Optomechanical Design and Application of Solar-Skylight Spectroradiometer
Abstract
:1. Introduction
2. Instrument Characterization
2.1. Overview Design
2.2. Light-Path Design
2.3. Radiometer System with Embedded Linux
2.3.1. Two-Axis Turntable
2.3.2. Measuring Probe
2.3.3. Temperature Control System
2.4. Workflow
- During the process of direct-sun measurement, solar tracking and radiation collection programs circulate in the microprocessor, so that the direct solar irradiance of the whole day sequence from sunrise to sunset can be obtained. Using the relative flux of directly transmitted radiance varying with the zenith angle, atmospheric parameters such as atmospheric transmittance and water vapor column can be calculated by the inversion model.
- In diffuse-sky measurement, dual-mode tracking technology is executed to accurately track solar position, after which the spectroradiometer scans the solar principal plane (SPP) and almucantar (ALM) shown in Figure 7 at non-equal intervals to obtain the whole sky radiance.
- As for fixed-point observation, the measuring probe aims at a specific direction to obtain continuous fixed-point radiance. The measurement cycle and integration time of the spectrometer can be dynamically adjusted, but the increase in integration time will lead to the elevation of dark noise and compression of the signal-to-noise ratio. Therefore, the adjustment of integration time adopts the principle of 1~320 ms classification.
3. Calibration
3.1. Calibration of Diffuse-Sky Radiance Measurement
3.2. Calibration of Direct-Sun Irradiance Measurement
- , is the output voltage produced by the spectroradiometer at wavelength when points to the sun at the ground and at the atmospheric top, respectively. is the relative Earth–Sun correction factor.
- is the optical airmass, which describes the increase in the direct optical pathlength from the sun to the detector.
- is the total atmospheric optical depth at wavelength , equal to the sum of aerosol (), ozone () and Rayleigh () optical depth.
4. Result Analysis
4.1. Verification of Transmittance and Water Vapor
4.1.1. Whole Atmospheric Transmittance
4.1.2. Total Water Vapor
4.2. Continuous Spectrum Transmittance
4.3. Diffuse-Sky Radiance
- The radiance distribution under cloud conditions (Figure 15a) is affected by the clouds and the solar zenith angle, which presents an ambiguous result and no obvious regularity.
- On a sunny day, the radiation in the whole sky shows a symmetrical distribution concerning the line connecting the Sun and the zenith. The solar zenith angle is the main factor determining the value of sky radiance. With the increase in solar zenith angle, the sky radiance decreases accordingly.
4.4. Fixed-Point Radiance
- Under clear-sky conditions, the radiation curve is relatively smooth with slight fluctuation. With the solar zenith angle becoming lower, the proportion of shortwave radiation decreases and the long-wave radiation increases correspondingly.
- The existence of clouds will affect the distributions of sky radiation. In a partially cloudy condition, the radiation distributions in the entire waveband are relatively uniform, and the curve descent tends to be gentle. The proportion of long-wave radiation is significantly higher when compared to that in the clear-sky condition.
5. Conclusions
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Acknowledgments
Conflicts of Interest
References
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Performance Characteristics | Specifications |
---|---|
Measurement waveband | 380~1100 nm |
Spectrum resolution | <1 nm |
Measuring mode | direct-sun irradiance, diffuse-sky radiance |
Field of view | 0.8° |
Tracking angle resolution | <5 arcsec |
Positioning accuracy | <40 arcsec |
Control architecture | ARM-Linux architecture |
Working temperature | −30~55 °C |
Date | Parameter | Selected Eight Wavebands | |||||||
---|---|---|---|---|---|---|---|---|---|
400 nm | 500 nm | 610 nm | 670 nm | 780 nm | 870 nm | 940 nm | 1050 nm | ||
29 January 2021 | InG0 | 11.0146 | 13.0431 | 13.5085 | 13.2467 | 12.3778 | 11.52 | 12.5569 | 11.236 |
R | −0.9990 | −0.9994 | −0.9986 | −0.9988 | −0.9985 | −0.9984 | −0.9957 | −0.9969 | |
SD | 0.00237 | 0.00132 | 0.00163 | 0.00132 | 0.00126 | 0.0012 | 0.00261 | 0.00163 |
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Qi, Z.; Li, J.; Xu, W.; Zhu, W.; Sun, F.; Huang, Y.; Xu, G.; Dai, C. Optomechanical Design and Application of Solar-Skylight Spectroradiometer. Sensors 2021, 21, 3751. https://doi.org/10.3390/s21113751
Qi Z, Li J, Xu W, Zhu W, Sun F, Huang Y, Xu G, Dai C. Optomechanical Design and Application of Solar-Skylight Spectroradiometer. Sensors. 2021; 21(11):3751. https://doi.org/10.3390/s21113751
Chicago/Turabian StyleQi, Zhaoyang, Jianyu Li, Wenqing Xu, Wenyue Zhu, Fengying Sun, Yao Huang, Gang Xu, and Congming Dai. 2021. "Optomechanical Design and Application of Solar-Skylight Spectroradiometer" Sensors 21, no. 11: 3751. https://doi.org/10.3390/s21113751