The importance of the sampling frequency in determining short-time-averaged irradiance and illuminance for rapidly changing cloud cover

DeLaunay, James; Rommel, Matthias; Geisler, J. E.

doi:10.1016/0038-092x(94)90662-9

Cited by 4 publications

(2 citation statements)

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“…In particular, we are interested in analyzing short-term fluctuations in overcast horizontal illuminance and zenith luminance as measured every 30 seconds for total elapsed times t el Յ 2 h. Our choice of sampling frequency and maximum measurement period reflects constraints im-posed by (1) our spectroradiometers' long integration times at twilight illuminance levels and (2) measurement interruptions due to the onset of rain or clearing in some overcasts. Although our chosen sampling frequency would be too low to capture all photometric details of the most rapidly changing partly cloudy skies, 9 for many overcasts it is more than adequate to reveal a remarkable range of illuminance and luminance fluctuations.…”

Section: Introductionmentioning

confidence: 99%

Short-term variability of overcast brightness

Lee

Hernández‐Andrés

2005

Appl. Opt.

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Overcasts seen from below seldom are uniform, unchanging cloud shields, yet little is known about their short-term photometric variability (periods < or = 2 h). Visible-wavelength spectra of daytime and twilight overcast skies measured at 30-s intervals reveal unexpected temporal variability in horizontal illuminance E(v) and zenith luminance L(v). Fourier analysis of these time series shows peak fluctuations at periods of 2-40 min. Factors such as cloud type and optical depth, presence of fog or snow, and instrument field of view can affect overcast brightness variability. Surprisingly, under some circumstances overcast twilight E(v) exceeds clear-sky E(v) at the same Sun elevation.

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Section: Introductionmentioning

confidence: 99%

Short-term variability of overcast brightness

Lee

Hernández‐Andrés

2005

Appl. Opt.

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“…Very few authors, however, have discussed short-term irradiance or illuminance changes (Delaunay et al, 1994;Morf, 2002;Walkenhorst et al, 2002). The application of hourly irradiance time-series for illuminance reference years would seem to be incorrect.…”

Section: Introductionmentioning

confidence: 99%

Sunshine duration and daily courses of illuminance in Bratislava

Darula¹,

Kittler²

2004

Intl Journal of Climatology

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The occurrences of typical sky conditions during overcast days are close to the CIE Overcast Sky Standard in the Bratislava area; their variation is specified by the diffuse coefficient k dd = D v /E v where D v is the horizontal diffuse illuminance and E v is the extraterrestrial illuminance. Luminance distributions on cloudless days are close to the CIE Clear Sky Standard. Complex daylight conditions can be expected during cloudy days when moving clouds cause frequent sun disk shading with abrupt changes in illuminance levels. Since sunshine duration is one of the basic climatic parameters that describes sunny situations, the present study attempts to investigate its relation to daily illuminance levels. However, the average daily value of sunshine duration does not exactly correspond to the same illuminance course, as it depends on the temporal distribution of sunny periods within the day. Anyhow, the estimation of daytime illuminance levels is mainly influenced by the presence or absence of sunshine with frequent sky luminance patterns.

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Enhanced values of global irradiance due to the presence of clouds in Eastern Mediterranean

Tapakis

Charalambides

2014

Renewable Energy

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The importance of the sampling frequency in determining short-time-averaged irradiance and illuminance for rapidly changing cloud cover

Cited by 4 publications

References 2 publications

Short-term variability of overcast brightness

Short-term variability of overcast brightness

Sunshine duration and daily courses of illuminance in Bratislava

Enhanced values of global irradiance due to the presence of clouds in Eastern Mediterranean

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