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Discussion papers | Copyright
https://doi.org/10.5194/amt-2017-432
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 11 Jan 2018

Research article | 11 Jan 2018

Review status
This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Atmospheric Measurement Techniques (AMT) and is expected to appear here in due course.

The instrument constant of sky radiometer (POM-02), Part I: Calibration constant

Akihiro Uchiyama1, Tsuneo Matsunaga1, and Akihiro Yamazaki2 Akihiro Uchiyama et al.
  • 1Center for Global Environmental Research, National Institute for Environmental Studies, Tsukuba, Ibaraki, 305-8506, Japan
  • 2Meteorological Research Institute, Japan Meteorological Agency, Tsukuba, Ibaraki, 305-0052, Japan

Abstract. Ground-based networks have been developed to determine the spatiotemporal distribution of aerosols using radiometers. In this study, the accuracy of the calibration constant (V0) for the sky radiometer (POM-02) which is used by SKYNET was investigated. The temperature dependence of the sensor output was also investigated, and the dependence in the 340, 380, and 2200nm channels was found to be larger than for other channels, and varied with the instrument. In the summer, the sensor output had to be corrected by a factor of 1.5 to 2% in the 340 and 380nm channels and by 4% in the 2200nm channel in the measurements at Tsukuba. In the other channels, the correction factors were less than 0.5%. The accuracy of V0 from the normal Langley method is between 0.2 and 1.3%, except in the 940nm channel. The effect of gas absorption was less than 1% in the 1225, 1627, and 2200nm channels. The degradation of V0 for shorter wavelengths was larger than that for longer wavelengths. The accuracy of V0 estimated from the side-by-side measurements was 0.1 to 0.5%. The V0 determined by the improved Langley (IML) method had a seasonal variation of 1 to 3%. The RMS error from the IML method was about 0.6 to 2.5%, and in some cases, the maximum difference reached 5%. The trend in V0 after removing the seasonal variation was almost the same as for the normal Langley method. The calibration method for water vapor in the 940nm channel was developed using an empirical formula for transmittance. The accuracy of V0 was better than 1% on relatively stable and fine days. A calibration method for the near-infrared channels, 1225, 1627, and 2200nm, was also developed. The logarithm of the ratio of the sensor output can be written as a linear function of the airmass, by assuming that the ratio of the optical thicknesses between the two channels is constant. The accuracy of V0 was better than 1% on days with good conditions.

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Akihiro Uchiyama et al.
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Atmospheric aerosols are an important constituent of the atmosphere. Measurement networks using radiometers such as SKYNET have been developed. There are two constants that we must determine to make accurate measurements. One of them is the calibration constant. The accuracy of the current method to determine it was investigated and the new method for a water vapor and near infrared channels was developed. Utilizing the results of this paper, SKYNET measurement data will become more reliable.
Atmospheric aerosols are an important constituent of the atmosphere. Measurement networks using...
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