研究内容 > 太陽光と天空光のスペクトル計測
Spectral measurement of solar and skylight radiation
 
   人工衛星で観測された放射輝度値を大気補正して正確な地表面反射率を導出するには、衛星通過時のエアロゾルの光学特性を正確に評価する必要があります。従来、この目的にはスカイラジオメータなどの地上設置分光放射計が用いられてきましたが、太陽追尾装置が比較的大型であるため、簡便な計測には必ずしも適合していませんでした。環境リモートセンシング研究センターでは、携帯型分光放射計(英弘精機、MS-720)を用いて直達太陽光(視野角5°)、太陽周縁光(5°-20°)、および散乱太陽光(20°)のスペクトルを観測し、これらのスペクトルをMie散乱理論および大気中の放射伝達計算でフィットすることによってエアロゾルの光学特性を精度よく導出できることを示しました。

   Recently we have shown that the use of a compact, stand-alone spectroradiometer (EKO, MS-720) enables the spectral measurements of direct solar radiation (DSR), solar aureole (AUR) and scattered solar radiation (SSR) (Manago & Kuze, 2010; Manago et al., 2010). Since the instrument is powered by batteries with no PC requirement during measurements, it provides better portability compared to a skyradiometer. The wavelength coverage between 350 and 1050 nm with a resolution of 10 nm is useful for precise evaluation of the aerosol optical properties as well as that of the water vapor column amount. The wide dynamic-range measurement of both the direct and scattered solar radiation is attained by means of a thick diffuser and a stable photodiode array, in combination with the automatic exposure control equipped to the handy spectroradiometer (MS-720). In order to facilitate the radiation transfer calculation in the retrieval procedure, home-made baffle tubes are used to limit the field of view (FOV) of the observation to 20 deg (SSR) and 5 deg (DSR).

References
Manago, N., Kuze, H., Determination of tropospheric aerosol characteristics by spectral measurements of solar radiation using a compact, stand-alone spectroradiometer. Applied Optics, 49, (2010), pp. 1446-1458, ISSN 1539-4522
Manago, N., Miyazawa, S., Bannu, Kuze, H., Seasonal variation of tropospheric aerosol properties by direct and scattered solar radiation spectroscopy. J. Quantitative Spectroscopy & Radiative Transfer, 112(2), (2011), pp. 285-291, ISSN 0022-4073



Calibration of the MS-720 spectroradiometer at the Subaru-site on the Mauna Kea Mountain in Hawaii.



An example of the aerosol optical property determined from the direct and scattered solar radiation in Chiba.

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