Abstract

Clear air turbulence (CAT) ahead of an aircraft can be detected in real time by an infrared radiometer. The alert time and reliability depend on the passband of the infrared filter used and the altitude of the aircraft. Preliminary results and analyses show that a nominal passband of 26 to 35 μm appears optimal to alert CAT from 1.5 to 6.0 min ahead of the encounter. The alert time increases with higher altitude as the atmospheric absorption, determining the horizontal weighting, is reduced.

© 1978 Optical Society of America

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References

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  1. P. Kuhn, F. Caracena, C. M. Gillespie, “Clear air turbulence; detection by infrared observations of water vapor,” Science 196, 1099–1100 (1977).
    [CrossRef] [PubMed]
  2. P. C. Patnaik, F. S. Sherman, G. M. Corcos, “A numerical simulation of Kelvin–Helmholtz waves of finite amplitude,” J. Fluid Mech. 73, 215 (1976); E. R. Reiter, “Stratospheric–tropospheric exchange processes,” Rev. Geophys. Space Phys. 13, 459–474 (1975); N. Possiel, J. R. Scoggins, “Curvature of the wind profile in the troposphere versus regions of CAT and non-CAT in the stratosphere,” Mon. Weather Rev. 104, 57–62 (1976).
    [CrossRef]
  3. M. A. Bender, H. A. Panofsky, C. A. Pesten, “Temperature gradients and clear-air turbulence,” J. Appl. Meteorol. 15, 1193–1199 (1976).
    [CrossRef]
  4. R. A. McClatchey, W. S. Benedict, S. A. Clough, D. E. Burch, R. F. Calfee, K. Fox, L. S. Rothman, J. S. Garing, “AFCRL Atmospheric Absorption Line Parameters Compilation,” AFCRL Technical Report 0096 (1973).
  5. W. Kaiser, W. G. Spitzer, R. H. Kaiser, L. E. Howarth, “Infrared properties of CaF2 and BaF2,” Phys. Rev. 127, 1950 (1962).
    [CrossRef]

1977

P. Kuhn, F. Caracena, C. M. Gillespie, “Clear air turbulence; detection by infrared observations of water vapor,” Science 196, 1099–1100 (1977).
[CrossRef] [PubMed]

1976

P. C. Patnaik, F. S. Sherman, G. M. Corcos, “A numerical simulation of Kelvin–Helmholtz waves of finite amplitude,” J. Fluid Mech. 73, 215 (1976); E. R. Reiter, “Stratospheric–tropospheric exchange processes,” Rev. Geophys. Space Phys. 13, 459–474 (1975); N. Possiel, J. R. Scoggins, “Curvature of the wind profile in the troposphere versus regions of CAT and non-CAT in the stratosphere,” Mon. Weather Rev. 104, 57–62 (1976).
[CrossRef]

M. A. Bender, H. A. Panofsky, C. A. Pesten, “Temperature gradients and clear-air turbulence,” J. Appl. Meteorol. 15, 1193–1199 (1976).
[CrossRef]

1962

W. Kaiser, W. G. Spitzer, R. H. Kaiser, L. E. Howarth, “Infrared properties of CaF2 and BaF2,” Phys. Rev. 127, 1950 (1962).
[CrossRef]

Bender, M. A.

M. A. Bender, H. A. Panofsky, C. A. Pesten, “Temperature gradients and clear-air turbulence,” J. Appl. Meteorol. 15, 1193–1199 (1976).
[CrossRef]

Benedict, W. S.

R. A. McClatchey, W. S. Benedict, S. A. Clough, D. E. Burch, R. F. Calfee, K. Fox, L. S. Rothman, J. S. Garing, “AFCRL Atmospheric Absorption Line Parameters Compilation,” AFCRL Technical Report 0096 (1973).

Burch, D. E.

R. A. McClatchey, W. S. Benedict, S. A. Clough, D. E. Burch, R. F. Calfee, K. Fox, L. S. Rothman, J. S. Garing, “AFCRL Atmospheric Absorption Line Parameters Compilation,” AFCRL Technical Report 0096 (1973).

Calfee, R. F.

R. A. McClatchey, W. S. Benedict, S. A. Clough, D. E. Burch, R. F. Calfee, K. Fox, L. S. Rothman, J. S. Garing, “AFCRL Atmospheric Absorption Line Parameters Compilation,” AFCRL Technical Report 0096 (1973).

Caracena, F.

P. Kuhn, F. Caracena, C. M. Gillespie, “Clear air turbulence; detection by infrared observations of water vapor,” Science 196, 1099–1100 (1977).
[CrossRef] [PubMed]

Clough, S. A.

R. A. McClatchey, W. S. Benedict, S. A. Clough, D. E. Burch, R. F. Calfee, K. Fox, L. S. Rothman, J. S. Garing, “AFCRL Atmospheric Absorption Line Parameters Compilation,” AFCRL Technical Report 0096 (1973).

Corcos, G. M.

P. C. Patnaik, F. S. Sherman, G. M. Corcos, “A numerical simulation of Kelvin–Helmholtz waves of finite amplitude,” J. Fluid Mech. 73, 215 (1976); E. R. Reiter, “Stratospheric–tropospheric exchange processes,” Rev. Geophys. Space Phys. 13, 459–474 (1975); N. Possiel, J. R. Scoggins, “Curvature of the wind profile in the troposphere versus regions of CAT and non-CAT in the stratosphere,” Mon. Weather Rev. 104, 57–62 (1976).
[CrossRef]

Fox, K.

R. A. McClatchey, W. S. Benedict, S. A. Clough, D. E. Burch, R. F. Calfee, K. Fox, L. S. Rothman, J. S. Garing, “AFCRL Atmospheric Absorption Line Parameters Compilation,” AFCRL Technical Report 0096 (1973).

Garing, J. S.

R. A. McClatchey, W. S. Benedict, S. A. Clough, D. E. Burch, R. F. Calfee, K. Fox, L. S. Rothman, J. S. Garing, “AFCRL Atmospheric Absorption Line Parameters Compilation,” AFCRL Technical Report 0096 (1973).

Gillespie, C. M.

P. Kuhn, F. Caracena, C. M. Gillespie, “Clear air turbulence; detection by infrared observations of water vapor,” Science 196, 1099–1100 (1977).
[CrossRef] [PubMed]

Howarth, L. E.

W. Kaiser, W. G. Spitzer, R. H. Kaiser, L. E. Howarth, “Infrared properties of CaF2 and BaF2,” Phys. Rev. 127, 1950 (1962).
[CrossRef]

Kaiser, R. H.

W. Kaiser, W. G. Spitzer, R. H. Kaiser, L. E. Howarth, “Infrared properties of CaF2 and BaF2,” Phys. Rev. 127, 1950 (1962).
[CrossRef]

Kaiser, W.

W. Kaiser, W. G. Spitzer, R. H. Kaiser, L. E. Howarth, “Infrared properties of CaF2 and BaF2,” Phys. Rev. 127, 1950 (1962).
[CrossRef]

Kuhn, P.

P. Kuhn, F. Caracena, C. M. Gillespie, “Clear air turbulence; detection by infrared observations of water vapor,” Science 196, 1099–1100 (1977).
[CrossRef] [PubMed]

McClatchey, R. A.

R. A. McClatchey, W. S. Benedict, S. A. Clough, D. E. Burch, R. F. Calfee, K. Fox, L. S. Rothman, J. S. Garing, “AFCRL Atmospheric Absorption Line Parameters Compilation,” AFCRL Technical Report 0096 (1973).

Panofsky, H. A.

M. A. Bender, H. A. Panofsky, C. A. Pesten, “Temperature gradients and clear-air turbulence,” J. Appl. Meteorol. 15, 1193–1199 (1976).
[CrossRef]

Patnaik, P. C.

P. C. Patnaik, F. S. Sherman, G. M. Corcos, “A numerical simulation of Kelvin–Helmholtz waves of finite amplitude,” J. Fluid Mech. 73, 215 (1976); E. R. Reiter, “Stratospheric–tropospheric exchange processes,” Rev. Geophys. Space Phys. 13, 459–474 (1975); N. Possiel, J. R. Scoggins, “Curvature of the wind profile in the troposphere versus regions of CAT and non-CAT in the stratosphere,” Mon. Weather Rev. 104, 57–62 (1976).
[CrossRef]

Pesten, C. A.

M. A. Bender, H. A. Panofsky, C. A. Pesten, “Temperature gradients and clear-air turbulence,” J. Appl. Meteorol. 15, 1193–1199 (1976).
[CrossRef]

Rothman, L. S.

R. A. McClatchey, W. S. Benedict, S. A. Clough, D. E. Burch, R. F. Calfee, K. Fox, L. S. Rothman, J. S. Garing, “AFCRL Atmospheric Absorption Line Parameters Compilation,” AFCRL Technical Report 0096 (1973).

Sherman, F. S.

P. C. Patnaik, F. S. Sherman, G. M. Corcos, “A numerical simulation of Kelvin–Helmholtz waves of finite amplitude,” J. Fluid Mech. 73, 215 (1976); E. R. Reiter, “Stratospheric–tropospheric exchange processes,” Rev. Geophys. Space Phys. 13, 459–474 (1975); N. Possiel, J. R. Scoggins, “Curvature of the wind profile in the troposphere versus regions of CAT and non-CAT in the stratosphere,” Mon. Weather Rev. 104, 57–62 (1976).
[CrossRef]

Spitzer, W. G.

W. Kaiser, W. G. Spitzer, R. H. Kaiser, L. E. Howarth, “Infrared properties of CaF2 and BaF2,” Phys. Rev. 127, 1950 (1962).
[CrossRef]

J. Appl. Meteorol.

M. A. Bender, H. A. Panofsky, C. A. Pesten, “Temperature gradients and clear-air turbulence,” J. Appl. Meteorol. 15, 1193–1199 (1976).
[CrossRef]

J. Fluid Mech.

P. C. Patnaik, F. S. Sherman, G. M. Corcos, “A numerical simulation of Kelvin–Helmholtz waves of finite amplitude,” J. Fluid Mech. 73, 215 (1976); E. R. Reiter, “Stratospheric–tropospheric exchange processes,” Rev. Geophys. Space Phys. 13, 459–474 (1975); N. Possiel, J. R. Scoggins, “Curvature of the wind profile in the troposphere versus regions of CAT and non-CAT in the stratosphere,” Mon. Weather Rev. 104, 57–62 (1976).
[CrossRef]

Phys. Rev.

W. Kaiser, W. G. Spitzer, R. H. Kaiser, L. E. Howarth, “Infrared properties of CaF2 and BaF2,” Phys. Rev. 127, 1950 (1962).
[CrossRef]

Science

P. Kuhn, F. Caracena, C. M. Gillespie, “Clear air turbulence; detection by infrared observations of water vapor,” Science 196, 1099–1100 (1977).
[CrossRef] [PubMed]

Other

R. A. McClatchey, W. S. Benedict, S. A. Clough, D. E. Burch, R. F. Calfee, K. Fox, L. S. Rothman, J. S. Garing, “AFCRL Atmospheric Absorption Line Parameters Compilation,” AFCRL Technical Report 0096 (1973).

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Figures (4)

Fig. 1
Fig. 1

A calculation of radiance along an elevated slant path as a function of receiver position. The lower panel is a cross section of isolines of water-vapor mixing ratio in parts per million by mass. The upper panel displays the calculated radiance as a function of radiometer position along a hypothetical flight path.

Fig. 2
Fig. 2

Planck radiance weighting functions for three pass-bands as described in the text. The calculation assumes the nominal passbands given in Fig. 3, a pressure altitude of 200 mbar (11.9 km), and a water vapor mixing ratio of 8 g g−1.

Fig. 3
Fig. 3

Measured system passband response functions for the three different passbands.

Fig. 4
Fig. 4

The standard deviations of the radiometer signal (in arbitrary units) as a function of time before a turbulence encounter. Here S represents the average of six turbulence encounters observed on a flight at 12.5-km altitude and with the middle-range (SrF2) filter. The dashed line shows the standard deviation or baseline level when not in proximity to turbulence. Airspeed was 13.6 km per minute.

Equations (4)

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τ ( z ) = exp [ - 1 R T 0 z K ¯ Δ v p q ¯ sec ( θ ) d z ] .
N ( W cm - 2 sr - 1 ) = - v v 2 0 B ( v , T ) sec ( θ ) ϕ ( v ) × τ ( q , v , z ) ln ( z ) d z z d v ,
d τ = - K ¯ Δ v p q ¯ sec θ d z / R T ,
d τ / d ln ( z ) = - τ k Δ v p q ¯ sec θ z / R T ,

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