Abstract

A simple and inexpensive fully automated all-sky imaging system based on a commercial digital camera with a fish-eye lens and a rotating polarizer is presented. The system is characterized and two examples of applications in atmospheric physics are given: polarization maps and cloud detection. All-sky polarization maps are obtained by acquiring images at different polarizer angles and computing Stokes vectors. The polarization in the principal plane, a vertical cut through the sky containing the Sun, is compared to measurements of a well-characterized spectroradiometer with polarized radiance optics to validate the method. The images are further used for automated cloud detection using a simple color- ratio algorithm. The resulting cloud cover is validated against synoptic cloud observations. A Sun coverage parameter is introduced that shows, in combination with the total cloud cover, useful correlation with UV irradiance.

© 2009 Optical Society of America

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  1. S. B. Mende, S. E. Harris, H. U. Frey, V. Angelopoulos, C. T. Russell, E. Donovan, B. Jackel, M. Greffen, and L. M. Peticolas, “The THEMIS array of ground-based observatories for the study of auroral substorms,” Space Sci. Rev. , doi: 10.1007/s11214-008-9380-x (2007).
  2. G. Zotti, “Measuring light pollution with a calibrated high dynamic range all-sky image acquisition system,” presented at the DARKSKY2007--7th European Symposium for the Protection of the Night Sky, Bled, Slovenia (2007).
  3. R. L. Chazdon and C. B. Field, “Photographic estimation of photosynthetically active radiation: evaluation of a computerized technique,” Oecologia 73, 525-532 (1987).
    [CrossRef]
  4. T. E. Pickering, “The MMT all-sky camera,” Proc. SPIE 6267, 62671A (2006).
    [CrossRef]
  5. Y. Liu and K. Voss, “Polarized radiance distribution measurements of skylight. I. System description and characterization,” Appl. Opt. 36, 6083-6094 (1997).
    [CrossRef] [PubMed]
  6. N. J. Pust and J. A. Shaw, “Dual-field imaging polarimeter using liquid crystal variable retarders,” Appl. Opt. 45, 5470-5478 (2006).
    [CrossRef] [PubMed]
  7. J. Gál, G. Horváth, V. B. Meyer-Rochow, and R. Wehner, “Polarization patterns of the summer sky and its neutral points measured by full-sky imaging polarimetry in Finnish Lapland north of the Arctic Circle,” Proc. R. Soc. A 457, 1385-1399 (2001).
    [CrossRef]
  8. J. A. North and M. J. Duggin, “Stokes vector imaging of the polarized sky-dome,” Appl. Opt. 36, 723-730 (1997).
    [CrossRef] [PubMed]
  9. M. V. Berry, M. R. Dennis, and R. L. Lee, Jr., “Polarization singularities in the clear sky,” New J. Phys. 6, 162 (2004).
    [CrossRef]
  10. G. Horváth, A. Barta, J. Gál, B. Suhai, and O. Haiman, “Ground-based full-sky imaging polarimetry of rapidly changing skies and its use for polarimetric cloud detection,” Appl. Opt. 41, 543-559 (2002).
    [CrossRef] [PubMed]
  11. C. N. Long, J. M. Sabburg, J. Calbé, and D. Pagès, “Retrieving cloud characteristics from ground-based daytime color all-sky images,” J. Atmos. Ocean. Technol. 23, 633-652(2006).
    [CrossRef]
  12. N. H. Schade, A. Macke, H. Sandmann, and C. Stick, “Total and partial cloud detection during summermonths 2005 at Westerland (Sylt, Germany),” Atmos. Chem. Phys. Discuss. 8, 13479-13505 (2008).
    [CrossRef]
  13. U. Feister, J. Shields, M. Karr, R. 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,” in Proceedings of Climate Monitoring--Satellite Application Facility Training Workshop (Dresden, 2000).
  14. U. Feister and J. Shields, “Cloud and radiance measurements with the VIS/NIR Daylight Whole Sky Imager at Lindenberg (Germany),” Meteor. Zeitschr. 14, 627-639 (2005).
    [CrossRef]
  15. K. A. Buch and C. H. Sun, “Cloud classification using whole-sky imager data,” presented at Ninth Symposium on Meteoriological Observations and Instrumentation, paper 7.5, Charlotte, North Carolina, 1995.
  16. G. Pfister, R. L. McKenzie, J. B. Liley, A. Thomas, B. W. Forgan, and C. N. Long, “Cloud Coverage Based on All-Sky Imaging and Its Impact on Surface Solar Irradiance,” J. Appl. Meteorol. 42, 1421-1434 (2003).
    [CrossRef]
  17. N. H. Schade, A. Macke, H. Sandmann, and C. Stick, “Enhanced solar global irradiance during cloudy sky conditions,” Meteor. Zeitschr. 16, 295-303 (2007).
    [CrossRef]
  18. J. M. Sabburg and C. N. Long, “Improved sky imaging for studies of enhanced UV irradiance,” Atmos. Chem. Phys. 4, 2543-2552 (2004).
    [CrossRef]
  19. J. Stumpfel, C. Thou, A. Jones, T. Hawkins, A. Wenger, and P. Debevec, Proceedings of the Third International Conference on Computer Graphics, Virtual Reality, Visualisation and Interaction in Africa (Association for Computing Machinery, 2004), pp. 145-149.
    [CrossRef]
  20. C. A. Poynton, Digital Video and HDTV: Algorithms and Interfaces (Morgan Kaufmann, 2003).
  21. K. L. Coulson, Polarization and Intensity of Light in the Atmosphere (Deepak, 1988).
  22. J. W. Strutt, “On the light from the sky, its polarisation and color,” Philos. Mag. 41, 107-120274-279 (1871).
  23. G. Horváth, J. Gál, I. Pomozi, and R. Wehner, “Polarization portrait of the Arago Point: video-polarimetric imaging of the neutral points of skylight polarization,” Naturwissenschaften 85, 333-339 (1998).
    [CrossRef]
  24. M. Blumthaler, B. Schallhart, M. Schwarzmann, R. McKenzie, P. Johnston, M. Kotkamp, and H. Shiona, “Spectral UV measurements of global irradiance, solar radiance, and actinic flux in New Zealand: intercomparison between instruments and model calculations,” J. Atmos. Ocean. Technol. 25, 945-958(2008).
    [CrossRef]
  25. S. Twomey, Atmospheric Aerosols (Elsevier, 1977).
  26. B. Schallhart, M. Blumthaler, J. Schreder, and J. Verdebout, “A method to generate near real time UV-index maps of Austria,” Atmos. Chem. Phys. 8, 7483-7491 (2008).
    [CrossRef]

2008 (3)

N. H. Schade, A. Macke, H. Sandmann, and C. Stick, “Total and partial cloud detection during summermonths 2005 at Westerland (Sylt, Germany),” Atmos. Chem. Phys. Discuss. 8, 13479-13505 (2008).
[CrossRef]

M. Blumthaler, B. Schallhart, M. Schwarzmann, R. McKenzie, P. Johnston, M. Kotkamp, and H. Shiona, “Spectral UV measurements of global irradiance, solar radiance, and actinic flux in New Zealand: intercomparison between instruments and model calculations,” J. Atmos. Ocean. Technol. 25, 945-958(2008).
[CrossRef]

B. Schallhart, M. Blumthaler, J. Schreder, and J. Verdebout, “A method to generate near real time UV-index maps of Austria,” Atmos. Chem. Phys. 8, 7483-7491 (2008).
[CrossRef]

2007 (2)

N. H. Schade, A. Macke, H. Sandmann, and C. Stick, “Enhanced solar global irradiance during cloudy sky conditions,” Meteor. Zeitschr. 16, 295-303 (2007).
[CrossRef]

S. B. Mende, S. E. Harris, H. U. Frey, V. Angelopoulos, C. T. Russell, E. Donovan, B. Jackel, M. Greffen, and L. M. Peticolas, “The THEMIS array of ground-based observatories for the study of auroral substorms,” Space Sci. Rev. , doi: 10.1007/s11214-008-9380-x (2007).

2006 (3)

T. E. Pickering, “The MMT all-sky camera,” Proc. SPIE 6267, 62671A (2006).
[CrossRef]

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

N. J. Pust and J. A. Shaw, “Dual-field imaging polarimeter using liquid crystal variable retarders,” Appl. Opt. 45, 5470-5478 (2006).
[CrossRef] [PubMed]

2005 (1)

U. Feister and J. Shields, “Cloud and radiance measurements with the VIS/NIR Daylight Whole Sky Imager at Lindenberg (Germany),” Meteor. Zeitschr. 14, 627-639 (2005).
[CrossRef]

2004 (2)

M. V. Berry, M. R. Dennis, and R. L. Lee, Jr., “Polarization singularities in the clear sky,” New J. Phys. 6, 162 (2004).
[CrossRef]

J. M. Sabburg and C. N. Long, “Improved sky imaging for studies of enhanced UV irradiance,” Atmos. Chem. Phys. 4, 2543-2552 (2004).
[CrossRef]

2003 (1)

G. Pfister, R. L. McKenzie, J. B. Liley, A. Thomas, B. W. Forgan, and C. N. Long, “Cloud Coverage Based on All-Sky Imaging and Its Impact on Surface Solar Irradiance,” J. Appl. Meteorol. 42, 1421-1434 (2003).
[CrossRef]

2002 (1)

2001 (1)

J. Gál, G. Horváth, V. B. Meyer-Rochow, and R. Wehner, “Polarization patterns of the summer sky and its neutral points measured by full-sky imaging polarimetry in Finnish Lapland north of the Arctic Circle,” Proc. R. Soc. A 457, 1385-1399 (2001).
[CrossRef]

1998 (1)

G. Horváth, J. Gál, I. Pomozi, and R. Wehner, “Polarization portrait of the Arago Point: video-polarimetric imaging of the neutral points of skylight polarization,” Naturwissenschaften 85, 333-339 (1998).
[CrossRef]

1997 (2)

1987 (1)

R. L. Chazdon and C. B. Field, “Photographic estimation of photosynthetically active radiation: evaluation of a computerized technique,” Oecologia 73, 525-532 (1987).
[CrossRef]

1871 (1)

J. W. Strutt, “On the light from the sky, its polarisation and color,” Philos. Mag. 41, 107-120274-279 (1871).

Angelopoulos, V.

S. B. Mende, S. E. Harris, H. U. Frey, V. Angelopoulos, C. T. Russell, E. Donovan, B. Jackel, M. Greffen, and L. M. Peticolas, “The THEMIS array of ground-based observatories for the study of auroral substorms,” Space Sci. Rev. , doi: 10.1007/s11214-008-9380-x (2007).

Barta, A.

Berry, M. V.

M. V. Berry, M. R. Dennis, and R. L. Lee, Jr., “Polarization singularities in the clear sky,” New J. Phys. 6, 162 (2004).
[CrossRef]

Blumthaler, M.

M. Blumthaler, B. Schallhart, M. Schwarzmann, R. McKenzie, P. Johnston, M. Kotkamp, and H. Shiona, “Spectral UV measurements of global irradiance, solar radiance, and actinic flux in New Zealand: intercomparison between instruments and model calculations,” J. Atmos. Ocean. Technol. 25, 945-958(2008).
[CrossRef]

B. Schallhart, M. Blumthaler, J. Schreder, and J. Verdebout, “A method to generate near real time UV-index maps of Austria,” Atmos. Chem. Phys. 8, 7483-7491 (2008).
[CrossRef]

Buch, K. A.

K. A. Buch and C. H. Sun, “Cloud classification using whole-sky imager data,” presented at Ninth Symposium on Meteoriological Observations and Instrumentation, paper 7.5, Charlotte, North Carolina, 1995.

Calbé, J.

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

Chazdon, R. L.

R. L. Chazdon and C. B. Field, “Photographic estimation of photosynthetically active radiation: evaluation of a computerized technique,” Oecologia 73, 525-532 (1987).
[CrossRef]

Coulson, K. L.

K. L. Coulson, Polarization and Intensity of Light in the Atmosphere (Deepak, 1988).

Debevec, P.

J. Stumpfel, C. Thou, A. Jones, T. Hawkins, A. Wenger, and P. Debevec, Proceedings of the Third International Conference on Computer Graphics, Virtual Reality, Visualisation and Interaction in Africa (Association for Computing Machinery, 2004), pp. 145-149.
[CrossRef]

Dehne, K.

U. Feister, J. Shields, M. Karr, R. 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,” in Proceedings of Climate Monitoring--Satellite Application Facility Training Workshop (Dresden, 2000).

Dennis, M. R.

M. V. Berry, M. R. Dennis, and R. L. Lee, Jr., “Polarization singularities in the clear sky,” New J. Phys. 6, 162 (2004).
[CrossRef]

Donovan, E.

S. B. Mende, S. E. Harris, H. U. Frey, V. Angelopoulos, C. T. Russell, E. Donovan, B. Jackel, M. Greffen, and L. M. Peticolas, “The THEMIS array of ground-based observatories for the study of auroral substorms,” Space Sci. Rev. , doi: 10.1007/s11214-008-9380-x (2007).

Duggin, M. J.

Feister, U.

U. Feister and J. Shields, “Cloud and radiance measurements with the VIS/NIR Daylight Whole Sky Imager at Lindenberg (Germany),” Meteor. Zeitschr. 14, 627-639 (2005).
[CrossRef]

U. Feister, J. Shields, M. Karr, R. 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,” in Proceedings of Climate Monitoring--Satellite Application Facility Training Workshop (Dresden, 2000).

Field, C. B.

R. L. Chazdon and C. B. Field, “Photographic estimation of photosynthetically active radiation: evaluation of a computerized technique,” Oecologia 73, 525-532 (1987).
[CrossRef]

Forgan, B. W.

G. Pfister, R. L. McKenzie, J. B. Liley, A. Thomas, B. W. Forgan, and C. N. Long, “Cloud Coverage Based on All-Sky Imaging and Its Impact on Surface Solar Irradiance,” J. Appl. Meteorol. 42, 1421-1434 (2003).
[CrossRef]

Frey, H. U.

S. B. Mende, S. E. Harris, H. U. Frey, V. Angelopoulos, C. T. Russell, E. Donovan, B. Jackel, M. Greffen, and L. M. Peticolas, “The THEMIS array of ground-based observatories for the study of auroral substorms,” Space Sci. Rev. , doi: 10.1007/s11214-008-9380-x (2007).

Gál, J.

G. Horváth, A. Barta, J. Gál, B. Suhai, and O. Haiman, “Ground-based full-sky imaging polarimetry of rapidly changing skies and its use for polarimetric cloud detection,” Appl. Opt. 41, 543-559 (2002).
[CrossRef] [PubMed]

J. Gál, G. Horváth, V. B. Meyer-Rochow, and R. Wehner, “Polarization patterns of the summer sky and its neutral points measured by full-sky imaging polarimetry in Finnish Lapland north of the Arctic Circle,” Proc. R. Soc. A 457, 1385-1399 (2001).
[CrossRef]

G. Horváth, J. Gál, I. Pomozi, and R. Wehner, “Polarization portrait of the Arago Point: video-polarimetric imaging of the neutral points of skylight polarization,” Naturwissenschaften 85, 333-339 (1998).
[CrossRef]

Greffen, M.

S. B. Mende, S. E. Harris, H. U. Frey, V. Angelopoulos, C. T. Russell, E. Donovan, B. Jackel, M. Greffen, and L. M. Peticolas, “The THEMIS array of ground-based observatories for the study of auroral substorms,” Space Sci. Rev. , doi: 10.1007/s11214-008-9380-x (2007).

Haiman, O.

Harris, S. E.

S. B. Mende, S. E. Harris, H. U. Frey, V. Angelopoulos, C. T. Russell, E. Donovan, B. Jackel, M. Greffen, and L. M. Peticolas, “The THEMIS array of ground-based observatories for the study of auroral substorms,” Space Sci. Rev. , doi: 10.1007/s11214-008-9380-x (2007).

Hawkins, T.

J. Stumpfel, C. Thou, A. Jones, T. Hawkins, A. Wenger, and P. Debevec, Proceedings of the Third International Conference on Computer Graphics, Virtual Reality, Visualisation and Interaction in Africa (Association for Computing Machinery, 2004), pp. 145-149.
[CrossRef]

Horváth, G.

G. Horváth, A. Barta, J. Gál, B. Suhai, and O. Haiman, “Ground-based full-sky imaging polarimetry of rapidly changing skies and its use for polarimetric cloud detection,” Appl. Opt. 41, 543-559 (2002).
[CrossRef] [PubMed]

J. Gál, G. Horváth, V. B. Meyer-Rochow, and R. Wehner, “Polarization patterns of the summer sky and its neutral points measured by full-sky imaging polarimetry in Finnish Lapland north of the Arctic Circle,” Proc. R. Soc. A 457, 1385-1399 (2001).
[CrossRef]

G. Horváth, J. Gál, I. Pomozi, and R. Wehner, “Polarization portrait of the Arago Point: video-polarimetric imaging of the neutral points of skylight polarization,” Naturwissenschaften 85, 333-339 (1998).
[CrossRef]

Jackel, B.

S. B. Mende, S. E. Harris, H. U. Frey, V. Angelopoulos, C. T. Russell, E. Donovan, B. Jackel, M. Greffen, and L. M. Peticolas, “The THEMIS array of ground-based observatories for the study of auroral substorms,” Space Sci. Rev. , doi: 10.1007/s11214-008-9380-x (2007).

Johnson, R.

U. Feister, J. Shields, M. Karr, R. 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,” in Proceedings of Climate Monitoring--Satellite Application Facility Training Workshop (Dresden, 2000).

Johnston, P.

M. Blumthaler, B. Schallhart, M. Schwarzmann, R. McKenzie, P. Johnston, M. Kotkamp, and H. Shiona, “Spectral UV measurements of global irradiance, solar radiance, and actinic flux in New Zealand: intercomparison between instruments and model calculations,” J. Atmos. Ocean. Technol. 25, 945-958(2008).
[CrossRef]

Jones, A.

J. Stumpfel, C. Thou, A. Jones, T. Hawkins, A. Wenger, and P. Debevec, Proceedings of the Third International Conference on Computer Graphics, Virtual Reality, Visualisation and Interaction in Africa (Association for Computing Machinery, 2004), pp. 145-149.
[CrossRef]

Karr, M.

U. Feister, J. Shields, M. Karr, R. 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,” in Proceedings of Climate Monitoring--Satellite Application Facility Training Workshop (Dresden, 2000).

Kotkamp, M.

M. Blumthaler, B. Schallhart, M. Schwarzmann, R. McKenzie, P. Johnston, M. Kotkamp, and H. Shiona, “Spectral UV measurements of global irradiance, solar radiance, and actinic flux in New Zealand: intercomparison between instruments and model calculations,” J. Atmos. Ocean. Technol. 25, 945-958(2008).
[CrossRef]

Lee, R. L.

M. V. Berry, M. R. Dennis, and R. L. Lee, Jr., “Polarization singularities in the clear sky,” New J. Phys. 6, 162 (2004).
[CrossRef]

Liley, J. B.

G. Pfister, R. L. McKenzie, J. B. Liley, A. Thomas, B. W. Forgan, and C. N. Long, “Cloud Coverage Based on All-Sky Imaging and Its Impact on Surface Solar Irradiance,” J. Appl. Meteorol. 42, 1421-1434 (2003).
[CrossRef]

Liu, Y.

Long, C. N.

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

J. M. Sabburg and C. N. Long, “Improved sky imaging for studies of enhanced UV irradiance,” Atmos. Chem. Phys. 4, 2543-2552 (2004).
[CrossRef]

G. Pfister, R. L. McKenzie, J. B. Liley, A. Thomas, B. W. Forgan, and C. N. Long, “Cloud Coverage Based on All-Sky Imaging and Its Impact on Surface Solar Irradiance,” J. Appl. Meteorol. 42, 1421-1434 (2003).
[CrossRef]

Macke, A.

N. H. Schade, A. Macke, H. Sandmann, and C. Stick, “Total and partial cloud detection during summermonths 2005 at Westerland (Sylt, Germany),” Atmos. Chem. Phys. Discuss. 8, 13479-13505 (2008).
[CrossRef]

N. H. Schade, A. Macke, H. Sandmann, and C. Stick, “Enhanced solar global irradiance during cloudy sky conditions,” Meteor. Zeitschr. 16, 295-303 (2007).
[CrossRef]

McKenzie, R.

M. Blumthaler, B. Schallhart, M. Schwarzmann, R. McKenzie, P. Johnston, M. Kotkamp, and H. Shiona, “Spectral UV measurements of global irradiance, solar radiance, and actinic flux in New Zealand: intercomparison between instruments and model calculations,” J. Atmos. Ocean. Technol. 25, 945-958(2008).
[CrossRef]

McKenzie, R. L.

G. Pfister, R. L. McKenzie, J. B. Liley, A. Thomas, B. W. Forgan, and C. N. Long, “Cloud Coverage Based on All-Sky Imaging and Its Impact on Surface Solar Irradiance,” J. Appl. Meteorol. 42, 1421-1434 (2003).
[CrossRef]

Mende, S. B.

S. B. Mende, S. E. Harris, H. U. Frey, V. Angelopoulos, C. T. Russell, E. Donovan, B. Jackel, M. Greffen, and L. M. Peticolas, “The THEMIS array of ground-based observatories for the study of auroral substorms,” Space Sci. Rev. , doi: 10.1007/s11214-008-9380-x (2007).

Meyer-Rochow, V. B.

J. Gál, G. Horváth, V. B. Meyer-Rochow, and R. Wehner, “Polarization patterns of the summer sky and its neutral points measured by full-sky imaging polarimetry in Finnish Lapland north of the Arctic Circle,” Proc. R. Soc. A 457, 1385-1399 (2001).
[CrossRef]

North, J. A.

Pagès, D.

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

Peticolas, L. M.

S. B. Mende, S. E. Harris, H. U. Frey, V. Angelopoulos, C. T. Russell, E. Donovan, B. Jackel, M. Greffen, and L. M. Peticolas, “The THEMIS array of ground-based observatories for the study of auroral substorms,” Space Sci. Rev. , doi: 10.1007/s11214-008-9380-x (2007).

Pfister, G.

G. Pfister, R. L. McKenzie, J. B. Liley, A. Thomas, B. W. Forgan, and C. N. Long, “Cloud Coverage Based on All-Sky Imaging and Its Impact on Surface Solar Irradiance,” J. Appl. Meteorol. 42, 1421-1434 (2003).
[CrossRef]

Pickering, T. E.

T. E. Pickering, “The MMT all-sky camera,” Proc. SPIE 6267, 62671A (2006).
[CrossRef]

Pomozi, I.

G. Horváth, J. Gál, I. Pomozi, and R. Wehner, “Polarization portrait of the Arago Point: video-polarimetric imaging of the neutral points of skylight polarization,” Naturwissenschaften 85, 333-339 (1998).
[CrossRef]

Poynton, C. A.

C. A. Poynton, Digital Video and HDTV: Algorithms and Interfaces (Morgan Kaufmann, 2003).

Pust, N. J.

Russell, C. T.

S. B. Mende, S. E. Harris, H. U. Frey, V. Angelopoulos, C. T. Russell, E. Donovan, B. Jackel, M. Greffen, and L. M. Peticolas, “The THEMIS array of ground-based observatories for the study of auroral substorms,” Space Sci. Rev. , doi: 10.1007/s11214-008-9380-x (2007).

Sabburg, J. M.

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

J. M. Sabburg and C. N. Long, “Improved sky imaging for studies of enhanced UV irradiance,” Atmos. Chem. Phys. 4, 2543-2552 (2004).
[CrossRef]

Sandmann, H.

N. H. Schade, A. Macke, H. Sandmann, and C. Stick, “Total and partial cloud detection during summermonths 2005 at Westerland (Sylt, Germany),” Atmos. Chem. Phys. Discuss. 8, 13479-13505 (2008).
[CrossRef]

N. H. Schade, A. Macke, H. Sandmann, and C. Stick, “Enhanced solar global irradiance during cloudy sky conditions,” Meteor. Zeitschr. 16, 295-303 (2007).
[CrossRef]

Schade, N. H.

N. H. Schade, A. Macke, H. Sandmann, and C. Stick, “Total and partial cloud detection during summermonths 2005 at Westerland (Sylt, Germany),” Atmos. Chem. Phys. Discuss. 8, 13479-13505 (2008).
[CrossRef]

N. H. Schade, A. Macke, H. Sandmann, and C. Stick, “Enhanced solar global irradiance during cloudy sky conditions,” Meteor. Zeitschr. 16, 295-303 (2007).
[CrossRef]

Schallhart, B.

M. Blumthaler, B. Schallhart, M. Schwarzmann, R. McKenzie, P. Johnston, M. Kotkamp, and H. Shiona, “Spectral UV measurements of global irradiance, solar radiance, and actinic flux in New Zealand: intercomparison between instruments and model calculations,” J. Atmos. Ocean. Technol. 25, 945-958(2008).
[CrossRef]

B. Schallhart, M. Blumthaler, J. Schreder, and J. Verdebout, “A method to generate near real time UV-index maps of Austria,” Atmos. Chem. Phys. 8, 7483-7491 (2008).
[CrossRef]

Schreder, J.

B. Schallhart, M. Blumthaler, J. Schreder, and J. Verdebout, “A method to generate near real time UV-index maps of Austria,” Atmos. Chem. Phys. 8, 7483-7491 (2008).
[CrossRef]

Schwarzmann, M.

M. Blumthaler, B. Schallhart, M. Schwarzmann, R. McKenzie, P. Johnston, M. Kotkamp, and H. Shiona, “Spectral UV measurements of global irradiance, solar radiance, and actinic flux in New Zealand: intercomparison between instruments and model calculations,” J. Atmos. Ocean. Technol. 25, 945-958(2008).
[CrossRef]

Shaw, J. A.

Shields, J.

U. Feister and J. Shields, “Cloud and radiance measurements with the VIS/NIR Daylight Whole Sky Imager at Lindenberg (Germany),” Meteor. Zeitschr. 14, 627-639 (2005).
[CrossRef]

U. Feister, J. Shields, M. Karr, R. 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,” in Proceedings of Climate Monitoring--Satellite Application Facility Training Workshop (Dresden, 2000).

Shiona, H.

M. Blumthaler, B. Schallhart, M. Schwarzmann, R. McKenzie, P. Johnston, M. Kotkamp, and H. Shiona, “Spectral UV measurements of global irradiance, solar radiance, and actinic flux in New Zealand: intercomparison between instruments and model calculations,” J. Atmos. Ocean. Technol. 25, 945-958(2008).
[CrossRef]

Stick, C.

N. H. Schade, A. Macke, H. Sandmann, and C. Stick, “Total and partial cloud detection during summermonths 2005 at Westerland (Sylt, Germany),” Atmos. Chem. Phys. Discuss. 8, 13479-13505 (2008).
[CrossRef]

N. H. Schade, A. Macke, H. Sandmann, and C. Stick, “Enhanced solar global irradiance during cloudy sky conditions,” Meteor. Zeitschr. 16, 295-303 (2007).
[CrossRef]

Strutt, J. W.

J. W. Strutt, “On the light from the sky, its polarisation and color,” Philos. Mag. 41, 107-120274-279 (1871).

Stumpfel, J.

J. Stumpfel, C. Thou, A. Jones, T. Hawkins, A. Wenger, and P. Debevec, Proceedings of the Third International Conference on Computer Graphics, Virtual Reality, Visualisation and Interaction in Africa (Association for Computing Machinery, 2004), pp. 145-149.
[CrossRef]

Suhai, B.

Sun, C. H.

K. A. Buch and C. H. Sun, “Cloud classification using whole-sky imager data,” presented at Ninth Symposium on Meteoriological Observations and Instrumentation, paper 7.5, Charlotte, North Carolina, 1995.

Thomas, A.

G. Pfister, R. L. McKenzie, J. B. Liley, A. Thomas, B. W. Forgan, and C. N. Long, “Cloud Coverage Based on All-Sky Imaging and Its Impact on Surface Solar Irradiance,” J. Appl. Meteorol. 42, 1421-1434 (2003).
[CrossRef]

Thou, C.

J. Stumpfel, C. Thou, A. Jones, T. Hawkins, A. Wenger, and P. Debevec, Proceedings of the Third International Conference on Computer Graphics, Virtual Reality, Visualisation and Interaction in Africa (Association for Computing Machinery, 2004), pp. 145-149.
[CrossRef]

Twomey, S.

S. Twomey, Atmospheric Aerosols (Elsevier, 1977).

Verdebout, J.

B. Schallhart, M. Blumthaler, J. Schreder, and J. Verdebout, “A method to generate near real time UV-index maps of Austria,” Atmos. Chem. Phys. 8, 7483-7491 (2008).
[CrossRef]

Voss, K.

Wehner, R.

J. Gál, G. Horváth, V. B. Meyer-Rochow, and R. Wehner, “Polarization patterns of the summer sky and its neutral points measured by full-sky imaging polarimetry in Finnish Lapland north of the Arctic Circle,” Proc. R. Soc. A 457, 1385-1399 (2001).
[CrossRef]

G. Horváth, J. Gál, I. Pomozi, and R. Wehner, “Polarization portrait of the Arago Point: video-polarimetric imaging of the neutral points of skylight polarization,” Naturwissenschaften 85, 333-339 (1998).
[CrossRef]

Wenger, A.

J. Stumpfel, C. Thou, A. Jones, T. Hawkins, A. Wenger, and P. Debevec, Proceedings of the Third International Conference on Computer Graphics, Virtual Reality, Visualisation and Interaction in Africa (Association for Computing Machinery, 2004), pp. 145-149.
[CrossRef]

Woldt, M.

U. Feister, J. Shields, M. Karr, R. 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,” in Proceedings of Climate Monitoring--Satellite Application Facility Training Workshop (Dresden, 2000).

Zotti, G.

G. Zotti, “Measuring light pollution with a calibrated high dynamic range all-sky image acquisition system,” presented at the DARKSKY2007--7th European Symposium for the Protection of the Night Sky, Bled, Slovenia (2007).

Appl. Opt. (4)

Atmos. Chem. Phys. (2)

J. M. Sabburg and C. N. Long, “Improved sky imaging for studies of enhanced UV irradiance,” Atmos. Chem. Phys. 4, 2543-2552 (2004).
[CrossRef]

B. Schallhart, M. Blumthaler, J. Schreder, and J. Verdebout, “A method to generate near real time UV-index maps of Austria,” Atmos. Chem. Phys. 8, 7483-7491 (2008).
[CrossRef]

Atmos. Chem. Phys. Discuss. (1)

N. H. Schade, A. Macke, H. Sandmann, and C. Stick, “Total and partial cloud detection during summermonths 2005 at Westerland (Sylt, Germany),” Atmos. Chem. Phys. Discuss. 8, 13479-13505 (2008).
[CrossRef]

J. Appl. Meteorol. (1)

G. Pfister, R. L. McKenzie, J. B. Liley, A. Thomas, B. W. Forgan, and C. N. Long, “Cloud Coverage Based on All-Sky Imaging and Its Impact on Surface Solar Irradiance,” J. Appl. Meteorol. 42, 1421-1434 (2003).
[CrossRef]

J. Atmos. Ocean. Technol. (2)

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

M. Blumthaler, B. Schallhart, M. Schwarzmann, R. McKenzie, P. Johnston, M. Kotkamp, and H. Shiona, “Spectral UV measurements of global irradiance, solar radiance, and actinic flux in New Zealand: intercomparison between instruments and model calculations,” J. Atmos. Ocean. Technol. 25, 945-958(2008).
[CrossRef]

Meteor. Zeitschr. (2)

N. H. Schade, A. Macke, H. Sandmann, and C. Stick, “Enhanced solar global irradiance during cloudy sky conditions,” Meteor. Zeitschr. 16, 295-303 (2007).
[CrossRef]

U. Feister and J. Shields, “Cloud and radiance measurements with the VIS/NIR Daylight Whole Sky Imager at Lindenberg (Germany),” Meteor. Zeitschr. 14, 627-639 (2005).
[CrossRef]

Naturwissenschaften (1)

G. Horváth, J. Gál, I. Pomozi, and R. Wehner, “Polarization portrait of the Arago Point: video-polarimetric imaging of the neutral points of skylight polarization,” Naturwissenschaften 85, 333-339 (1998).
[CrossRef]

New J. Phys. (1)

M. V. Berry, M. R. Dennis, and R. L. Lee, Jr., “Polarization singularities in the clear sky,” New J. Phys. 6, 162 (2004).
[CrossRef]

Oecologia (1)

R. L. Chazdon and C. B. Field, “Photographic estimation of photosynthetically active radiation: evaluation of a computerized technique,” Oecologia 73, 525-532 (1987).
[CrossRef]

Philos. Mag. (1)

J. W. Strutt, “On the light from the sky, its polarisation and color,” Philos. Mag. 41, 107-120274-279 (1871).

Proc. R. Soc. A (1)

J. Gál, G. Horváth, V. B. Meyer-Rochow, and R. Wehner, “Polarization patterns of the summer sky and its neutral points measured by full-sky imaging polarimetry in Finnish Lapland north of the Arctic Circle,” Proc. R. Soc. A 457, 1385-1399 (2001).
[CrossRef]

Proc. SPIE (1)

T. E. Pickering, “The MMT all-sky camera,” Proc. SPIE 6267, 62671A (2006).
[CrossRef]

Space Sci. Rev. (1)

S. B. Mende, S. E. Harris, H. U. Frey, V. Angelopoulos, C. T. Russell, E. Donovan, B. Jackel, M. Greffen, and L. M. Peticolas, “The THEMIS array of ground-based observatories for the study of auroral substorms,” Space Sci. Rev. , doi: 10.1007/s11214-008-9380-x (2007).

Other (7)

G. Zotti, “Measuring light pollution with a calibrated high dynamic range all-sky image acquisition system,” presented at the DARKSKY2007--7th European Symposium for the Protection of the Night Sky, Bled, Slovenia (2007).

K. A. Buch and C. H. Sun, “Cloud classification using whole-sky imager data,” presented at Ninth Symposium on Meteoriological Observations and Instrumentation, paper 7.5, Charlotte, North Carolina, 1995.

U. Feister, J. Shields, M. Karr, R. 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,” in Proceedings of Climate Monitoring--Satellite Application Facility Training Workshop (Dresden, 2000).

S. Twomey, Atmospheric Aerosols (Elsevier, 1977).

J. Stumpfel, C. Thou, A. Jones, T. Hawkins, A. Wenger, and P. Debevec, Proceedings of the Third International Conference on Computer Graphics, Virtual Reality, Visualisation and Interaction in Africa (Association for Computing Machinery, 2004), pp. 145-149.
[CrossRef]

C. A. Poynton, Digital Video and HDTV: Algorithms and Interfaces (Morgan Kaufmann, 2003).

K. L. Coulson, Polarization and Intensity of Light in the Atmosphere (Deepak, 1988).

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Figures (9)

Fig. 1
Fig. 1

Linearization function f ( C ) to convert pixel counts into relative radiance for the blue channel. Data points are fitted with a 3rd order polynomial.

Fig. 2
Fig. 2

(a) Blue pixel counts C from JPEG images at four polarizer angles. Counts are converted to relative radiance and inserted into Eqs. (5, 6) to yield the polarization map. (b) Corresponding polarization map of the cloud-free sky for a wavelength of 450 ± 50 nm (blue channel). The degree of polarization is coded in gray shades, undetermined areas are rendered white on 26 February 2008, 10:30 UTC.

Fig. 3
Fig. 3

Analysis of a fully polarized test field (white reflectance place) at different angles of incidence and polarizer angle offsets 0 ° , 15 ° , and 30 ° . Within the experimental uncertainty, no influence of these parameters on the measured polarization can be found.

Fig. 4
Fig. 4

Comparison of the all-sky camera blue polarization and spectroradiometer radiance measurements in the principal plane on a clear-sky day, 26 February 2008, 10:30 UTC. Solar zenith angle is 58 ° .

Fig. 5
Fig. 5

Comparison of the polarization in the principal plane, with and without obscuring the Sun using a shadow arm. The measured polarization is only perturbed at the locations of the reflections around 45 ° and around the Sun (Solar zenith angle = 62 ° ). 24 October 2008, 09:46 and 09:48 UTC.

Fig. 6
Fig. 6

(a) Polarization map at dawn, solar elevation is 6 ° and the Sun has set behind the mountains. Note the neutral points at about ± 70 ° zenith angle (9 September 2008, 17:00 UTC). (b) Polarization map around noon with high and low clouds. (24 September 2008, 12:00 UTC).

Fig. 7
Fig. 7

(a) Image of a sky with convective cloud type (cumulus) of low and medium height. This cloud type has a sharp contrast and is relatively easy to discriminate from the clear sky. (19 September 2008,12:00 UTC). (b) Processed image after cloud detection, clouds are rendered white, while clear sky is gray and mask is black. The underexposed image (not shown here) allows good discrimination close to the Sun. Total cloud cover here is 0.63. (c) Image of a sky with both low and high clouds, including altostratus and a contrail. (24 September 2008, 12:00 UTC). (d) Total cloud cover is 0.29. Note the problematic area near the Sun when thin clouds are present.

Fig. 8
Fig. 8

Comparison of total cloud cover (TCC) obtained from the camera images and SYNOP cloud observations ( TCC camera - TCC SYNOP ). 73% of a total of 3903 analyzed camera images agree within 1   octa with the SYNOP-observations.

Fig. 9
Fig. 9

(a) For SCP of 1, the Sun is totally occluded, which coincides with a TCC near 1. The ratio of measured UVI and clear-sky prediction is peaked around 0.3. In the range 0.98 < TCC < 1 , more than 620 data points are accumulated. (b) SCP of 0 implies a partially covered Sun. In this case increasing TCC is correlated with a decreasing ratio of measured-to-clear-sky prediction. (c) For SCP of 0, the Sun is assumed totally unobscured, which correlates with small TCC and the measured UVI converging toward the clear-sky prediction.

Equations (6)

Equations on this page are rendered with MathJax. Learn more.

[ r ϕ ] polar [ r · Θ max r max ϕ ] [ Θ ϕ ] sky .
R = k · f ( C ) ,
[ I Q U V ] = [ E l E l * + E r E r * E l E l * E r E r * E l E r * + E r E l * i ( E l E r * + E r E l * ) ] ,
[ I Q U V ] = [ I 0 + I 90 I 0 I 90 I 45 I 135 I + I ] ,
[ I Q U ] = [ R 0 + R 90 R 0 R 90 R 45 R 135 ] .
Π = Q 2 + U 2 I , χ = 0.5 arctan ( U Q ) .

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