Abstract

A new compact light-emitting diode (LED) sun photometer, in which a LED is used as a spectrally selective photodetector as well as a nonlinear feedback element in the operational amplifier, has been developed. The output voltage that is proportional to the logarithm of the incident solar intensity permits the direct measurement of atmospheric optical depths in selected spectral bands. Measurements made over Ahmedabad, India, show good agreement, within a few percent, of optical depths derived with a LED as a photodetector in a linear mode and with a LED as both a photodetector and a feedback element in an operational amplifier in log mode. The optical depths are also found to compare well with those obtained simultaneously with a conventional filter photometer

© 1995 Optical Society of America

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References

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  1. S. Twomey, Atmospheric Aerosols (Elsevier, New York, 1977).
  2. G. E. Shaw, “Sun photometry,” Bull. Am. Meteorol. Soc. 64, 4–10 (1983).
    [CrossRef]
  3. F. E. Volz, “Spectral sky light and solar radiance measurements in the Caribbean: maritime aerosols and Sahara dust,” J. Atmos. Sci. 27, 1041–1047 (1970).
    [CrossRef]
  4. E. C. Flowers, R. A. McCormick, K. R. Kurfis, “Atmospheric turbidity over the United States,” J. Appl. Meteorol. 8, 1961–1966 (1969).
    [CrossRef]
  5. A. Ångström, “Techniques for determining the turbidity of the atmosphere,” Tellus 13, 214–223 (1961).
    [CrossRef]
  6. H. Horvath, “Atmospheric light absorption—a review,” Atmos. Environ. A 27, 293–317 (1993).
    [CrossRef]
  7. G. A. d’Almeida, P. Koepke, E. P. Shettle, Atmospheric Aerosols: Global Climatology and Radiative Characteristics (Deepak, Hampton, Va., 1991).
  8. F. M. Mims, “Sun photometer with light emitting diodes as spectrally selective detectors,” Appl. Opt. 31, 6965–6967 (1992).
    [CrossRef]
  9. R. Lynch, The Role of Compositionally Graded GaAlAs Devices in Optical Communication (IBM Electronics Systems Center, New York, 1972).
  10. R. N. Misra, Y. B. Acharya, “Current ratio log amplifier using light emitting diodes,” Int. J. Electron. 53(1), 91–94 (1982).
    [CrossRef]
  11. S. Ramachandran, A. Jayaraman, Y. B. Acharya, B. H. Subbaraya, “Features of aerosol optical depths measured using sun-tracking photometer over Ahmedabad,” Atmos. Phys. 67, 57–70, 1994.

1994 (1)

S. Ramachandran, A. Jayaraman, Y. B. Acharya, B. H. Subbaraya, “Features of aerosol optical depths measured using sun-tracking photometer over Ahmedabad,” Atmos. Phys. 67, 57–70, 1994.

1993 (1)

H. Horvath, “Atmospheric light absorption—a review,” Atmos. Environ. A 27, 293–317 (1993).
[CrossRef]

1992 (1)

1983 (1)

G. E. Shaw, “Sun photometry,” Bull. Am. Meteorol. Soc. 64, 4–10 (1983).
[CrossRef]

1982 (1)

R. N. Misra, Y. B. Acharya, “Current ratio log amplifier using light emitting diodes,” Int. J. Electron. 53(1), 91–94 (1982).
[CrossRef]

1970 (1)

F. E. Volz, “Spectral sky light and solar radiance measurements in the Caribbean: maritime aerosols and Sahara dust,” J. Atmos. Sci. 27, 1041–1047 (1970).
[CrossRef]

1969 (1)

E. C. Flowers, R. A. McCormick, K. R. Kurfis, “Atmospheric turbidity over the United States,” J. Appl. Meteorol. 8, 1961–1966 (1969).
[CrossRef]

1961 (1)

A. Ångström, “Techniques for determining the turbidity of the atmosphere,” Tellus 13, 214–223 (1961).
[CrossRef]

Acharya, Y. B.

S. Ramachandran, A. Jayaraman, Y. B. Acharya, B. H. Subbaraya, “Features of aerosol optical depths measured using sun-tracking photometer over Ahmedabad,” Atmos. Phys. 67, 57–70, 1994.

R. N. Misra, Y. B. Acharya, “Current ratio log amplifier using light emitting diodes,” Int. J. Electron. 53(1), 91–94 (1982).
[CrossRef]

Ångström, A.

A. Ångström, “Techniques for determining the turbidity of the atmosphere,” Tellus 13, 214–223 (1961).
[CrossRef]

d’Almeida, G. A.

G. A. d’Almeida, P. Koepke, E. P. Shettle, Atmospheric Aerosols: Global Climatology and Radiative Characteristics (Deepak, Hampton, Va., 1991).

Flowers, E. C.

E. C. Flowers, R. A. McCormick, K. R. Kurfis, “Atmospheric turbidity over the United States,” J. Appl. Meteorol. 8, 1961–1966 (1969).
[CrossRef]

Horvath, H.

H. Horvath, “Atmospheric light absorption—a review,” Atmos. Environ. A 27, 293–317 (1993).
[CrossRef]

Jayaraman, A.

S. Ramachandran, A. Jayaraman, Y. B. Acharya, B. H. Subbaraya, “Features of aerosol optical depths measured using sun-tracking photometer over Ahmedabad,” Atmos. Phys. 67, 57–70, 1994.

Koepke, P.

G. A. d’Almeida, P. Koepke, E. P. Shettle, Atmospheric Aerosols: Global Climatology and Radiative Characteristics (Deepak, Hampton, Va., 1991).

Kurfis, K. R.

E. C. Flowers, R. A. McCormick, K. R. Kurfis, “Atmospheric turbidity over the United States,” J. Appl. Meteorol. 8, 1961–1966 (1969).
[CrossRef]

Lynch, R.

R. Lynch, The Role of Compositionally Graded GaAlAs Devices in Optical Communication (IBM Electronics Systems Center, New York, 1972).

McCormick, R. A.

E. C. Flowers, R. A. McCormick, K. R. Kurfis, “Atmospheric turbidity over the United States,” J. Appl. Meteorol. 8, 1961–1966 (1969).
[CrossRef]

Mims, F. M.

Misra, R. N.

R. N. Misra, Y. B. Acharya, “Current ratio log amplifier using light emitting diodes,” Int. J. Electron. 53(1), 91–94 (1982).
[CrossRef]

Ramachandran, S.

S. Ramachandran, A. Jayaraman, Y. B. Acharya, B. H. Subbaraya, “Features of aerosol optical depths measured using sun-tracking photometer over Ahmedabad,” Atmos. Phys. 67, 57–70, 1994.

Shaw, G. E.

G. E. Shaw, “Sun photometry,” Bull. Am. Meteorol. Soc. 64, 4–10 (1983).
[CrossRef]

Shettle, E. P.

G. A. d’Almeida, P. Koepke, E. P. Shettle, Atmospheric Aerosols: Global Climatology and Radiative Characteristics (Deepak, Hampton, Va., 1991).

Subbaraya, B. H.

S. Ramachandran, A. Jayaraman, Y. B. Acharya, B. H. Subbaraya, “Features of aerosol optical depths measured using sun-tracking photometer over Ahmedabad,” Atmos. Phys. 67, 57–70, 1994.

Twomey, S.

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

Volz, F. E.

F. E. Volz, “Spectral sky light and solar radiance measurements in the Caribbean: maritime aerosols and Sahara dust,” J. Atmos. Sci. 27, 1041–1047 (1970).
[CrossRef]

Appl. Opt. (1)

Atmos. Environ. A (1)

H. Horvath, “Atmospheric light absorption—a review,” Atmos. Environ. A 27, 293–317 (1993).
[CrossRef]

Atmos. Phys. (1)

S. Ramachandran, A. Jayaraman, Y. B. Acharya, B. H. Subbaraya, “Features of aerosol optical depths measured using sun-tracking photometer over Ahmedabad,” Atmos. Phys. 67, 57–70, 1994.

Bull. Am. Meteorol. Soc. (1)

G. E. Shaw, “Sun photometry,” Bull. Am. Meteorol. Soc. 64, 4–10 (1983).
[CrossRef]

Int. J. Electron. (1)

R. N. Misra, Y. B. Acharya, “Current ratio log amplifier using light emitting diodes,” Int. J. Electron. 53(1), 91–94 (1982).
[CrossRef]

J. Appl. Meteorol. (1)

E. C. Flowers, R. A. McCormick, K. R. Kurfis, “Atmospheric turbidity over the United States,” J. Appl. Meteorol. 8, 1961–1966 (1969).
[CrossRef]

J. Atmos. Sci. (1)

F. E. Volz, “Spectral sky light and solar radiance measurements in the Caribbean: maritime aerosols and Sahara dust,” J. Atmos. Sci. 27, 1041–1047 (1970).
[CrossRef]

Tellus (1)

A. Ångström, “Techniques for determining the turbidity of the atmosphere,” Tellus 13, 214–223 (1961).
[CrossRef]

Other (3)

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

G. A. d’Almeida, P. Koepke, E. P. Shettle, Atmospheric Aerosols: Global Climatology and Radiative Characteristics (Deepak, Hampton, Va., 1991).

R. Lynch, The Role of Compositionally Graded GaAlAs Devices in Optical Communication (IBM Electronics Systems Center, New York, 1972).

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Figures (8)

Fig. 1
Fig. 1

Current–voltage characteristics of green, yellow, and red LED’s.

Fig. 2
Fig. 2

Schematic of a LED sun photometer operating in the log mode configuration. OPA 104 is an operational amplifier.

Fig. 3
Fig. 3

LED emission spectra.

Fig. 4
Fig. 4

Schematic of LED sun photometer operating in the linear-mode configuration.

Fig. 5
Fig. 5

Results of measurements (Langley plots) made of the LED sun photometer operated in the linear mode on 19 January 1994 (afternoon hours).

Fig. 6
Fig. 6

Plots of LED sun photometer outputs along with the simultaneous dark current observations for (a) green, (b) yellow, (c) red.

Fig. 7
Fig. 7

Results of measurements (Langley plots) made of the LED sun photometer operated in the log mode on 19 January 1994 (afternoon hours).

Fig. 8
Fig. 8

Total optical depths obtained over Ahmedabad between 30 April and 8 May 1994 with LED photometers operated in the log mode and with a conventional filter photometer at 500 nm.

Tables (2)

Tables Icon

Table 1 Spectral Characteristics of the LED’s Used

Tables Icon

Table 2 Results of LED Sun Photometer Observations made over Ahmedabada

Equations (10)

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

I = I 0 exp ( - τ m )
ln I = - τ m + ln I 0 ,
m = sec { [ ( r 2 cos 2 χ + 2 r H + H 2 ) 1 / 2 - r cos χ ] / H } ,
τ = τ rs + τ aerosol + τ ma ,
I = I s [ exp ( q V / n k T ) - 1 ] ,
I in = I s exp ( q V o / n k T ) - I s .
I in = I s exp ( q V o / n k T ) ,
q V o / n k T = ln I in - ln I s ,
- τ m + ln I 0 = V o / K 1 + ln I s ,
V o = - K 1 τ m + K 2 ,

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