- 著者
- TAKAMURA Tamio KHATRI Pradeep
- 出版者
- Meteorological Society of Japan
- 雑誌
- 気象集誌. 第2輯 (ISSN:00261165)
- 巻号頁・発行日
- pp.2021-075, (Released:2021-09-06)
- 被引用文献数
- 1
A rotating shadow-band spectro-radiometer system is a powerful tool for surveying light in the environment. It can provide the following spectral components of the solar irradiance without using any traditional solar tracking tool: direct normal irradiance (spDNI), diffuse horizontal irradiance (spDHI), and global horizontal irradiance (spGHI). Both irradiances, spDNI and spDHI, are derived from the combination of spGHI observations at different shadow-band positions. The shadow-band system induces basic errors caused by the imperfect corrections of the diffuse irradiance shadowed by band. To restrict the basic errors to within 2 %, the band slant-angle should be within 72 deg for a usual operating condition of the MS-700 spectro-radiometer manufactured by EKO Instruments Co., Ltd. with the MB-20 shadow-band system for MS-700. The errors in the spDNI and spDHI estimation are evaluated quantitatively by using realistic models that consider instrumental and atmospheric conditions. Estimates of spDNI can result in optical depth errors. The relative error in this estimation is described by using a correction coefficient Cfwd defined by the ratio of the true diffuse irradiance simulated by the shadowed irradiance to the approximate value observed. The value of Cfwd depends on the magnitude of the aerosol optical depth as well as the aerosol type. This error analysis should help to improve the accuracy of this system of measurements.
- 著者
- KHATRI Pradeep HAYASAKA Tadahiro IWABUCHI Hironobu TAKAMURA Tamio IRIE Hitoshi NAKAJIMA Takashi Y.
- 出版者
- Meteorological Society of Japan
- 雑誌
- 気象集誌. 第2輯 (ISSN:00261165)
- 巻号頁・発行日
- pp.2018-036, (Released:2018-04-09)
- 被引用文献数
- 9
The present study implements long-term surface observed radiation data (pyranometer observed global flux and sky radiometer observed spectral zenith transmittance data) of multiple SKYNET sites to validate water cloud optical properties (cloud optical depth COD and effective radius Re) observed from space by MODIS onboard TERRA and AQUA satellites and AHI onboard Himawari-8 satellite. Despite some degrees of differences in COD and Re between MODIS and AHI, they both showed common features when validated using surface based global flux data as well as cloud properties retrieved from sky radiometer observed zenith transmittance data. In general, CODs from both satellite sensors are found to overestimated when clouds are optically thin. Among a number of factors (spatial and temporal variations of cloud, sensor and solar zenith angles), the solar zenith angle (SZA) is found to have an impact on COD difference between reflectance based satellite sensor and transmittance based sky radiometer. The Re values from the sky radiometer and satellite sensor are generally poorly correlated. The difference in Re between the sky radiometer and satellite sensor is negatively correlated with COD difference between them, which is likely due to the inherent influence of Re retrieval precision on COD retrieval and vice versa in transmittance based sky radiometer.