Abstract

Clear air turbulence (CAT) is frequently associated with horizontal temperature gradients of the atmosphere. An instrument has been developed for detecting such gradients remotely by sensing the infrared radiation emitted by the carbon dioxide in the atmosphere. Three of these instruments have been installed on commercial jet aircraft, to evalute this technique for providing advance warning of CAT. Many light turbulence encounters have been detected as much as 80 miles (130 km) (8 min) in advance. A high false alarm rate was experienced because of temperature gradients not associated with turbulence. No severe turbulence has been encountered to date. It is hoped that the temperature effects associated with severe turbulence will be large enough to permit establishing higher alarm threshold levels which will substantially reduce the false alarm rate. Future plans include evaluation of a vertical scan mode for detection of temperature inversions.

© 1970 Optical Society of America

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References

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  1. P. W. Kadlec, “Exploration of the Relationship between Atmospheric Temperature Change and CAT,” Joint ION–SAE Conference on CAT, Feb. 1966, Washington, D.C.
  2. L. D. Kaplan, J. Opt. Soc. Amer. 49, 1004 (1959).
    [CrossRef]
  3. D. Q. Wark, H. E. Fleming, Monthly Weather Rev. 94, 351 (1966).
    [CrossRef]
  4. G. K. Mather, M. Weiss, in Proc. 5th Symp. Remote Sensing Environ., April 1968, University of Michigan.
  5. F. A. Mitchell, D. T. Prophet, in Clear Air Turbulence and Its Detection, Y. H. Pao, A. Goldburg, Eds. (Plenum Press, New York, 1969), pp. 144–82.
  6. W. L. Wolfe, Ed. Handbook of Military Infrared Technology (Office of Naval Research, Washington, D.C., 1965), Chap. 18.
  7. V. R. Stull, P. J. Wyatt, G. N. Plass, Infrared Transmission Studies, Vol. 3, , Space Systems Division, Air Force Systems Command.
  8. R. Jimenez, M. Weiss, “Some Results of Inflight Testing an Infrared Sensor as a CAT Detector,” 6th Symp. Remote Sensing Environ., Oct. 1969, University of Michigan.
  9. E. F. Flint, see Ref. 5, pp. 449–75

1966 (1)

D. Q. Wark, H. E. Fleming, Monthly Weather Rev. 94, 351 (1966).
[CrossRef]

1959 (1)

L. D. Kaplan, J. Opt. Soc. Amer. 49, 1004 (1959).
[CrossRef]

Fleming, H. E.

D. Q. Wark, H. E. Fleming, Monthly Weather Rev. 94, 351 (1966).
[CrossRef]

Flint, E. F.

E. F. Flint, see Ref. 5, pp. 449–75

Jimenez, R.

R. Jimenez, M. Weiss, “Some Results of Inflight Testing an Infrared Sensor as a CAT Detector,” 6th Symp. Remote Sensing Environ., Oct. 1969, University of Michigan.

Kadlec, P. W.

P. W. Kadlec, “Exploration of the Relationship between Atmospheric Temperature Change and CAT,” Joint ION–SAE Conference on CAT, Feb. 1966, Washington, D.C.

Kaplan, L. D.

L. D. Kaplan, J. Opt. Soc. Amer. 49, 1004 (1959).
[CrossRef]

Mather, G. K.

G. K. Mather, M. Weiss, in Proc. 5th Symp. Remote Sensing Environ., April 1968, University of Michigan.

Mitchell, F. A.

F. A. Mitchell, D. T. Prophet, in Clear Air Turbulence and Its Detection, Y. H. Pao, A. Goldburg, Eds. (Plenum Press, New York, 1969), pp. 144–82.

Plass, G. N.

V. R. Stull, P. J. Wyatt, G. N. Plass, Infrared Transmission Studies, Vol. 3, , Space Systems Division, Air Force Systems Command.

Prophet, D. T.

F. A. Mitchell, D. T. Prophet, in Clear Air Turbulence and Its Detection, Y. H. Pao, A. Goldburg, Eds. (Plenum Press, New York, 1969), pp. 144–82.

Stull, V. R.

V. R. Stull, P. J. Wyatt, G. N. Plass, Infrared Transmission Studies, Vol. 3, , Space Systems Division, Air Force Systems Command.

Wark, D. Q.

D. Q. Wark, H. E. Fleming, Monthly Weather Rev. 94, 351 (1966).
[CrossRef]

Weiss, M.

G. K. Mather, M. Weiss, in Proc. 5th Symp. Remote Sensing Environ., April 1968, University of Michigan.

R. Jimenez, M. Weiss, “Some Results of Inflight Testing an Infrared Sensor as a CAT Detector,” 6th Symp. Remote Sensing Environ., Oct. 1969, University of Michigan.

Wyatt, P. J.

V. R. Stull, P. J. Wyatt, G. N. Plass, Infrared Transmission Studies, Vol. 3, , Space Systems Division, Air Force Systems Command.

J. Opt. Soc. Amer. (1)

L. D. Kaplan, J. Opt. Soc. Amer. 49, 1004 (1959).
[CrossRef]

Monthly Weather Rev. (1)

D. Q. Wark, H. E. Fleming, Monthly Weather Rev. 94, 351 (1966).
[CrossRef]

Other (7)

G. K. Mather, M. Weiss, in Proc. 5th Symp. Remote Sensing Environ., April 1968, University of Michigan.

F. A. Mitchell, D. T. Prophet, in Clear Air Turbulence and Its Detection, Y. H. Pao, A. Goldburg, Eds. (Plenum Press, New York, 1969), pp. 144–82.

W. L. Wolfe, Ed. Handbook of Military Infrared Technology (Office of Naval Research, Washington, D.C., 1965), Chap. 18.

V. R. Stull, P. J. Wyatt, G. N. Plass, Infrared Transmission Studies, Vol. 3, , Space Systems Division, Air Force Systems Command.

R. Jimenez, M. Weiss, “Some Results of Inflight Testing an Infrared Sensor as a CAT Detector,” 6th Symp. Remote Sensing Environ., Oct. 1969, University of Michigan.

E. F. Flint, see Ref. 5, pp. 449–75

P. W. Kadlec, “Exploration of the Relationship between Atmospheric Temperature Change and CAT,” Joint ION–SAE Conference on CAT, Feb. 1966, Washington, D.C.

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Figures (14)

Fig. 1
Fig. 1

Spectral emission of CO2.

Fig. 2
Fig. 2

Comparison of spectral and temporal methods for determining remote temperature.

Fig. 3
Fig. 3

Sectional view of IRCAT sensing head.

Fig. 4
Fig. 4

Photograph of IRCAT sensor head.

Fig. 5
Fig. 5

Location of IRCAT sensor head on aircraft.

Fig. 6
Fig. 6

Atmospheric transmission at 38,000-ft (11.6-km) altitude.

Fig. 7
Fig. 7

Atmospheric transmission at 18,000-ft (5.5-km) altitude.

Fig. 8
Fig. 8

Weighting function for 20–40 mile (32.6–65.2-km) interval vs spectral band.

Fig. 9
Fig. 9

Weighting function of 13.8–14.5-μ filter for 5 mile (8.15 km) intervals at 38,000-ft (11.6-km) altitude.

Fig. 10
Fig. 10

IRCAT response on approach to temperature plateau and ramp.

Fig. 11
Fig. 11

Flight record showing IRCAT signal when approaching steep temperature rise.

Fig. 12
Fig. 12

Flight record showing IRCAT signal when approaching gradual temperature rise.

Fig. 13
Fig. 13

Flight record showing IRCAT responses to cloud with 13.3–14.0-μ filter.

Fig. 14
Fig. 14

IRCAT signals in vertical scan mode.

Equations (5)

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NEN = α 1 2 ( Δ f ) 1 2 D * e A ω = 0.6 ( 10 ) 7 W cm 2 sr 1 ,
d N r = N x F x d x ,
F x = d ( t x ) / d x .
N r = N x ( t 1 t 2 ) .
S d = 0 F ( x d ) Δ T x d x .

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