Abstract

Based on a CCD camera, we have developed an in-house sky imager system for the purpose of cloud cover estimation and characterization. The system captures a multispectral image every 5min, and the analysis is done with a method based on an optimized neural network classification procedure and a genetic algorithm. The method discriminates between clear sky and two cloud classes: opaque and thin clouds. It also divides the image into sectors and finds the percentage of clouds in those different regions. We have validated the classification algorithm on two levels: image level, using the cloud observations included in the METAR register performed at the closest meteorological station, and pixel level, determining whether the final classification is correct.

© 2008 Optical Society of America

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  46. H. Lyamani, F. J. Olmo, A. Alcántara, and L. Alados-Arboledas, "Atmospheric aerosols during the 2003 heat wave in southeastern Spain I: spectral optical depth," Atmos. Environ. 40, 6453-6464 (2006).
    [CrossRef]
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2006 (5)

M. Stowaser and K. Hamilton, "Relationship between shortwave cloud radiative forcing and local meteorological variables compared in observations and several global climate models," J. Clim. 19, 4344-4359 (2006).
[CrossRef]

J. M. Sabburg and A. V. Parisi, "Spectral dependency of cloud enhanced UV irradiance," Atmos. Res. 81, 206-214 (2006).
[CrossRef]

C. J. Long, J. Sabburg, J. Calbó, and D. Pagès, "Retrieving cloud characteristics from ground-based daytime color all-sky images," J. Atmos. Ocean. Technol. 23, 633-652 (2006).
[CrossRef]

M. P. Souza-Echer, E. B. Pereira, L. S. Bins, and M. A. R. Andrade, "A simple method for the assessment of the cloud cover state in high-latitude regions by a ground based digital camera," J. Atmos. Ocean. Technol. 23, 437-447 (2006).
[CrossRef]

H. Lyamani, F. J. Olmo, A. Alcántara, and L. Alados-Arboledas, "Atmospheric aerosols during the 2003 heat wave in southeastern Spain I: spectral optical depth," Atmos. Environ. 40, 6453-6464 (2006).
[CrossRef]

2005 (6)

H. Lyamani, F. J. Olmo, and L. Alados-Arboledas, "Saharan dust outbreak over southeastern Spain as detected by sun photometer," Atmos. Environ. 39, 7276-7284 (2005).

M. Escudero, S. Castillo, X. Querol, A. Avila, M. Alarcón, M. M. Viana, A. Alastuey, E. Cuevas, and S. Rodríguez, "Wet and dry African dust episodes over eastern Spain," J. Geophys. Res. 110(D18), D18S08 (2005).
[CrossRef]

J. E. Gil, A. Cazorla, F. J. Olmo, and L. Alados-Arboledas, "Experimental set up to study the cloud radiative effects on UVB at Granada (Spain)," in Proceedings of the European Geosciences Union General Assembly, A.K.Richter, ed. (EGU, 2005) Vol. 1, papers EGU05-A-00320, AS1.08.1WE2P-0059.

S. A. Marcos, M. Soriano, and C. Saloma, "Classification of coral reef images from underwater video using neural networks," Opt. Express 13, 8766-8771 (2005).
[CrossRef] [PubMed]

J. Calbó, D. Pages, and J. A. González, "Empirical studies of cloud effects on UV radiation: a review," Rev. Geophys. 43, 2 (2005).
[CrossRef]

J. C. van der Leun and P. D. Forbes, "Ultraviolet tanning equipment: six questions," Photodermatol. Photoimmunol. Photomed. 21, 254-259 (2005).
[CrossRef] [PubMed]

2004 (3)

J. M. Gutiérrez, R. Cano, A. S. Cofiño, and C. Sordo, Redes Probabilísticas y Neuronales en las Ciencias Atmosféricas (Probabilistic and Neural Networks on Atmospheric Sciences) (Ministerio de Medio Ambiente, Dirección General del Instituto Nacional de Meteorología, 2004).
[PubMed]

I. Alados, J. A. Mellado, F. Ramos, and L. Alados-Arboledas, "Estimating UV erythemal irradiance by means of neural networks," Photochem. Photobiol. 80, 351-358 (2004).
[CrossRef] [PubMed]

J. M. Sabburg and C. N. Long, "Improved sky imaging for studies of enhanced UV irradiance," Atmos. Chem. Phys. Discuss. 4, 6213-6238 (2004).
[CrossRef]

2003 (2)

L. Alados-Arboledas, I. Alados, I. Foyo-Moreno, A. Alcántara, and F. J. Olmo, "The influence of clouds on surface UV erythemal irradiance," Atmos. Res. 66, 273-290 (2003).
[CrossRef]

I. Foyo-Moreno, J. Vida, I. Alados, F. J. Olmo, and L. Alados-Arboledas, "The influence of clouds on UV global irradiance (295-385nm)," Agric. Forest Meteorol. 120, 101-111 (2003).
[CrossRef]

2002 (4)

2000 (4)

J. Matthijsen, H. Slaper, H. Reinen, and G. Velders, "Reduction of solar UV by clouds: a comparison between satellite-derived cloud effects and ground-based radiation measurements," J. Geophys. Res. 105(D4), 5069-5080 (2000).
[CrossRef]

U. Feister, J. E. Shields, M. E. Karr, R. W. Johnson, K. Dehne, and M. Woldt, "Ground-based cloud images and sky radiances in the visible and near infrared region from whole sky imager measurements," presented at the Climate Monitoring--Satellite Application Facility Training Workshop, Dresden, Germany, November 20-22, 2000.

J. Sabburg, "Quantification of cloud around the sun and its correlation with global UV measurement," Ph.D. thesis (Queensland University of Technology, Brisbane, Australia, 2000).

J. Sabburg and J. Wong, "Evaluation of a sky/cloud formula for estimating UV-B irradiance under cloudy conditions," J. Geophys. Res. 105, 29685-29691 (2000).
[CrossRef]

1999 (1)

J. Sabburg and J. Wong, "Evaluation of a sky camera for use in radiation measurement," J. Atmos. Ocean. Technol. 16, 752-759 (1999).
[CrossRef]

1998 (2)

J. E. Shields, R. W. Johnson, M. E. Karr, and J. L. Wertz, "Automated day/night whole sky imagers for field assessment of cloud cover distributions and radiance distributions," presented at the 10th Symposium on Meteorological Observations and Instrumentation of the American Meteorological Society, Boston, Massachusetts, January 11-16, 1998.

J. E. Shields, M. E. Karr, T. P. Tooman, D. H. Sowle, and S. T. Moore, "The whole sky imager--a year of progress," presented at the Eighth Atmospheric Radiation Measurement (ARM) Science Team Meeting, Tucson, Arizona, March 23-27, 1998.

1997 (1)

D. Barber and C. M. Bishop, "Ensemble learning for multi-layer networks," in Advances in Neural Information Processing Systems, M.I.Jordan, M.J.Kearns, and S.A.Solla, eds. (MIT Press, 1997), pp. 395-401.

1996 (2)

J. G. Estupiñan, S. Raman, G. H. Crescenti, J. J. Streicher, and W. F. Barnard, "Effects of clouds and haze on UV-B radiation," J. Geophys. Res. 101(D11), 16807-16816 (1996).
[CrossRef]

S. Greenberg and H. Guterman, "Neural-network classifiers for automatic real-world aerial image recognition," Appl. Opt. 35, 4598-4609 (1996).
[CrossRef] [PubMed]

1995 (4)

C. M. Bishop, Neural Networks for Pattern Recognition (Oxford U. Press, 1995).

Anon., Guía Resumida del Clima en España 1961-1990 (Resumed guide of Spain Climate 1961-1990) (Ministerio de Obras Públicas, Transporte y Medio Ambiente, Dirección General del Instituto Nacional de Meteorología, 1995).

L. Alados-Arboledas, J. Vida, and F. J. Olmo, "The estimation of thermal radiation under cloudy conditions," Int. J. Climatol. 15, 107-116 (1995).
[CrossRef]

WMO, Manual on Codes, Publication No. 306 (World Meteorological Organization, 1995).

1993 (2)

M. Riedmiller and H. Braun, "A direct adaptive method for faster backpropagation learning: the RPROP algorithm, in Proceedings of the IEEE International Conference on Neural Networks (IEEE, 1993), pp. 586-591.
[CrossRef]

J. E. Shields, R. W. Johnson, and T. E. Koehler, "Automated whole sky imaging systems for cloud field assessment," presented at the Fourth Symposium on Global Change Studies of the American Meteorological Society, Boston, Massachusetts, January 17-22, 1993.

1992 (1)

Z. Michalewicz, Genetic Algorithms + Data Structures = Evolution Programs (Springer-Verlag, 1992).

1990 (1)

T. Khanna, Foundations of Neural Networks (Addison-Wesley, 1990).

1989 (2)

R. R. Rogers and M. K. Yau, A Short Course in Cloud Physics (Pergamon, 1989).

D. E. Goldberg, Genetic Algorithms in Search, Optimization and Machine Learning (Addison-Wesley, 1989).

1987 (1)

R. Lippman, "An introduction to computing with neural nets," IEEE ASSP Mag. 4(2), 4-22 (1987).
[CrossRef]

1986 (1)

D. E. Rumerlhart, G. E. Hilton, and R. J. Williams, "Learning internal representations by errors propagation," in Parallel Distributed Processing: Exploitations in the Microstructure of Cognition Foundations, D.E.Rumelhart and J.L.MacClelland, eds. (MIT Press, 1986), Vol. 1, pp. 318-362.

1983 (1)

WMO, Guide to Meteorological Practice, Publication No. 168 (World Meteorological Organization, 1983).

1964 (1)

A. Ångström, "The parameters of atmospheric turbidity," Tellus 16, 64-75 (1964).
[CrossRef]

1962 (2)

J. H. Holland, "Outline for a logical theory of adaptive systems," J. Assoc. Comput. Mach. 9, 297-314 (1962).
[CrossRef]

H. J. Bremermann, "Optimization through evolution and recombination," in Self Organizing Systems, M.C.Yovits, G.T.Jacobi, and G.D.Goldstein, eds. (Spartan, 1962), pp. 93-106.

1961 (1)

B. Rosenblatt, Principles of Neurodynamics: Perceptrons and the Theory of Brain Mechanisms (Spartan, 1961).

Alados, I.

I. Alados, J. A. Mellado, F. Ramos, and L. Alados-Arboledas, "Estimating UV erythemal irradiance by means of neural networks," Photochem. Photobiol. 80, 351-358 (2004).
[CrossRef] [PubMed]

L. Alados-Arboledas, I. Alados, I. Foyo-Moreno, A. Alcántara, and F. J. Olmo, "The influence of clouds on surface UV erythemal irradiance," Atmos. Res. 66, 273-290 (2003).
[CrossRef]

I. Foyo-Moreno, J. Vida, I. Alados, F. J. Olmo, and L. Alados-Arboledas, "The influence of clouds on UV global irradiance (295-385nm)," Agric. Forest Meteorol. 120, 101-111 (2003).
[CrossRef]

Alados-Arboledas, L.

H. Lyamani, F. J. Olmo, A. Alcántara, and L. Alados-Arboledas, "Atmospheric aerosols during the 2003 heat wave in southeastern Spain I: spectral optical depth," Atmos. Environ. 40, 6453-6464 (2006).
[CrossRef]

H. Lyamani, F. J. Olmo, and L. Alados-Arboledas, "Saharan dust outbreak over southeastern Spain as detected by sun photometer," Atmos. Environ. 39, 7276-7284 (2005).

J. E. Gil, A. Cazorla, F. J. Olmo, and L. Alados-Arboledas, "Experimental set up to study the cloud radiative effects on UVB at Granada (Spain)," in Proceedings of the European Geosciences Union General Assembly, A.K.Richter, ed. (EGU, 2005) Vol. 1, papers EGU05-A-00320, AS1.08.1WE2P-0059.

I. Alados, J. A. Mellado, F. Ramos, and L. Alados-Arboledas, "Estimating UV erythemal irradiance by means of neural networks," Photochem. Photobiol. 80, 351-358 (2004).
[CrossRef] [PubMed]

I. Foyo-Moreno, J. Vida, I. Alados, F. J. Olmo, and L. Alados-Arboledas, "The influence of clouds on UV global irradiance (295-385nm)," Agric. Forest Meteorol. 120, 101-111 (2003).
[CrossRef]

L. Alados-Arboledas, I. Alados, I. Foyo-Moreno, A. Alcántara, and F. J. Olmo, "The influence of clouds on surface UV erythemal irradiance," Atmos. Res. 66, 273-290 (2003).
[CrossRef]

L. Alados-Arboledas, J. Vida, and F. J. Olmo, "The estimation of thermal radiation under cloudy conditions," Int. J. Climatol. 15, 107-116 (1995).
[CrossRef]

Alarcón, M.

M. Escudero, S. Castillo, X. Querol, A. Avila, M. Alarcón, M. M. Viana, A. Alastuey, E. Cuevas, and S. Rodríguez, "Wet and dry African dust episodes over eastern Spain," J. Geophys. Res. 110(D18), D18S08 (2005).
[CrossRef]

Alastuey, A.

M. Escudero, S. Castillo, X. Querol, A. Avila, M. Alarcón, M. M. Viana, A. Alastuey, E. Cuevas, and S. Rodríguez, "Wet and dry African dust episodes over eastern Spain," J. Geophys. Res. 110(D18), D18S08 (2005).
[CrossRef]

Alcántara, A.

H. Lyamani, F. J. Olmo, A. Alcántara, and L. Alados-Arboledas, "Atmospheric aerosols during the 2003 heat wave in southeastern Spain I: spectral optical depth," Atmos. Environ. 40, 6453-6464 (2006).
[CrossRef]

L. Alados-Arboledas, I. Alados, I. Foyo-Moreno, A. Alcántara, and F. J. Olmo, "The influence of clouds on surface UV erythemal irradiance," Atmos. Res. 66, 273-290 (2003).
[CrossRef]

Andrade, M. A. R.

M. P. Souza-Echer, E. B. Pereira, L. S. Bins, and M. A. R. Andrade, "A simple method for the assessment of the cloud cover state in high-latitude regions by a ground based digital camera," J. Atmos. Ocean. Technol. 23, 437-447 (2006).
[CrossRef]

Ångström, A.

A. Ångström, "The parameters of atmospheric turbidity," Tellus 16, 64-75 (1964).
[CrossRef]

Avila, A.

M. Escudero, S. Castillo, X. Querol, A. Avila, M. Alarcón, M. M. Viana, A. Alastuey, E. Cuevas, and S. Rodríguez, "Wet and dry African dust episodes over eastern Spain," J. Geophys. Res. 110(D18), D18S08 (2005).
[CrossRef]

Barber, D.

D. Barber and C. M. Bishop, "Ensemble learning for multi-layer networks," in Advances in Neural Information Processing Systems, M.I.Jordan, M.J.Kearns, and S.A.Solla, eds. (MIT Press, 1997), pp. 395-401.

Barnard, W. F.

J. G. Estupiñan, S. Raman, G. H. Crescenti, J. J. Streicher, and W. F. Barnard, "Effects of clouds and haze on UV-B radiation," J. Geophys. Res. 101(D11), 16807-16816 (1996).
[CrossRef]

Bins, L. S.

M. P. Souza-Echer, E. B. Pereira, L. S. Bins, and M. A. R. Andrade, "A simple method for the assessment of the cloud cover state in high-latitude regions by a ground based digital camera," J. Atmos. Ocean. Technol. 23, 437-447 (2006).
[CrossRef]

Bishop, C. M.

D. Barber and C. M. Bishop, "Ensemble learning for multi-layer networks," in Advances in Neural Information Processing Systems, M.I.Jordan, M.J.Kearns, and S.A.Solla, eds. (MIT Press, 1997), pp. 395-401.

C. M. Bishop, Neural Networks for Pattern Recognition (Oxford U. Press, 1995).

Braun, H.

M. Riedmiller and H. Braun, "A direct adaptive method for faster backpropagation learning: the RPROP algorithm, in Proceedings of the IEEE International Conference on Neural Networks (IEEE, 1993), pp. 586-591.
[CrossRef]

Bremermann, H. J.

H. J. Bremermann, "Optimization through evolution and recombination," in Self Organizing Systems, M.C.Yovits, G.T.Jacobi, and G.D.Goldstein, eds. (Spartan, 1962), pp. 93-106.

Burrows, J. P.

Calbó, J.

C. J. Long, J. Sabburg, J. Calbó, and D. Pagès, "Retrieving cloud characteristics from ground-based daytime color all-sky images," J. Atmos. Ocean. Technol. 23, 633-652 (2006).
[CrossRef]

J. Calbó, D. Pages, and J. A. González, "Empirical studies of cloud effects on UV radiation: a review," Rev. Geophys. 43, 2 (2005).
[CrossRef]

Cano, R.

J. M. Gutiérrez, R. Cano, A. S. Cofiño, and C. Sordo, Redes Probabilísticas y Neuronales en las Ciencias Atmosféricas (Probabilistic and Neural Networks on Atmospheric Sciences) (Ministerio de Medio Ambiente, Dirección General del Instituto Nacional de Meteorología, 2004).
[PubMed]

Castillo, S.

M. Escudero, S. Castillo, X. Querol, A. Avila, M. Alarcón, M. M. Viana, A. Alastuey, E. Cuevas, and S. Rodríguez, "Wet and dry African dust episodes over eastern Spain," J. Geophys. Res. 110(D18), D18S08 (2005).
[CrossRef]

Cazorla, A.

J. E. Gil, A. Cazorla, F. J. Olmo, and L. Alados-Arboledas, "Experimental set up to study the cloud radiative effects on UVB at Granada (Spain)," in Proceedings of the European Geosciences Union General Assembly, A.K.Richter, ed. (EGU, 2005) Vol. 1, papers EGU05-A-00320, AS1.08.1WE2P-0059.

Chami, M.

Cofiño, A. S.

J. M. Gutiérrez, R. Cano, A. S. Cofiño, and C. Sordo, Redes Probabilísticas y Neuronales en las Ciencias Atmosféricas (Probabilistic and Neural Networks on Atmospheric Sciences) (Ministerio de Medio Ambiente, Dirección General del Instituto Nacional de Meteorología, 2004).
[PubMed]

Crescenti, G. H.

J. G. Estupiñan, S. Raman, G. H. Crescenti, J. J. Streicher, and W. F. Barnard, "Effects of clouds and haze on UV-B radiation," J. Geophys. Res. 101(D11), 16807-16816 (1996).
[CrossRef]

Cuevas, E.

M. Escudero, S. Castillo, X. Querol, A. Avila, M. Alarcón, M. M. Viana, A. Alastuey, E. Cuevas, and S. Rodríguez, "Wet and dry African dust episodes over eastern Spain," J. Geophys. Res. 110(D18), D18S08 (2005).
[CrossRef]

de Gruijl, F. R.

J. C. van der Leun and F. R. de Gruijl, "Climate change and skin cancer," Photochem. Photobiol. Sci. 1, 324-326 (2002).
[CrossRef]

Dehne, K.

U. Feister, J. E. Shields, M. E. Karr, R. W. Johnson, K. Dehne, and M. Woldt, "Ground-based cloud images and sky radiances in the visible and near infrared region from whole sky imager measurements," presented at the Climate Monitoring--Satellite Application Facility Training Workshop, Dresden, Germany, November 20-22, 2000.

Dolenko, S. A.

Dolenko, T. A.

Escudero, M.

M. Escudero, S. Castillo, X. Querol, A. Avila, M. Alarcón, M. M. Viana, A. Alastuey, E. Cuevas, and S. Rodríguez, "Wet and dry African dust episodes over eastern Spain," J. Geophys. Res. 110(D18), D18S08 (2005).
[CrossRef]

Estupiñan, J. G.

J. G. Estupiñan, S. Raman, G. H. Crescenti, J. J. Streicher, and W. F. Barnard, "Effects of clouds and haze on UV-B radiation," J. Geophys. Res. 101(D11), 16807-16816 (1996).
[CrossRef]

Fadeev, V. V.

Feister, U.

U. Feister, J. E. Shields, M. E. Karr, R. W. Johnson, K. Dehne, and M. Woldt, "Ground-based cloud images and sky radiances in the visible and near infrared region from whole sky imager measurements," presented at the Climate Monitoring--Satellite Application Facility Training Workshop, Dresden, Germany, November 20-22, 2000.

Forbes, P. D.

J. C. van der Leun and P. D. Forbes, "Ultraviolet tanning equipment: six questions," Photodermatol. Photoimmunol. Photomed. 21, 254-259 (2005).
[CrossRef] [PubMed]

Foyo-Moreno, I.

L. Alados-Arboledas, I. Alados, I. Foyo-Moreno, A. Alcántara, and F. J. Olmo, "The influence of clouds on surface UV erythemal irradiance," Atmos. Res. 66, 273-290 (2003).
[CrossRef]

I. Foyo-Moreno, J. Vida, I. Alados, F. J. Olmo, and L. Alados-Arboledas, "The influence of clouds on UV global irradiance (295-385nm)," Agric. Forest Meteorol. 120, 101-111 (2003).
[CrossRef]

Gerdova, I. V.

Gil, J. E.

J. E. Gil, A. Cazorla, F. J. Olmo, and L. Alados-Arboledas, "Experimental set up to study the cloud radiative effects on UVB at Granada (Spain)," in Proceedings of the European Geosciences Union General Assembly, A.K.Richter, ed. (EGU, 2005) Vol. 1, papers EGU05-A-00320, AS1.08.1WE2P-0059.

Goldberg, D. E.

D. E. Goldberg, Genetic Algorithms in Search, Optimization and Machine Learning (Addison-Wesley, 1989).

González, J. A.

J. Calbó, D. Pages, and J. A. González, "Empirical studies of cloud effects on UV radiation: a review," Rev. Geophys. 43, 2 (2005).
[CrossRef]

Greenberg, S.

Guterman, H.

Gutiérrez, J. M.

J. M. Gutiérrez, R. Cano, A. S. Cofiño, and C. Sordo, Redes Probabilísticas y Neuronales en las Ciencias Atmosféricas (Probabilistic and Neural Networks on Atmospheric Sciences) (Ministerio de Medio Ambiente, Dirección General del Instituto Nacional de Meteorología, 2004).
[PubMed]

Hamilton, K.

M. Stowaser and K. Hamilton, "Relationship between shortwave cloud radiative forcing and local meteorological variables compared in observations and several global climate models," J. Clim. 19, 4344-4359 (2006).
[CrossRef]

Hilton, G. E.

D. E. Rumerlhart, G. E. Hilton, and R. J. Williams, "Learning internal representations by errors propagation," in Parallel Distributed Processing: Exploitations in the Microstructure of Cognition Foundations, D.E.Rumelhart and J.L.MacClelland, eds. (MIT Press, 1986), Vol. 1, pp. 318-362.

Holland, J. H.

J. H. Holland, "Outline for a logical theory of adaptive systems," J. Assoc. Comput. Mach. 9, 297-314 (1962).
[CrossRef]

Johnson, R. W.

U. Feister, J. E. Shields, M. E. Karr, R. W. Johnson, K. Dehne, and M. Woldt, "Ground-based cloud images and sky radiances in the visible and near infrared region from whole sky imager measurements," presented at the Climate Monitoring--Satellite Application Facility Training Workshop, Dresden, Germany, November 20-22, 2000.

J. E. Shields, R. W. Johnson, M. E. Karr, and J. L. Wertz, "Automated day/night whole sky imagers for field assessment of cloud cover distributions and radiance distributions," presented at the 10th Symposium on Meteorological Observations and Instrumentation of the American Meteorological Society, Boston, Massachusetts, January 11-16, 1998.

J. E. Shields, R. W. Johnson, and T. E. Koehler, "Automated whole sky imaging systems for cloud field assessment," presented at the Fourth Symposium on Global Change Studies of the American Meteorological Society, Boston, Massachusetts, January 17-22, 1993.

Kaifel, A.

Karr, M. E.

U. Feister, J. E. Shields, M. E. Karr, R. W. Johnson, K. Dehne, and M. Woldt, "Ground-based cloud images and sky radiances in the visible and near infrared region from whole sky imager measurements," presented at the Climate Monitoring--Satellite Application Facility Training Workshop, Dresden, Germany, November 20-22, 2000.

J. E. Shields, M. E. Karr, T. P. Tooman, D. H. Sowle, and S. T. Moore, "The whole sky imager--a year of progress," presented at the Eighth Atmospheric Radiation Measurement (ARM) Science Team Meeting, Tucson, Arizona, March 23-27, 1998.

J. E. Shields, R. W. Johnson, M. E. Karr, and J. L. Wertz, "Automated day/night whole sky imagers for field assessment of cloud cover distributions and radiance distributions," presented at the 10th Symposium on Meteorological Observations and Instrumentation of the American Meteorological Society, Boston, Massachusetts, January 11-16, 1998.

Khanna, T.

T. Khanna, Foundations of Neural Networks (Addison-Wesley, 1990).

Koehler, T. E.

J. E. Shields, R. W. Johnson, and T. E. Koehler, "Automated whole sky imaging systems for cloud field assessment," presented at the Fourth Symposium on Global Change Studies of the American Meteorological Society, Boston, Massachusetts, January 17-22, 1993.

Lippman, R.

R. Lippman, "An introduction to computing with neural nets," IEEE ASSP Mag. 4(2), 4-22 (1987).
[CrossRef]

Long, C. J.

C. J. Long, J. Sabburg, J. Calbó, and D. Pagès, "Retrieving cloud characteristics from ground-based daytime color all-sky images," J. Atmos. Ocean. Technol. 23, 633-652 (2006).
[CrossRef]

Long, C. N.

J. M. Sabburg and C. N. Long, "Improved sky imaging for studies of enhanced UV irradiance," Atmos. Chem. Phys. Discuss. 4, 6213-6238 (2004).
[CrossRef]

Lyamani, H.

H. Lyamani, F. J. Olmo, A. Alcántara, and L. Alados-Arboledas, "Atmospheric aerosols during the 2003 heat wave in southeastern Spain I: spectral optical depth," Atmos. Environ. 40, 6453-6464 (2006).
[CrossRef]

H. Lyamani, F. J. Olmo, and L. Alados-Arboledas, "Saharan dust outbreak over southeastern Spain as detected by sun photometer," Atmos. Environ. 39, 7276-7284 (2005).

Marcos, S. A.

Matthijsen, J.

J. Matthijsen, H. Slaper, H. Reinen, and G. Velders, "Reduction of solar UV by clouds: a comparison between satellite-derived cloud effects and ground-based radiation measurements," J. Geophys. Res. 105(D4), 5069-5080 (2000).
[CrossRef]

Mellado, J. A.

I. Alados, J. A. Mellado, F. Ramos, and L. Alados-Arboledas, "Estimating UV erythemal irradiance by means of neural networks," Photochem. Photobiol. 80, 351-358 (2004).
[CrossRef] [PubMed]

Michalewicz, Z.

Z. Michalewicz, Genetic Algorithms + Data Structures = Evolution Programs (Springer-Verlag, 1992).

Moore, S. T.

J. E. Shields, M. E. Karr, T. P. Tooman, D. H. Sowle, and S. T. Moore, "The whole sky imager--a year of progress," presented at the Eighth Atmospheric Radiation Measurement (ARM) Science Team Meeting, Tucson, Arizona, March 23-27, 1998.

Müller, M. D.

Olmo, F. J.

H. Lyamani, F. J. Olmo, A. Alcántara, and L. Alados-Arboledas, "Atmospheric aerosols during the 2003 heat wave in southeastern Spain I: spectral optical depth," Atmos. Environ. 40, 6453-6464 (2006).
[CrossRef]

H. Lyamani, F. J. Olmo, and L. Alados-Arboledas, "Saharan dust outbreak over southeastern Spain as detected by sun photometer," Atmos. Environ. 39, 7276-7284 (2005).

J. E. Gil, A. Cazorla, F. J. Olmo, and L. Alados-Arboledas, "Experimental set up to study the cloud radiative effects on UVB at Granada (Spain)," in Proceedings of the European Geosciences Union General Assembly, A.K.Richter, ed. (EGU, 2005) Vol. 1, papers EGU05-A-00320, AS1.08.1WE2P-0059.

I. Foyo-Moreno, J. Vida, I. Alados, F. J. Olmo, and L. Alados-Arboledas, "The influence of clouds on UV global irradiance (295-385nm)," Agric. Forest Meteorol. 120, 101-111 (2003).
[CrossRef]

L. Alados-Arboledas, I. Alados, I. Foyo-Moreno, A. Alcántara, and F. J. Olmo, "The influence of clouds on surface UV erythemal irradiance," Atmos. Res. 66, 273-290 (2003).
[CrossRef]

L. Alados-Arboledas, J. Vida, and F. J. Olmo, "The estimation of thermal radiation under cloudy conditions," Int. J. Climatol. 15, 107-116 (1995).
[CrossRef]

Pages, D.

J. Calbó, D. Pages, and J. A. González, "Empirical studies of cloud effects on UV radiation: a review," Rev. Geophys. 43, 2 (2005).
[CrossRef]

Pagès, D.

C. J. Long, J. Sabburg, J. Calbó, and D. Pagès, "Retrieving cloud characteristics from ground-based daytime color all-sky images," J. Atmos. Ocean. Technol. 23, 633-652 (2006).
[CrossRef]

Parisi, A. V.

J. M. Sabburg and A. V. Parisi, "Spectral dependency of cloud enhanced UV irradiance," Atmos. Res. 81, 206-214 (2006).
[CrossRef]

Pereira, E. B.

M. P. Souza-Echer, E. B. Pereira, L. S. Bins, and M. A. R. Andrade, "A simple method for the assessment of the cloud cover state in high-latitude regions by a ground based digital camera," J. Atmos. Ocean. Technol. 23, 437-447 (2006).
[CrossRef]

Querol, X.

M. Escudero, S. Castillo, X. Querol, A. Avila, M. Alarcón, M. M. Viana, A. Alastuey, E. Cuevas, and S. Rodríguez, "Wet and dry African dust episodes over eastern Spain," J. Geophys. Res. 110(D18), D18S08 (2005).
[CrossRef]

Raman, S.

J. G. Estupiñan, S. Raman, G. H. Crescenti, J. J. Streicher, and W. F. Barnard, "Effects of clouds and haze on UV-B radiation," J. Geophys. Res. 101(D11), 16807-16816 (1996).
[CrossRef]

Ramos, F.

I. Alados, J. A. Mellado, F. Ramos, and L. Alados-Arboledas, "Estimating UV erythemal irradiance by means of neural networks," Photochem. Photobiol. 80, 351-358 (2004).
[CrossRef] [PubMed]

Reinen, H.

J. Matthijsen, H. Slaper, H. Reinen, and G. Velders, "Reduction of solar UV by clouds: a comparison between satellite-derived cloud effects and ground-based radiation measurements," J. Geophys. Res. 105(D4), 5069-5080 (2000).
[CrossRef]

Reuter, R.

Riedmiller, M.

M. Riedmiller and H. Braun, "A direct adaptive method for faster backpropagation learning: the RPROP algorithm, in Proceedings of the IEEE International Conference on Neural Networks (IEEE, 1993), pp. 586-591.
[CrossRef]

Robilliard, D.

Rodríguez, S.

M. Escudero, S. Castillo, X. Querol, A. Avila, M. Alarcón, M. M. Viana, A. Alastuey, E. Cuevas, and S. Rodríguez, "Wet and dry African dust episodes over eastern Spain," J. Geophys. Res. 110(D18), D18S08 (2005).
[CrossRef]

Rogers, R. R.

R. R. Rogers and M. K. Yau, A Short Course in Cloud Physics (Pergamon, 1989).

Rosenblatt, B.

B. Rosenblatt, Principles of Neurodynamics: Perceptrons and the Theory of Brain Mechanisms (Spartan, 1961).

Rumerlhart, D. E.

D. E. Rumerlhart, G. E. Hilton, and R. J. Williams, "Learning internal representations by errors propagation," in Parallel Distributed Processing: Exploitations in the Microstructure of Cognition Foundations, D.E.Rumelhart and J.L.MacClelland, eds. (MIT Press, 1986), Vol. 1, pp. 318-362.

Sabburg, J.

C. J. Long, J. Sabburg, J. Calbó, and D. Pagès, "Retrieving cloud characteristics from ground-based daytime color all-sky images," J. Atmos. Ocean. Technol. 23, 633-652 (2006).
[CrossRef]

J. Sabburg, "Quantification of cloud around the sun and its correlation with global UV measurement," Ph.D. thesis (Queensland University of Technology, Brisbane, Australia, 2000).

J. Sabburg and J. Wong, "Evaluation of a sky/cloud formula for estimating UV-B irradiance under cloudy conditions," J. Geophys. Res. 105, 29685-29691 (2000).
[CrossRef]

J. Sabburg and J. Wong, "Evaluation of a sky camera for use in radiation measurement," J. Atmos. Ocean. Technol. 16, 752-759 (1999).
[CrossRef]

Sabburg, J. M.

J. M. Sabburg and A. V. Parisi, "Spectral dependency of cloud enhanced UV irradiance," Atmos. Res. 81, 206-214 (2006).
[CrossRef]

J. M. Sabburg and C. N. Long, "Improved sky imaging for studies of enhanced UV irradiance," Atmos. Chem. Phys. Discuss. 4, 6213-6238 (2004).
[CrossRef]

Saloma, C.

Shields, J. E.

U. Feister, J. E. Shields, M. E. Karr, R. W. Johnson, K. Dehne, and M. Woldt, "Ground-based cloud images and sky radiances in the visible and near infrared region from whole sky imager measurements," presented at the Climate Monitoring--Satellite Application Facility Training Workshop, Dresden, Germany, November 20-22, 2000.

J. E. Shields, M. E. Karr, T. P. Tooman, D. H. Sowle, and S. T. Moore, "The whole sky imager--a year of progress," presented at the Eighth Atmospheric Radiation Measurement (ARM) Science Team Meeting, Tucson, Arizona, March 23-27, 1998.

J. E. Shields, R. W. Johnson, M. E. Karr, and J. L. Wertz, "Automated day/night whole sky imagers for field assessment of cloud cover distributions and radiance distributions," presented at the 10th Symposium on Meteorological Observations and Instrumentation of the American Meteorological Society, Boston, Massachusetts, January 11-16, 1998.

J. E. Shields, R. W. Johnson, and T. E. Koehler, "Automated whole sky imaging systems for cloud field assessment," presented at the Fourth Symposium on Global Change Studies of the American Meteorological Society, Boston, Massachusetts, January 17-22, 1993.

Slaper, H.

J. Matthijsen, H. Slaper, H. Reinen, and G. Velders, "Reduction of solar UV by clouds: a comparison between satellite-derived cloud effects and ground-based radiation measurements," J. Geophys. Res. 105(D4), 5069-5080 (2000).
[CrossRef]

Sordo, C.

J. M. Gutiérrez, R. Cano, A. S. Cofiño, and C. Sordo, Redes Probabilísticas y Neuronales en las Ciencias Atmosféricas (Probabilistic and Neural Networks on Atmospheric Sciences) (Ministerio de Medio Ambiente, Dirección General del Instituto Nacional de Meteorología, 2004).
[PubMed]

Soriano, M.

Souza-Echer, M. P.

M. P. Souza-Echer, E. B. Pereira, L. S. Bins, and M. A. R. Andrade, "A simple method for the assessment of the cloud cover state in high-latitude regions by a ground based digital camera," J. Atmos. Ocean. Technol. 23, 437-447 (2006).
[CrossRef]

Sowle, D. H.

J. E. Shields, M. E. Karr, T. P. Tooman, D. H. Sowle, and S. T. Moore, "The whole sky imager--a year of progress," presented at the Eighth Atmospheric Radiation Measurement (ARM) Science Team Meeting, Tucson, Arizona, March 23-27, 1998.

Stowaser, M.

M. Stowaser and K. Hamilton, "Relationship between shortwave cloud radiative forcing and local meteorological variables compared in observations and several global climate models," J. Clim. 19, 4344-4359 (2006).
[CrossRef]

Streicher, J. J.

J. G. Estupiñan, S. Raman, G. H. Crescenti, J. J. Streicher, and W. F. Barnard, "Effects of clouds and haze on UV-B radiation," J. Geophys. Res. 101(D11), 16807-16816 (1996).
[CrossRef]

Tooman, T. P.

J. E. Shields, M. E. Karr, T. P. Tooman, D. H. Sowle, and S. T. Moore, "The whole sky imager--a year of progress," presented at the Eighth Atmospheric Radiation Measurement (ARM) Science Team Meeting, Tucson, Arizona, March 23-27, 1998.

van der Leun, J. C.

J. C. van der Leun and P. D. Forbes, "Ultraviolet tanning equipment: six questions," Photodermatol. Photoimmunol. Photomed. 21, 254-259 (2005).
[CrossRef] [PubMed]

J. C. van der Leun and F. R. de Gruijl, "Climate change and skin cancer," Photochem. Photobiol. Sci. 1, 324-326 (2002).
[CrossRef]

Velders, G.

J. Matthijsen, H. Slaper, H. Reinen, and G. Velders, "Reduction of solar UV by clouds: a comparison between satellite-derived cloud effects and ground-based radiation measurements," J. Geophys. Res. 105(D4), 5069-5080 (2000).
[CrossRef]

Viana, M. M.

M. Escudero, S. Castillo, X. Querol, A. Avila, M. Alarcón, M. M. Viana, A. Alastuey, E. Cuevas, and S. Rodríguez, "Wet and dry African dust episodes over eastern Spain," J. Geophys. Res. 110(D18), D18S08 (2005).
[CrossRef]

Vida, J.

I. Foyo-Moreno, J. Vida, I. Alados, F. J. Olmo, and L. Alados-Arboledas, "The influence of clouds on UV global irradiance (295-385nm)," Agric. Forest Meteorol. 120, 101-111 (2003).
[CrossRef]

L. Alados-Arboledas, J. Vida, and F. J. Olmo, "The estimation of thermal radiation under cloudy conditions," Int. J. Climatol. 15, 107-116 (1995).
[CrossRef]

Weber, M.

Wertz, J. L.

J. E. Shields, R. W. Johnson, M. E. Karr, and J. L. Wertz, "Automated day/night whole sky imagers for field assessment of cloud cover distributions and radiance distributions," presented at the 10th Symposium on Meteorological Observations and Instrumentation of the American Meteorological Society, Boston, Massachusetts, January 11-16, 1998.

Williams, R. J.

D. E. Rumerlhart, G. E. Hilton, and R. J. Williams, "Learning internal representations by errors propagation," in Parallel Distributed Processing: Exploitations in the Microstructure of Cognition Foundations, D.E.Rumelhart and J.L.MacClelland, eds. (MIT Press, 1986), Vol. 1, pp. 318-362.

Woldt, M.

U. Feister, J. E. Shields, M. E. Karr, R. W. Johnson, K. Dehne, and M. Woldt, "Ground-based cloud images and sky radiances in the visible and near infrared region from whole sky imager measurements," presented at the Climate Monitoring--Satellite Application Facility Training Workshop, Dresden, Germany, November 20-22, 2000.

Wong, J.

J. Sabburg and J. Wong, "Evaluation of a sky/cloud formula for estimating UV-B irradiance under cloudy conditions," J. Geophys. Res. 105, 29685-29691 (2000).
[CrossRef]

J. Sabburg and J. Wong, "Evaluation of a sky camera for use in radiation measurement," J. Atmos. Ocean. Technol. 16, 752-759 (1999).
[CrossRef]

Yau, M. K.

R. R. Rogers and M. K. Yau, A Short Course in Cloud Physics (Pergamon, 1989).

Agric. Forest Meteorol. (1)

I. Foyo-Moreno, J. Vida, I. Alados, F. J. Olmo, and L. Alados-Arboledas, "The influence of clouds on UV global irradiance (295-385nm)," Agric. Forest Meteorol. 120, 101-111 (2003).
[CrossRef]

Appl. Opt. (4)

Atmos. Chem. Phys. Discuss. (1)

J. M. Sabburg and C. N. Long, "Improved sky imaging for studies of enhanced UV irradiance," Atmos. Chem. Phys. Discuss. 4, 6213-6238 (2004).
[CrossRef]

Atmos. Environ. (2)

H. Lyamani, F. J. Olmo, and L. Alados-Arboledas, "Saharan dust outbreak over southeastern Spain as detected by sun photometer," Atmos. Environ. 39, 7276-7284 (2005).

H. Lyamani, F. J. Olmo, A. Alcántara, and L. Alados-Arboledas, "Atmospheric aerosols during the 2003 heat wave in southeastern Spain I: spectral optical depth," Atmos. Environ. 40, 6453-6464 (2006).
[CrossRef]

Atmos. Res. (2)

J. M. Sabburg and A. V. Parisi, "Spectral dependency of cloud enhanced UV irradiance," Atmos. Res. 81, 206-214 (2006).
[CrossRef]

L. Alados-Arboledas, I. Alados, I. Foyo-Moreno, A. Alcántara, and F. J. Olmo, "The influence of clouds on surface UV erythemal irradiance," Atmos. Res. 66, 273-290 (2003).
[CrossRef]

IEEE ASSP Mag. (1)

R. Lippman, "An introduction to computing with neural nets," IEEE ASSP Mag. 4(2), 4-22 (1987).
[CrossRef]

Int. J. Climatol. (1)

L. Alados-Arboledas, J. Vida, and F. J. Olmo, "The estimation of thermal radiation under cloudy conditions," Int. J. Climatol. 15, 107-116 (1995).
[CrossRef]

J. Assoc. Comput. Mach. (1)

J. H. Holland, "Outline for a logical theory of adaptive systems," J. Assoc. Comput. Mach. 9, 297-314 (1962).
[CrossRef]

J. Atmos. Ocean. Technol. (3)

C. J. Long, J. Sabburg, J. Calbó, and D. Pagès, "Retrieving cloud characteristics from ground-based daytime color all-sky images," J. Atmos. Ocean. Technol. 23, 633-652 (2006).
[CrossRef]

M. P. Souza-Echer, E. B. Pereira, L. S. Bins, and M. A. R. Andrade, "A simple method for the assessment of the cloud cover state in high-latitude regions by a ground based digital camera," J. Atmos. Ocean. Technol. 23, 437-447 (2006).
[CrossRef]

J. Sabburg and J. Wong, "Evaluation of a sky camera for use in radiation measurement," J. Atmos. Ocean. Technol. 16, 752-759 (1999).
[CrossRef]

J. Clim. (1)

M. Stowaser and K. Hamilton, "Relationship between shortwave cloud radiative forcing and local meteorological variables compared in observations and several global climate models," J. Clim. 19, 4344-4359 (2006).
[CrossRef]

J. Geophys. Res. (4)

J. Matthijsen, H. Slaper, H. Reinen, and G. Velders, "Reduction of solar UV by clouds: a comparison between satellite-derived cloud effects and ground-based radiation measurements," J. Geophys. Res. 105(D4), 5069-5080 (2000).
[CrossRef]

J. G. Estupiñan, S. Raman, G. H. Crescenti, J. J. Streicher, and W. F. Barnard, "Effects of clouds and haze on UV-B radiation," J. Geophys. Res. 101(D11), 16807-16816 (1996).
[CrossRef]

J. Sabburg and J. Wong, "Evaluation of a sky/cloud formula for estimating UV-B irradiance under cloudy conditions," J. Geophys. Res. 105, 29685-29691 (2000).
[CrossRef]

M. Escudero, S. Castillo, X. Querol, A. Avila, M. Alarcón, M. M. Viana, A. Alastuey, E. Cuevas, and S. Rodríguez, "Wet and dry African dust episodes over eastern Spain," J. Geophys. Res. 110(D18), D18S08 (2005).
[CrossRef]

Opt. Express (1)

Photochem. Photobiol. (1)

I. Alados, J. A. Mellado, F. Ramos, and L. Alados-Arboledas, "Estimating UV erythemal irradiance by means of neural networks," Photochem. Photobiol. 80, 351-358 (2004).
[CrossRef] [PubMed]

Photochem. Photobiol. Sci. (1)

J. C. van der Leun and F. R. de Gruijl, "Climate change and skin cancer," Photochem. Photobiol. Sci. 1, 324-326 (2002).
[CrossRef]

Photodermatol. Photoimmunol. Photomed. (1)

J. C. van der Leun and P. D. Forbes, "Ultraviolet tanning equipment: six questions," Photodermatol. Photoimmunol. Photomed. 21, 254-259 (2005).
[CrossRef] [PubMed]

Rev. Geophys. (1)

J. Calbó, D. Pages, and J. A. González, "Empirical studies of cloud effects on UV radiation: a review," Rev. Geophys. 43, 2 (2005).
[CrossRef]

Tellus (1)

A. Ångström, "The parameters of atmospheric turbidity," Tellus 16, 64-75 (1964).
[CrossRef]

Other (20)

WMO, Guide to Meteorological Practice, Publication No. 168 (World Meteorological Organization, 1983).

R. R. Rogers and M. K. Yau, A Short Course in Cloud Physics (Pergamon, 1989).

J. E. Shields, R. W. Johnson, and T. E. Koehler, "Automated whole sky imaging systems for cloud field assessment," presented at the Fourth Symposium on Global Change Studies of the American Meteorological Society, Boston, Massachusetts, January 17-22, 1993.

J. E. Shields, M. E. Karr, T. P. Tooman, D. H. Sowle, and S. T. Moore, "The whole sky imager--a year of progress," presented at the Eighth Atmospheric Radiation Measurement (ARM) Science Team Meeting, Tucson, Arizona, March 23-27, 1998.

U. Feister, J. E. Shields, M. E. Karr, R. W. Johnson, K. Dehne, and M. Woldt, "Ground-based cloud images and sky radiances in the visible and near infrared region from whole sky imager measurements," presented at the Climate Monitoring--Satellite Application Facility Training Workshop, Dresden, Germany, November 20-22, 2000.

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Figures (10)

Fig. 1
Fig. 1

(a) All-Sky Imager and the Sun Tracker. (b) Schematic of the housing.

Fig. 2
Fig. 2

Sky image example captured with the All-Sky Imager.

Fig. 3
Fig. 3

(a) Schema of the optimization procedure. (b) Flux diagram for the GA program. (c) Flux diagrams for the NN program.

Fig. 4
Fig. 4

Schema of the final procedure. It receives a sky image and generates the resulting image.

Fig. 5
Fig. 5

Position of the octants for the output parameters. (The image is rotated to calculate the percent in regions; hence the south is always placed at the bottom of the image.)

Fig. 6
Fig. 6

Comparison of monthly average oktas of METAR records for clouds (and its standard deviation) and the All-Sky Imager. The averages are computed by using all the measurements in every month.

Fig. 7
Fig. 7

Number of images registered by the All-Sky Imager every month.

Fig. 8
Fig. 8

Absolute difference between All-Sky Imager estimated oktas and METAR report for clouds. The ordinates axis also gives the values of the Ångström alpha parameter.

Fig. 9
Fig. 9

Estimation of cloud cover and METAR report during a dust event (May 29, 2006).

Fig. 10
Fig. 10

Relative frequency histogram for the difference between All-Sky Imager oktas and METAR records for cloud cover in temporally coincident measurements over the whole data set.

Tables (1)

Tables Icon

Table 1 Contingency of the Relative Frequency of Pixel Classification a

Metrics