Abstract

In a previous work [J. Opt. Soc. Am. A 24, 942–956 (2007)] we showed how to design an optimum multispectral system aimed at spectral recovery of skylight. Since high-resolution multispectral images of skylight could be interesting for many scientific disciplines, here we also propose a nonoptimum but much cheaper and faster approach to achieve this goal by using a trichromatic RGB charge-coupled device (CCD) digital camera. The camera is attached to a fish-eye lens, hence permitting us to obtain a spectrum of every point of the skydome corresponding to each pixel of the image. In this work we show how to apply multispectral techniques to the sensors’ responses of a common trichromatic camera in order to obtain skylight spectra from them. This spectral information is accurate enough to estimate experimental values of some climate parameters or to be used in algorithms for automatic cloud detection, among many other possible scientific applications.

© 2008 Optical Society of America

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References

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  1. J. Y. Hardeberg, “Acquisition and reproduction of color images: colorimetric and multispectral approaches,” (Dissertation.com, 2001). (Revised second edition of Ph.D. dissertation, Ecole Nationale Supérieure des Télécommunications, 1999), pp. 121-174.
  2. M. A. López-Álvarez, J. Hernández-Andrés, J. Romero, and R. L. Lee Jr. , “Designing a practical system for spectral imaging of skylight,” Appl. Opt. 44, 5688-5695 (2005).
    [CrossRef] [PubMed]
  3. M. A. López-Álvarez, J. Hernández-Andrés, E. M. Valero, and J. Romero, “Selecting algorithms, sensors and linear bases for optimum spectral recovery of skylight,” J. Opt. Soc. Am. A 24, 942-956 (2007).
    [CrossRef]
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  6. http://micro.magnet.fsu.edu/primer/java/filters/aotf/index.html.
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    [CrossRef]
  8. J. Hernández-Andrés, J. Romero, and R. L. Lee, Jr., “Colorimetric and spectroradiometric characteristics of narrow-field of view clear skylight in Granada, Spain,” J. Opt. Soc. Am. A 18, 412-420 (2001).
    [CrossRef]
  9. 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).
    [CrossRef]
  10. A. Cazorla, F. J. Olmo, and L. Alados-Arboledas, “Using a sky imager for aerosol characterization,” Atms. Environ. 42, 2739-2745 (2008).
    [CrossRef]
  11. A. Ferrero, J. Campos, and A. Pons, “Low-uncertainty absolute radiometric calibration of a CCD,” Metrologia 43, S17-S21(2006).
    [CrossRef]
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    [CrossRef]
  14. R. Schettini, G. Y. Novati, and P. Pellegri, “Training set and filters selection for the efficient use of multispectral acquisition systems,” in Proceedings of the 2nd European Conference on Colour Graphics, Image and Vision (IS&T, 2002), pp. 422-426.
  15. M. Mohammadi, M. Nezamabadi, R. S. Berns, and L. A. Taplin, “Spectral imaging target development based on hierarchical cluster analysis”, in Proceedings of 12th Color Imaging Conference: Color Science and Engineering, Systems, Technologies and Applications (IS&T, 2004), pp. 59-64, www.art-si.org.
  16. B. P. Lathi, Modern Digital and Analog Communication Systems, 2nd ed. (Oxford University Press, 1989), pp. 132-212.
  17. J. J. Michalsky, “Estimation of continuous solar spectral distributions from discrete filter measurements: II. A demonstration of practicability,” Sol. Energy 34, 439-445 (1985).
    [CrossRef]
  18. M. Shi and G. Healey, “Using reflectance models for color scanner calibration,” J. Opt. Soc. Am. A 19, 645-656 (2002).
    [CrossRef]
  19. F. J. Olmo, A. Cazorla, L. Alados-Arboledas, M. A. López-Álvarez, J. Hernández-Andrés, and J. Romero, “Proposal of a procedure for the retrieval of the optical depth by an All-Sky CCD camera,” submitted to Appl. Opt.
    [PubMed]
  20. R. M. Goody and Y. L. Yung, Atmospheric Radiation, Theoretical Basis, 2nd ed. (Oxford University Press, 1995), Chap. 5.
  21. F. H. Imai, M. R. Rosen, and R. S. Berns, “Comparative study of metrics for spectral match quality,” in Proceedings of the 1st European Conference on Colour in Graphics, Image and Vision (Society for Imaging Science and Technology, 2002), pp. 492-496.
  22. J. A. S. Viggiano, “Metrics for evaluating spectral matches: a quantitative comparison,” in Proceedings of the 2nd European Conference on Colour in Graphics, Imaging and Vision (Society for Imaging Science and Technology, 2004), pp. 286-291.
  23. M. A. López-Álvarez, J. Hernández-Andrés, E. M. Valero, and J. L. Nieves, “Colorimetric and spectral combined metric for the optimization of multispectral systems,” in Proceedings of the 10th Congress of the International Colour Association (AIC'05), J. Hernández-Andrés and J. L. Nieves, eds. (Association Internationale de la Couleur, 2005), pp. 1685-1688.

2008 (2)

A. Cazorla, F. J. Olmo, and L. Alados-Arboledas, “Using a sky imager for aerosol characterization,” Atms. Environ. 42, 2739-2745 (2008).
[CrossRef]

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).
[CrossRef]

2007 (3)

2006 (2)

2005 (1)

2002 (2)

2001 (1)

1985 (1)

J. J. Michalsky, “Estimation of continuous solar spectral distributions from discrete filter measurements: II. A demonstration of practicability,” Sol. Energy 34, 439-445 (1985).
[CrossRef]

Alados-Arboledas, L.

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).
[CrossRef]

A. Cazorla, F. J. Olmo, and L. Alados-Arboledas, “Using a sky imager for aerosol characterization,” Atms. Environ. 42, 2739-2745 (2008).
[CrossRef]

F. J. Olmo, A. Cazorla, L. Alados-Arboledas, M. A. López-Álvarez, J. Hernández-Andrés, and J. Romero, “Proposal of a procedure for the retrieval of the optical depth by an All-Sky CCD camera,” submitted to Appl. Opt.
[PubMed]

Alsam, A.

Antikainen, J.

J. Antikainen, M. Hauta-Kasari, J. Parkkinen, and T. Jaaskelainen, “Using two line scanning based spectral cameras simultaneously in one measurement process to create a wider spectral area from the measured target,” in Proceedings of the IEEE International Workshop on Imaging, Systems and Techniques--IST 2007 (IEEE, 2007), pp. 1-5.
[CrossRef]

Arjona, M.

Berns, R. S.

M. Mohammadi, M. Nezamabadi, R. S. Berns, and L. A. Taplin, “Spectral imaging target development based on hierarchical cluster analysis”, in Proceedings of 12th Color Imaging Conference: Color Science and Engineering, Systems, Technologies and Applications (IS&T, 2004), pp. 59-64, www.art-si.org.

F. H. Imai, M. R. Rosen, and R. S. Berns, “Comparative study of metrics for spectral match quality,” in Proceedings of the 1st European Conference on Colour in Graphics, Image and Vision (Society for Imaging Science and Technology, 2002), pp. 492-496.

Campos, J.

A. Ferrero, J. Campos, and A. Pons, “Low-uncertainty absolute radiometric calibration of a CCD,” Metrologia 43, S17-S21(2006).
[CrossRef]

Cazorla, A.

A. Cazorla, F. J. Olmo, and L. Alados-Arboledas, “Using a sky imager for aerosol characterization,” Atms. Environ. 42, 2739-2745 (2008).
[CrossRef]

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).
[CrossRef]

F. J. Olmo, A. Cazorla, L. Alados-Arboledas, M. A. López-Álvarez, J. Hernández-Andrés, and J. Romero, “Proposal of a procedure for the retrieval of the optical depth by an All-Sky CCD camera,” submitted to Appl. Opt.
[PubMed]

de Lasarte, M.

Ferreira, F. P.

Ferrero, A.

A. Ferrero, J. Campos, and A. Pons, “Low-uncertainty absolute radiometric calibration of a CCD,” Metrologia 43, S17-S21(2006).
[CrossRef]

Foster, D. H.

Goody, R. M.

R. M. Goody and Y. L. Yung, Atmospheric Radiation, Theoretical Basis, 2nd ed. (Oxford University Press, 1995), Chap. 5.

Hardeberg, J. Y.

J. Y. Hardeberg, “Acquisition and reproduction of color images: colorimetric and multispectral approaches,” (Dissertation.com, 2001). (Revised second edition of Ph.D. dissertation, Ecole Nationale Supérieure des Télécommunications, 1999), pp. 121-174.

Hauta-Kasari, M.

J. Antikainen, M. Hauta-Kasari, J. Parkkinen, and T. Jaaskelainen, “Using two line scanning based spectral cameras simultaneously in one measurement process to create a wider spectral area from the measured target,” in Proceedings of the IEEE International Workshop on Imaging, Systems and Techniques--IST 2007 (IEEE, 2007), pp. 1-5.
[CrossRef]

Healey, G.

Hernández-Andrés, J.

M. A. López-Álvarez, J. Hernández-Andrés, E. M. Valero, and J. Romero, “Selecting algorithms, sensors and linear bases for optimum spectral recovery of skylight,” J. Opt. Soc. Am. A 24, 942-956 (2007).
[CrossRef]

M. A. López-Álvarez, J. Hernández-Andrés, J. Romero, and R. L. Lee Jr. , “Designing a practical system for spectral imaging of skylight,” Appl. Opt. 44, 5688-5695 (2005).
[CrossRef] [PubMed]

J. Hernández-Andrés, J. Romero, and R. L. Lee, Jr., “Colorimetric and spectroradiometric characteristics of narrow-field of view clear skylight in Granada, Spain,” J. Opt. Soc. Am. A 18, 412-420 (2001).
[CrossRef]

M. A. López-Álvarez, J. Hernández-Andrés, E. M. Valero, and J. L. Nieves, “Colorimetric and spectral combined metric for the optimization of multispectral systems,” in Proceedings of the 10th Congress of the International Colour Association (AIC'05), J. Hernández-Andrés and J. L. Nieves, eds. (Association Internationale de la Couleur, 2005), pp. 1685-1688.

F. J. Olmo, A. Cazorla, L. Alados-Arboledas, M. A. López-Álvarez, J. Hernández-Andrés, and J. Romero, “Proposal of a procedure for the retrieval of the optical depth by an All-Sky CCD camera,” submitted to Appl. Opt.
[PubMed]

Imai, F. H.

F. H. Imai, M. R. Rosen, and R. S. Berns, “Comparative study of metrics for spectral match quality,” in Proceedings of the 1st European Conference on Colour in Graphics, Image and Vision (Society for Imaging Science and Technology, 2002), pp. 492-496.

Jaaskelainen, T.

J. Antikainen, M. Hauta-Kasari, J. Parkkinen, and T. Jaaskelainen, “Using two line scanning based spectral cameras simultaneously in one measurement process to create a wider spectral area from the measured target,” in Proceedings of the IEEE International Workshop on Imaging, Systems and Techniques--IST 2007 (IEEE, 2007), pp. 1-5.
[CrossRef]

Lathi, B. P.

B. P. Lathi, Modern Digital and Analog Communication Systems, 2nd ed. (Oxford University Press, 1989), pp. 132-212.

Lee, R. L.

Lenz, R.

López-Álvarez, M. A.

M. A. López-Álvarez, J. Hernández-Andrés, E. M. Valero, and J. Romero, “Selecting algorithms, sensors and linear bases for optimum spectral recovery of skylight,” J. Opt. Soc. Am. A 24, 942-956 (2007).
[CrossRef]

M. A. López-Álvarez, J. Hernández-Andrés, J. Romero, and R. L. Lee Jr. , “Designing a practical system for spectral imaging of skylight,” Appl. Opt. 44, 5688-5695 (2005).
[CrossRef] [PubMed]

F. J. Olmo, A. Cazorla, L. Alados-Arboledas, M. A. López-Álvarez, J. Hernández-Andrés, and J. Romero, “Proposal of a procedure for the retrieval of the optical depth by an All-Sky CCD camera,” submitted to Appl. Opt.
[PubMed]

M. A. López-Álvarez, J. Hernández-Andrés, E. M. Valero, and J. L. Nieves, “Colorimetric and spectral combined metric for the optimization of multispectral systems,” in Proceedings of the 10th Congress of the International Colour Association (AIC'05), J. Hernández-Andrés and J. L. Nieves, eds. (Association Internationale de la Couleur, 2005), pp. 1685-1688.

Michalsky, J. J.

J. J. Michalsky, “Estimation of continuous solar spectral distributions from discrete filter measurements: II. A demonstration of practicability,” Sol. Energy 34, 439-445 (1985).
[CrossRef]

Mohammadi, M.

M. Mohammadi, M. Nezamabadi, R. S. Berns, and L. A. Taplin, “Spectral imaging target development based on hierarchical cluster analysis”, in Proceedings of 12th Color Imaging Conference: Color Science and Engineering, Systems, Technologies and Applications (IS&T, 2004), pp. 59-64, www.art-si.org.

Nascimento, S. M. C.

Nezamabadi, M.

M. Mohammadi, M. Nezamabadi, R. S. Berns, and L. A. Taplin, “Spectral imaging target development based on hierarchical cluster analysis”, in Proceedings of 12th Color Imaging Conference: Color Science and Engineering, Systems, Technologies and Applications (IS&T, 2004), pp. 59-64, www.art-si.org.

Nieves, J. L.

M. A. López-Álvarez, J. Hernández-Andrés, E. M. Valero, and J. L. Nieves, “Colorimetric and spectral combined metric for the optimization of multispectral systems,” in Proceedings of the 10th Congress of the International Colour Association (AIC'05), J. Hernández-Andrés and J. L. Nieves, eds. (Association Internationale de la Couleur, 2005), pp. 1685-1688.

Novati, G. Y.

R. Schettini, G. Y. Novati, and P. Pellegri, “Training set and filters selection for the efficient use of multispectral acquisition systems,” in Proceedings of the 2nd European Conference on Colour Graphics, Image and Vision (IS&T, 2002), pp. 422-426.

Olmo, F. J.

A. Cazorla, F. J. Olmo, and L. Alados-Arboledas, “Using a sky imager for aerosol characterization,” Atms. Environ. 42, 2739-2745 (2008).
[CrossRef]

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).
[CrossRef]

F. J. Olmo, A. Cazorla, L. Alados-Arboledas, M. A. López-Álvarez, J. Hernández-Andrés, and J. Romero, “Proposal of a procedure for the retrieval of the optical depth by an All-Sky CCD camera,” submitted to Appl. Opt.
[PubMed]

Parkkinen, J.

J. Antikainen, M. Hauta-Kasari, J. Parkkinen, and T. Jaaskelainen, “Using two line scanning based spectral cameras simultaneously in one measurement process to create a wider spectral area from the measured target,” in Proceedings of the IEEE International Workshop on Imaging, Systems and Techniques--IST 2007 (IEEE, 2007), pp. 1-5.
[CrossRef]

Pellegri, P.

R. Schettini, G. Y. Novati, and P. Pellegri, “Training set and filters selection for the efficient use of multispectral acquisition systems,” in Proceedings of the 2nd European Conference on Colour Graphics, Image and Vision (IS&T, 2002), pp. 422-426.

Pons, A.

A. Ferrero, J. Campos, and A. Pons, “Low-uncertainty absolute radiometric calibration of a CCD,” Metrologia 43, S17-S21(2006).
[CrossRef]

Pujol, J.

Romero, J.

Rosen, M. R.

F. H. Imai, M. R. Rosen, and R. S. Berns, “Comparative study of metrics for spectral match quality,” in Proceedings of the 1st European Conference on Colour in Graphics, Image and Vision (Society for Imaging Science and Technology, 2002), pp. 492-496.

Schettini, R.

R. Schettini, G. Y. Novati, and P. Pellegri, “Training set and filters selection for the efficient use of multispectral acquisition systems,” in Proceedings of the 2nd European Conference on Colour Graphics, Image and Vision (IS&T, 2002), pp. 422-426.

Shi, M.

Taplin, L. A.

M. Mohammadi, M. Nezamabadi, R. S. Berns, and L. A. Taplin, “Spectral imaging target development based on hierarchical cluster analysis”, in Proceedings of 12th Color Imaging Conference: Color Science and Engineering, Systems, Technologies and Applications (IS&T, 2004), pp. 59-64, www.art-si.org.

Valero, E. M.

M. A. López-Álvarez, J. Hernández-Andrés, E. M. Valero, and J. Romero, “Selecting algorithms, sensors and linear bases for optimum spectral recovery of skylight,” J. Opt. Soc. Am. A 24, 942-956 (2007).
[CrossRef]

M. A. López-Álvarez, J. Hernández-Andrés, E. M. Valero, and J. L. Nieves, “Colorimetric and spectral combined metric for the optimization of multispectral systems,” in Proceedings of the 10th Congress of the International Colour Association (AIC'05), J. Hernández-Andrés and J. L. Nieves, eds. (Association Internationale de la Couleur, 2005), pp. 1685-1688.

Viggiano, J. A. S.

J. A. S. Viggiano, “Metrics for evaluating spectral matches: a quantitative comparison,” in Proceedings of the 2nd European Conference on Colour in Graphics, Imaging and Vision (Society for Imaging Science and Technology, 2004), pp. 286-291.

Vilaseca, M.

Yung, Y. L.

R. M. Goody and Y. L. Yung, Atmospheric Radiation, Theoretical Basis, 2nd ed. (Oxford University Press, 1995), Chap. 5.

Appl. Opt. (4)

Atms. Environ. (1)

A. Cazorla, F. J. Olmo, and L. Alados-Arboledas, “Using a sky imager for aerosol characterization,” Atms. Environ. 42, 2739-2745 (2008).
[CrossRef]

J. Opt. Soc. Am. A (6)

Metrologia (1)

A. Ferrero, J. Campos, and A. Pons, “Low-uncertainty absolute radiometric calibration of a CCD,” Metrologia 43, S17-S21(2006).
[CrossRef]

Sol. Energy (1)

J. J. Michalsky, “Estimation of continuous solar spectral distributions from discrete filter measurements: II. A demonstration of practicability,” Sol. Energy 34, 439-445 (1985).
[CrossRef]

Other (10)

R. M. Goody and Y. L. Yung, Atmospheric Radiation, Theoretical Basis, 2nd ed. (Oxford University Press, 1995), Chap. 5.

F. H. Imai, M. R. Rosen, and R. S. Berns, “Comparative study of metrics for spectral match quality,” in Proceedings of the 1st European Conference on Colour in Graphics, Image and Vision (Society for Imaging Science and Technology, 2002), pp. 492-496.

J. A. S. Viggiano, “Metrics for evaluating spectral matches: a quantitative comparison,” in Proceedings of the 2nd European Conference on Colour in Graphics, Imaging and Vision (Society for Imaging Science and Technology, 2004), pp. 286-291.

M. A. López-Álvarez, J. Hernández-Andrés, E. M. Valero, and J. L. Nieves, “Colorimetric and spectral combined metric for the optimization of multispectral systems,” in Proceedings of the 10th Congress of the International Colour Association (AIC'05), J. Hernández-Andrés and J. L. Nieves, eds. (Association Internationale de la Couleur, 2005), pp. 1685-1688.

J. Y. Hardeberg, “Acquisition and reproduction of color images: colorimetric and multispectral approaches,” (Dissertation.com, 2001). (Revised second edition of Ph.D. dissertation, Ecole Nationale Supérieure des Télécommunications, 1999), pp. 121-174.

http://micro.magnet.fsu.edu/primer/java/filters/aotf/index.html.

J. Antikainen, M. Hauta-Kasari, J. Parkkinen, and T. Jaaskelainen, “Using two line scanning based spectral cameras simultaneously in one measurement process to create a wider spectral area from the measured target,” in Proceedings of the IEEE International Workshop on Imaging, Systems and Techniques--IST 2007 (IEEE, 2007), pp. 1-5.
[CrossRef]

R. Schettini, G. Y. Novati, and P. Pellegri, “Training set and filters selection for the efficient use of multispectral acquisition systems,” in Proceedings of the 2nd European Conference on Colour Graphics, Image and Vision (IS&T, 2002), pp. 422-426.

M. Mohammadi, M. Nezamabadi, R. S. Berns, and L. A. Taplin, “Spectral imaging target development based on hierarchical cluster analysis”, in Proceedings of 12th Color Imaging Conference: Color Science and Engineering, Systems, Technologies and Applications (IS&T, 2004), pp. 59-64, www.art-si.org.

B. P. Lathi, Modern Digital and Analog Communication Systems, 2nd ed. (Oxford University Press, 1989), pp. 132-212.

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Figures (6)

Fig. 1
Fig. 1

Complete imaging system used to acquire spectral images of the skydome.

Fig. 2
Fig. 2

Typical image captured by the CCD RGB camera attached to the fish-eye lens. Note that direct sunlight is avoided by the black sphere. The field of view of the PR650 spectroradiometer corresponds to a circle placed in its corresponding location in the image, with different radius depending on the elevation of the measurement (left, 3 pixels at elevation of 45 ° ; center, 4 pixels at zenith).

Fig. 3
Fig. 3

CIE-31 chromaticity diagram showing the xy coordinates of the complete set of 902 skylight measurements taken in Granada (circle) and those xy coordinates of the 40 training samples selected with our grouping method maximazing the CSCM metric (rhombus). The Planckian locus is shown as a line.

Fig. 4
Fig. 4

Mean value of the CSCM metric when recovering the complete test set of 902 skylight measurements taken in Granada by using different training sets of various numbers of samples when using the proposed grouping method. Linear pseudoinverse algorithm is used for the spectral estimations.

Fig. 5
Fig. 5

(a) 10th percentile ( CSCM = 2.15 ) and (b) 90th percentile ( CSCM = 25.56 ) of the CSCM metric over the complete test set of 902 skylight spectral measurements taken in Granada when recovered with the RGB CCD QImaging camera and the linear pseudoinverse method (dotted line) trained with m = 100 spectra. The spectroradiometric measurement with the PR650 is shown by the solid line.

Fig. 6
Fig. 6

90th percentile of the CSCM metric ( CSCM = 5.69 ) over the complete test set of 902 skylight spectral measurements after normalization. The spectroradiometric measurement with the PR650 is shown by the solid line, while the spectral estimation with the Qimaging CCD camera and the linear pseudoinverse method trained with m = 100 spectra is shown by the dotted line.

Tables (4)

Tables Icon

Table 1 Measurements Developed with the RGB Camera and the PR650 Spectroradiometer in Granada a

Tables Icon

Table 2 Mean Values ± Standard Deviations of the CSCM metric when Recovering the Complete Test Set of 902 Skylight Spectral Measurements Using the Linear Pseudoinverse Method with the Training Set of 40 Samples Obtained with Each of the Methods

Tables Icon

Table 3 Mean ± Standard Deviation Values of Various Metrics when Recovering the Complete Test Set of 902 Skylight Spectral Measurements Taken in Granada from the RGB Responses of the CCD Camera ( m = 100 Training Spectra are Used)

Tables Icon

Table 4 Mean ± Standard Deviation Values of Various metrics when Recovering the Complete Test Set of 902 Skylight Spectral Measurements Taken in Granada from the RGB responses of the CCD Camera After Normalization of the Spectral Curves ( m = 100 Training Spectra were Used)

Equations (4)

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

W = E t s ρ t s + ,
E R = W ρ ,
ρ = R t E + σ .
CSCM = Ln ( 1 + 1000 ( 1 GFC ) ) + Δ E a b * + IRE ( % ) ,

Metrics