OSA's Digital Library

Journal of the Optical Society of America A

Journal of the Optical Society of America A


  • Editor: Stephen A. Burns
  • Vol. 25, Iss. 1 — Jan. 1, 2008
  • pp: 29–39

Development of a sky imager for cloud cover assessment

A. Cazorla, F. J. Olmo, and L. Alados-Arboledas  »View Author Affiliations

JOSA A, Vol. 25, Issue 1, pp. 29-39 (2008)

View Full Text Article

Enhanced HTML    Acrobat PDF (939 KB)

Browse Journals / Lookup Meetings

Browse by Journal and Year


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools



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 5 min , 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

OCIS Codes
(010.1290) Atmospheric and oceanic optics : Atmospheric optics
(010.3920) Atmospheric and oceanic optics : Meteorology
(100.5010) Image processing : Pattern recognition
(120.0280) Instrumentation, measurement, and metrology : Remote sensing and sensors
(150.0150) Machine vision : Machine vision
(200.4260) Optics in computing : Neural networks

ToC Category:
Atmospheric and oceanic optics

Original Manuscript: June 22, 2007
Revised Manuscript: October 16, 2007
Manuscript Accepted: October 17, 2007
Published: December 5, 2007

A. Cazorla, F. J. Olmo, and L. Alados-Arboledas, "Development of a sky imager for cloud cover assessment," J. Opt. Soc. Am. A 25, 29-39 (2008)

Sort:  Author  |  Year  |  Journal  |  Reset  


  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]
  2. 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]
  3. J. Calbó, D. Pages, and J. A. González, "Empirical studies of cloud effects on UV radiation: a review," Rev. Geophys. 43, 2 (2005). [CrossRef]
  4. 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]
  5. J. C. van der Leun and F. R. de Gruijl, "Climate change and skin cancer," Photochem. Photobiol. Sci. 1, 324-326 (2002). [CrossRef]
  6. J. C. van der Leun and P. D. Forbes, "Ultraviolet tanning equipment: six questions," Photodermatol. Photoimmunol. Photomed. 21, 254-259 (2005). [CrossRef] [PubMed]
  7. 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]
  8. 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]
  9. 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]
  10. J. M. Sabburg and A. V. Parisi, "Spectral dependency of cloud enhanced UV irradiance," Atmos. Res. 81, 206-214 (2006). [CrossRef]
  11. WMO, Guide to Meteorological Practice, Publication No. 168 (World Meteorological Organization, 1983).
  12. R. R. Rogers and M. K. Yau, A Short Course in Cloud Physics (Pergamon, 1989).
  13. 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.
  14. 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.
  15. J. Sabburg and J. Wong, "Evaluation of a sky camera for use in radiation measurement," J. Atmos. Ocean. Technol. 16, 752-759 (1999). [CrossRef]
  16. 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.
  17. 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).
  18. 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]
  19. 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]
  20. 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]
  21. 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]
  22. 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.
  23. 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).
  24. 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]
  25. 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.
  26. R. Lippman, "An introduction to computing with neural nets," IEEE ASSP Mag. 4(2), 4-22 (1987). [CrossRef]
  27. T. Khanna, Foundations of Neural Networks (Addison-Wesley, 1990).
  28. C. M. Bishop, Neural Networks for Pattern Recognition (Oxford U. Press, 1995).
  29. 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]
  30. 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]
  31. S. Greenberg and H. Guterman, "Neural-network classifiers for automatic real-world aerial image recognition," Appl. Opt. 35, 4598-4609 (1996). [CrossRef] [PubMed]
  32. T. A. Dolenko, V. V. Fadeev, I. V. Gerdova, S. A. Dolenko, and R. Reuter, "Fluorescence diagnostics of oil pollution in coastal marine waters by use of artificial neural networks," Appl. Opt. 41, 5155-5166 (2002). [CrossRef] [PubMed]
  33. 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]
  34. M. D. Müller, A. Kaifel, M. Weber, and J. P. Burrows, "Neural network scheme for the retrieval of total ozone from Global Ozone Monitoring Experiment data," Appl. Opt. 41, 5051-5058 (2002). [CrossRef] [PubMed]
  35. M. Chami and D. Robilliard, "Inversion of oceanic constituents in case I and II water with genetic programming algorithms," Appl. Opt. 41, 6260-6275 (2002). [CrossRef] [PubMed]
  36. B. Rosenblatt, Principles of Neurodynamics: Perceptrons and the Theory of Brain Mechanisms (Spartan, 1961).
  37. 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.
  38. 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.
  39. 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]
  40. J. H. Holland, "Outline for a logical theory of adaptive systems," J. Assoc. Comput. Mach. 9, 297-314 (1962). [CrossRef]
  41. 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.
  42. D. E. Goldberg, Genetic Algorithms in Search, Optimization and Machine Learning (Addison-Wesley, 1989).
  43. Z. Michalewicz, Genetic Algorithms + Data Structures = Evolution Programs (Springer-Verlag, 1992).
  44. WMO, Manual on Codes, Publication No. 306 (World Meteorological Organization, 1995).
  45. 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).
  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]
  47. A. Ångström, "The parameters of atmospheric turbidity," Tellus 16, 64-75 (1964). [CrossRef]

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.

« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited