Fraunhofer spectral line benchmark-based generation and calibration method and system, and medium
By measuring the solar direct radiation spectrum in a ground-based spectrometer, selecting the non-absorption band, and extracting the Fraunhofer line, the problems of calibration accuracy and stability of ground-based spectrometers were solved, and high-precision spectral calibration was achieved.
Patent Information
- Application Number
- CN202511699161.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-19
- Publication Date
- 2026-02-17
AI Technical Summary
Ground-based spectrometers cannot directly acquire pure AMO solar spectra. The traditional Langley method suffers from poor calibration accuracy and stability due to atmospheric absorption gases, and cannot effectively utilize Fraunhofer lines for high-precision calibration.
The solar direct radiation spectrum at different solar zenith angles was measured using a ground-based spectrometer. Atmospheric mass was calculated, and non-absorption bands unaffected by atmospheric interference were selected to extract the Fraunhofer line for spectral calibration.
It achieves high-precision spectral calibration of ground-based spectrometers, avoids standard lamp attenuation and atmospheric effects, has good long-term stability, and can be directly traced back to the AM0 standard.
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Figure CN121540282A_ABST
Abstract
Description
Technical Field
[0001] This disclosure relates to the field of ground-based detectors, and in particular to a method, system, and medium for generating and calibrating based on the Fraunhofer spectral reference. Background Technology
[0002] The solar spectrum is the primary source of energy for the Earth system, and accurately knowing the solar spectrum outside the atmosphere (AM0) (i.e., the Fraunhofer line) is crucial for the on-orbit absolute radiometric calibration of satellite remote sensors. The Langley method (also known as the aerosol spectral extinction method) is a classic ground-based remote sensing method. Its basic principle is that, under the assumption of a homogeneous and stable atmosphere, the intensity of direct solar radiation at a specific wavelength decays exponentially with the optical quality of the atmosphere it passes through. By selecting a clear, cloudless environment, measuring the radiation intensity at different atmospheric masses (i.e., different solar zenith angles) throughout the day, and then logarithmically and linearly extrapolating to the case where the atmospheric mass is zero, the solar irradiance at the top of the atmosphere at that wavelength can be obtained.
[0003] However, the traditional Langley method has a significant drawback: the solar spectrum contains numerous Fraunhofer lines formed by the absorption of elements in the solar atmosphere, while gases such as water vapor, oxygen, and carbon dioxide in the Earth's atmosphere also exhibit strong absorption in specific wavelengths. When applying the Langley method to these absorption bands, the spatiotemporal variations in the content of absorbing gases (especially water vapor) disrupt the assumption of atmospheric "homogeneity and stability," causing data points on logarithmic coordinates to deviate from straight lines and introducing substantial extrapolation errors. This makes directly applying the Langley method to regions that visually resemble "absorption lines" like Fraunhofer lines unreliable.
[0004] Furthermore, it is worth noting that the technique of using Fraunhofer lines for spectral calibration is already very mature on spaceborne remote sensors. Its fundamental advantage lies in the fact that spaceborne spectrometers are located outside the atmosphere and can directly acquire stable and clear top-of-atmosphere (AM0) solar spectra. Fraunhofer lines, as inherent spectral fingerprints, can be directly used as the absolute reference standard for calibration.
[0005] The situation is quite different for ground-based spectrometers (which are spectral analysis devices installed on the ground or surface facilities, primarily used to measure the reflection, absorption, or scattering spectral characteristics of ground objects, providing ground-based measured data support for remote sensing monitoring, environmental assessment, etc., also known as ground-based spectroscopic detectors). Ground-based spectrometers always observe through a thick and variable atmosphere, making it impossible to directly obtain pure AMO solar spectra. The absorption and scattering effects of the atmosphere (especially variable gases such as water vapor and ozone) severely distort the true shape and depth of the Fraunhofer line, making it impossible for ground-based spectrometers to perform high-precision calibration directly using the Fraunhofer line like spaceborne spectrometers. Currently, the spectral calibration of ground-based spectrometers usually relies on matching laboratory standard lamps or downlink solar spectra with standard spectral libraries. The former suffers from standard lamp attenuation and transmission errors, while the latter is greatly affected by the atmospheric conditions at the time and place, limiting its accuracy and long-term stability.
[0006] Therefore, a long-standing technical challenge in this field lies in how to establish a high-precision spectral calibration method for ground-based spectrometers that can "strip" away atmospheric influences and directly trace back to the AMO reference, thus allowing ground-based spectrometers to enjoy the advantages of calibration using stable Fraunhofer lines, similar to those of spaceborne spectrometers. The traditional Langley method, due to the aforementioned shortcomings, is inadequate for this task. Therefore, there is an urgent need in this field for a calibration method and system that can distinguish and utilize "safe" regions (regions unaffected by the atmosphere) in the spectrum, thereby improving the accuracy of AMO spectral extrapolation in the Fraunhofer line region. Summary of the Invention
[0007] Therefore, it is necessary to provide a method, system, and medium for generating and calibrating ground-based spectrometers based on Fraunhofer spectral lines, which addresses the problem of poor accuracy and long-term stability caused by atmospheric conditions in the calibration methods of ground-based spectrometers.
[0008] To solve the above problems, the present disclosure adopts the following technical solution: Firstly, this disclosure provides a method for generating and calibrating a Fraunhofer spectral reference, including: Step 1: Measure the solar direct radiation spectrum at different solar zenith angles using a ground-based spectrometer, and calculate the atmospheric mass at each measurement time for each solar direct radiation spectrum. Step 2: Calculate the solar spectral irradiance at the top of Earth's atmosphere; Step 3: Select the non-absorption band that is not affected by atmospheric interference based on atmospheric transmittance; Step 4: Locate the Fraunhofer line in the non-absorption band and perform spectral calibration on the ground-based spectrometer.
[0009] In a preferred embodiment, the measurement of the solar direct radiation spectrum at different solar zenith angles using a ground-based spectrometer specifically involves measuring the solar direct radiation spectrum at different solar zenith angles using a ground-based spectrometer equipped with an automatic solar tracker under clear weather and clean atmospheric conditions.
[0010] In a preferred embodiment, according to the formula or formula Calculate the solar spectral irradiance at the top of Earth's atmosphere; where, This represents the amount of solar irradiance reaching the Earth's surface after passing through the entire atmosphere. Indicates wavelength. Indicates the solar spectral irradiance at the top of Earth's atmosphere. Indicates the atmospheric optical thickness in the zenith direction. Indicates air quality, It represents the solar zenith angle.
[0011] In a preferred embodiment, step 3 specifically involves: calculating the first derivative of transmittance abs(dT), the local standard deviation of the second derivative abs(ddT), and the local standard deviation T_std. The bands corresponding to transmittance that simultaneously satisfy the following conditions are defined as the non-absorption bands unaffected by atmospheric interference: abs(dT) is less than the first derivative threshold, abs(ddT) is less than the second derivative threshold, and T_std is less than the local standard deviation threshold.
[0012] In a preferred embodiment, the method further includes obtaining the theoretically measured solar spectral irradiance from a ground-based spectrometer. The steps; specifically step 4 is: for Fraunhofer lines were extracted from the solar spectral irradiance at the top of the Earth's atmosphere and the extracted Fraunhofer lines, and the ground-based spectrometer was calibrated based on the extracted Fraunhofer lines.
[0013] In a preferred embodiment, a control module controls a ground-based spectrometer to measure the solar direct radiation spectrum at different solar zenith angles. A first calculation module calculates the atmospheric mass at each measurement time in each solar direct radiation spectrum. A second calculation module calculates the solar spectral irradiance at the top of the Earth's atmosphere. A selection module selects non-absorption bands that are not affected by atmospheric interference based on atmospheric transmittance. A search module searches for Fraunhofer lines within the non-absorption bands.
[0014] Secondly, this disclosure provides a system for generating and calibrating a Fraunhofer spectral line reference, comprising: The measurement unit is used to measure the solar direct radiation spectrum at different solar zenith angles using a ground-based spectrometer. The first calculation unit is used to calculate the atmospheric mass at each spectral measurement moment in each solar direct radiation spectrum; The second calculation unit is used to calculate the solar spectral irradiance at the top of the Earth's atmosphere; The selection unit is used to select the non-absorption band that is not affected by atmospheric interference based on atmospheric transmittance. The search unit is used to locate Fraunhofer lines in the non-absorption band. The calibration unit is used to perform spectral calibration on ground-based spectrometers.
[0015] In a preferred embodiment, the second calculation unit is specifically used to calculate according to the formula or formula Calculate the solar spectral irradiance at the top of Earth's atmosphere; where, This represents the amount of solar irradiance reaching the Earth's surface after passing through the entire atmosphere. Indicates wavelength. Indicates the solar spectral irradiance at the top of Earth's atmosphere. Indicates the atmospheric optical thickness in the zenith direction. Indicates air quality, It represents the solar zenith angle.
[0016] In a preferred embodiment, the selection unit is specifically used to calculate the first derivative of transmittance abs(dT), the local standard deviation of the second derivative abs(ddT), and the local standard deviation T_std, and to select the band corresponding to the transmittance that simultaneously satisfies the following conditions: abs(dT) is less than the first derivative threshold, abs(ddT) is less than the second derivative threshold, and T_std is less than the local standard deviation threshold as the non-absorption band that is not affected by atmospheric interference.
[0017] Thirdly, this disclosure provides a computer-readable storage medium including instructions that, when executed on a computer, cause the computer to perform a method for generating and calibrating a Fraunhofer spectral reference as described in the first aspect.
[0018] The aforementioned method, system, and medium for generating and calibrating the Fraunhofer spectral line reference are a method and system for establishing a Fraunhofer spectral line reference for ground-based spectrometers. This disclosure is based on ground-based spectrometers measuring the direct solar radiation spectrum at different solar zenith angles, calculating the atmospheric mass at each measurement time in each direct solar radiation spectrum; calculating the solar spectral irradiance at the top of the Earth's atmosphere; selecting non-absorption bands unaffected by atmospheric interference based on atmospheric transmittance; and then extracting the Fraunhofer line to achieve spectral calibration of the ground-based spectrometer. This disclosure does not require laboratory standard lamps, avoiding the problems of standard lamp attenuation and transmission errors. The calibration of this disclosure can distinguish and utilize regions in the spectrum unaffected by the atmosphere, exhibiting good accuracy and long-term stability, and can directly trace back to the high accuracy of the AMO reference, thus improving the AMO spectral extrapolation accuracy in the Fraunhofer line region and enabling ground-based spectrometers to be calibrated using stable Fraunhofer lines. Attached Figure Description
[0019] Figure 1 This is a flowchart illustrating a method in one embodiment of the present disclosure; Figure 2 This is a schematic diagram of the theoretical solar spectrum and the measured solar spectrum of an instrument at the top of the atmosphere before correction in one embodiment of this disclosure; Figure 3 This is a schematic diagram of non-absorption band region screening in one embodiment of this disclosure; Figure 4 This is a schematic diagram of the corrected data in one embodiment of this disclosure. Detailed Implementation
[0020] The technical solutions of this disclosure will now be described in detail with reference to the accompanying drawings and preferred embodiments.
[0021] In existing technologies, ground-based spectroscopic instruments always observe through a thick and variable atmosphere, making it impossible to directly obtain pure AMO solar spectra. For the calibration of ground-based spectroscopic instruments, existing technologies face a common dilemma: the standard light source calibration method (standard lamp method) relies on laboratory standard lamps, which cannot meet the requirements for field and long-term stability, and suffers from standard lamp attenuation and transmission errors; the "matching calibration method" based on standard AMO spectral databases is limited by models and external databases, is not absolutely traceable, and is greatly affected by the atmospheric conditions at the time and place, thus limiting accuracy and long-term stability; spaceborne spectroscopic instruments can directly obtain "pure" solar spectra containing Fraunhofer lines, but for ground-based spectroscopic instruments, due to atmospheric absorption, the actual observed solar spectrum contains various gas and molecular absorptions, making it impossible to obtain Fraunhofer lines.
[0022] Therefore, this disclosure provides a method, system, and medium for generating and calibrating based on the Fraunhofer spectral reference.
[0023] See Figure 1 This disclosure provides a method for generating and calibrating based on the Fraunhofer spectral standard, including the following steps: Step 1: Measure the solar direct radiation spectrum at different solar zenith angles using a ground-based spectrometer, and calculate the atmospheric mass at each measurement time for each solar direct radiation spectrum. Step 2: Calculate the solar spectral irradiance at the top of Earth's atmosphere; Step 3: Select the non-absorption band that is not affected by atmospheric interference based on atmospheric transmittance; Step 4: Locate the Fraunhofer line in the non-absorption band and perform spectral calibration on the ground-based spectrometer.
[0024] The specific steps of the generation and calibration method are as follows: Step 1 involves automatically measuring the direct solar radiation spectrum at different solar zenith angles using a ground-based spectrometer. Specifically, under clear and stable atmospheric conditions, and ideally in clear weather with clean air, the ground-based spectrometer (such as a high-resolution spectroradiometer) equipped with an automatic solar tracker continuously measures the direct solar radiation spectrum at different solar zenith angles throughout the day, from sunrise to sunset. The measurement time and corresponding geographical location for each spectrum are recorded, and the atmospheric mass at each measurement moment is calculated. This step obtains the basic dataset necessary for applying the Langley method.
[0025] Understandably, measuring the spectrum of direct solar radiation yields the wavelength of direct solar radiation and the corresponding irradiance of the sun reaching the ground after passing through the entire atmosphere.
[0026] As an example, the definition of clean air is that air is composed of 78.06%~78.08% nitrogen, 20.94%~20.95% oxygen, 0.93% carbon dioxide, 0.03% rare gases, and other gases and impurities with a volume of less than or equal to 0.02%. Obviously, the percentages such as 78.06% are all volume percentages.
[0027] In one embodiment, the atmospheric mass at each spectral measurement moment in each solar direct radiation spectrum is automatically calculated by the first calculation module. The measurement module is used to measure the solar direct radiation spectrum at different solar zenith angles using a ground-based spectrometer. Furthermore, the measurements by the (automatic solar tracker and) ground-based spectrometer are intelligently controlled by the control module of the measurement module. The control module can not only control the ground-based spectrometer measurements and the operation of the solar tracker, but also control the first calculation module to start the calculation.
[0028] Here, the solar spectrum at the top of the atmosphere is obtained by extrapolation using the Langley method. However, the large range of atmospheric mass variation throughout the day may lead to slight nonlinearity. To further improve the extrapolation accuracy, the piecewise Langley method (fitting data for different atmospheric mass ranges separately) or the weighted least squares method (assigning greater weight to data points with smaller atmospheric mass and higher signal-to-noise ratio) can be used for regression.
[0029] Step 2, according to Beer-Lamber's law, the solar irradiance reaching the ground after passing through the entire atmosphere is:
[0030] In the formula: This indicates the amount of solar irradiance reaching the ground after passing through the entire atmosphere; Indicates wavelength; Indicates the solar spectral irradiance at the top of Earth's atmosphere; Indicates the atmospheric optical thickness in the zenith direction; Indicates air quality; It represents the solar zenith angle.
[0031] Taking the logarithm of both sides of the above formula yields: .
[0032] When the atmosphere is clean and stable This can be considered a constant. Therefore, the following is established: and A linear relationship can be used to find out. This refers to the solar spectrum at the top of the atmosphere as measured by a ground-based spectrometer.
[0033] Here are the data obtained in step 1 for different solar zenith angles (solar direct radiation spectra measured by ground-based spectrometers at different solar zenith angles). air quality ),according to Process the response to obtain .
[0034] Specifically, the solar spectral irradiance at the top of the Earth's atmosphere is calculated using the second calculation module.
[0035] Step 3, Intelligent Filtering of Non-Absorption Bands. Specifically, the selection module selects non-absorption bands that are not affected by atmospheric interference based on atmospheric transmittance. Non-absorption bands that are not affected by atmospheric interference refer to bands where electromagnetic waves are not significantly absorbed or scattered by atmospheric components (such as oxygen, water vapor, ozone, etc.) when passing through the Earth's atmosphere. It is understood that the definition of "significant absorption" or "significant scattering" is determined based on actual circumstances.
[0036] Since in the solar spectrum at the top of the atmosphere obtained in Step 2, due to being sensitive to aerosols, water vapor, etc., the bands sensitive to them are invalid, so this part of the band range needs to be removed. Here, non-absorption bands that are not affected by the atmosphere are selected according to the atmospheric transmittance.
[0037] In this embodiment, the requirements for selecting non-absorption bands are as follows: the transmittance T is relatively smooth without valleys. The specific method is as follows: Determine the first derivative threshold slopeTh and the second derivative threshold curveTh of the transmittance T, as well as the local standard deviation threshold stdTh of the transmittance. Perform derivative operation and standard deviation operation on the transmittance T to obtain abs(dT), abs(ddT), and T_std; The following three requirements need to be met simultaneously: Requirement 1: The first derivative (slope) abs(dT) of the transmittance T satisfies: abs(dT) < slopeTh, ensuring that the change of the transmittance T is slow; Requirement 2: The second derivative (curvature) abs(ddT) of the transmittance T satisfies: abs(ddT) < curveTh, ensuring that the change of the transmittance T is gentle (without large bends); Requirement 3: The local standard deviation T_std of the transmittance T satisfies: T_std < stdTh, ensuring that the transmittance fluctuates little within a window.
[0038] Then, connect the band regions that simultaneously meet the above three requirements into a window, and further require that the window width is greater than the set minimum width.
[0039] The selection of the non-absorption band region can be adjusted according to actual needs. The solution can be to use dynamic thresholds. For example, according to the statistical distribution of the average transmittance of all wavelength points (such as selecting the top 10% of wavelength points), or automatically adjusting the threshold according to the overall atmospheric stability during the observation period to make the screening criteria more adaptable and robust.
[0040] Step 4: Extraction and calibration of Fraunhofer lines.
[0041] Here, according to the non-absorption band region determined in Step 3, find the Fraunhofer lines within this non-absorption band region, and then perform spectral calibration according to the spectral matching method.
[0042] Specifically, search for Fraunhofer lines within the non-absorption band through a search module; further, perform spectral calibration according to the Fraunhofer lines through a calibration module.
[0043] The specific operation is as follows: Convolve the standard internationally recognized solar spectrum with the ground-based spectral instrument to be calibrated to obtain the solar spectral irradiance theoretically measured by the instrument , As a reference spectral irradiance; The solar spectral irradiance obtained by instrument extrapolation is... ; In the non-absorption band region, respectively for and Extract the Fraunhofer line; Calculate pairs Extracting Fraunhofer lines and pairs The differences in the extracted Fraunhofer lines were used to complete the spectral calibration using polynomial fitting.
[0044] This also includes obtaining the theoretically measured solar spectral irradiance from ground-based spectrometers. The steps; specifically, the ground-based spectrometer involves: […]. And the solar spectral irradiance at the top of Earth's atmosphere calculated in step 2 Fraunhofer lines were extracted separately, and the ground-based spectrometer was calibrated based on the extracted Fraunhofer lines.
[0045] This study uses a ground-based spectrometer (ground-based solar irradiance meter) operating in Lijiang City, Yunnan Province, China, to test a method for generating and calibrating the Fraunhofer spectral standard. Based on this method, the ground-based spectrometer was used in Lijiang to conduct tests under clear weather conditions, obtaining a series of data at different solar zenith angles. The Langley method was used to extrapolate the data to obtain the solar spectrum at the top of the atmosphere. The standard solar spectrum was then obtained by convolving the standard spectrum with the instrument's response function, as shown below. Figure 2 As shown. The non-absorption band region is determined by atmospheric transmittance, as shown below. Figure 3 As shown, the blue (or light purple) regions (regions 1 to 8) are non-absorption band regions, and Fraunhofer lines are extracted within these regions for spectral calibration. After wavelength correction, as shown... Figure 4 As shown in Table 1, the wavelength deviations before and after partial wavelength correction are shown.
[0046] Table 1
[0047] It is evident that the method disclosed herein can effectively correct the spectrum, and can completely correct it even when the spectral shift is 1 nm.
[0048] This disclosure also provides a system for generating and calibrating based on the Fraunhofer spectral line reference, the system comprising: The measurement unit is used to measure the solar direct radiation spectrum at different solar zenith angles using a ground-based spectrometer. The first calculation unit is used to calculate the atmospheric mass at each spectral measurement moment in each solar direct radiation spectrum; The second calculation unit is used to calculate the solar spectral irradiance at the top of the Earth's atmosphere; The selection unit is used to select the non-absorption band that is not affected by atmospheric interference based on atmospheric transmittance. The search unit is used to locate Fraunhofer lines in the non-absorption band. The calibration unit is used to perform spectral calibration on ground-based spectrometers.
[0049] In this embodiment, the second calculation unit is specifically used to calculate according to the formula. or formula Calculate the solar spectral irradiance at the top of Earth's atmosphere; where, This represents the amount of solar irradiance reaching the Earth's surface after passing through the entire atmosphere. Indicates wavelength. Indicates the solar spectral irradiance at the top of Earth's atmosphere. Indicates the atmospheric optical thickness in the zenith direction. Indicates air quality, It represents the solar zenith angle.
[0050] In this embodiment, the selection unit is specifically used to calculate the first derivative of transmittance abs(dT), the local standard deviation of the second derivative abs(ddT), and the local standard deviation T_std, and to select the band corresponding to the transmittance that simultaneously satisfies the following conditions: abs(dT) is less than the first derivative threshold, abs(ddT) is less than the second derivative threshold, and T_std is less than the local standard deviation threshold as the non-absorption band that is not affected by atmospheric interference.
[0051] In this embodiment, the measurement of the direct solar radiation spectrum at different solar zenith angles using a ground-based spectrometer specifically involves measuring the direct solar radiation spectrum at different solar zenith angles using a ground-based spectrometer equipped with an automatic solar tracker under clear weather and clean atmospheric conditions.
[0052] In this embodiment, the system further includes an acquisition module for obtaining the solar spectral irradiance theoretically measured by the ground-based spectrometer. The steps; the search unit is specifically used for... The Fraunhofer lines are extracted from the solar spectral irradiance at the top of the Earth's atmosphere, respectively; the calibration unit is specifically used to perform spectral calibration on the ground-based spectrometer based on the extracted Fraunhofer lines.
[0053] In specific implementation, the system can refer to the generation and calibration method based on Fraunhofer spectral line reference in any of the above embodiments to achieve spectral calibration. The specific implementation steps will not be repeated here.
[0054] An electronic device can be implemented according to the method of this disclosure, the electronic device comprising: a memory; one or more processors; one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, the one or more programs comprising instructions for executing a method for generating and calibrating a Fraunhofer spectral reference according to any of the above embodiments.
[0055] This disclosure also provides a computer-readable storage medium including instructions that, when executed on a computer, cause the computer to perform the steps of the method for generating and calibrating a Fraunhofer spectral reference as described in any of the above embodiments.
[0056] The advantages of the method, system, and medium for generating and calibrating based on the Fraunhofer spectral standard disclosed herein are as follows: This disclosure presents a method and system for generating and calibrating a Fraunhofer spectral line reference for ground-based spectrometers. It establishes a Fraunhofer spectral line reference for ground-based spectrometers. Based on measurements of direct solar radiation spectra at different solar zenith angles, the method calculates the atmospheric mass at each measurement time within each direct solar radiation spectrum; calculates the solar spectral irradiance at the top of the Earth's atmosphere; selects non-absorption bands unaffected by atmospheric interference based on atmospheric transmittance; and extracts the Fraunhofer line to calibrate the ground-based spectrometer. This method eliminates the need for laboratory standard lamps, avoiding the problems of standard lamp attenuation and transmission errors. The calibration method can distinguish and utilize atmospheric-independent regions of the spectrum, exhibiting good accuracy and long-term stability. It can directly trace back to the high-precision AMO reference, thus improving the AMO spectral extrapolation accuracy in the Fraunhofer line region and enabling ground-based spectrometers to be calibrated using stable Fraunhofer lines. This allows ground-based spectrometers to enjoy the advantages of calibration using stable Fraunhofer lines, similar to those of spaceborne spectrometers.
[0057] This disclosure improves upon the on-board extraspectral calibration method by introducing an atmospheric absorption suppression mechanism based on the different observation paths of ground-based and spaceborne spectrometers. Through the combined effects of Langley extrapolation and atmospheric transmittance, the solar irradiance at the top of the Earth's atmosphere measured by the ground-based spectrometer is obtained. Based on this, the Fraunhofer line is identified as a stable Fraunhofer line, enabling the ground-based spectrometer to be calibrated using the stable Fraunhofer line.
[0058] This disclosure enables automated spectral calibration, intelligently distinguishing and utilizing "safe" regions in the spectrum, thereby improving the accuracy of AMO spectral extrapolation in the Fraunhofer line region.
[0059] In existing technologies, the Langley method is commonly used for radiometric calibration of ground-based spectrometers, and standard solar spectra are often used for solar spectra at the top of the atmosphere. However, these are not the actual measured data of the instrument to be calibrated, and therefore cannot accurately reflect the instrument's performance to some extent. In this application, the ground-based spectrometer in step 1 can be the same ground-based spectrometer used for spectral calibration in step 4. Step 1 uses the ground-based spectrometer to measure the direct solar radiation spectrum at different solar zenith angles, and then performs spectral calibration on it, which can accurately reflect the instrument's performance to some extent.
[0060] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0061] The embodiments described above are merely illustrative of several implementations of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this disclosure, and these all fall within the protection scope of this disclosure. Therefore, the protection scope of this patent should be determined by the appended claims.
Claims
1. A method for generating and calibrating a reference based on a Fraunhofer spectral line, characterized in that, The method comprises the following steps: Step 1, measuring the solar direct radiation spectrum at different solar zenith angles by a ground-based spectral instrument, and calculating the atmospheric quality at each spectral measurement time in each solar direct radiation spectrum; Step 2, calculating the solar spectrum irradiance at the top of the earth's atmosphere; Step 3, selecting a non-absorption wave band not disturbed by the atmosphere according to the atmospheric transmittance; Step 4, searching for a Fraunhofer line in the non-absorption wave band, and performing spectral calibration on the ground-based spectral instrument.
2. The method for generating and calibrating based on a reference of a Fraunhofer spectral line according to claim 1, characterized in that, The step of measuring the solar direct radiation spectrum at different solar zenith angles by the ground-based spectral instrument specifically comprises the following steps: in clear weather and under clean atmospheric conditions, a ground-based spectral instrument equipped with an automatic sun tracker is used to measure the solar direct radiation spectrum at different solar zenith angles.
3. The method of claim 1, wherein the method further comprises: The solar spectral irradiance at the top of the Earth's atmosphere is calculated according to the formula or the formula wherein represents the irradiance of the sun as it passes through the entire atmosphere to reach the Earth's surface, represents the wavelength, represents the solar spectral irradiance at the top of the Earth's atmosphere, represents the atmospheric optical thickness in the zenith direction, represents the atmospheric mass, represents the solar zenith angle.
4. The method of claim 1, wherein the method further comprises: The step 3 specifically comprises the following steps: the first derivative abs(dT), the second derivative local standard deviation abs(ddT) and the local standard deviation T_std of the transmittance are calculated, and the wave band corresponding to the transmittance satisfying the conditions that the first derivative abs(dT) is less than the first derivative threshold, the second derivative abs(ddT) is less than the second derivative threshold, and the local standard deviation T_std is less than the local standard deviation threshold is selected as the non-absorption wave band not disturbed by the atmosphere.
5. The method of claim 1, wherein the method further comprises: This also includes obtaining the theoretically measured solar spectral irradiance from ground-based spectrometers. The steps; specifically step 4 is: for Fraunhofer lines were extracted from the solar spectral irradiance at the top of the Earth's atmosphere and the extracted Fraunhofer lines, and the ground-based spectrometer was calibrated based on the extracted Fraunhofer lines.
6. A method for generating and calibrating a reference based on a Fraunhofer spectral line according to any of claims 1 to 5, characterized in that The ground-based spectral instrument is controlled by the control module to measure the solar direct radiation spectrum at different solar zenith angles, the first calculation module is used to calculate the atmospheric quality at each spectral measurement time in each solar direct radiation spectrum, the second calculation module is used to calculate the solar spectrum irradiance at the top of the earth's atmosphere, the selection module is used to select a non-absorption wave band not disturbed by the atmosphere according to the atmospheric transmittance, and the search module is used to search for a Fraunhofer line in the non-absorption wave band.
7. A generation and calibration system based on a reference of a Fraunhofer spectral line, characterized in that, The method comprises the following steps: A measurement unit is configured to measure the solar direct radiation spectrum at different solar zenith angles by a ground-based spectral instrument; A first calculation unit is configured to calculate the atmospheric quality at each spectral measurement time in each solar direct radiation spectrum; A second calculation unit is configured to calculate the solar spectrum irradiance at the top of the earth's atmosphere; A selection unit is configured to select a non-absorption wave band not disturbed by the atmosphere according to the atmospheric transmittance; A search unit is configured to search for a Fraunhofer line in the non-absorption wave band; A calibration unit is configured to perform spectral calibration on the ground-based spectral instrument.
8. A system for generating and calibrating a reference based on a Fraunhofer spectral line according to claim 7, characterized in that The second calculation unit is specifically configured to calculate the solar spectral irradiance at the top of the Earth's atmosphere according to a formula or a formula ; wherein, represents the irradiance of the sun reaching the ground through the whole atmosphere, represents the wavelength, represents the solar spectral irradiance at the top of the Earth's atmosphere, represents the atmospheric optical thickness in the zenith direction, represents the atmospheric mass, represents the solar zenith angle.
9. A system for generating and calibrating a reference based on a Fraunhofer spectral line as recited in claim 1, wherein, The selection unit is specifically configured to calculate the first derivative abs(dT), the second derivative local standard deviation abs(ddT) and the local standard deviation T_std of the transmittance, and to select a wave band corresponding to the transmittance satisfying the conditions that the first derivative abs(dT) is less than the first derivative threshold, the second derivative abs(ddT) is less than the second derivative threshold, and the local standard deviation T_std is less than the local standard deviation threshold as the non-absorption wave band not disturbed by the atmosphere.
10. A computer-readable storage medium, characterized in that, The computer readable storage medium comprises instructions which, when executed on a computer, cause the computer to perform a method for generating and calibrating a Fraunhofer line reference according to any one of claims 1 to 6.