Evaluation of Himawari-8 surface downwelling solar radiation by SKYNET observations

Abstract

Abstract.Observations from the new Japanese geostationary satellite Himawari-8 permit quasi-real-time estimation of global shortwave radiation at an unprecedented temporal resolution. However, accurate comparisons with ground truthing observations are essential to assess their uncertainty. In this study, we evaluated the Himawari-8 global radiation product AMATERASS using observations recorded at four SKYNET stations in Japan and, for certain analyses, from the surface 15 network of the Japanese Meteorological Agency in 2016. We found that the spatiotemporal variability of the satellite estimates was smaller than that of the ground observations; variability decreased with increases in the time step and spatial domain. Cloud variability was the main source of uncertainty in the satellite radiation estimates, followed by direct effects caused by aerosols and bright albedo. Under all-sky conditions, good agreement was found between satellite and groundbased data, with a mean bias in the range of 20-30 W/m 2 (i.e., AMATERASS overestimated ground observations) and a root 20 mean square error of approximately 80 W/m 2 . However, results depended on the time step used in the validation exercise and on the spatial domain. We also detected a limited overestimation in the number of clear-sky episodes, particularly at the pixel level. Overall, satellite-based estimates were higher under overcast conditions, whereas frequent episodes of cloudinduced enhanced surface radiation (i.e., measured radiation was greater than expected clear-sky radiation) tended to reduce this difference. Finally, the total mean bias was reduced to approximately 10-15 W/m 2 under clear-sky conditions, mainly 25 because of overall instantaneous direct aerosol forcing efficiency in the range of 120-150 W/m 2 per unit of aerosol optical depth (AOD). A seasonal anti-correlation between AOD and global radiation differences was evident at all stations and was also observed within the diurnal cycle.

Estimation of satellite‐derived regional photovoltaic power generation using a satellite‐estimated solar radiation data

“…Figure also shows an overestimation of satellite‐derived regionally integrated values compared with the Kyushu‐ and TEPCO‐estimated PV power generation data for the spring and summer seasons. One reason for this is the overestimation of the GHI from Himawari‐8 data under cloudy conditions . Damiani et al indicated point‐by‐point validation results of satellite‐derived solar irradiance in 2016 based on ground observations at the Chiba station (in the TEPCO area) (Figure in the paper by Damiani et al), and noted that the correlation coefficient was approximately 0.95, the MBE was approximately 20‐30 W/m 2 , and the RMSE ranged from approximately 80‐100 W/m 2 .…”

“…Current satellite‐estimated GHI data (AMATERASS data) shows the overestimation of the GHI compared to surface observations . GHI values are calculated using algorithms that were developed in a previous study, not including actual information on aerosol optical depth (AOD) .…”

“…Current satellite-estimated GHI data (AMATERASS data) shows the overestimation of the GHI compared to surface observations. 17 GHI values are calculated using algorithms that were developed in a previous study, 7 not including actual information on aerosol optical depth (AOD). 9 Therefore, an overestimation of PV power generation could result in cases where a thick aerosol event takes place under electric power demand for Kyushu.…”

“…In the algorithm, cloud properties (eg, optical thickness, particle size, and cloud‐top temperature) that influence the GHI are considered . Damiani et al validated the satellite‐estimated GHI data with ground‐based data under clear‐sky conditions and they reported a total mean bias error (MBE) within the range of 10‐15 W/m 2 .…”

“…One reason for this is the overestimation of the GHI from Himawari-8 data under cloudy conditions. 17 They also suggested that this overall influence on the RMSE was associated with cloudy conditions. The solar radiation consortium will improve the treatment of aerosol distribution for satellite-estimated GHI products (personal communication with members of the solar radiation consortium 9 ).…”