate and spectral calibration using direct illumination. 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 diffuse transmission panels, the particles on the rough surface of frosted glass are not perfectly spherical. The calculated results can achieve a 70-80% correction for on-orbit spectral calibration. This method can only provide high-precision spectral calibration for spectrometers using diffuse transmission or diffuse reflection panels, and therefore has certain limitations. The closer the particles in the diffuse transmission panel are to micron size, the better the spectral calibration and the stronger the correction capability. Therefore, the correction effect is affected by the particle size of the diffuse transmission panel.

[0004] In summary, current high-precision spectral calibration and correction for spectrometers using diffuse transmission or reflection panels has certain limitations. Spectral calibration of an on-orbit spectrometer in the visible band revealed a 0.11nm offset at 546.07nm. This method can only correct 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 provides 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: Deep simulation of the light scattering process inside the diffuse transmission plate;

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

[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 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] Based on the measured light source parameters, an initial light field model of the reference light source is constructed and the light field parameters 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 of light in the diffuse transmission plate is as follows:

[0023] The diffuse transmission plate is divided into numerous tiny units, and the scattering, absorption, and reflection of light passing through the particle group in each unit are calculated in detail;

[0024] By gradually accumulating the effects of each unit, the distribution state of the light field after scattering 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 four 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] Perform Gaussian fitting on the added irradiance distribution to find the central wavelength, compare it with the standard wavelength of the corresponding calibration light source, and obtain the wavelength offset, thereby making a good correction for the spectral calibration.

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

[0031] The present invention's method for spectral calibration and correction of an on-orbit grating spectrometer can achieve high-precision spectral calibration and further improve calibration accuracy. By utilizing the different inclinations of the mercury lamp incident on the spectrometer's diffuse transmission plate, theoretical analysis, and spectral calibration correction, this analysis enables high-precision spectral calibration.

[0032] The method of the present invention for spectral calibration and correction of an on-orbit grating spectrometer 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 will be further described in detail below with reference to the accompanying drawings and specific embodiments.

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

[0035] Figure 2 Schematic diagram of the grating projected onto the diffuse transmission plate area through a certain point of the slit.

[0036] Figure 3 (a), (b), and (c) are schematic diagrams of the slit irradiance distribution when the light source is inclined at 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 figure is a flow chart diagram of the method for spectral calibration and correction of an on-orbit grating spectrometer according to the present invention. DETAILED DESCRIPTION

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

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

[0041] To accurately analyze the light scattering caused by particles in the diffuse transmission plate, the present method for spectral calibration and correction of an on-track grating spectrometer incorporates MIE scattering theory during the calculation process. This theory accurately describes the scattering phenomenon caused by the interaction of light with tiny particles, which is crucial for a deeper understanding of the propagation characteristics of light in the diffuse transmission plate and provides an important theoretical foundation for subsequent calculations.

[0042] Based on MIE scattering theory and the principles of spectral energy transfer, the present method for spectral calibration and correction of on-orbit grating spectrometers calculates the energy distribution of light arriving at the spectrometer entrance pupil after it is scattered by a diffuse transmission plate from a reference light source. This complex calculation fully considers the various energy conversion mechanisms involved in light transmission, including absorption, scattering, and reflection. Through rigorous mathematical models and precise parameter settings, the accuracy and reliability of the results are ensured.

[0043] Since the energy distribution of the entrance pupil and the energy distribution of 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 spectrum calibration and correction of the on-track 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 offset 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 present invention's method for spectral calibration and correction of an on-orbit grating spectrometer, with the precise analysis and calculation of exit pupil energy as its core, provides 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, it is possible to provide a practical solution to the problem of spectral offset caused by oblique incidence of light sources. This not only helps to break through the technical bottlenecks 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, providing 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, based on 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, accurate physical equations are used to calculate the irradiance distribution of the light source irradiating the surface of the diffuse transmission plate. 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 according to 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] A high-precision spectrometer and optical power meter are used to perform comprehensive and detailed measurements of the reference light source. Light intensity values ​​at different wavelengths are recorded in detail, creating an accurate spectral distribution curve. A professional polarimeter is used to determine the light source's polarization state, and a beam profiler is used to accurately measure key parameters such as the light source's divergence angle.

[0050] Based on the extensive light source parameters measured, an initial light field model of the reference light source is constructed in advanced optical design software. During the modeling process, parameters such as the light field's propagation direction, initial light intensity distribution, and polarization characteristics are precisely set, providing an accurate and reliable starting model for subsequent calculations of light transmission throughout the system.

[0051] Step 2: Deep simulation of the light scattering process inside the diffuse transmission plate;

[0052] A high-precision particle size analyzer is used to comprehensively analyze the tiny particles within the diffuse transmission plate, obtaining physical parameters such as particle size distribution, average particle size, and refractive index. Chemical analysis methods are also used to determine the material composition of the diffuse transmission plate, enabling more accurate calculations of the interaction between light and the plate.

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

[0054] Based on the calculated scattering parameters and combined with the geometric and physical properties of the diffuse transmission panel, such as its actual thickness, particle concentration, and spatial distribution, a detailed simulation of light propagation within the panel is performed. The panel is divided into numerous tiny cells, and the scattering, absorption, and reflection of light as it passes through the particle clusters within each cell are calculated in detail. By gradually accumulating the effects of each cell, the distribution of the light field after scattering by the diffuse transmission panel is accurately determined.

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

[0056] In order to calculate the distribution of the radiation flux at the entrance pupil slit of the spectrometer, the reversible propagation of light 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 point of the slit 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, a plurality of quadrilaterals with 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, by mapping the scattered radiance on the rear surface of the diffuse transmission plate to the infinitesimal points of the slit and then calculating the spot area of ​​each transmission point on the target surface, we can ultimately derive the precise energy distribution of the scattered light from the diffuse transmission plate to the spectrometer entrance pupil, i.e., the slit. This method allows us to perform detailed energy distribution calculations at the spectrometer entrance pupil, 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 at different heights can be calculated from the previous steps. The spectral bandwidth of the radiation at the exit slit is obtained by adding the irradiance of a row at the same slit height. The spectrum broadens as it passes through the spectrometer, and its waveform conforms to a 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 together; a Gaussian fit is performed on the added irradiance distribution to obtain 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 using a double grating spectrometer. The calibration light source (mercury lamp) is incident at different angles, and the exact spectral position offset can be obtained 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 transmission plate 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 transmission plate through a certain point of the slit. This diffusely projected area can reach the grating through a point of the slit. The irradiance at this point of the slit is recorded, and the slit is divided into M*N points. This method can be used to obtain the irradiance distribution of the slit M*N.

[0065] Figure 3 The calculation results of the simulation calculation part are as follows: when the light source is inclined at 45°, 55°, and 65°, the radiance distribution of the spectrometer entrance slit shows 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 greater the spectral drift. This proves that frosted glass cannot be regarded as simple Lambertian scattering and MIE scattering, but through the modified MIE scattering theory, the irregular spherical scatterer (ground glass) is modeled to discover and correct the size of the spectral drift to meet the requirements of on-track optical precision spectral calibration and ensure the accuracy of spectral data.

[0066] Figure 4The experimental verification part found that when the calibration light source is at an oblique incidence, the spectral signal will drift to a certain extent. Based on the Gaussian fit of the calibration light source, it is found that the results of normal and oblique incidence do have similar trends to the theoretical calculation results. Therefore, the experiment can confirm the correctness of the theory and provide strong experimental support for the method.

[0067] The present invention's method for spectral calibration and correction of an on-orbit grating spectrometer can achieve high-precision spectral calibration and further improve calibration accuracy. By utilizing the different inclinations of the mercury lamp incident on the spectrometer's diffuse transmission plate, theoretical analysis, and spectral calibration correction, this analysis enables high-precision spectral calibration.

[0068] The method of the present invention for spectral calibration and correction of an on-orbit grating spectrometer 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 clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present 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: Deep simulation of the light scattering process inside the diffuse transmission plate; Step 3: Comprehensive calculation of the process of light transmission to the spectrometer entrance pupil; Step 4: Spectral offset correction strategy formulation and implementation; Step 1 is as follows: Measure the reference light source, record the intensity 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; Based on the measured light source parameters, an initial light field model of the reference light source is constructed and the light field parameters are set; 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; 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. Finally, the precise energy distribution of the scattered light from the diffuse transmission plate to the entrance pupil of the spectrometer is derived. 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; Perform Gaussian fitting on the added irradiance distribution to find the central wavelength, compare it with the standard wavelength of the corresponding calibration light source, and obtain the wavelength offset, thereby making a good correction for the spectral calibration.

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

3. The method for spectral calibration and correction of an on-orbit grating spectrometer according to claim 1, characterized in that: In step 2, the specific process of simulating the propagation of light in the diffuse transmission plate is as follows: The diffuse transmission plate is divided into numerous tiny units, and the scattering, absorption, and reflection of light passing through the particle group in 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 obtained.

Images