Short-term variability of experimental ultraviolet and total solar irradiance in Southeastern Spain

Antón, Manuel; Gil, J. E.; Cazorla, A.; Fernández‐Gálvez, J.; Foyo-Moreno, I.; Olmo, F.J.; Alados-Arboledas, L.

doi:10.1016/j.atmosenv.2011.06.020

Cited by 27 publications

(9 citation statements)

References 52 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…From the energy production point of view, solar energy systems are strongly affected by cloud presence. Especially in the case of concentration solar power plants and concentration photovoltaic systems, that strongly depend on direct beam solar irradiance, their energy output is highly reduced when the sun is obstructed by clouds (Beyer et al, 1994;Frederick and Steele, 1995;Bartlett et al, 1998;Antón et al, 2011;Cazorla et al, 2015). Both climate and solar energy issues motivate the need for cloud observations.…”

Section: Introductionmentioning

confidence: 99%

Cloud cover detection combining high dynamic range sky images and ceilometer measurements

Román

Cazorla

Toledano

et al. 2017

Atmospheric Research

Self Cite

View full text Add to dashboard Cite

This paper presents a new algorithm for cloud detection based on high dynamic range images from a sky camera and ceilometer measurements. The algorithm is also able to detect the obstruction of the sun. This algorithm, called CPC (Camera Plus Ceilometer), is based on the assumption that under cloud-free conditions the sky field must show symmetry. The symmetry criteria are applied depending on ceilometer measurements of the cloud base height. CPC algorithm is applied in two Spanish locations (Granada and Valladolid). The performance of CPC retrieving the sun conditions (obstructed or unobstructed) is analyzed in detail using as reference pyranometer measurements at Granada. CPC retrievals are in agreement with those derived from the reference pyranometer in 85% of the cases (it seems that this agreement does not depend on aerosol size or optical depth). The agreement percentage goes down to only 48% when another algorithm, based on Red-Blue Ratio (RBR), is applied to the sky camera images. The retrieved cloud cover at Granada and Valladolid is compared with that registered by trained meteorological observers. CPC cloud cover is in agreement with the reference showing a slight overestimation and a mean absolute error around 1 okta. A major advantage of the CPC algorithm with respect to the RBR method is that the determined cloud cover is independent of aerosol properties. The RBR algorithm overestimates cloud cover for coarse aerosols and high loads. Cloud cover obtained only from ceilometer shows similar results than CPC algorithm; but the horizontal distribution cannot be obtained. In addition, it has been observed that under quick and strong changes on cloud cover ceilometers retrieve a cloud cover fitting worse with the real cloud cover.

show abstract

Section: Introductionmentioning

confidence: 99%

Cloud cover detection combining high dynamic range sky images and ceilometer measurements

Román

Cazorla

Toledano

et al. 2017

Atmospheric Research

Self Cite

View full text Add to dashboard Cite

show abstract

“…The influence of the cloudiness on solar radiation has a significant spectral dependence, being weaker when the wavelength is shorter (Foyo-Moreno et al, 2001;Bilbao et al, 2011;de Miguel et al, 2011a). On the other hand, the clouds can also produce the enhancement of the solar radiation at surface, reaching levels even higher than its value at the top of atmosphere (Piacentini et al, 2010;Antón et al, 2011a). Therefore, studies about the behaviour of sky radiance and clouds are important for a better understanding of cloud-radiation interaction.…”

Section: R Román Et Al: Calibration Of An All-sky Cameramentioning

confidence: 99%

Calibration of an all-sky camera for obtaining sky radiance at three wavelengths

et al. 2012

Self Cite

View full text Add to dashboard Cite

Abstract. This paper proposes a method to obtain spectral sky radiances, at three wavelengths (464, 534 and 626 nm), from hemispherical sky images. Images are registered with the All-Sky Imager installed at the Andalusian Center for Environmental Research (CEAMA) in Granada (Spain). The methodology followed in this work for the absolute calibration in radiance of this instrument is based on the comparison of its output measurements with modelled sky radiances derived from the LibRadtran/UVSPEC radiative transfer code under cloud-free conditions. Previously, in order to check the goodness of the simulated radiances, these are compared with experimental values recorded by a CIMEL sunphotometer. In general, modelled radiances are in agreement with experimental data, showing mean differences lower than 20 % except for the pixels located next to the Sun position that show larger errors.The relationship between the output signal of the All-Sky Imager and the modelled sky radiances provides a calibration matrix for each image. The variability of the matrix coefficients is analyzed, showing no significant changes along a period of 5 months. Therefore, a unique calibration matrix per channel is obtained for all selected images (a total of 705 images per channel). Camera radiances are compared with CIMEL radiances, finding mean absolute differences between 2 % and 15 % except for pixels near to the Sun and high scattering angles. We apply these calibration matrices to three images in order to study the sky radiance distributions for three different sky conditions: cloudless, overcast and partially cloudy. Horizon brightening under cloudless conditions has been observed together with the enhancement effect of individual clouds on sky radiance.

show abstract

“…Overirradiance caused by cloud enhancement has been plenty discussed by many authors throughout the years (Antón et al, 2011;Emck and Ritcher, 2008;Gu et al, 2001;Hansen et al, 2010;Luoma et al, 2012;Piacentini et al, 2003Piacentini et al, , 2011Piedehierro et al, 2014;Suehrcke and McCormick, 1988;Tapakis and Charalambides, 2014;Weigl et al, 2012;Yordanov et al, 2013a,b), and the phenomenon is expected to be more intense at tropical latitudes in the Southern Hemisphere, at high plateaus and mountains (Yordanov et al, 2013b). Cloud enhancement has been traditionally related to reflection of sun radiation on the borders of Cumulus clouds around the sun disc, with the sun unobstructed.…”

Section: Introductionmentioning

confidence: 99%

Extreme overirradiance events in São Paulo, Brazil

2014

View full text Add to dashboard Cite

show abstract

Short-term variability of experimental ultraviolet and total solar irradiance in Southeastern Spain

Cited by 27 publications

References 52 publications

Cloud cover detection combining high dynamic range sky images and ceilometer measurements

Cloud cover detection combining high dynamic range sky images and ceilometer measurements

Calibration of an all-sky camera for obtaining sky radiance at three wavelengths

Extreme overirradiance events in São Paulo, Brazil

Contact Info

Product

Resources

About