CN115900939A - Spectral radiometer scattering channel real-time calibration method based on direct solar irradiance - Google Patents
Spectral radiometer scattering channel real-time calibration method based on direct solar irradiance Download PDFInfo
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Abstract
The invention discloses a spectral radiometer scattering channel real-time calibration method based on direct solar irradiance, which comprises the following steps: obtaining a calibration value of a full wave band of a direct radiation channel of the spectrum radiometer by a Langley calibration method of a non-absorption wave band and a mixed calibration method combining top solar irradiance of an atmospheric layer of a strong absorption wave band based on theoretical calculation; the spectral irradiance and the atmospheric transmittance reaching the radiometer optical acquisition system are accurately obtained through the direct-injection channel calibration; the real-time calibration value of the full-waveband scattering channel is obtained by utilizing the direct solar radiation and the atmospheric transmittance which are measured in real time and penetrate through the atmosphere and combining the solar irradiance at the top of the atmospheric layer and the optical component parameters of the instrument. The invention transfers the direct channel calibration of the spectrum radiometer to the scattering channel calibration on the premise of not using other auxiliary materials, and can be applied to equipment for simultaneously measuring direct solar light and atmospheric scattered light.
Description
Technical Field
The invention relates to the field of calibration research of optical parameter measuring instruments, in particular to a spectral radiometer scattering channel real-time calibration method based on direct solar irradiance.
Background
The solar radiation forms sky spectrum brightness after being scattered in the atmosphere, and a large amount of information of atmospheric components and states can be obtained through inversion by measuring the sky spectrum brightness reaching the ground, so that the method has a great deal of application in the field of atmospheric science. The spectral radiometer is a widely used instrument and can be used for measuring atmospheric optical parameters such as atmospheric transmittance, total amount of water vapor and optical thickness. In the scattering channel measurement, the output signal of the instrument needs to be converted into an actual value of the total sky radiance, namely, a calibration process is performed, and then the spectral radiance of all wavelengths is integrated to obtain the sky spectral radiance. The calibration of the scattering channel of the traditional solar radiometer usually adopts absolute radiometric calibration, which depends on an indoor stable light source with known spectral radiance, such as an integrating sphere, and obtains the calibration value of the scattering channel by establishing a quantitative relation between a digital signal value output by the spectral radiometer and the actual radiance of the integrating sphere. Meanwhile, the integrating sphere calibration is an instrument with higher maintenance cost, so that the calibration cost is greatly improved; and the stability of the integrating sphere changes along with the change of time, and the calibration accuracy is also influenced.
Therefore, it is desirable to provide a method for calibrating a scattering channel in real time with high accuracy to reduce the cost and improve the calibration efficiency and the calibration accuracy.
Disclosure of Invention
In order to solve the problem of low calibration efficiency of a scattering channel of the spectral radiometer, the invention provides a real-time calibration method of the scattering channel of the spectral radiometer based on the direct solar irradiance, which does not need to rely on a stable light source with known external radiance, saves the cost and improves the calibration efficiency.
In order to achieve the purpose, the invention adopts the technical scheme that:
a real-time calibration method for a scattering channel of a spectral radiometer based on direct solar irradiance comprises the following steps:
step 1) when the atmospheric condition meets the requirement of cleanness and stability, calculating a discrete calibration value by using a Langley method in a non-absorption wave band, and calculating to obtain a discrete instrument response value by combining the solar irradiance at the top of an atmospheric layer:
in direct measurement mode, the instrument measures the voltage response of the solar spectrum arriving at the ground as:
V(λ)＝I 0 (λ)K(λ)T(λ) (1)
in the formula: v (λ) is the instrumental measurement, I 0 (lambda) is the top solar irradiance of the atmosphere, K (lambda) is the instrument response function, T (lambda) is the slope transmittance of solar radiation through the atmosphere, and lambda is the wavelength measured by the spectral radiometer;
when the atmospheric quality factor is 0, the atmospheric slope transmittance T (lambda) is 1, the value measured by the instrument is the scaling coefficient, and the direct projection channel full-wave band scaling coefficient V 0 (λ) is expressed as:
V 0 (λ)＝I 0 (λ)K(λ) (2)
solar irradiance I on top of atmospheric layer 0 (λ) is expressed as:
I 0 (λ)＝∫I 0 (λ')φ(λ-λ')dλ' (3)
in the formula: phi (lambda-lambda ') is the instrument function, lambda' is the wavelength of the top atmospheric solar irradiance;
the instrument response function K (λ) assumes a linear variation between its wavelengths over a narrow band of wavelengths, namely:
K(λ)＝a+bλ (4)
wherein a and b are coefficients;
interpolating and fitting the instrument response values K which are discrete at adjacent intervals to obtain a full-wave-band continuous instrument response function K (lambda);
after obtaining the instrument response function K (lambda), the solar irradiance I at the top of the atmospheric layer is combined again 0 (λ) calculated according to the formula (2)A direct path calibration value of the spectral radiometer;
step 2) in actual measurement, the direct radiation channel of the spectral radiometer obtains the direct atmospheric irradiance, the direct radiation channel calibration value is used for calculating the real-time atmospheric transmittance, the atmospheric layer top solar irradiance and the optical parameters of the instrument are combined again, the scattering channel real-time calibration value is calculated, and the calculation formula is as follows:
in the formula, C a (λ) is the scattering channel full-band scaling factor, D is the transmission of the attenuation sheet, Ω ν Is the angle of view of a spectral radiometer, I 0 (λ) is the top solar irradiance of the atmospheric layer, T (λ) is the atmospheric transmittance, V (λ) is the direct solar radiation measured in real time by the spectral radiometer, and λ is the wavelength measured by the spectral radiometer.
The invention has the beneficial effects that:
(1) The invention can perform real-time calibration of the spectrum radiometer without depending on auxiliary materials, and calculate the total radiance of the sky spectrum brightness. Compared with the integrating sphere calibration, the method does not need to rely on a stable light source with known external radiance, saves the cost and improves the calibration efficiency;
(2) The invention can improve the calibration accuracy, the performance of the integrating sphere becomes unstable gradually along with the time change, the sun is a stable light source, and the calibration accuracy of the invention can be ensured on the basis of higher calibration accuracy of a direct channel.
Drawings
FIG. 1 is a flow chart of a method for real-time calibration of a scattering channel of a spectral radiometer based on direct solar irradiance;
FIG. 2a and FIG. 2b are diagrams illustrating the calculation of the calibration value of the scattering channel by using the calibration method; wherein, fig. 2a is a visible light tube, and fig. 2b is a near-infrared light tube;
FIG. 3 is a total sky radiance map calculated using scaled values;
fig. 4 is a graph of spectral radiance at 0 ° zenith angle calculated using the scaled values calculated by integrating sphere scaling and real-time scaling.
Detailed Description
The following detailed description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings, will make the advantages and features of the invention easier to understand by those skilled in the art, and thus will clearly and clearly define the scope of the invention.
As shown in fig. 1, the method for real-time calibration of scattering channel of spectral radiometer based on direct solar irradiance in the embodiment of the present invention comprises the following steps:
step 1, when the atmospheric condition meets the requirement of cleanness and stability, calculating a discrete calibration value by using a Langley method in a non-absorption wave band, combining with the top solar irradiance of the atmospheric layer, calculating to obtain a discrete instrument response value, obtaining an instrument response function through linear interpolation, combining with the top solar irradiance of the atmospheric layer again, calculating to obtain a calibration value of a direct irradiation channel of the spectral radiometer, and specifically comprising the following steps of:
the spectral radiometer has direct and scattering measurement channels, and in order to invert atmospheric optical parameters, the two channels need to be calibrated, that is, the measurement value of the instrument is converted into actual spectral irradiance. The direct path and the scattering path of the spectrum radiometer share one light path, and the difference of the working modes during measurement is only that an attenuation sheet for preventing the optical sensor from being saturated is needed during measurement of the direct path. In addition, the size of the field angle is known from the optical path design of the spectral radiometer. The direct irradiation scaling coefficient can be transmitted to the scattering channel scaling process based on the direct irradiation of the sun measured in real time by the direct irradiation channel.
In the calibration process of the direct path, a hybrid calibration method is utilized, namely under the condition that the atmospheric condition is met, enough discrete calibration values can be directly obtained by utilizing Langley legal calibration calculation in a non-absorption wave band, and the discrete calibration values are divided by the atmospheric layer top solar irradiance in the corresponding wave band to obtain discrete instrument response values. Obtaining an instrument response function and the solar irradiance at the top of the atmospheric layer, and then combining the following formula to obtain a direct-irradiation channel full-wave-band scaling coefficient:
V 0 (λ)＝I 0 (λ)K(λ) (2)
in the formula, V 0 (λ) is the direct path full-band scaling factor, I 0 (λ) is the atmospheric layer top solar irradiance, K (λ) is the instrument response function, λ is the wavelength.
Solar irradiance I at top of atmospheric layer 0 (λ) can be expressed as:
I 0 (λ)＝∫I 0 (λ')φ(λ-λ')dλ' (3)
in the formula: φ (λ - λ ') is the instrument function, λ' is the wavelength of the solar irradiance at the top of the atmospheric layer.
The instrument response function K (λ) is a slowly varying function of wavelength, and a linear variation between wavelengths can be simply assumed in a narrow band, i.e.:
K(λ)＝a+bλ (4)
wherein a and b are coefficients.
Therefore, the full-band continuous K (lambda) can be obtained by interpolation fitting of adjacent spaced discrete K values.
in the formula, C a (lambda) is the scattering channel full-band scaling factor, D is the transmittance of the attenuation sheet, omega v Is an apparatusSolid angle, I 0 (λ) is the top solar irradiance of the atmospheric layer, V 0 (λ) is the scaling factor of the direct path of the spectral radiometer.
Because V (λ) = V 0 (λ) · T (λ), and the direct path of the spectroradiometer can measure the atmospheric transmittance T (λ) at different times, so that, in actual measurement, the near-real-time scaling factor of the scattering path can be obtained as follows:
where V (λ) is the direct solar radiation measured in real time by the spectroradiometer. The instrument can only measure direct data or scattering data at one moment, but the calculated calibration value at any moment is consistent according to the uniqueness of the calibration coefficient of the scattering channel.
With reference to fig. 2, because the spectral resolution of the spectral radiometer is less than 1nm and the integration times of the internally used spectrometers are different, when the calibration coefficient is calculated, a uniform instrument function width is needed to smooth the solar irradiance at the top of the atmospheric layer and the output value of the instrument, and the integration time is normalized at the same time, so that a unique calibration coefficient of the scattering channel is finally obtained. The spectral range of the visible light cylinder of the spectrum radiometer is 400-700nm, the spectral range of the near-infrared light cylinder is 700-1100nm, and the spectral resolution is 1nm.
In connection with fig. 3, the scaling coefficients of the scattering channels are applied to the calculation of the total sky background radiation. If a complete background map of the skylight is to be obtained, the integral radiance at all measured azimuth angles and zenith angles needs to be calculated. And multiplying the data in the wave band of 400-700nm of the measurement data of the visible light tube and the data in the wave band of 700-1100nm of the near-infrared light tube by a calibration coefficient, and integrating to obtain the actual all-sky background radiation.
In conjunction with fig. 4, the calibration coefficients of the scattering channels are applied to the calculation of the spectral radiance, and it can be found from the graph that the spectral radiance distributions calculated by the two calibration methods are consistent, and the radiance decreases with the decrease of the wavelength, and exhibits a concave state in the strong absorption band, compared with the results of the integrating sphere calibration. The real-time calibration has higher accuracy.
The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all equivalent structures or equivalent flow transformations that are made by using the contents of the specification and the drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.
Claims (1)
1. A spectral radiometer scattering channel real-time calibration method based on direct solar irradiance is characterized by comprising the following steps:
step 1) when the atmospheric condition meets the requirement of cleanness and stability, calculating a discrete calibration value by using a Langley method in a non-absorption wave band, and calculating to obtain a discrete instrument response value by combining the solar irradiance at the top of an atmospheric layer:
in direct measurement mode, the instrument measures the voltage response of the solar spectrum arriving at the ground as:
V(λ)＝I 0 (λ)K(λ)T(λ) (1)
in the formula: v (λ) is the instrumental measurement, I 0 (lambda) is the top solar irradiance of the atmosphere, K (lambda) is the instrument response function, T (lambda) is the slope transmittance of solar radiation through the atmosphere, and lambda is the wavelength measured by the spectral radiometer;
when the atmospheric quality factor is 0, the atmospheric slope transmittance T (lambda) is 1, the value measured by the instrument is the scaling coefficient, and the direct projection channel full-wave band scaling coefficient V 0 (λ) is expressed as:
V 0 (λ)＝I 0 (λ)K(λ) (2)
solar irradiance I on top of atmospheric layer 0 (λ) is expressed as:
I 0 (λ)＝∫I 0 (λ')φ(λ-λ')dλ' (3)
in the formula: φ (λ - λ ') is the instrument function, λ' is the wavelength of the solar irradiance at the top of the atmospheric layer;
the instrument response function K (λ) assumes a linear variation between its wavelengths over a narrow band of wavelengths, namely:
K(λ)＝a+bλ (4)
wherein a and b are coefficients;
interpolating and fitting the instrument response values K which are discrete at adjacent intervals to obtain a full-wave-band continuous instrument response function K (lambda);
after obtaining the instrument response function K (lambda), the solar irradiance I at the top of the atmospheric layer is combined again 0 (lambda), calculating to obtain a direct radiation channel calibration value of the spectrum radiometer according to the formula (2);
step 2) in actual measurement, the direct radiation channel of the spectral radiometer obtains the direct atmospheric irradiance, the direct radiation channel calibration value is used for calculating the real-time atmospheric transmittance, the atmospheric layer top solar irradiance and the optical parameters of the instrument are combined again, the scattering channel real-time calibration value is calculated, and the calculation formula is as follows:
in the formula, C a (λ) is the scattering channel full-band scaling factor, D is the transmission of the attenuation sheet, Ω ν Is the angle of view of a spectral radiometer, I 0 (λ) is the top solar irradiance of the atmospheric layer, T (λ) is the atmospheric transmittance, V (λ) is the direct solar radiation measured in real time by the spectral radiometer, and λ is the wavelength measured by the spectral radiometer.
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| CN116793494A (en) * | 2023-06-15 | 2023-09-22 | 中国科学院合肥物质科学研究院 | MAX-DOAS wavelength automatic calibration method, system and computer equipment based on sequence matching |
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| CN116793494A (en) * | 2023-06-15 | 2023-09-22 | 中国科学院合肥物质科学研究院 | MAX-DOAS wavelength automatic calibration method, system and computer equipment based on sequence matching |
| CN116793494B (en) * | 2023-06-15 | 2024-04-30 | 中国科学院合肥物质科学研究院 | MAX-DOAS wavelength automatic calibration method, system and computer equipment based on sequence matching |
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