Abstract

The GL (GLobal radiation) physical model was developed to compute global solar irradiance at ground level from (VIS) visible channel imagery of geostationary satellites. Currently, its version 1.2 (GL1.2) runs at Brazilian Center for Weather Forecast and Climate Studies/National Institute for Space Research (CPTEC/INPE) based on GOES-East VIS imagery. This study presents an extensive validation of GL1.2 global solar irradiance estimates using ground-based measurements from 409 stations belonging to the Brazilian National Institute of Meteorology (INMET) over Brazil for the year 2016. The INMET reasonably dense network allows characterizing the spatial distribution of GL1.2 data uncertainties. It is found that the GL1.2 estimates have a tendency to overestimate the ground data, but the magnitude varies according to region. On a daily basis, the best performances are observed for the Northeast, Southeast, and South regions, with a mean bias error (MBE) between 2.5 and 4.9 W m−2 (1.2% and 2.1%) and a root mean square error (RMSE) between 21.1 and 26.7 W m−2 (10.8% and 11.8%). However, larger differences occur in the North and Midwest regions, with MBE between 12.7 and 23.5 W m−2 (5.9% and 11.7%) and RMSE between 27 and 33.4 W m−2 (12.7% and 16.7%). These errors are most likely due to the simplified assumptions adopted by the GL1.2 algorithm for clear sky reflectance (Rmin) and aerosols as well as the uncertainty of the water vapor data. Further improvements in determining these parameters are needed. Additionally, the results also indicate that the GL1.2 operational product can help to improve the quality control of radiometric data from a large network, such as INMET's. Overall, the GL1.2 data are suitable for use in various regional applications.

Highlights

  • Accurate estimates of global solar irradiance at the ground level are essential for a variety of applications in meteorology, hydrology, agriculture, and renewable energy

  • The main examples are the network of the Brazilian National Institute of Meteorology (INMET, see http://www.inmet.gov.br) and the network of Data Collection Platforms managed by National Institute for Space Research (INPE, see http://sinda.crn.inpe.br/PCD/SITE/novo/site/index.php)

  • It differs from previous efforts (e.g., [25,28]; for others go to the publication tab at http://satelite.cptec.inpe.br/radiacao/) in several aspects, as the number of stations and the analysis of spatial characteristics of model performance

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Summary

Introduction

Accurate estimates of global solar irradiance at the ground level are essential for a variety of applications in meteorology, hydrology, agriculture, and renewable energy. Since 1998, the GL (GLobal radiation) model has been run at the Center for Weather Forecast and Climate Studies (CPTEC/INPE) generating solar irradiance fields at daily and monthly time scales with about 4 km resolution It uses GOES-East VIS imagery covering South America and neighboring oceanic areas (see http://satelite.cptec.inpe.br/radiacao/). This article presents a comprehensive evaluation of GL1.2 model performance based on comparison with ground data from 409 INMET stations throughout Brazil for a complete year (2016) It differs from previous efforts (e.g., [25,28]; for others go to the publication tab at http://satelite.cptec.inpe.br/radiacao/) in several aspects, as the number of stations and the analysis of spatial characteristics of model performance.

GL Model Overview
GL Satellite Product
Data Quality Control
Performance Metrics and Analysis
Comparing GL with Two Ground-Based Reference Networks
Monthly Evaluation
Daily Evaluation
Conclusions
Full Text
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