Abstract

We have designed and developed a feedback mechanism for continuous monitoring in a long-pass differential optical absorption spectroscopy (LP-DOAS) setup. This allows one to correct photo-thermal deflection due to the local fluctuations refraction index of the air. For this purpose, using an unbalanced beam splitter, a small fraction of the collected DOAS signal is imaged onto a low-cost CCD camera using a biconvex lens, while the other portion of the signal is coupled into a fiber optic for trace gas detection. By monitoring the registered signal at the CCD camera, a feedback mechanism acting on the transversal position of the lens is able to compensate an arbitrary transversal displacement of the collected signal at the focal plane of the receiver telescope, allowing an optimal coupling into the optical fiber.

© 2012 Optical Society of America

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References

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  1. D. Perner, D. H. Ehhalt, H. W. Patz, U. Platt, E. P. Roth, and A. Volz, “OH-radicals in the lower troposphere,” Geophys. Res. Lett. 3, 466–468 (1976).
    [CrossRef]
  2. U. Platt and J. Stutz, Differential Optical Absortion Spectroscopy, Principles and Applications (Springer, 2008).
  3. C. Kern, S. Trick, B. Rippel, and U. Platt, “Applicability of light-emitting diodes as light sources for active differential optical absorption spectroscopy measurements,” Appl. Opt. 45, 2077–2088 (2006).
    [CrossRef]
  4. F. Xu, Z. Lv, X. Lou, Y. Zhang, and Z. Zhang, “Nitrogen dioxide monitoring using a blue LED,” Appl. Opt. 47, 5337–5340 (2008).
    [CrossRef]
  5. H. Sihler, C. Kern, D. Pöhler, and U. Platt, “Applying light-emitting diodes with narrowband emission features in differential spectroscopy,” Opt. Lett. 34, 3716–3718 (2009).
    [CrossRef]
  6. U. Platt, K. Pfeilsticker, and M. Vollmer, “Radiation and optics in the atmosphere,” in Springer Handbook of Lasers and Optics, F. Trager, ed. (Springer, 2007), pp. 1165–1203.
  7. F. Lohberger, G. Honninger, and U. Platt, “Ground-based imaging differential optical spectroscopy of atmospheric gases,” Appl. Opt. 43, 4711–4717 (2004).
    [CrossRef]
  8. N. Bobrowski, G. Honninger, F. Lohberger, and U. Platt, “IDOAS: a new monitoring technique to study the 2D distribution of volcanic gas emissions,” J. Volcanol. Geotherm. Res. 150, 329–338 (2005).
    [CrossRef]
  9. J. W. Hardy, Adaptive Optics for Astronomical Telescopes(Oxford University, 1998), pp. 77–101.
  10. C. F. Bohren and E. E. Clothiaux, Fundamentals of Atmospheric Radiation: an Introduction with 400 Problems(Wiley-VCH, 2006), pp. 418–425.
  11. B. Edlén, “The refractive index of air,” Metrologia 2, 71–80 (1966).
    [CrossRef]
  12. K. P. Birch and M. J. Downs, “Updated Edlén equation for the refractive index of air,” Metrologia 30, 155–162 (1993).
    [CrossRef]
  13. K. P. Birch and M. J. Downs, “Correction to the updated Edlén equation for the refractive index of air,” Metrologia 31, 315–316 (1994).
    [CrossRef]
  14. J. Orphal and K. Chance, “Ultraviolet and visible absorption cross-sections for HITRAN,” J. Quant. Spectrosc. Radiat. Transfer 82, 491–504 (2003).
    [CrossRef]
  15. E. R. Peck and K. Reeder, “Dispersion of air,” J. Opt. Soc. Am. 68, 958–962 (1972).
    [CrossRef]

2009 (1)

2008 (1)

2006 (1)

2005 (1)

N. Bobrowski, G. Honninger, F. Lohberger, and U. Platt, “IDOAS: a new monitoring technique to study the 2D distribution of volcanic gas emissions,” J. Volcanol. Geotherm. Res. 150, 329–338 (2005).
[CrossRef]

2004 (1)

2003 (1)

J. Orphal and K. Chance, “Ultraviolet and visible absorption cross-sections for HITRAN,” J. Quant. Spectrosc. Radiat. Transfer 82, 491–504 (2003).
[CrossRef]

1994 (1)

K. P. Birch and M. J. Downs, “Correction to the updated Edlén equation for the refractive index of air,” Metrologia 31, 315–316 (1994).
[CrossRef]

1993 (1)

K. P. Birch and M. J. Downs, “Updated Edlén equation for the refractive index of air,” Metrologia 30, 155–162 (1993).
[CrossRef]

1976 (1)

D. Perner, D. H. Ehhalt, H. W. Patz, U. Platt, E. P. Roth, and A. Volz, “OH-radicals in the lower troposphere,” Geophys. Res. Lett. 3, 466–468 (1976).
[CrossRef]

1972 (1)

E. R. Peck and K. Reeder, “Dispersion of air,” J. Opt. Soc. Am. 68, 958–962 (1972).
[CrossRef]

1966 (1)

B. Edlén, “The refractive index of air,” Metrologia 2, 71–80 (1966).
[CrossRef]

Birch, K. P.

K. P. Birch and M. J. Downs, “Correction to the updated Edlén equation for the refractive index of air,” Metrologia 31, 315–316 (1994).
[CrossRef]

K. P. Birch and M. J. Downs, “Updated Edlén equation for the refractive index of air,” Metrologia 30, 155–162 (1993).
[CrossRef]

Bobrowski, N.

N. Bobrowski, G. Honninger, F. Lohberger, and U. Platt, “IDOAS: a new monitoring technique to study the 2D distribution of volcanic gas emissions,” J. Volcanol. Geotherm. Res. 150, 329–338 (2005).
[CrossRef]

Bohren, C. F.

C. F. Bohren and E. E. Clothiaux, Fundamentals of Atmospheric Radiation: an Introduction with 400 Problems(Wiley-VCH, 2006), pp. 418–425.

Chance, K.

J. Orphal and K. Chance, “Ultraviolet and visible absorption cross-sections for HITRAN,” J. Quant. Spectrosc. Radiat. Transfer 82, 491–504 (2003).
[CrossRef]

Clothiaux, E. E.

C. F. Bohren and E. E. Clothiaux, Fundamentals of Atmospheric Radiation: an Introduction with 400 Problems(Wiley-VCH, 2006), pp. 418–425.

Downs, M. J.

K. P. Birch and M. J. Downs, “Correction to the updated Edlén equation for the refractive index of air,” Metrologia 31, 315–316 (1994).
[CrossRef]

K. P. Birch and M. J. Downs, “Updated Edlén equation for the refractive index of air,” Metrologia 30, 155–162 (1993).
[CrossRef]

Edlén, B.

B. Edlén, “The refractive index of air,” Metrologia 2, 71–80 (1966).
[CrossRef]

Ehhalt, D. H.

D. Perner, D. H. Ehhalt, H. W. Patz, U. Platt, E. P. Roth, and A. Volz, “OH-radicals in the lower troposphere,” Geophys. Res. Lett. 3, 466–468 (1976).
[CrossRef]

Hardy, J. W.

J. W. Hardy, Adaptive Optics for Astronomical Telescopes(Oxford University, 1998), pp. 77–101.

Honninger, G.

N. Bobrowski, G. Honninger, F. Lohberger, and U. Platt, “IDOAS: a new monitoring technique to study the 2D distribution of volcanic gas emissions,” J. Volcanol. Geotherm. Res. 150, 329–338 (2005).
[CrossRef]

F. Lohberger, G. Honninger, and U. Platt, “Ground-based imaging differential optical spectroscopy of atmospheric gases,” Appl. Opt. 43, 4711–4717 (2004).
[CrossRef]

Kern, C.

Lohberger, F.

N. Bobrowski, G. Honninger, F. Lohberger, and U. Platt, “IDOAS: a new monitoring technique to study the 2D distribution of volcanic gas emissions,” J. Volcanol. Geotherm. Res. 150, 329–338 (2005).
[CrossRef]

F. Lohberger, G. Honninger, and U. Platt, “Ground-based imaging differential optical spectroscopy of atmospheric gases,” Appl. Opt. 43, 4711–4717 (2004).
[CrossRef]

Lou, X.

Lv, Z.

Orphal, J.

J. Orphal and K. Chance, “Ultraviolet and visible absorption cross-sections for HITRAN,” J. Quant. Spectrosc. Radiat. Transfer 82, 491–504 (2003).
[CrossRef]

Patz, H. W.

D. Perner, D. H. Ehhalt, H. W. Patz, U. Platt, E. P. Roth, and A. Volz, “OH-radicals in the lower troposphere,” Geophys. Res. Lett. 3, 466–468 (1976).
[CrossRef]

Peck, E. R.

E. R. Peck and K. Reeder, “Dispersion of air,” J. Opt. Soc. Am. 68, 958–962 (1972).
[CrossRef]

Perner, D.

D. Perner, D. H. Ehhalt, H. W. Patz, U. Platt, E. P. Roth, and A. Volz, “OH-radicals in the lower troposphere,” Geophys. Res. Lett. 3, 466–468 (1976).
[CrossRef]

Pfeilsticker, K.

U. Platt, K. Pfeilsticker, and M. Vollmer, “Radiation and optics in the atmosphere,” in Springer Handbook of Lasers and Optics, F. Trager, ed. (Springer, 2007), pp. 1165–1203.

Platt, U.

H. Sihler, C. Kern, D. Pöhler, and U. Platt, “Applying light-emitting diodes with narrowband emission features in differential spectroscopy,” Opt. Lett. 34, 3716–3718 (2009).
[CrossRef]

C. Kern, S. Trick, B. Rippel, and U. Platt, “Applicability of light-emitting diodes as light sources for active differential optical absorption spectroscopy measurements,” Appl. Opt. 45, 2077–2088 (2006).
[CrossRef]

N. Bobrowski, G. Honninger, F. Lohberger, and U. Platt, “IDOAS: a new monitoring technique to study the 2D distribution of volcanic gas emissions,” J. Volcanol. Geotherm. Res. 150, 329–338 (2005).
[CrossRef]

F. Lohberger, G. Honninger, and U. Platt, “Ground-based imaging differential optical spectroscopy of atmospheric gases,” Appl. Opt. 43, 4711–4717 (2004).
[CrossRef]

D. Perner, D. H. Ehhalt, H. W. Patz, U. Platt, E. P. Roth, and A. Volz, “OH-radicals in the lower troposphere,” Geophys. Res. Lett. 3, 466–468 (1976).
[CrossRef]

U. Platt and J. Stutz, Differential Optical Absortion Spectroscopy, Principles and Applications (Springer, 2008).

U. Platt, K. Pfeilsticker, and M. Vollmer, “Radiation and optics in the atmosphere,” in Springer Handbook of Lasers and Optics, F. Trager, ed. (Springer, 2007), pp. 1165–1203.

Pöhler, D.

Reeder, K.

E. R. Peck and K. Reeder, “Dispersion of air,” J. Opt. Soc. Am. 68, 958–962 (1972).
[CrossRef]

Rippel, B.

Roth, E. P.

D. Perner, D. H. Ehhalt, H. W. Patz, U. Platt, E. P. Roth, and A. Volz, “OH-radicals in the lower troposphere,” Geophys. Res. Lett. 3, 466–468 (1976).
[CrossRef]

Sihler, H.

Stutz, J.

U. Platt and J. Stutz, Differential Optical Absortion Spectroscopy, Principles and Applications (Springer, 2008).

Trick, S.

Vollmer, M.

U. Platt, K. Pfeilsticker, and M. Vollmer, “Radiation and optics in the atmosphere,” in Springer Handbook of Lasers and Optics, F. Trager, ed. (Springer, 2007), pp. 1165–1203.

Volz, A.

D. Perner, D. H. Ehhalt, H. W. Patz, U. Platt, E. P. Roth, and A. Volz, “OH-radicals in the lower troposphere,” Geophys. Res. Lett. 3, 466–468 (1976).
[CrossRef]

Xu, F.

Zhang, Y.

Zhang, Z.

Appl. Opt. (3)

Geophys. Res. Lett. (1)

D. Perner, D. H. Ehhalt, H. W. Patz, U. Platt, E. P. Roth, and A. Volz, “OH-radicals in the lower troposphere,” Geophys. Res. Lett. 3, 466–468 (1976).
[CrossRef]

J. Opt. Soc. Am. (1)

E. R. Peck and K. Reeder, “Dispersion of air,” J. Opt. Soc. Am. 68, 958–962 (1972).
[CrossRef]

J. Quant. Spectrosc. Radiat. Transfer (1)

J. Orphal and K. Chance, “Ultraviolet and visible absorption cross-sections for HITRAN,” J. Quant. Spectrosc. Radiat. Transfer 82, 491–504 (2003).
[CrossRef]

J. Volcanol. Geotherm. Res. (1)

N. Bobrowski, G. Honninger, F. Lohberger, and U. Platt, “IDOAS: a new monitoring technique to study the 2D distribution of volcanic gas emissions,” J. Volcanol. Geotherm. Res. 150, 329–338 (2005).
[CrossRef]

Metrologia (3)

B. Edlén, “The refractive index of air,” Metrologia 2, 71–80 (1966).
[CrossRef]

K. P. Birch and M. J. Downs, “Updated Edlén equation for the refractive index of air,” Metrologia 30, 155–162 (1993).
[CrossRef]

K. P. Birch and M. J. Downs, “Correction to the updated Edlén equation for the refractive index of air,” Metrologia 31, 315–316 (1994).
[CrossRef]

Opt. Lett. (1)

Other (4)

U. Platt, K. Pfeilsticker, and M. Vollmer, “Radiation and optics in the atmosphere,” in Springer Handbook of Lasers and Optics, F. Trager, ed. (Springer, 2007), pp. 1165–1203.

J. W. Hardy, Adaptive Optics for Astronomical Telescopes(Oxford University, 1998), pp. 77–101.

C. F. Bohren and E. E. Clothiaux, Fundamentals of Atmospheric Radiation: an Introduction with 400 Problems(Wiley-VCH, 2006), pp. 418–425.

U. Platt and J. Stutz, Differential Optical Absortion Spectroscopy, Principles and Applications (Springer, 2008).

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Figures (11)

Fig. 1.
Fig. 1.

Diagrammatic scheme of the apparent position O of a beam of light propagating from the source, located in position O, up to the image plane in the receiver, in a media with a gradient of the refraction index. The imager system located at plane I will form an inverted image y regarding to the optical axis OI¯, to the distance Δy of one real source O on the plane Σ. The new apparent position O of the source at ΔY will form a deflection angle δ between the points OIO.

Fig. 2.
Fig. 2.

Ray trace diagram of the double imaging system of the spot of light at the focal plane of the telescope at Σ-plane onto Σ1 and Σ2 planes. (a) A biconvex lens with a focal distance of f=60mm in a finite conjugate 11 ratio is inserted between the above-mentioned planes, allowing an optimal coupling of the collected DOAS signal into the core of the fiber optics of the spectrometer. An unbalanced BS, with transmission and reflection of 5% and 95%, respectively, allows one to send the beam of light toward both the CCD camera and the optical fiber of the spectrometer. (b) A deviation Δx over the Σ-plane is mapped onto the new imaging planes. (c) A transversal translation Δx/2 of the lens allows one to recover the original position of the spot of light at the center of Σ1 and Σ2 planes. Alternatively, instead of having a feedback mechanism acting on the lens L, fluctuations of atmospheric refraction can be corrected moving the fiber–BS–CCD assembly. However, we choose to act on the lens instead of the assembly because of its low weight; thus the used stepper motors are less demanding.

Fig. 3.
Fig. 3.

Diagram of the bistatic LP-DOAS setup used in the experimental study of the correction system. The length of the air column between the emission and reception telescope was L = 938 m. The beam of light was collected by the objective mirror of the receiver telescope and a plane mirror sent the collected light to the focal plane Σ. The image of the spot of light is double imaged onto Σ1 and Σ2 by means of both a biconvex lens in a finite conjugate 11 ratio configuration and a BS.

Fig. 4.
Fig. 4.

Temporal evolution of the atmospheric parameters: (a) temperature, (b) pressure, and (c) relative humidity in a two-day measurement interval of the DOAS signal. The sunrise (orange) and sunset (cyan) are indicated with vertical lines.

Fig. 5.
Fig. 5.

Temporal evolution of air refraction index computed using the modified Edlén’s model [11,12]. In this model the wavelength was assumed to be λ=0.46μm (the center of the LED emission) and a standard CO2 concentration of 390 ppm. The largest variation of the refraction index Δn=1.41×105.

Fig. 6.
Fig. 6.

Image of the spot of the collected DOAS signal at the CCD camera, Σ2-plane, spot of light position at times 2012-01-17 (a) 07:47:31 and (b) 12:05:23. In (b) the original position of the spot of light is shown with a circle (red). Atmospheric parameters are also shown. It can be observed that in image (b), close to midday, the background increases.

Fig. 7.
Fig. 7.

Temporal evolution of the deflection of the collected DOAS signal at Σ2-plane: (a) horizontal Δx (blue), (b) vertical Δy (red). In addition, total deflection ΔTΔT is shown in (c).

Fig. 8.
Fig. 8.

Fluctuation of the atmospheric refraction can deviate the propagated beam of light in such a way that at the reception plane the light source appears to come from apparent positions y or y, which are displaced with regard to the optical axis O.

Fig. 9.
Fig. 9.

Intensity of the LP-DOAS signal coupled to the fiber optic at Σ2 plane as a function of time, in arbitrary units. This signal was manually corrected once an hour for the first 6 h, after which the system evolves freely. It can be noted that the signal exponentially decays up the background intensity level and recovers up to the following day; after that it exponentially decays again.

Fig. 10.
Fig. 10.

Temporal evolution of the collected LP-DOAS signal at Σ2-plane when the feedback mechanism is turned on. The following signal coordinates are plotted: (a) horizontal Δx (blue), (b) vertical Δy (red). Besides, total deflection ΔT is shown in (c).

Fig. 11.
Fig. 11.

Normalized intensity at the fiber optic coupled to the spectrometer as a function of time over a period of 34 h of continuous operation of the LP-DOAS setup.

Equations (6)

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

1(n1)dndt=1PdPdt1TdTdt.
n1=12[arctanΔyf]2.
(n1)Tp=(n1)sp96095.43[1+108(3.256020.00972T)p](2.15*106+0.0036610T),
(n1)s×108=8342.54+2406147130λ2+1599838.9λ2,
nTpfnTp=pp[3.73450.0401λ2]×1010.
(n1)x=(n1)s(1+0.5327(x0.0004)),

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