Validation of Hourly Global Horizontal Irradiance for Two Satellite-Derived Datasets in Northeast Iraq

Bikhtiyar Ameen,Mathilde Marchand,Claire Jarvis,Etienne Wey,Claire Thomas,Heiko Balzter

doi:10.3390/rs10101651

Abstract

Several sectors need global horizontal irradiance (GHI) data for various purposes. However, the availability of a long-term time series of high quality in situ GHI measurements is limited. Therefore, several studies have tried to estimate GHI by re-analysing climate data or satellite images. Validation is essential for the later use of GHI data in the regions with a scarcity of ground-recorded data. This study contributes to previous studies that have been carried out in the past to validate HelioClim-3 version 5 (HC3v5) and the Copernicus Atmosphere Monitoring Service, using radiation service version 3 (CRSv3) data of hourly GHI from satellite-derived datasets (SDD) with nine ground stations in northeast Iraq, which have not been used previously. The validation is carried out with station data at the pixel locations and two other data points in the vicinity of each station, which is something that is rarely seen in the literature. The temporal and spatial trends of the ground data are well captured by the two SDDs. Correlation ranges from 0.94 to 0.97 in all-sky and clear-sky conditions in most cases, while for cloudy-sky conditions, it is between 0.51–0.72 and 0.82–0.89 for the clearness index. The bias is negative for most of the cases, except for three positive cases. It ranges from −7% to 4%, and −8% to 3% for the all-sky and clear-sky conditions, respectively. For cloudy-sky conditions, the bias is positive, and differs from one station to another, from 16% to 85%. The root mean square error (RMSE) ranges between 12–20% and 8–12% for all-sky and clear-sky conditions, respectively. In contrast, the RMSE range is significantly higher in cloudy-sky conditions: above 56%. The bias and RMSE for the clearness index are nearly the same as those for the GHI for all-sky conditions. The spatial variability of hourly GHI SDD differs only by 2%, depending on the station location compared to the data points around each station. The variability of two SDDs is quite similar to the ground data, based on the mean and standard deviation of hourly GHI in a month. Having station data at different timescales and the small number of stations with GHI records in the region are the main limitations of this analysis.

Highlights

Global horizontal irradiance (GHI), both in the atmosphere and on the earth’s surface, is a crucial parameter in the fields of atmosphere interaction, solar energy, architecture, and agriculture.High-resolution GHI data are required for studying those fields
This study aims to validate the hourly GHI from HelioClim-3 version 5 (HC3v5) and CRSv3 against ground measurements at nine stations in the northeast of Iraq, being the first study validating those satellite-derived datasets (SDD) in that region
Some other positive rates were recorded at Halsho and Maydan stations, which were lower than 2% for both SDDs (Figure 7, the other stations by nearly W/m2 (Table 3))

Summary

Introduction

High-resolution GHI data are required for studying those fields. Several studies have tried to estimate solar radiation (SR) and its components from either ground measurements or satellite images using several models [1,2,3,4,5,6]. Most of the affordable satellite images for that purpose are the geostationary satellite images, namely Meteosat First Generation (MFG) and Meteosat Second Generation (MSG)/Spinning Enhanced Visible and Infrared Imager (SEVIRI), The Japanese Geostationary Meteorological Satellite (GMS), and the Geostationary Operational Environmental Satellite system (GOES) [7] Others such as the Moderate Resolution Imaging Spectroradiometer (MODIS) [8] and Landsat images have been used [9], but their temporal resolution is not acceptable

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