• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.199.2-199.2
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• 2010

The main purpose of the calibration procedure is to perform a one to one comparison of the reference pyranometer and the test pyranometer. In order to achieve this, both pyranometers need to be exposed to exactly the same irradiance, under the same circumstances. There are a number of error sources that could result in a wrong measurement. Most importantly Lamp instability, pyranometer offsets, thermal offsets of junctions, voltmeter offset, voltmeter instability, reference pyranometer instability, tilting of the pyranometers and differences in sensor height. Another sun-disc calibration procedure compares the computed vertical component of the direct irradiance as measured by a pyranometer with that measured by the pyranometer to be calibrated. Readings are taken with the levelled pyranometer on a clear day. Firstly the global irradiance and then the diffuse component are measured. Simultaneously measurement of direct irradiance is made with the pyrheliometer. The ways of performing the calibration and the subsequent calculation have been chosen such that the effect all these error sources has been eliminated as much as possible.

• Asia-Pacific Journal of Atmospheric Sciences
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• v.54 no.4
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• pp.639-648
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• 2018

The pyranometer for observing the solar radiation reaching the surface of the earth is manufactured by various companies around the world. The sensitivity of the pyranometer at the observatory is required to be properly controlled based on the reference value of the World Radiometric Center (WRC) and the observatory environment; otherwise, the observational data may be subject to a large error. Since the sensitivity of the pyranometer can be calibrated in an indoor or outdoor calibration, this study used a CSTMUSS-4000C Integrating Sphere by Labsphere Inc. (USA) to calibrate the sensitivity of CMP22 pyranometer by Kipp&Zonen Inc. (Netherlands). Consequently, the factory sensitivity of CMP22 was corrected from $8.68{\mu}V{\cdot}(Wm^{-2})^{-1}$ to $8.98{\mu}V{\cdot}(Wm^{-2})^{-1}$, and the result from the outdoor calibration according to the observatory environment was $8.90{\mu}V{\cdot}(Wm^{-2})^{-1}$. After the indoor calibration of the pyranometer sensitivity, the root mean square error (RMSE) of the observational data at the observatory on a clear day without clouds (July 13, 2017) was $7.11Wm^{-2}$ in comparison to the reference pyranometer. After the outdoor calibration of the pyranometer sensitivity based on these results, the RMSE of the observational data was $1.74Wm^{-2}$ on the same day. Periodic inspections are required because the decrease of sensitivity over time is inevitable in the pyranometer data produced at the observatory. The initial sensitivity after indoor calibration ($8.98{\mu}V{\cdot}(Wm^{-2})^{-1}$) is important, and the sensitivity after outdoor calibration ($8.90{\mu}V{\cdot}(Wm^{-2})^{-1})$ can be compared to the data at the Baseline Surface Radiation Network (BSRN) or can be used for various studies and daily applications.

• Journal of the Korean Solar Energy Society
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• v.35 no.1
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• pp.9-19
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• 2015

Pyranometer have many uncertainty factors (sensitivity function, thermal offset, other spectral effect, geometric, environment, and equipment etc.) than pyrheliometer. The solution for most of the uncertainty factors have been researched, but the problem for thermal offset is being continued research so far. Under the clear sky, due to the thermal offset of pyranometer, the diffuse and global radiation have been negative value for the nighttime and lower value for the daytime, respectively. In order to understand the uncertainty of the thermal offset effect, solar radiation are observed and analyzed using Ji and Tsay method and data from modified pyranometer. As a result of performing temperature correction using the modified pyranometer, the slope (dome factor; k) and intercept ($r_0$) from a linear regression method are 0.064 and $3.457g{\cdot}m^{-2}{\cdot}k^{-1}$, respectively. And the solar radiation is decreased significantly due to the effect of thermal offset during nighttime. The solar radiation from modified pyranometer increased approximately 8% higher than its observed by general pyranometer during daytime. By the way, these results did not generalize because its result is for only single case in clear sky. Accordingly, it is to required for accurate results obtained by the various cases (clear, cloudy and rainy) with longterm observations.

• Journal of the Korean Solar Energy Society
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• v.30 no.5
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• pp.25-31
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• 2010

A Precision Spectral Pyranometer (PSP) is mainly used as a reference to calibrate other pyranometers due to its high accuracy and sensitivity in response to the spectrum wavelength range of 0.285 ${\mu}$ to 2.8 ${\mu}$, while the sensitivity of photovoltaic-type Li-Cor pyranometer is limited within a certain spectral range from 0.4 ${\mu}$ to 1.1 ${\mu}$. In this study, two Eppley PSPs($PSP_1$ and $PSP_2$) were first compared to the calibrated Eppley PSPs from National Renewable Energy Laboratory (NREL), resulting in two linear correction factors based on the comparison between the logger output (V) from the test PSP and the solar radiation (W/m2) from the NREL PSP. The Li-Cor pyranometer used in this study was then corrected based on the comparison of measured solar radiation ($W/m^2$) from the corrected $PSP_1$ and the Li-Cor pyranometer. In addition, instrument scale corrections were also performed for the PSPs and the Li-Cor from the transmitter to the data logger. From the comparisons, a linear correction factor (1.0214) with R=0.9998 was developed for the scale correction between$PSP_1$ and $PSP_2$, while the Li-Cor pyranometer has a scale(1.0597) and offset (32.046) with R=0.9998 against$PSP_1$. As a result, it was identified that there were good agreements within ${\pm}$ 10 W/ $m^2$ between Eppley $PSP_1$ vs. $PSP_2$ solar radiation and within ${\pm}$ 20 W/$m^2$ between$PSP_1$ vs Li-Cor solar radiation after the empirical scale corrections developed in this study.

• Current Optics and Photonics
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• v.1 no.4
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• pp.263-270
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• 2017

Solar radiation data measured by pyranometers is of fundamental use in various fields. In the field of atmospheric optics, the measurement of solar energy must be precise, and the equipment needs to be maintained frequently. However, there seem to be many errors with the existing type of pyranometer, which is an element of the solar-energy observation apparatus. In particular, the error caused by the thermal dome effect occurs because of the thermal offset generated from a temperature difference between outer dome and inner casing. To resolve the thermal dome effect, intensive observation was conducted using the method and instrument designed by Ji and Tsay. The characteristics of the observed global solar radiation were analyzed by classifying the observation period into clear, cloudy, and rainy cases. For the clear-weather case, the temperature difference between the pyranometer's case and dome was highest, and the thermal dome effect was $0.88MJ\;m^{-2}\;day^{-1}$. Meanwhile, the thermal dome effect in the cloudy case was $0.69MJ\;m^{-2}\;day^{-1}$, because the reduced global solar radiation thus reduced the temperature difference between case and dome. In addition, the rainy case had the smallest temperature difference of $0.21MJ\;m^{-2}\;day^{-1}$. The quantification of this thermal dome effect with respect to the daily accumulated global solar radiation gives calculated errors in the cloudy, rainy, and clear cases of 6.53%, 6.38%, and 5.41% respectively.

• Korean Journal of Remote Sensing
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• v.22 no.5
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• pp.389-396
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• 2006

Surface Solar Insolation is important for vegetation productivity, hydrology, crop growth, etc. In this study, Surface Solar Insolation is estimated using Multi-functional Transport Satellite (MTSAT-1R) in clear and cloudy conditions. For the Cloudy sky cases, the surface solar insolation is estimated by taking into account the cloud transmittance and multiple scattering between cloud and surface. This model integrated Kawamura's model and SMAC code computes surface solar insolation with a $5\;km{\times}5\;km$ spatial resolution in hourly basis. The daily value is derived from the available hourly Surface Solar Insolation, independently for every pixel. To validation, this study uses ground truth data recorded from the pyranometer installed by the Korea Meteorological Agency (KMA). The validation of estimated value is performed through a match-up with ground truth. Various match-up with ground truth. Various match-up window sizes are tested with $3{\times}3,\;5{\times}5,\;7{\times}7,\;9{\times}9,\;10{\times}10,\;11{\times}11,\;13{\times}pixels to define the spatial representativity of pyranometer measurement, and to consider drifting clouds from adjacent pixels across the ground station during the averaging interval of 1 hour are taken into account.

• Korean Journal of Remote Sensing
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• v.24 no.6
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• pp.605-612
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• 2008

In this study, we estimate solar surface insolation (SSI) by using physical methods with MTSAT-1R data. SSI is regarded as crucial parameter when interpreting solar-earth energy system, climate change, and agricultural production predict application. Most of SSI estimation model mainly uses ground based-measurement such as pyranometer to tune the constructed model and to validate retrieved SSI data from optical channels. When compared estimated SSI with pyranometer measurements, there are some systemic differences between those instruments. The pyranometer data observed upward-looking hemispherical solid angle and distributed hourly measurements data which are averaged every 2 minute instantaneous observation. Whereas MTSAT-1R channels data are taken instantaneously images at fixed measurement time over scan area, and are pixel-based observation with a much smaller solid angle view. Those temporal discrepancies result from systemic differences can induce validation error. In this study, we adjust hour when estimate SSI to improve the retrieved accurate SSI.

• Proceedings of the KSRS Conference
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• 2005.10a
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• pp.458-461
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• 2005

Surface Solar Insolation is important for vegetation productivity, hydrology, crop growth, etc. However, ground base measurement stations installed pyranometer are often sparsely distributed, especially over oceans. In this study, Surface Solar Insolation is estimated using the visible and infrared spin scan radiometer(VISSR) data on board Geostationary Meteorological Satellite (GMS)-S covering from March 2001 to December 2001 in clear and cloudy conditions. To retrieve atmospheric factor, such as, optical depth, the amount of ozone, H20, and aerosol, SMAC (Simplified Method for Atmospheric Correction) code, is adopted. The hourly Surface Solar Insolation is estimated with a spatial resolution of $5km\;\times\;5km$ grid. The daily Surface Solar Insolation is derived from the available hourly Surface solar irradiance, independently for every pixel. The pyranometer by the Korea Meteorological Agency (KMA) is used to validate the estimated Surface Solar Insolation with a spatial resolution of $3\;\times\;3Pixels.$

• 한국태양에너지학회:학술대회논문집
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• 2008.11a
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• pp.161-166
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• 2008

The major purpose of this paper is to develop an uncertainty estimate for the calibration of thermopile instruments used to measure solar radiation parameters. We briefly describe the solar radiation parameters most often measured, instrumentation, reference standards, and calibration techniques. The bulk of the paper describes elemental sources of error and their magnitude. We then apply a standard error analysis methodology to combine these elemental error estimates into a statement of total uncertainty for the instrument calibration factor. Our results allow one to evaluate the accuracy of a radiometric measurement using thermopile instrumentation in the light of the application, such as engineering test evaluation or for validation of theoretical models.

• Magazine of the Korean Society of Agricultural Engineers
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• v.43 no.3
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• pp.39-45
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• 2001

The purpose of this study is to develop an economic and practical radiation sensor using photo diodes which is useful for estimating ET in greenhouse environment. An electronic circuit was then designed. Out put signal of photo diode is amplified with a LM318 transistor and is displayed in a LCD with value from zero to 255. The output signal was compared with that of a ready-made pyranometer. The behavior of the photo diode radiation sensor was evaluated by increasing number of photo diodes. The sensor became more reliable with increased number of photo diodes. Developed radiometer was tested with calibrated relation between pyranometer radiation and photo diode output. It was showed that the photo diodes radiometer would be applicable for the greenhouse environment.