Abstract

Brownout, the loss of visibility caused by dust resultant of helicopter downwash, is a factor in the large majority of military helicopter accidents. As terahertz radiation readily propagates through the associated dust aerosols and is attenuated by atmospheric water vapor within short distances, it can provide low-profile imaging that improves effective pilot visibility. In order to model this application of terahertz imaging, it is necessary to determine the optical properties of obscurants at these frequencies. We present here a method of empirical calculation and experimental measurement of the complex refractive index of the obscuring aerosols. Results derived from terahertz time-domain spectral measurements are incorporated into the AFIT CDE Laser Environmental Effects Definition and Reference (LEEDR) software.

© 2012 Optical Society of America

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References

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  1. S. T. Fiorino, R. J. Bartell, M. J. Krizo, G. L. Caylor, K. P. Moore, and S. J. Cusumano, “Validation of a worldwide physics-based high-spectral resolution atmospheric characterization and propagation package for UV to RF wavelengths,” Proc. SPIE 7090, 70900I (2008).
    [CrossRef]
  2. D. Mittleman, Sensing with Terahertz Radiation (Springer, 2002), pp. 1–145.
  3. T. W. Crowe, D. W. Porterfield, J. L. Hesler, W. L. Bishop, D. S. Kurtz, and K. Hui, “Terahertz sources and detectors,” in Terahertz for Military and Security Applications III, R. J. Hwu, D. L. Woolard, and M. J. Rosker, eds., SPIE International Society for Optical Engineering (Bellingham, WA, 2005), pp. 271–280.
  4. P. H. Siegel, “Terahertz technology,” IEEE Trans. Microwave Theory Tech. 50, 910–928 (2002).
    [CrossRef]
  5. S. L. Marek, “A computational tool for evaluating THz imaging performance in brownout conditions at land sites throughout the world,” Master’s thesis (Air Force Institute of Technology, 2009).
  6. S. T. Fiorino, R. J. Bartell, M. J. Krizo, S. L. Marek, M. J. Bohn, R. M. Randall, and S. J. Cusumano, “A computational tool for evaluating THz imaging performance in brownout conditions at land sites throughout the world,” Proc. SPIE 7324, 732410 (2009).
    [CrossRef]
  7. M. Hess, P. Koepke, and I. Schult, “Optical properties of aerosols and clouds: the software package OPAC,” Bull. Am. Meteorol. Soc. 79, 831–844 (1998).
    [CrossRef]
  8. M. Naftaly and R. E. Miles, “Terahertz time-domain spectroscopy of silicate glasses and the relationship to material properties,” J. Appl. Phys. 102, 043517 (2007).
    [CrossRef]
  9. W. J. Wiscombe, “Improved Mie scattering algorithms,” Appl. Opt., 19, 1505–1510 (1980).
    [CrossRef]
  10. S. T. Fiorino, P. M. Grice, M. J. Krizo, R. J. Bartell, J. D. Haiducek, and S. J. Cusumano, “Lab measurements to support modeling terahertz propagation in brownout conditions,” Proc. SPIE 7671, 767131 (2010).
    [CrossRef]
  11. M. Van exter and D. R. Grischkowsky, “Characterization of an optoelectronic terahertz beam system,” IEEE Trans. Microwave Theory Tech. 38, 1684–1691 (1990).
    [CrossRef]
  12. C. D. Stoik, “Nondestructive evaluation of aircraft composites using terahertz time domain spectroscopy,” Ph.D. dissertation (Air Force Institute of Technology, 2008).
  13. C. D. Stoik, M. J. Bohn, and J. L. Blackshire, “Nondestructive evaluation of aircraft composites using transmissive terahertz time domain spectroscopy,” Opt. Express 16, 17039–17051 (2008).
    [CrossRef]
  14. J. V. Rudd, J. L. Johnson, and D. M. Mittleman, “Quadrupole radiation from terahertz dipole antennas,” Opt. Lett. 25, 1556–1558 (2000).
    [CrossRef]
  15. C. Emde, R. Buras, B. Mayer, and M. Blumthaler, “The impact of aerosols on polarized sky radiance: model development, validation, and applications,” Atmos. Chem. Phys. 10, 383–396 (2010).
    [CrossRef]
  16. W. Withayachumnankul, B. M. Fischer, H. Lin, and D. Abbott, “Uncertainty in terahertz time-domain spectroscopy measurement,” J. Opt. Soc. Am. B 25, 1059–1072 (2008).
    [CrossRef]

2010

S. T. Fiorino, P. M. Grice, M. J. Krizo, R. J. Bartell, J. D. Haiducek, and S. J. Cusumano, “Lab measurements to support modeling terahertz propagation in brownout conditions,” Proc. SPIE 7671, 767131 (2010).
[CrossRef]

C. Emde, R. Buras, B. Mayer, and M. Blumthaler, “The impact of aerosols on polarized sky radiance: model development, validation, and applications,” Atmos. Chem. Phys. 10, 383–396 (2010).
[CrossRef]

2009

S. T. Fiorino, R. J. Bartell, M. J. Krizo, S. L. Marek, M. J. Bohn, R. M. Randall, and S. J. Cusumano, “A computational tool for evaluating THz imaging performance in brownout conditions at land sites throughout the world,” Proc. SPIE 7324, 732410 (2009).
[CrossRef]

2008

S. T. Fiorino, R. J. Bartell, M. J. Krizo, G. L. Caylor, K. P. Moore, and S. J. Cusumano, “Validation of a worldwide physics-based high-spectral resolution atmospheric characterization and propagation package for UV to RF wavelengths,” Proc. SPIE 7090, 70900I (2008).
[CrossRef]

W. Withayachumnankul, B. M. Fischer, H. Lin, and D. Abbott, “Uncertainty in terahertz time-domain spectroscopy measurement,” J. Opt. Soc. Am. B 25, 1059–1072 (2008).
[CrossRef]

C. D. Stoik, M. J. Bohn, and J. L. Blackshire, “Nondestructive evaluation of aircraft composites using transmissive terahertz time domain spectroscopy,” Opt. Express 16, 17039–17051 (2008).
[CrossRef]

2007

M. Naftaly and R. E. Miles, “Terahertz time-domain spectroscopy of silicate glasses and the relationship to material properties,” J. Appl. Phys. 102, 043517 (2007).
[CrossRef]

2002

P. H. Siegel, “Terahertz technology,” IEEE Trans. Microwave Theory Tech. 50, 910–928 (2002).
[CrossRef]

2000

1998

M. Hess, P. Koepke, and I. Schult, “Optical properties of aerosols and clouds: the software package OPAC,” Bull. Am. Meteorol. Soc. 79, 831–844 (1998).
[CrossRef]

1990

M. Van exter and D. R. Grischkowsky, “Characterization of an optoelectronic terahertz beam system,” IEEE Trans. Microwave Theory Tech. 38, 1684–1691 (1990).
[CrossRef]

1980

Abbott, D.

Bartell, R. J.

S. T. Fiorino, P. M. Grice, M. J. Krizo, R. J. Bartell, J. D. Haiducek, and S. J. Cusumano, “Lab measurements to support modeling terahertz propagation in brownout conditions,” Proc. SPIE 7671, 767131 (2010).
[CrossRef]

S. T. Fiorino, R. J. Bartell, M. J. Krizo, S. L. Marek, M. J. Bohn, R. M. Randall, and S. J. Cusumano, “A computational tool for evaluating THz imaging performance in brownout conditions at land sites throughout the world,” Proc. SPIE 7324, 732410 (2009).
[CrossRef]

S. T. Fiorino, R. J. Bartell, M. J. Krizo, G. L. Caylor, K. P. Moore, and S. J. Cusumano, “Validation of a worldwide physics-based high-spectral resolution atmospheric characterization and propagation package for UV to RF wavelengths,” Proc. SPIE 7090, 70900I (2008).
[CrossRef]

Bishop, W. L.

T. W. Crowe, D. W. Porterfield, J. L. Hesler, W. L. Bishop, D. S. Kurtz, and K. Hui, “Terahertz sources and detectors,” in Terahertz for Military and Security Applications III, R. J. Hwu, D. L. Woolard, and M. J. Rosker, eds., SPIE International Society for Optical Engineering (Bellingham, WA, 2005), pp. 271–280.

Blackshire, J. L.

Blumthaler, M.

C. Emde, R. Buras, B. Mayer, and M. Blumthaler, “The impact of aerosols on polarized sky radiance: model development, validation, and applications,” Atmos. Chem. Phys. 10, 383–396 (2010).
[CrossRef]

Bohn, M. J.

S. T. Fiorino, R. J. Bartell, M. J. Krizo, S. L. Marek, M. J. Bohn, R. M. Randall, and S. J. Cusumano, “A computational tool for evaluating THz imaging performance in brownout conditions at land sites throughout the world,” Proc. SPIE 7324, 732410 (2009).
[CrossRef]

C. D. Stoik, M. J. Bohn, and J. L. Blackshire, “Nondestructive evaluation of aircraft composites using transmissive terahertz time domain spectroscopy,” Opt. Express 16, 17039–17051 (2008).
[CrossRef]

Buras, R.

C. Emde, R. Buras, B. Mayer, and M. Blumthaler, “The impact of aerosols on polarized sky radiance: model development, validation, and applications,” Atmos. Chem. Phys. 10, 383–396 (2010).
[CrossRef]

Caylor, G. L.

S. T. Fiorino, R. J. Bartell, M. J. Krizo, G. L. Caylor, K. P. Moore, and S. J. Cusumano, “Validation of a worldwide physics-based high-spectral resolution atmospheric characterization and propagation package for UV to RF wavelengths,” Proc. SPIE 7090, 70900I (2008).
[CrossRef]

Crowe, T. W.

T. W. Crowe, D. W. Porterfield, J. L. Hesler, W. L. Bishop, D. S. Kurtz, and K. Hui, “Terahertz sources and detectors,” in Terahertz for Military and Security Applications III, R. J. Hwu, D. L. Woolard, and M. J. Rosker, eds., SPIE International Society for Optical Engineering (Bellingham, WA, 2005), pp. 271–280.

Cusumano, S. J.

S. T. Fiorino, P. M. Grice, M. J. Krizo, R. J. Bartell, J. D. Haiducek, and S. J. Cusumano, “Lab measurements to support modeling terahertz propagation in brownout conditions,” Proc. SPIE 7671, 767131 (2010).
[CrossRef]

S. T. Fiorino, R. J. Bartell, M. J. Krizo, S. L. Marek, M. J. Bohn, R. M. Randall, and S. J. Cusumano, “A computational tool for evaluating THz imaging performance in brownout conditions at land sites throughout the world,” Proc. SPIE 7324, 732410 (2009).
[CrossRef]

S. T. Fiorino, R. J. Bartell, M. J. Krizo, G. L. Caylor, K. P. Moore, and S. J. Cusumano, “Validation of a worldwide physics-based high-spectral resolution atmospheric characterization and propagation package for UV to RF wavelengths,” Proc. SPIE 7090, 70900I (2008).
[CrossRef]

Emde, C.

C. Emde, R. Buras, B. Mayer, and M. Blumthaler, “The impact of aerosols on polarized sky radiance: model development, validation, and applications,” Atmos. Chem. Phys. 10, 383–396 (2010).
[CrossRef]

Fiorino, S. T.

S. T. Fiorino, P. M. Grice, M. J. Krizo, R. J. Bartell, J. D. Haiducek, and S. J. Cusumano, “Lab measurements to support modeling terahertz propagation in brownout conditions,” Proc. SPIE 7671, 767131 (2010).
[CrossRef]

S. T. Fiorino, R. J. Bartell, M. J. Krizo, S. L. Marek, M. J. Bohn, R. M. Randall, and S. J. Cusumano, “A computational tool for evaluating THz imaging performance in brownout conditions at land sites throughout the world,” Proc. SPIE 7324, 732410 (2009).
[CrossRef]

S. T. Fiorino, R. J. Bartell, M. J. Krizo, G. L. Caylor, K. P. Moore, and S. J. Cusumano, “Validation of a worldwide physics-based high-spectral resolution atmospheric characterization and propagation package for UV to RF wavelengths,” Proc. SPIE 7090, 70900I (2008).
[CrossRef]

Fischer, B. M.

Grice, P. M.

S. T. Fiorino, P. M. Grice, M. J. Krizo, R. J. Bartell, J. D. Haiducek, and S. J. Cusumano, “Lab measurements to support modeling terahertz propagation in brownout conditions,” Proc. SPIE 7671, 767131 (2010).
[CrossRef]

Grischkowsky, D. R.

M. Van exter and D. R. Grischkowsky, “Characterization of an optoelectronic terahertz beam system,” IEEE Trans. Microwave Theory Tech. 38, 1684–1691 (1990).
[CrossRef]

Haiducek, J. D.

S. T. Fiorino, P. M. Grice, M. J. Krizo, R. J. Bartell, J. D. Haiducek, and S. J. Cusumano, “Lab measurements to support modeling terahertz propagation in brownout conditions,” Proc. SPIE 7671, 767131 (2010).
[CrossRef]

Hesler, J. L.

T. W. Crowe, D. W. Porterfield, J. L. Hesler, W. L. Bishop, D. S. Kurtz, and K. Hui, “Terahertz sources and detectors,” in Terahertz for Military and Security Applications III, R. J. Hwu, D. L. Woolard, and M. J. Rosker, eds., SPIE International Society for Optical Engineering (Bellingham, WA, 2005), pp. 271–280.

Hess, M.

M. Hess, P. Koepke, and I. Schult, “Optical properties of aerosols and clouds: the software package OPAC,” Bull. Am. Meteorol. Soc. 79, 831–844 (1998).
[CrossRef]

Hui, K.

T. W. Crowe, D. W. Porterfield, J. L. Hesler, W. L. Bishop, D. S. Kurtz, and K. Hui, “Terahertz sources and detectors,” in Terahertz for Military and Security Applications III, R. J. Hwu, D. L. Woolard, and M. J. Rosker, eds., SPIE International Society for Optical Engineering (Bellingham, WA, 2005), pp. 271–280.

Johnson, J. L.

Koepke, P.

M. Hess, P. Koepke, and I. Schult, “Optical properties of aerosols and clouds: the software package OPAC,” Bull. Am. Meteorol. Soc. 79, 831–844 (1998).
[CrossRef]

Krizo, M. J.

S. T. Fiorino, P. M. Grice, M. J. Krizo, R. J. Bartell, J. D. Haiducek, and S. J. Cusumano, “Lab measurements to support modeling terahertz propagation in brownout conditions,” Proc. SPIE 7671, 767131 (2010).
[CrossRef]

S. T. Fiorino, R. J. Bartell, M. J. Krizo, S. L. Marek, M. J. Bohn, R. M. Randall, and S. J. Cusumano, “A computational tool for evaluating THz imaging performance in brownout conditions at land sites throughout the world,” Proc. SPIE 7324, 732410 (2009).
[CrossRef]

S. T. Fiorino, R. J. Bartell, M. J. Krizo, G. L. Caylor, K. P. Moore, and S. J. Cusumano, “Validation of a worldwide physics-based high-spectral resolution atmospheric characterization and propagation package for UV to RF wavelengths,” Proc. SPIE 7090, 70900I (2008).
[CrossRef]

Kurtz, D. S.

T. W. Crowe, D. W. Porterfield, J. L. Hesler, W. L. Bishop, D. S. Kurtz, and K. Hui, “Terahertz sources and detectors,” in Terahertz for Military and Security Applications III, R. J. Hwu, D. L. Woolard, and M. J. Rosker, eds., SPIE International Society for Optical Engineering (Bellingham, WA, 2005), pp. 271–280.

Lin, H.

Marek, S. L.

S. T. Fiorino, R. J. Bartell, M. J. Krizo, S. L. Marek, M. J. Bohn, R. M. Randall, and S. J. Cusumano, “A computational tool for evaluating THz imaging performance in brownout conditions at land sites throughout the world,” Proc. SPIE 7324, 732410 (2009).
[CrossRef]

S. L. Marek, “A computational tool for evaluating THz imaging performance in brownout conditions at land sites throughout the world,” Master’s thesis (Air Force Institute of Technology, 2009).

Mayer, B.

C. Emde, R. Buras, B. Mayer, and M. Blumthaler, “The impact of aerosols on polarized sky radiance: model development, validation, and applications,” Atmos. Chem. Phys. 10, 383–396 (2010).
[CrossRef]

Miles, R. E.

M. Naftaly and R. E. Miles, “Terahertz time-domain spectroscopy of silicate glasses and the relationship to material properties,” J. Appl. Phys. 102, 043517 (2007).
[CrossRef]

Mittleman, D.

D. Mittleman, Sensing with Terahertz Radiation (Springer, 2002), pp. 1–145.

Mittleman, D. M.

Moore, K. P.

S. T. Fiorino, R. J. Bartell, M. J. Krizo, G. L. Caylor, K. P. Moore, and S. J. Cusumano, “Validation of a worldwide physics-based high-spectral resolution atmospheric characterization and propagation package for UV to RF wavelengths,” Proc. SPIE 7090, 70900I (2008).
[CrossRef]

Naftaly, M.

M. Naftaly and R. E. Miles, “Terahertz time-domain spectroscopy of silicate glasses and the relationship to material properties,” J. Appl. Phys. 102, 043517 (2007).
[CrossRef]

Porterfield, D. W.

T. W. Crowe, D. W. Porterfield, J. L. Hesler, W. L. Bishop, D. S. Kurtz, and K. Hui, “Terahertz sources and detectors,” in Terahertz for Military and Security Applications III, R. J. Hwu, D. L. Woolard, and M. J. Rosker, eds., SPIE International Society for Optical Engineering (Bellingham, WA, 2005), pp. 271–280.

Randall, R. M.

S. T. Fiorino, R. J. Bartell, M. J. Krizo, S. L. Marek, M. J. Bohn, R. M. Randall, and S. J. Cusumano, “A computational tool for evaluating THz imaging performance in brownout conditions at land sites throughout the world,” Proc. SPIE 7324, 732410 (2009).
[CrossRef]

Rudd, J. V.

Schult, I.

M. Hess, P. Koepke, and I. Schult, “Optical properties of aerosols and clouds: the software package OPAC,” Bull. Am. Meteorol. Soc. 79, 831–844 (1998).
[CrossRef]

Siegel, P. H.

P. H. Siegel, “Terahertz technology,” IEEE Trans. Microwave Theory Tech. 50, 910–928 (2002).
[CrossRef]

Stoik, C. D.

C. D. Stoik, M. J. Bohn, and J. L. Blackshire, “Nondestructive evaluation of aircraft composites using transmissive terahertz time domain spectroscopy,” Opt. Express 16, 17039–17051 (2008).
[CrossRef]

C. D. Stoik, “Nondestructive evaluation of aircraft composites using terahertz time domain spectroscopy,” Ph.D. dissertation (Air Force Institute of Technology, 2008).

Van exter, M.

M. Van exter and D. R. Grischkowsky, “Characterization of an optoelectronic terahertz beam system,” IEEE Trans. Microwave Theory Tech. 38, 1684–1691 (1990).
[CrossRef]

Wiscombe, W. J.

Withayachumnankul, W.

Appl. Opt.

Atmos. Chem. Phys.

C. Emde, R. Buras, B. Mayer, and M. Blumthaler, “The impact of aerosols on polarized sky radiance: model development, validation, and applications,” Atmos. Chem. Phys. 10, 383–396 (2010).
[CrossRef]

Bull. Am. Meteorol. Soc.

M. Hess, P. Koepke, and I. Schult, “Optical properties of aerosols and clouds: the software package OPAC,” Bull. Am. Meteorol. Soc. 79, 831–844 (1998).
[CrossRef]

IEEE Trans. Microwave Theory Tech.

M. Van exter and D. R. Grischkowsky, “Characterization of an optoelectronic terahertz beam system,” IEEE Trans. Microwave Theory Tech. 38, 1684–1691 (1990).
[CrossRef]

P. H. Siegel, “Terahertz technology,” IEEE Trans. Microwave Theory Tech. 50, 910–928 (2002).
[CrossRef]

J. Appl. Phys.

M. Naftaly and R. E. Miles, “Terahertz time-domain spectroscopy of silicate glasses and the relationship to material properties,” J. Appl. Phys. 102, 043517 (2007).
[CrossRef]

J. Opt. Soc. Am. B

Opt. Express

Opt. Lett.

Proc. SPIE

S. T. Fiorino, R. J. Bartell, M. J. Krizo, S. L. Marek, M. J. Bohn, R. M. Randall, and S. J. Cusumano, “A computational tool for evaluating THz imaging performance in brownout conditions at land sites throughout the world,” Proc. SPIE 7324, 732410 (2009).
[CrossRef]

S. T. Fiorino, P. M. Grice, M. J. Krizo, R. J. Bartell, J. D. Haiducek, and S. J. Cusumano, “Lab measurements to support modeling terahertz propagation in brownout conditions,” Proc. SPIE 7671, 767131 (2010).
[CrossRef]

S. T. Fiorino, R. J. Bartell, M. J. Krizo, G. L. Caylor, K. P. Moore, and S. J. Cusumano, “Validation of a worldwide physics-based high-spectral resolution atmospheric characterization and propagation package for UV to RF wavelengths,” Proc. SPIE 7090, 70900I (2008).
[CrossRef]

Other

D. Mittleman, Sensing with Terahertz Radiation (Springer, 2002), pp. 1–145.

T. W. Crowe, D. W. Porterfield, J. L. Hesler, W. L. Bishop, D. S. Kurtz, and K. Hui, “Terahertz sources and detectors,” in Terahertz for Military and Security Applications III, R. J. Hwu, D. L. Woolard, and M. J. Rosker, eds., SPIE International Society for Optical Engineering (Bellingham, WA, 2005), pp. 271–280.

S. L. Marek, “A computational tool for evaluating THz imaging performance in brownout conditions at land sites throughout the world,” Master’s thesis (Air Force Institute of Technology, 2009).

C. D. Stoik, “Nondestructive evaluation of aircraft composites using terahertz time domain spectroscopy,” Ph.D. dissertation (Air Force Institute of Technology, 2008).

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Figures (12)

Fig. 1.
Fig. 1.

The LEEDR 3.1 input GUI. The user is able to define various scenarios and environmental conditions. Dark circles on the map represent ExPERT sites.

Fig. 2.
Fig. 2.

Schematic of method used to determine optical properties from extinction.

Fig. 3.
Fig. 3.

Extinction evaluation results, using real index from reference.

Fig. 4.
Fig. 4.

(a) Real portion of the refractive index was found to be between 1.1 and 1.2 ; the previous model suggested a real index value between 2.3 and 2.4. Dotted lines show ± 1 standard deviation. (b) Imaginary portion of refractive index, data filtration during calculation results in a smooth, piecewise curve. Discontinuity at f = 0.4 is likely a calculation artifact. Dotted lines show ± 1 standard deviation.

Fig. 5.
Fig. 5.

Schematic of off-axis terahertz time-domain spectrometer measurements.

Fig. 6.
Fig. 6.

Representative time-domain (left) and frequency domain (right) data taken using the off-axis terahertz time-domain spectrometer measurements.

Fig. 7.
Fig. 7.

Large sand particles, as observed under a microscope.

Fig. 8.
Fig. 8.

Off-axis spectral amplitude ratios collected through a range of angle increments, for four samples.

Fig. 9.
Fig. 9.

Three laboratory-measured and initial calculated phase functions. All phase functions evaluated at 1 THz.

Fig. 10.
Fig. 10.

A portion of the modified LEEDR GUI, including five new input fields corresponding to the sample parameters.

Fig. 11.
Fig. 11.

Clockwise from upper left: Variations in particle size, real index, imaginary index, and imaginary index with a lower real refractive index value. Leftmost plots include an empirically determined phase function for reference; represented as a dotted line. In all cases, the frequency is set at 1 THz.

Fig. 12.
Fig. 12.

Three empirical phase functions, in gray, alongside the function predicted by the modified LEEDR model, in black. All functions were evaluated at a frequency of 1 THz.

Tables (1)

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Table 1. Sample Particle Sizes

Equations (1)

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p ( θ ) = 4 π R 2 I SCA β I 0 d v .

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