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Christian A Gueymard - One of the best experts on this subject based on the ideXlab platform.

  • cloud and albedo enhancement impacts on solar Irradiance using high frequency measurements from thermopile and photodiode radiometers part 1 impacts on global horizontal Irradiance
    Solar Energy, 2017
    Co-Authors: Christian A Gueymard
    Abstract:

    Abstract Using many years of high-quality measurements from a variety of radiometers at both 1-min and 1-s resolution, this study provides a detailed analysis of cloud enhancement (CE) and albedo enhancement (AE) effects on solar Irradiance. This first part focuses on global horizontal Irradiance. Various possible definitions of the CE phenomenon are extracted from the literature and discussed, in the context of PV applications most importantly. Based on 10 years of 1-min measurements of all shortwave Irradiance components at a high-elevation site (1829 m) on the foothills of the Rocky Mountains in Colorado, a frequency analysis of extreme events triggered by enhancement effects is carried out, using three different criteria to delineate enhancement effects: global horizontal Irradiance (GHI) above 1 sun, and clearness index (KT) above either 0.8 or 1.0. This analysis shows that the annual frequency of these extreme events is extremely variable, and also largely dependent on the type of instrumentation (thermopile vs. photodiode). Although the scattering of light off cumulus-type cloud edges is Directly associated with CE effects, three different types of CE phenomenon are proposed, which depend on the relative mix of diffuse and Direct Irradiance prior and during an episode, and on the magnitude of the regional albedo. The maximum observed global Irradiance varies between 1546 and 1891 W m−2 at this site, depending on type of instrument and temporal resolution. The latter value (≈1.9 suns), obtained with a photodiode sensor at 1-s resolution, corresponds to KT = 1.62 and appears to constitute a new GHI world record. It results from the combination of CE and AE effects, the latter being caused by strong backscattering, itself triggered by a fresh snow cover over the region. If the magnitude and frequency of enhancement events are critical to detect rapid transients that can be harmful to PV installations, it is suggested to rely on photodiode sensors at 1-s resolution or better.

  • is the average photon energy a unique characteristic of the spectral distribution of global Irradiance
    Solar Energy, 2017
    Co-Authors: G Nofuentes, Christian A Gueymard, J Aguilera, M D Perezgodoy, Francisco Charte
    Abstract:

    Abstract The average photon energy (APE) has become a popular index to qualitatively assess whether shorter or longer wavelengths are enhanced in a specific spectral distribution of Irradiance when compared to the AM1.5G standard spectrum. According to some previous assessments, this index might uniquely distinguish individual global tilted Irradiance and global horizontal Irradiance spectra. This paper basically applies the same methodology as that used in these studies, i.e., a statistical analysis based on spectral distributions grouped in 0.02-eV APE bins and their standard deviation across all 50-nm bands into which the wavelength range under scrutiny (350–1050 nm) is divided. Two years of spectral global tilted Irradiance datasets collected at two Spanish locations, 333 km apart, are analyzed here. The same brand and model of spectroradiometer is used in each site with identical experimental protocols. It is found here that the coefficient of variation—a more meaningful statistical coefficient than the standard deviation to quantify dispersion around the mean—remains below 3.3% over the 450–900-nm waveband, whereas values up to 5–11% occur outside of it. It is shown that these higher values can be explained by the separate or combined impacts of experimental uncertainty and the Direct effect of aerosols and water vapor. Based on radiative transfer principles related to these two atmospheric constituents, it is argued that APE cannot be a unique characteristic of the complete spectrum, thus confirming previous results that pertained to Direct Irradiance only. In practical terms, however, it is reasonable to ascertain that APE may be considered approximately unique relative to the spectrum distribution under the climate of the two sites under scrutiny over the limited 450–900-nm spectral range. This conclusion presumably holds for most of Spain, or even for locations with sunny inland climates similar to those of Jaen and Madrid.

  • Extensive worldwide validation and climate sensitivity analysis of Direct Irradiance predictions from 1-min global Irradiance
    Solar Energy, 2016
    Co-Authors: Christian A Gueymard, José A. Ruiz-arias
    Abstract:

    Abstract A comprehensive evaluation study of the performance of 140 separation models selected from the literature to predict Direct normal Irradiance (DNI) from global horizontal Irradiance (GHI) is presented here. The assessment is conducted using high-quality 1-min data of GHI and DNI at 54 research-class stations from 7 continents. The observational dataset provides (after a posteriori quality control) more than 25 million valid data points, thereby representing an unprecedented level of effort. The stations are grouped into 4 distinct climate zones: arid, temperate, tropical and high-albedo. To evaluate the performance of each model at each site, three summary statistics are calculated. Additionally, with the emphasis on selecting models that perform consistently well under the general conditions of each climate zone, the robustness of each model is evaluated using a few consistency criteria. It is found that, for all models, the errors are exacerbated by cloud enhancement and high-albedo induced effects. A higher number of predictors used by a model appears to improve its performance, but not in a consistent way, since there are many exceptions. These are attributed to possible excessive model localization and/or overfitting. In general, models that consider both a variability predictor and an estimate of coincident clear-sky Irradiance tend to perform better. No model performs consistently well over the high-albedo zone, even those rare ones that do consider ground albedo as a predictor. Over the arid, temperate and tropical zones, two models consistently deliver the best predictions. One of them is recommended as a “quasi-universal” model for general use for 1-min DNI prediction wherever and whenever low- to moderate-albedo conditions prevail.

  • clear sky Irradiance predictions for solar resource mapping and large scale applications improved validation methodology and detailed performance analysis of 18 broadband radiative models
    Solar Energy, 2012
    Co-Authors: Christian A Gueymard
    Abstract:

    Abstract The intrinsic performance of 18 broadband radiative models is assessed, using high-quality datasets from five sites in widely different climates. The selected models can predict Direct, diffuse and global Irradiances under clear skies from atmospheric data, and have all been (or still are) involved in large-scale applications, for instance to prepare solar resource maps and datasets, or to evaluate solar radiation in GIS software. The input data to the models include accurate aerosol and water vapor measurements by collocated sunphotometers, if needed. Cloud occurrences are meticulously scrutinized through the use of various tools to avoid cloud contamination of the test data. The intrinsic performance of the models is evaluated by comparison between their predictions and measurements at high frequency (1-minute time step at four sites, 3-minute at one site). The total expanded uncertainty of these measurements is estimated at 3% for Direct Irradiance, and 5% for diffuse and global Irradiance. Various statistics are calculated to evaluate the systematic and random differences between the data series, as well as the agreement between the cumulative distribution functions. In the latter case, stringent statistics based on the Komolgorov–Smirnov (KS) test are used. Large differences in performance are apparent between models. Those that require more atmospheric inputs perform usually better than simpler models. Whereas many models can predict the global horizontal Irradiance within uncertainty limits similar to those of the radiation measurements, the prediction of Direct Irradiance is less accurate. Moreover, the prediction of diffuse horizontal Irradiance is particularly deficient in most models. The cumulative distribution functions also denote areas of concern. A ranking of all models is proposed, based on four statistical indicators: mean bias difference (MBD), root mean square difference (RMSD), total uncertainty with 95% confidence limits (U95), and the newly introduced Combined Performance Index (CPI), which optimally combines two KS indices with RMSD. For Direct Irradiance, consistently high rankings are obtained with five models (REST2, Ineichen, Hoyt, Bird, and Iqbal-C, in decreasing order of performance) that require a relatively large number of atmospheric inputs. The inferior performance of models requiring little or no atmospheric inputs suggests that large-scale solar resource products derived from them may be inappropriate for serious solar applications. Additionally, prediction uncertainties under ideal clear-sky conditions can propagate and affect all-sky predictions as well—resulting in potential biases in existing solar resource maps at the continent scale, for instance.

  • progress in Direct Irradiance modeling and validation
    2010
    Co-Authors: Christian A Gueymard
    Abstract:

    The intrinsic performance of two categories of models that can be used to predict Direct normal Irradiance (DNI) for solar concentration applications is analyzed here. A first group consists of five broadband radiative models that can predict DNI under clear skies from atmospheric data. Highquality datasets from four sites in widely different climates are used, including precise aerosol and water vapor measurements by sunphotometers. Based on various tests, superior performance is achieved with the REST2, METSTAT and Ineichen models. A second group involves 18 separation methods frequently used to extract DNI from global Irradiance. Various effects are discussed, such as cloudiness and ground albedo. Although the literature abounds in such methods, none is found satisfactory overall, due to inconsistent results, in addition to high random errors and frequent bias, particularly under conditions of high ground albedo due to snow. Nevertheless, four separation methods appear to perform correctly under clear skies.

Kees Hoogendijk - One of the best experts on this subject based on the ideXlab platform.

  • Water Vapor Retrievals from Spectral Direct Irradiance Measured with an EKO MS-711 Spectroradiometer—Intercomparison with Other Techniques
    Remote Sensing, 2021
    Co-Authors: Victoria E. Cachorro, África Barreto, Ramón Ramos, R. D. García, Emilio Cuevas, Omaira García, Antonio Fernando Almansa, Pedro Miguel Romero-campos, Kees Hoogendijk
    Abstract:

    Precipitable water vapor retrievals are of major importance for assessing and understanding atmospheric radiative balance and solar radiation resources. On that basis, this study presents the first PWV values measured with a novel EKO MS-711 grating spectroradiometer from Direct normal Irradiance in the spectral range between 930 and 960 nm at the Izaña Observatory (IZO, Spain) between April and December 2019. The expanded uncertainty of PWV (UPWV) was theoretically evaluated using the Monte-Carlo method, obtaining an averaged value of 0.37 ± 0.11 mm. The estimated uncertainty presents a clear dependence on PWV. For PWV ≤ 5 mm (62% of the data), the mean UPWV is 0.31 ± 0.07 mm, while for PWV > 5 mm (38% of the data) is 0.47 ± 0.08 mm. In addition, the EKO PWV retrievals were comprehensively compared against the PWV measurements from several reference techniques available at IZO, including meteorological radiosondes, Global Navigation Satellite System (GNSS), CIMEL-AERONET sun photometer and Fourier Transform Infrared spectrometry (FTIR). The EKO PWV values closely align with the above mentioned different techniques, providing a mean bias and standard deviation of −0.30 ± 0.89 mm, 0.02 ± 0.68 mm, −0.57 ± 0.68 mm, and 0.33 ± 0.59 mm, with respect to the RS92, GNSS, FTIR and CIMEL-AERONET, respectively. According to the theoretical analysis, MB decreases when comparing values for PWV > 5 mm, leading to a PWV MB between −0.45 mm (EKO vs. FTIR), and 0.11 mm (EKO vs. CIMEL-AERONET). These results confirm that the EKO MS-711 spectroradiometer is precise enough to provide reliable PWV data on a routine basis and, as a result, can complement existing ground-based PWV observations. The implementation of PWV measurements in a spectroradiometer increases the capabilities of these types of instruments to simultaneously obtain key parameters used in certain applications such as monitoring solar power plants performance.

  • Aerosol retrievals from the EKO MS-711 spectral Direct Irradiance measurements and corrections of the circumsolar radiation
    Atmospheric Measurement Techniques, 2020
    Co-Authors: Rosa Delia García-cabrera, Victoria E. Cachorro, Emilio Cuevas-agulló, África Barreto, Ramón Ramos, Kees Hoogendijk
    Abstract:

    Abstract. Spectral Direct UV–visible normal solar Irradiance (DNI) has been measured with an EKO MS-711 grating spectroradiometer, which has a spectral range of 300–1100 nm, and 0.4 nm step, at the Izana Atmospheric Observatory (IZO, Spain). It has been used to determine aerosol optical depth (AOD) at several wavelengths (340, 380, 440, 500, 675, and 870 nm) between April and September 2019, which has been compared with synchronous AOD measurements from a reference Cimel and Aerosol RObotic NETwork (AERONET) sun photometer. The EKO MS-711 has been calibrated at the Izana Atmospheric Observatory by using the Langley plot method during the study period. Although this instrument has been designed for spectral solar DNI measurements, and therefore has a field of view (FOV) of 5 ∘ that is twice the recommended amount in solar photometry for AOD determination, the AOD differences compared to the AERONET–Cimel reference instrument (FOV ∼ 1.2 ∘ ) are fairly small. A comparison of the results from the Cimel AOD and EKO MS-711 AOD presents a root mean square (rms) of 0.013 (24.6 %) at 340 and 380 nm, and 0.029 (19.5 %) for longer wavelengths (440, 500, 675, and 870 nm). However, under relatively high AOD, near-forward aerosol scattering might be significant because of the relatively large circumsolar radiation (CSR) due to the large EKO MS-711 FOV, which results in a small but significant AOD underestimation in the UV range. The AOD differences decrease considerably when CSR corrections, estimated from libRadtran radiative transfer model simulations, are performed and obtain an rms of 0.006 (14.9 %) at 340 and 380 nm, and 0.005 (11.1 %) for longer wavelengths. The percentage of 2 min synchronous EKO AOD–Cimel AOD differences within the World Meteorological Organization (WMO) traceability limits were ≥96 % at 500, 675, and 870 nm with no CSR corrections. After applying the CSR corrections, the percentage of AOD differences within the WMO traceability limits increased to >95 % for 380, 440, 500, 675, and 870 nm, while for 340 nm the percentage of AOD differences showed a poorer increase from 67 % to a modest 86 %.

  • Characterization of an EKO MS-711 spectroradiometer: aerosol retrieval from spectral Direct Irradiance measurements and corrections of the circumsolar radiation
    2019
    Co-Authors: Rosa Delia García-cabrera, Victoria E. Cachorro, Emilio Cuevas-agulló, África Barreto, Ramón Ramos, Kees Hoogendijk
    Abstract:

    Abstract. Spectral Direct UV-Visible normal solar Irradiance (DNI) measured with an EKO MS-711 spectroradiometer at the Izana Atmospheric Observatory (IZO, Spain) has been used to determine aerosol optical depth (AOD) at several wavelengths (340, 380, 440, 500, 675 and 870 nm) between April and September 2019 that have been compared with synchronous AOD measurements from a reference Cimel-AERONET (Aerosol RObotic NETwork) sunphotometer. The EKO MS-711 has been calibrated at Izana Observatory using the Langley-Plot method during the study period. Although this instrument has been designed for spectral solar DNI measurements, and therefore has a field of view (FOV) of 5° that is twice that recommended in solar photometry for AOD determination, the AOD differences compared against the AERONET Cimel reference instrument (FOV ∼ 1.2°), are fairly small. The comparison results between AOD Cimel and EKO MS-711 present a root mean square (RMS) of 0.013 (24.6 %) at 340, and 380 nm, and 0.029 (19.5 %) for longer wavelengths (440, 500, 675 and 870 nm). However, under relatively high AOD, near forward aerosol scattering might be significant because of the relatively large circumsolar radiation (CSR) due to the large EKO MS-711 FOV, resulting in a small but significant AOD underestimation in the UV range. The AOD differences decrease considerably when CSR corrections, estimated from LibRadtran radiative transfer model simulations, are performed, obtaining RMS of 0.006 (14.9 %) at 340 and 380 nm, and 0.005 (11.1 %) for longer wavelengths. The percentage of 2-minute synchronous EKO AOD–Cimel AOD differences within the World Meteorological Organization (WMO) traceability limits were ≥ 96 % at 500 nm, 675 nm and 870 nm with no CSR corrections. After applying the CSR corrections, the percentage of AOD differences within the WMO traceability limits increased to > 95 % for 380, 440, 500, 675 and 870 nm, while for 340 nm the percentage of AOD differences showed a poorer increase from 67 % to a modest 86 %.

Philippe Blanc - One of the best experts on this subject based on the ideXlab platform.

  • Improving the McClear model estimating the downwelling solar radiation at ground level in cloud-free conditions – McClear‑v3
    Meteorologische Zeitschrift, 2019
    Co-Authors: Benoît Gschwind, Philippe Blanc, Lucien Wald, Mireille Lefèvre, Marion Schroedter-homscheidt, Antti Arola
    Abstract:

    The fast McClear clear-sky model estimates the downwelling shortwave Direct and diffuse Irradiances received at ground level under cloud-free conditions. Several improvements are presented. They focus on the modeling of changes in Irradiances with the solar zenithal angle and on a better exploitation of the aerosol properties offered by the Copernicus Atmosphere Monitoring Service (CAMS). Irradiances from this new version McClear-v3 were compared to 1 min measurements made in cloud-free conditions at 11 stations belonging to the Baseline Surface Radiation Network and being located in various climates. The correlation coefficient ranges between 0.982 and 0.999 for the global Irradiance. The bias is positive (overestimation) and ranges between 1 W m −2 (0.1 % of the mean observed Irradiance) and 20 W m −2 (3.2 %), with the exception of Barrow in Alaska (18 W m −2). The standard deviation ranges between 16 W m −2 (2.3 %) and 30 W m −2 (3.8 %). The correlation coefficient for the Direct Irradiance ranges between 0.902 and 0.995. As expected, since the Direct in McClear does not comprise any circumsolar contribution, the bias is negative (underestimation) and ranges between 49 W m −2 (7.7 %) and 5 W m −2 (0.7 %), with two exceptions: Sede Boqer (79 W m −2) and Brasilia (13 W m −2). The standard deviation is comprised between 34 W m −2 (5.3 %) and 69 W m −2 (10.7 %). These results are similar to those obtained with McClear version 2. Compared to the latter, McClear-v3 removes several artifacts and its estimates are continuous in space and time.

  • Fast radiative transfer parameterisation for assessing the surface solar Irradiance: The Heliosat-4 method
    Meteorologische Zeitschrift, 2017
    Co-Authors: Armel Oumbe, Philippe Blanc, Bella Espinar, Benoît Gschwind, Mireille Lefèvre, Marion Schroedter-homscheidt, Gerhard Gesell, Lars Klüser, Laurent Saboret, Lucien Wald
    Abstract:

    The new Heliosat-4 method estimates the downwelling shortwave Irradiance received at ground level in all sky conditions. It provides the global Irradiance and its Direct and diffuse components on a horizontal plane and the Direct Irradiance for a plane normal to sun rays. It is a fully physical model using a fast, but still accurate approximation of radiative transfer modelling and is therefore well suited for geostationary satellite retrievals. It can also be used as a fast radiative transfer model in numerical weather prediction models. It is composed of two models based on abaci, also called look-up tables: the already-published McClear model calculating the Irradiance under cloud-free conditions and the new McCloud model calculating the extinction of Irradiance due to clouds. Both have been realized by using the libRadtran radiative transfer model. The main inputs to Heliosat-4 are aerosol properties, total column water vapour and ozone content as provided by the Copernicus Atmosphere Monitoring Service (CAMS) every 3 h. Cloud properties are derived from images of the Meteosat Second Generation (MSG) satellites in their 15 min temporal resolution using an adapted APOLLO (AVHRR Processing scheme Over cLouds, Land and Ocean) scheme. The 15 min means of Irradiance estimated by Heliosat-4 are compared to corresponding measurements made at 13 stations within the Baseline Surface Radiation Network and being located in the field of view of MSG and in various climates. The bias for global Irradiance is comprised between 2 and 32 W m −2. The root mean square error (RMSE) ranges between 74 and 94 W m −2. Relative RMSE values range between 15 % and 20 % of the mean observed Irradiance for stations in desert and Mediterranean climates, and between 26 % and 43 % for rainy climates with mild winters. Correlation coefficients between 0.91 and 0.97 are found. The bias for the Direct Irradiance at normal incidence is comprised between −163 and +50 W m −2. The RMSE ranges from 160 W m −2 (29 % of the mean observed Irradiance) to 288 W m −2 (63 %). The correlation coefficient ranges between 0.67 and 0.87.

  • Validating surface downwelling solar Irradiances estimated by the McClear model under cloud-free skies in the United Arab Emirates
    Solar Energy, 2015
    Co-Authors: Yehia Eissa, Philippe Blanc, Hosni Ghedira, Armel Oumbe, Lucien Wald, Hélène Bru, Saima Munawwar, Dominique Goffe
    Abstract:

    McClear, a fast model based on a radiative transfer solver, exploits the atmospheric properties provided by the EU-funded MACC project (Monitoring Atmospheric Composition and Climate) to estimate the surface downwelling solar Irradiances for cloud-free instances. This article presents the first validation of the McClear model for the specific climate of the United Arab Emirates where skies are frequently cloud-free but turbid. McClear accurately estimates the global horizontal Irradiance measured every 10 min at seven sites. The bias ranges from -9 W m-2 (-1% of the mean observed Irradiance) to +35 W m-2 (+6%). The root mean square error (RMSE) ranges from 22 W m-2 (4%) to 47 W m-2 (8%) and the coefficient of determination ranges from 0.980 to 0.990. Estimates of the Direct Irradiance at normal incidence exhibit an underestimation that is attributed to the overestimation of the aerosol optical depth in the MACC data set and not accounting for the circumsolar radiation in McClear. The corresponding bias ranges from -57 W m-2 (-8%) to +6 W m-2 (+1%). The RMSE ranges from 62 W m-2 (9%) to 87 W m-2 (13%) and the coefficient of determination ranges from 0.830 to 0.863. When compared to two other models in the literature, McClear is better able to capture the temporal variability of the Direct Irradiance at normal incidence. The validation results remain comparable for the global horizontal Irradiance.

  • mcclear a new model estimating downwelling solar radiation at ground level in clear sky conditions
    Atmospheric Measurement Techniques, 2013
    Co-Authors: Mireille Lefèvre, Philippe Blanc, Armel Oumbe, Lucien Wald, Marion Schroedterhomscheidt, Bella Espinar, Benoît Gschwind, Zhipeng Qu, Carsten Hoyerklick
    Abstract:

    Abstract. A new fast clear-sky model called McClear was developed to estimate the downwelling shortwave Direct and global Irradiances received at ground level under clear skies. It is a fully physical model replacing empirical relations or simpler models used before. It exploits the recent results on aerosol properties, and total column content in water vapour and ozone produced by the MACC project (Monitoring Atmosphere Composition and Climate). It accurately reproduces the Irradiance computed by the libRadtran reference radiative transfer model with a computational speed approximately 105 times greater by adopting the abaci, or look-up table, approach combined with interpolation functions. It is therefore suited for geostationary satellite retrievals or numerical weather prediction schemes with many pixels or grid points, respectively. McClear Irradiances were compared to 1 min measurements made in clear-sky conditions at several stations within the Baseline Surface Radiation Network in various climates. The bias for global Irradiance comprises between −6 and 25 W m−2. The RMSE ranges from 20 W m−2 (3% of the mean observed Irradiance) to 36 W m−2 (5%) and the correlation coefficient ranges between 0.95 and 0.99. The bias for the Direct Irradiance comprises between −48 and +33 W m−2. The root mean square error (RMSE) ranges from 33 W m−2 (5%) to 64 W m−2 (10%). The correlation coefficient ranges between 0.84 and 0.98. This work demonstrates the quality of the McClear model combined with MACC products, and inDirectly the quality of the aerosol properties modelled by the MACC reanalysis.

  • McClear: a new model estimating downwelling solar radiation at ground level in clear-sky conditions
    Atmospheric Measurement Techniques, 2013
    Co-Authors: Mireille Lefèvre, Philippe Blanc, Armel Oumbe, Lucien Wald, Bella Espinar, Benoît Gschwind, Marion Schroedter-homscheidt, Antti Arola, Carsten Hoyer-klick, Angela Benedetti
    Abstract:

    A new fast clear-sky model called McClear was developed to estimate the downwelling shortwave Direct and global Irradiances received at ground level under clear skies. It is a fully physical model replacing empirical relations or simpler models used before. It exploits the recent results on aerosol properties, and total column content in water vapour and ozone produced by the MACC project (Monitoring Atmosphere Composition and Climate). It accurately reproduces the Irradiance computed by the libRadtran reference radiative transfer model with a computational speed approximately 105 times greater by adopting the abaci, or look-up table, approach combined with interpolation functions. It is therefore suited for geostationary satellite retrievals or numerical weather prediction schemes with many pixels or grid points, respectively. McClear Irradiances were compared to 1 min measurements made in clear-sky conditions at several stations within the Baseline Surface Radiation Network in various climates. The bias for global Irradiance comprises between −6 and 25Wm−2. The RMSE ranges from 20Wm−2 (3% of the mean observed Irradiance) to 36Wm−2 (5 %) and the correlation coefficient ranges between 0.95 and 0.99. The bias for the Direct Irradiance comprises between −48 and +33Wm−2. The root mean square error (RMSE) ranges from 33Wm−2 (5 %) to 64Wm−2 (10 %). The correlation coefficient ranges between 0.84 and 0.98. This work demonstrates the quality of the McClear model combined with MACC products, and inDirectly the quality of the aerosol properties modelled by the MACC reanalysis.

Armel Oumbe - One of the best experts on this subject based on the ideXlab platform.

  • Fast radiative transfer parameterisation for assessing the surface solar Irradiance: The Heliosat-4 method
    Meteorologische Zeitschrift, 2017
    Co-Authors: Armel Oumbe, Philippe Blanc, Bella Espinar, Benoît Gschwind, Mireille Lefèvre, Marion Schroedter-homscheidt, Gerhard Gesell, Lars Klüser, Laurent Saboret, Lucien Wald
    Abstract:

    The new Heliosat-4 method estimates the downwelling shortwave Irradiance received at ground level in all sky conditions. It provides the global Irradiance and its Direct and diffuse components on a horizontal plane and the Direct Irradiance for a plane normal to sun rays. It is a fully physical model using a fast, but still accurate approximation of radiative transfer modelling and is therefore well suited for geostationary satellite retrievals. It can also be used as a fast radiative transfer model in numerical weather prediction models. It is composed of two models based on abaci, also called look-up tables: the already-published McClear model calculating the Irradiance under cloud-free conditions and the new McCloud model calculating the extinction of Irradiance due to clouds. Both have been realized by using the libRadtran radiative transfer model. The main inputs to Heliosat-4 are aerosol properties, total column water vapour and ozone content as provided by the Copernicus Atmosphere Monitoring Service (CAMS) every 3 h. Cloud properties are derived from images of the Meteosat Second Generation (MSG) satellites in their 15 min temporal resolution using an adapted APOLLO (AVHRR Processing scheme Over cLouds, Land and Ocean) scheme. The 15 min means of Irradiance estimated by Heliosat-4 are compared to corresponding measurements made at 13 stations within the Baseline Surface Radiation Network and being located in the field of view of MSG and in various climates. The bias for global Irradiance is comprised between 2 and 32 W m −2. The root mean square error (RMSE) ranges between 74 and 94 W m −2. Relative RMSE values range between 15 % and 20 % of the mean observed Irradiance for stations in desert and Mediterranean climates, and between 26 % and 43 % for rainy climates with mild winters. Correlation coefficients between 0.91 and 0.97 are found. The bias for the Direct Irradiance at normal incidence is comprised between −163 and +50 W m −2. The RMSE ranges from 160 W m −2 (29 % of the mean observed Irradiance) to 288 W m −2 (63 %). The correlation coefficient ranges between 0.67 and 0.87.

  • Validating surface downwelling solar Irradiances estimated by the McClear model under cloud-free skies in the United Arab Emirates
    Solar Energy, 2015
    Co-Authors: Yehia Eissa, Philippe Blanc, Hosni Ghedira, Armel Oumbe, Lucien Wald, Hélène Bru, Saima Munawwar, Dominique Goffe
    Abstract:

    McClear, a fast model based on a radiative transfer solver, exploits the atmospheric properties provided by the EU-funded MACC project (Monitoring Atmospheric Composition and Climate) to estimate the surface downwelling solar Irradiances for cloud-free instances. This article presents the first validation of the McClear model for the specific climate of the United Arab Emirates where skies are frequently cloud-free but turbid. McClear accurately estimates the global horizontal Irradiance measured every 10 min at seven sites. The bias ranges from -9 W m-2 (-1% of the mean observed Irradiance) to +35 W m-2 (+6%). The root mean square error (RMSE) ranges from 22 W m-2 (4%) to 47 W m-2 (8%) and the coefficient of determination ranges from 0.980 to 0.990. Estimates of the Direct Irradiance at normal incidence exhibit an underestimation that is attributed to the overestimation of the aerosol optical depth in the MACC data set and not accounting for the circumsolar radiation in McClear. The corresponding bias ranges from -57 W m-2 (-8%) to +6 W m-2 (+1%). The RMSE ranges from 62 W m-2 (9%) to 87 W m-2 (13%) and the coefficient of determination ranges from 0.830 to 0.863. When compared to two other models in the literature, McClear is better able to capture the temporal variability of the Direct Irradiance at normal incidence. The validation results remain comparable for the global horizontal Irradiance.

  • mcclear a new model estimating downwelling solar radiation at ground level in clear sky conditions
    Atmospheric Measurement Techniques, 2013
    Co-Authors: Mireille Lefèvre, Philippe Blanc, Armel Oumbe, Lucien Wald, Marion Schroedterhomscheidt, Bella Espinar, Benoît Gschwind, Zhipeng Qu, Carsten Hoyerklick
    Abstract:

    Abstract. A new fast clear-sky model called McClear was developed to estimate the downwelling shortwave Direct and global Irradiances received at ground level under clear skies. It is a fully physical model replacing empirical relations or simpler models used before. It exploits the recent results on aerosol properties, and total column content in water vapour and ozone produced by the MACC project (Monitoring Atmosphere Composition and Climate). It accurately reproduces the Irradiance computed by the libRadtran reference radiative transfer model with a computational speed approximately 105 times greater by adopting the abaci, or look-up table, approach combined with interpolation functions. It is therefore suited for geostationary satellite retrievals or numerical weather prediction schemes with many pixels or grid points, respectively. McClear Irradiances were compared to 1 min measurements made in clear-sky conditions at several stations within the Baseline Surface Radiation Network in various climates. The bias for global Irradiance comprises between −6 and 25 W m−2. The RMSE ranges from 20 W m−2 (3% of the mean observed Irradiance) to 36 W m−2 (5%) and the correlation coefficient ranges between 0.95 and 0.99. The bias for the Direct Irradiance comprises between −48 and +33 W m−2. The root mean square error (RMSE) ranges from 33 W m−2 (5%) to 64 W m−2 (10%). The correlation coefficient ranges between 0.84 and 0.98. This work demonstrates the quality of the McClear model combined with MACC products, and inDirectly the quality of the aerosol properties modelled by the MACC reanalysis.

  • McClear: a new model estimating downwelling solar radiation at ground level in clear-sky conditions
    Atmospheric Measurement Techniques, 2013
    Co-Authors: Mireille Lefèvre, Philippe Blanc, Armel Oumbe, Lucien Wald, Bella Espinar, Benoît Gschwind, Marion Schroedter-homscheidt, Antti Arola, Carsten Hoyer-klick, Angela Benedetti
    Abstract:

    A new fast clear-sky model called McClear was developed to estimate the downwelling shortwave Direct and global Irradiances received at ground level under clear skies. It is a fully physical model replacing empirical relations or simpler models used before. It exploits the recent results on aerosol properties, and total column content in water vapour and ozone produced by the MACC project (Monitoring Atmosphere Composition and Climate). It accurately reproduces the Irradiance computed by the libRadtran reference radiative transfer model with a computational speed approximately 105 times greater by adopting the abaci, or look-up table, approach combined with interpolation functions. It is therefore suited for geostationary satellite retrievals or numerical weather prediction schemes with many pixels or grid points, respectively. McClear Irradiances were compared to 1 min measurements made in clear-sky conditions at several stations within the Baseline Surface Radiation Network in various climates. The bias for global Irradiance comprises between −6 and 25Wm−2. The RMSE ranges from 20Wm−2 (3% of the mean observed Irradiance) to 36Wm−2 (5 %) and the correlation coefficient ranges between 0.95 and 0.99. The bias for the Direct Irradiance comprises between −48 and +33Wm−2. The root mean square error (RMSE) ranges from 33Wm−2 (5 %) to 64Wm−2 (10 %). The correlation coefficient ranges between 0.84 and 0.98. This work demonstrates the quality of the McClear model combined with MACC products, and inDirectly the quality of the aerosol properties modelled by the MACC reanalysis.

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  • Improving the McClear model estimating the downwelling solar radiation at ground level in cloud-free conditions – McClear‑v3
    Meteorologische Zeitschrift, 2019
    Co-Authors: Benoît Gschwind, Philippe Blanc, Lucien Wald, Mireille Lefèvre, Marion Schroedter-homscheidt, Antti Arola
    Abstract:

    The fast McClear clear-sky model estimates the downwelling shortwave Direct and diffuse Irradiances received at ground level under cloud-free conditions. Several improvements are presented. They focus on the modeling of changes in Irradiances with the solar zenithal angle and on a better exploitation of the aerosol properties offered by the Copernicus Atmosphere Monitoring Service (CAMS). Irradiances from this new version McClear-v3 were compared to 1 min measurements made in cloud-free conditions at 11 stations belonging to the Baseline Surface Radiation Network and being located in various climates. The correlation coefficient ranges between 0.982 and 0.999 for the global Irradiance. The bias is positive (overestimation) and ranges between 1 W m −2 (0.1 % of the mean observed Irradiance) and 20 W m −2 (3.2 %), with the exception of Barrow in Alaska (18 W m −2). The standard deviation ranges between 16 W m −2 (2.3 %) and 30 W m −2 (3.8 %). The correlation coefficient for the Direct Irradiance ranges between 0.902 and 0.995. As expected, since the Direct in McClear does not comprise any circumsolar contribution, the bias is negative (underestimation) and ranges between 49 W m −2 (7.7 %) and 5 W m −2 (0.7 %), with two exceptions: Sede Boqer (79 W m −2) and Brasilia (13 W m −2). The standard deviation is comprised between 34 W m −2 (5.3 %) and 69 W m −2 (10.7 %). These results are similar to those obtained with McClear version 2. Compared to the latter, McClear-v3 removes several artifacts and its estimates are continuous in space and time.

  • Fast radiative transfer parameterisation for assessing the surface solar Irradiance: The Heliosat-4 method
    Meteorologische Zeitschrift, 2017
    Co-Authors: Armel Oumbe, Philippe Blanc, Bella Espinar, Benoît Gschwind, Mireille Lefèvre, Marion Schroedter-homscheidt, Gerhard Gesell, Lars Klüser, Laurent Saboret, Lucien Wald
    Abstract:

    The new Heliosat-4 method estimates the downwelling shortwave Irradiance received at ground level in all sky conditions. It provides the global Irradiance and its Direct and diffuse components on a horizontal plane and the Direct Irradiance for a plane normal to sun rays. It is a fully physical model using a fast, but still accurate approximation of radiative transfer modelling and is therefore well suited for geostationary satellite retrievals. It can also be used as a fast radiative transfer model in numerical weather prediction models. It is composed of two models based on abaci, also called look-up tables: the already-published McClear model calculating the Irradiance under cloud-free conditions and the new McCloud model calculating the extinction of Irradiance due to clouds. Both have been realized by using the libRadtran radiative transfer model. The main inputs to Heliosat-4 are aerosol properties, total column water vapour and ozone content as provided by the Copernicus Atmosphere Monitoring Service (CAMS) every 3 h. Cloud properties are derived from images of the Meteosat Second Generation (MSG) satellites in their 15 min temporal resolution using an adapted APOLLO (AVHRR Processing scheme Over cLouds, Land and Ocean) scheme. The 15 min means of Irradiance estimated by Heliosat-4 are compared to corresponding measurements made at 13 stations within the Baseline Surface Radiation Network and being located in the field of view of MSG and in various climates. The bias for global Irradiance is comprised between 2 and 32 W m −2. The root mean square error (RMSE) ranges between 74 and 94 W m −2. Relative RMSE values range between 15 % and 20 % of the mean observed Irradiance for stations in desert and Mediterranean climates, and between 26 % and 43 % for rainy climates with mild winters. Correlation coefficients between 0.91 and 0.97 are found. The bias for the Direct Irradiance at normal incidence is comprised between −163 and +50 W m −2. The RMSE ranges from 160 W m −2 (29 % of the mean observed Irradiance) to 288 W m −2 (63 %). The correlation coefficient ranges between 0.67 and 0.87.

  • Validating surface downwelling solar Irradiances estimated by the McClear model under cloud-free skies in the United Arab Emirates
    Solar Energy, 2015
    Co-Authors: Yehia Eissa, Philippe Blanc, Hosni Ghedira, Armel Oumbe, Lucien Wald, Hélène Bru, Saima Munawwar, Dominique Goffe
    Abstract:

    McClear, a fast model based on a radiative transfer solver, exploits the atmospheric properties provided by the EU-funded MACC project (Monitoring Atmospheric Composition and Climate) to estimate the surface downwelling solar Irradiances for cloud-free instances. This article presents the first validation of the McClear model for the specific climate of the United Arab Emirates where skies are frequently cloud-free but turbid. McClear accurately estimates the global horizontal Irradiance measured every 10 min at seven sites. The bias ranges from -9 W m-2 (-1% of the mean observed Irradiance) to +35 W m-2 (+6%). The root mean square error (RMSE) ranges from 22 W m-2 (4%) to 47 W m-2 (8%) and the coefficient of determination ranges from 0.980 to 0.990. Estimates of the Direct Irradiance at normal incidence exhibit an underestimation that is attributed to the overestimation of the aerosol optical depth in the MACC data set and not accounting for the circumsolar radiation in McClear. The corresponding bias ranges from -57 W m-2 (-8%) to +6 W m-2 (+1%). The RMSE ranges from 62 W m-2 (9%) to 87 W m-2 (13%) and the coefficient of determination ranges from 0.830 to 0.863. When compared to two other models in the literature, McClear is better able to capture the temporal variability of the Direct Irradiance at normal incidence. The validation results remain comparable for the global horizontal Irradiance.

  • mcclear a new model estimating downwelling solar radiation at ground level in clear sky conditions
    Atmospheric Measurement Techniques, 2013
    Co-Authors: Mireille Lefèvre, Philippe Blanc, Armel Oumbe, Lucien Wald, Marion Schroedterhomscheidt, Bella Espinar, Benoît Gschwind, Zhipeng Qu, Carsten Hoyerklick
    Abstract:

    Abstract. A new fast clear-sky model called McClear was developed to estimate the downwelling shortwave Direct and global Irradiances received at ground level under clear skies. It is a fully physical model replacing empirical relations or simpler models used before. It exploits the recent results on aerosol properties, and total column content in water vapour and ozone produced by the MACC project (Monitoring Atmosphere Composition and Climate). It accurately reproduces the Irradiance computed by the libRadtran reference radiative transfer model with a computational speed approximately 105 times greater by adopting the abaci, or look-up table, approach combined with interpolation functions. It is therefore suited for geostationary satellite retrievals or numerical weather prediction schemes with many pixels or grid points, respectively. McClear Irradiances were compared to 1 min measurements made in clear-sky conditions at several stations within the Baseline Surface Radiation Network in various climates. The bias for global Irradiance comprises between −6 and 25 W m−2. The RMSE ranges from 20 W m−2 (3% of the mean observed Irradiance) to 36 W m−2 (5%) and the correlation coefficient ranges between 0.95 and 0.99. The bias for the Direct Irradiance comprises between −48 and +33 W m−2. The root mean square error (RMSE) ranges from 33 W m−2 (5%) to 64 W m−2 (10%). The correlation coefficient ranges between 0.84 and 0.98. This work demonstrates the quality of the McClear model combined with MACC products, and inDirectly the quality of the aerosol properties modelled by the MACC reanalysis.

  • McClear: a new model estimating downwelling solar radiation at ground level in clear-sky conditions
    Atmospheric Measurement Techniques, 2013
    Co-Authors: Mireille Lefèvre, Philippe Blanc, Armel Oumbe, Lucien Wald, Bella Espinar, Benoît Gschwind, Marion Schroedter-homscheidt, Antti Arola, Carsten Hoyer-klick, Angela Benedetti
    Abstract:

    A new fast clear-sky model called McClear was developed to estimate the downwelling shortwave Direct and global Irradiances received at ground level under clear skies. It is a fully physical model replacing empirical relations or simpler models used before. It exploits the recent results on aerosol properties, and total column content in water vapour and ozone produced by the MACC project (Monitoring Atmosphere Composition and Climate). It accurately reproduces the Irradiance computed by the libRadtran reference radiative transfer model with a computational speed approximately 105 times greater by adopting the abaci, or look-up table, approach combined with interpolation functions. It is therefore suited for geostationary satellite retrievals or numerical weather prediction schemes with many pixels or grid points, respectively. McClear Irradiances were compared to 1 min measurements made in clear-sky conditions at several stations within the Baseline Surface Radiation Network in various climates. The bias for global Irradiance comprises between −6 and 25Wm−2. The RMSE ranges from 20Wm−2 (3% of the mean observed Irradiance) to 36Wm−2 (5 %) and the correlation coefficient ranges between 0.95 and 0.99. The bias for the Direct Irradiance comprises between −48 and +33Wm−2. The root mean square error (RMSE) ranges from 33Wm−2 (5 %) to 64Wm−2 (10 %). The correlation coefficient ranges between 0.84 and 0.98. This work demonstrates the quality of the McClear model combined with MACC products, and inDirectly the quality of the aerosol properties modelled by the MACC reanalysis.