Abstract

Altitude profiles of atmospheric window radiance measured with upward-looking sensors frequently show a rapid decrease in radiance with increasing height over a narrow altitude region in the upper troposphere. This region of rapid decrease is termed a radiometric knee in the altitude profile. The top of this knee defines a radiometric tropopause with a latitudinal height dependence similar to that of the usually defined barometric tropopause. Atmospheric window (10–12-μm) radiance at these altitudes can be associated with the presence of ice particulates. Comparison of the measurements with predicted altitude profiles of atmospheric radiance from the lowtran 7 atmospheric model code shows that a well-defined knee occurs when there is a cloud layer (liquid or ice) such as a subvisual cirrus cloud present. The rate and magnitude of the radiance decrease depend on optical depth and, therefore, the water content of the layer. Atmospheric background radiance values for near horizontal (large zenith angle) viewing with upward-looking sensors can be as much as a factor of 100 lower above the knee than below it. Comparisons between calculated and observed radiance profiles were used to estimate the vertical extent, total optical depth, and water content of the clouds.

© 1990 Optical Society of America

Full Article  |  PDF Article

References

  • View by:
  • |
  • |
  • |

  1. W. J. Williams, D. G. Murcray, S. Proffitt, “Characterization of the Radiometric Tropopause,” in Proceedings, IRIS Meeting on Targets, Backgrounds and Discrimination (ERIM, Ann Arbor, Michigan, 1985).
  2. C. M. R. Platt, J. C. Scott, A. C. Dilley, “Remote Sensing of High Clouds. Part VI: Optical Properties of Midlatitude and Tropical Cirrus,” J. Atmos. Sci. 44, 729–747 (1987).
    [CrossRef]
  3. E. Schmidt, “High Altitude Cirrus Effects on Spectral Measurements,” Proc. Soc. Photo-Opt. Instrum. Eng. 924, 281–289 (1988).
  4. M. Chahine, “A General Relaxation Method for Inverse Solution of the Full Radiative Transfer Equation,” J. Atmos. Sci. 29, 741–747 (1972).
    [CrossRef]
  5. M. Chahine, “Remote Sounding of Cloudy Atmospheres. II. Multiple Cloud Formations,” J. Atmos. Sci. 34, 744–757 (1977).
    [CrossRef]
  6. E. Schmidt, “Secant Factor/Slow Roll Data Analysis,” Teledyne Brown Engineering, Technical Letter SA&T87-USASDC-006 (Jan.1987).
  7. R. Russell, Aerospace Corporation, private communication.
  8. E. E. Uthe, P. B. Russell, “Lidar Observations of Tropical High-Altitude Cirrus Clouds,” Radiation in the Atmosphere (Science Press, Garnisch-Partenkircheu, Germany, 1976), pp. 242–244.
  9. F. X. Kneizys et al., “Atmospheric Transmittance/Radiance: Computer Code lowtran6,” AFGL-TR-83-0187 (1983).
  10. V. E. Derr, “Attenuation of Solar Energy by High, Thin Clouds,” Atmos. Environ. 14, 719–729 (1980).
    [CrossRef]
  11. F. X. Kneizys et al., “User’s Guide to lowtran 7,” AFGL-TR-88-0177 (1988).
  12. E. P. Shettle, “Models of Aerosols, Clouds and Precipitation for Atmospheric Propagation Studies,” in Proceedings, AGARD Forty-Fifth Symposium (Oct. 1989).
  13. H. G. Houghton, Physical Meteorology (MIT Press, Cambridge, 1985), p. 153.
  14. E. Bauer, Institute for Defense Analysis, private communication.
  15. K.-N. Liou, An Introduction to Atmospheric Radiation (Academic, New York, 1980).
  16. S. Kinne, K.-N. Liou, “The Effects of the Nonsphericity and Size Distribution of Ice Crystals on the Radiative Transfer Properties of Cirrus Clouds,” Atmos. Res. 24, 273–284 (1989).
    [CrossRef]
  17. A. W. Gertler, R. L. Steele, “Experimental Verification of the Linear Relationship Between IR Extinction and Liquid Water Content of Clouds,” J. Appl. Meteorol. 19, 1314–1317 (1980).
    [CrossRef]
  18. J. Hallett, Desert Research Institute, private communication.
  19. A. J. Heymsfield, R. G. Knollenberg, “Properties of Cirrus Generating Cells,” J. Atmos. Sci. 9, 1358 (1972).
    [CrossRef]
  20. K. T. Griffith, S. K. Cox, R. G. Knollenberg, “Infrared Radiative Properties of Tropical Cirrus Clouds Inferred From Aircraft Measurements,” J. Atmos. Sci. 37, 1077 (1980).
    [CrossRef]

1989 (1)

S. Kinne, K.-N. Liou, “The Effects of the Nonsphericity and Size Distribution of Ice Crystals on the Radiative Transfer Properties of Cirrus Clouds,” Atmos. Res. 24, 273–284 (1989).
[CrossRef]

1988 (2)

E. Schmidt, “High Altitude Cirrus Effects on Spectral Measurements,” Proc. Soc. Photo-Opt. Instrum. Eng. 924, 281–289 (1988).

F. X. Kneizys et al., “User’s Guide to lowtran 7,” AFGL-TR-88-0177 (1988).

1987 (2)

C. M. R. Platt, J. C. Scott, A. C. Dilley, “Remote Sensing of High Clouds. Part VI: Optical Properties of Midlatitude and Tropical Cirrus,” J. Atmos. Sci. 44, 729–747 (1987).
[CrossRef]

E. Schmidt, “Secant Factor/Slow Roll Data Analysis,” Teledyne Brown Engineering, Technical Letter SA&T87-USASDC-006 (Jan.1987).

1983 (1)

F. X. Kneizys et al., “Atmospheric Transmittance/Radiance: Computer Code lowtran6,” AFGL-TR-83-0187 (1983).

1980 (3)

V. E. Derr, “Attenuation of Solar Energy by High, Thin Clouds,” Atmos. Environ. 14, 719–729 (1980).
[CrossRef]

A. W. Gertler, R. L. Steele, “Experimental Verification of the Linear Relationship Between IR Extinction and Liquid Water Content of Clouds,” J. Appl. Meteorol. 19, 1314–1317 (1980).
[CrossRef]

K. T. Griffith, S. K. Cox, R. G. Knollenberg, “Infrared Radiative Properties of Tropical Cirrus Clouds Inferred From Aircraft Measurements,” J. Atmos. Sci. 37, 1077 (1980).
[CrossRef]

1977 (1)

M. Chahine, “Remote Sounding of Cloudy Atmospheres. II. Multiple Cloud Formations,” J. Atmos. Sci. 34, 744–757 (1977).
[CrossRef]

1972 (2)

M. Chahine, “A General Relaxation Method for Inverse Solution of the Full Radiative Transfer Equation,” J. Atmos. Sci. 29, 741–747 (1972).
[CrossRef]

A. J. Heymsfield, R. G. Knollenberg, “Properties of Cirrus Generating Cells,” J. Atmos. Sci. 9, 1358 (1972).
[CrossRef]

Bauer, E.

E. Bauer, Institute for Defense Analysis, private communication.

Chahine, M.

M. Chahine, “Remote Sounding of Cloudy Atmospheres. II. Multiple Cloud Formations,” J. Atmos. Sci. 34, 744–757 (1977).
[CrossRef]

M. Chahine, “A General Relaxation Method for Inverse Solution of the Full Radiative Transfer Equation,” J. Atmos. Sci. 29, 741–747 (1972).
[CrossRef]

Cox, S. K.

K. T. Griffith, S. K. Cox, R. G. Knollenberg, “Infrared Radiative Properties of Tropical Cirrus Clouds Inferred From Aircraft Measurements,” J. Atmos. Sci. 37, 1077 (1980).
[CrossRef]

Derr, V. E.

V. E. Derr, “Attenuation of Solar Energy by High, Thin Clouds,” Atmos. Environ. 14, 719–729 (1980).
[CrossRef]

Dilley, A. C.

C. M. R. Platt, J. C. Scott, A. C. Dilley, “Remote Sensing of High Clouds. Part VI: Optical Properties of Midlatitude and Tropical Cirrus,” J. Atmos. Sci. 44, 729–747 (1987).
[CrossRef]

Gertler, A. W.

A. W. Gertler, R. L. Steele, “Experimental Verification of the Linear Relationship Between IR Extinction and Liquid Water Content of Clouds,” J. Appl. Meteorol. 19, 1314–1317 (1980).
[CrossRef]

Griffith, K. T.

K. T. Griffith, S. K. Cox, R. G. Knollenberg, “Infrared Radiative Properties of Tropical Cirrus Clouds Inferred From Aircraft Measurements,” J. Atmos. Sci. 37, 1077 (1980).
[CrossRef]

Hallett, J.

J. Hallett, Desert Research Institute, private communication.

Heymsfield, A. J.

A. J. Heymsfield, R. G. Knollenberg, “Properties of Cirrus Generating Cells,” J. Atmos. Sci. 9, 1358 (1972).
[CrossRef]

Houghton, H. G.

H. G. Houghton, Physical Meteorology (MIT Press, Cambridge, 1985), p. 153.

Kinne, S.

S. Kinne, K.-N. Liou, “The Effects of the Nonsphericity and Size Distribution of Ice Crystals on the Radiative Transfer Properties of Cirrus Clouds,” Atmos. Res. 24, 273–284 (1989).
[CrossRef]

Kneizys, F. X.

F. X. Kneizys et al., “User’s Guide to lowtran 7,” AFGL-TR-88-0177 (1988).

F. X. Kneizys et al., “Atmospheric Transmittance/Radiance: Computer Code lowtran6,” AFGL-TR-83-0187 (1983).

Knollenberg, R. G.

K. T. Griffith, S. K. Cox, R. G. Knollenberg, “Infrared Radiative Properties of Tropical Cirrus Clouds Inferred From Aircraft Measurements,” J. Atmos. Sci. 37, 1077 (1980).
[CrossRef]

A. J. Heymsfield, R. G. Knollenberg, “Properties of Cirrus Generating Cells,” J. Atmos. Sci. 9, 1358 (1972).
[CrossRef]

Liou, K.-N.

S. Kinne, K.-N. Liou, “The Effects of the Nonsphericity and Size Distribution of Ice Crystals on the Radiative Transfer Properties of Cirrus Clouds,” Atmos. Res. 24, 273–284 (1989).
[CrossRef]

K.-N. Liou, An Introduction to Atmospheric Radiation (Academic, New York, 1980).

Murcray, D. G.

W. J. Williams, D. G. Murcray, S. Proffitt, “Characterization of the Radiometric Tropopause,” in Proceedings, IRIS Meeting on Targets, Backgrounds and Discrimination (ERIM, Ann Arbor, Michigan, 1985).

Platt, C. M. R.

C. M. R. Platt, J. C. Scott, A. C. Dilley, “Remote Sensing of High Clouds. Part VI: Optical Properties of Midlatitude and Tropical Cirrus,” J. Atmos. Sci. 44, 729–747 (1987).
[CrossRef]

Proffitt, S.

W. J. Williams, D. G. Murcray, S. Proffitt, “Characterization of the Radiometric Tropopause,” in Proceedings, IRIS Meeting on Targets, Backgrounds and Discrimination (ERIM, Ann Arbor, Michigan, 1985).

Russell, P. B.

E. E. Uthe, P. B. Russell, “Lidar Observations of Tropical High-Altitude Cirrus Clouds,” Radiation in the Atmosphere (Science Press, Garnisch-Partenkircheu, Germany, 1976), pp. 242–244.

Russell, R.

R. Russell, Aerospace Corporation, private communication.

Schmidt, E.

E. Schmidt, “High Altitude Cirrus Effects on Spectral Measurements,” Proc. Soc. Photo-Opt. Instrum. Eng. 924, 281–289 (1988).

E. Schmidt, “Secant Factor/Slow Roll Data Analysis,” Teledyne Brown Engineering, Technical Letter SA&T87-USASDC-006 (Jan.1987).

Scott, J. C.

C. M. R. Platt, J. C. Scott, A. C. Dilley, “Remote Sensing of High Clouds. Part VI: Optical Properties of Midlatitude and Tropical Cirrus,” J. Atmos. Sci. 44, 729–747 (1987).
[CrossRef]

Shettle, E. P.

E. P. Shettle, “Models of Aerosols, Clouds and Precipitation for Atmospheric Propagation Studies,” in Proceedings, AGARD Forty-Fifth Symposium (Oct. 1989).

Steele, R. L.

A. W. Gertler, R. L. Steele, “Experimental Verification of the Linear Relationship Between IR Extinction and Liquid Water Content of Clouds,” J. Appl. Meteorol. 19, 1314–1317 (1980).
[CrossRef]

Uthe, E. E.

E. E. Uthe, P. B. Russell, “Lidar Observations of Tropical High-Altitude Cirrus Clouds,” Radiation in the Atmosphere (Science Press, Garnisch-Partenkircheu, Germany, 1976), pp. 242–244.

Williams, W. J.

W. J. Williams, D. G. Murcray, S. Proffitt, “Characterization of the Radiometric Tropopause,” in Proceedings, IRIS Meeting on Targets, Backgrounds and Discrimination (ERIM, Ann Arbor, Michigan, 1985).

AFGL-TR-83-0187 (1)

F. X. Kneizys et al., “Atmospheric Transmittance/Radiance: Computer Code lowtran6,” AFGL-TR-83-0187 (1983).

AFGL-TR-88-0177 (1)

F. X. Kneizys et al., “User’s Guide to lowtran 7,” AFGL-TR-88-0177 (1988).

Atmos. Environ. (1)

V. E. Derr, “Attenuation of Solar Energy by High, Thin Clouds,” Atmos. Environ. 14, 719–729 (1980).
[CrossRef]

Atmos. Res. (1)

S. Kinne, K.-N. Liou, “The Effects of the Nonsphericity and Size Distribution of Ice Crystals on the Radiative Transfer Properties of Cirrus Clouds,” Atmos. Res. 24, 273–284 (1989).
[CrossRef]

J. Appl. Meteorol. (1)

A. W. Gertler, R. L. Steele, “Experimental Verification of the Linear Relationship Between IR Extinction and Liquid Water Content of Clouds,” J. Appl. Meteorol. 19, 1314–1317 (1980).
[CrossRef]

J. Atmos. Sci. (5)

A. J. Heymsfield, R. G. Knollenberg, “Properties of Cirrus Generating Cells,” J. Atmos. Sci. 9, 1358 (1972).
[CrossRef]

K. T. Griffith, S. K. Cox, R. G. Knollenberg, “Infrared Radiative Properties of Tropical Cirrus Clouds Inferred From Aircraft Measurements,” J. Atmos. Sci. 37, 1077 (1980).
[CrossRef]

C. M. R. Platt, J. C. Scott, A. C. Dilley, “Remote Sensing of High Clouds. Part VI: Optical Properties of Midlatitude and Tropical Cirrus,” J. Atmos. Sci. 44, 729–747 (1987).
[CrossRef]

M. Chahine, “A General Relaxation Method for Inverse Solution of the Full Radiative Transfer Equation,” J. Atmos. Sci. 29, 741–747 (1972).
[CrossRef]

M. Chahine, “Remote Sounding of Cloudy Atmospheres. II. Multiple Cloud Formations,” J. Atmos. Sci. 34, 744–757 (1977).
[CrossRef]

Proc. Soc. Photo-Opt. Instrum. Eng. (1)

E. Schmidt, “High Altitude Cirrus Effects on Spectral Measurements,” Proc. Soc. Photo-Opt. Instrum. Eng. 924, 281–289 (1988).

Teledyne Brown Engineering, Technical Letter SA&T87-USASDC-006 (1)

E. Schmidt, “Secant Factor/Slow Roll Data Analysis,” Teledyne Brown Engineering, Technical Letter SA&T87-USASDC-006 (Jan.1987).

Other (8)

R. Russell, Aerospace Corporation, private communication.

E. E. Uthe, P. B. Russell, “Lidar Observations of Tropical High-Altitude Cirrus Clouds,” Radiation in the Atmosphere (Science Press, Garnisch-Partenkircheu, Germany, 1976), pp. 242–244.

J. Hallett, Desert Research Institute, private communication.

E. P. Shettle, “Models of Aerosols, Clouds and Precipitation for Atmospheric Propagation Studies,” in Proceedings, AGARD Forty-Fifth Symposium (Oct. 1989).

H. G. Houghton, Physical Meteorology (MIT Press, Cambridge, 1985), p. 153.

E. Bauer, Institute for Defense Analysis, private communication.

K.-N. Liou, An Introduction to Atmospheric Radiation (Academic, New York, 1980).

W. J. Williams, D. G. Murcray, S. Proffitt, “Characterization of the Radiometric Tropopause,” in Proceedings, IRIS Meeting on Targets, Backgrounds and Discrimination (ERIM, Ann Arbor, Michigan, 1985).

Cited By

OSA participates in CrossRef's Cited-By Linking service. Citing articles from OSA journals and other participating publishers are listed here.

Alert me when this article is cited.


Figures (13)

Fig. 1
Fig. 1

Williams’s radiometric knee measurements after conversion from the 45° zenith angle to 77° (balloon-borne COR).

Fig. 2
Fig. 2

Typical lowtran 7 model radiometric knees. Tropical water profile, common cloud base at 10 km, cloud thickness = 1.0 km, 10.1–12.6-μm filter, and 77° zenith angle are the standard parameters. The NOAA profile is included to show typical lowtran 6 results.

Fig. 3
Fig. 3

Subvisual cirrus model knee results for the tropical midlatitude winter and subarctic winter water profiles of lowtran 7 (other parameters standard).

Fig. 4
Fig. 4

lowtran 7 cloudless sky radiance profiles for tropical mid-latitude winter and subarctic winter water vapor profiles (77° zenith angle, 10.1–12.6-μm filter).

Fig. 5
Fig. 5

lowtran 7 subvisual cirrus model cloud thickness effects for the tropical model atmosphere. The knee magnitude varies with layer thickness as expected (common cloud base height of 10 km, standard parameters).

Fig. 6
Fig. 6

Radiometric knee generation via the user definition of the vertical extent and attenuation coefficient of a lowtran 7 knee. All profiles have a common cloud midpoint at 10.25 km and are filtered (10.1-12.6/tm) for a 770 viewing angle.

Fig. 7
Fig. 7

Williams’s data (4 Mar. 1970) fit by a tropical model radiometric knee with a cloud base height of 9 km (other parameters standard).

Fig. 8
Fig. 8

Translation of cloud base from 8 to 9 km for the standard parameter profile preserves the knee magnitude (total optical depth).

Fig. 9
Fig. 9

Williams’s data (10 Dec. 1969) fit by a tropical model radiometric knee (cloud thickness = 0.5 km, base at 4.5 km).

Fig. 10
Fig. 10

Williams’s data (6 May 1970) fit by a tropical radiometric knee with standard parameters.

Fig. 11
Fig. 11

Infrared tropical model transmittance knees vs normal attenuation for a 1-km thick cloud layer with a 10-km base height (standard parameters and three lowtran 7 cirrus models). The radiance analog is shown in Fig. 2.

Fig. 12
Fig. 12

Infrared radiance vs transmittance in a 10–12-μm window (filtered to 10.1–12.6 μm to model the sensor response) for the lowtran 7 subvisual cirrus model. Three zenith angles are used (0, 45, and 77°) to show secant scaling of magnitudes.

Fig. 13
Fig. 13

Infrared window radiance vs transmittance (filtered to 10.1–12.6 μm) for all three lowtran 7 cirrus models showing the range of radiances possible for a given transmittance (or total optical depth) (tropical model, 77° zenith angle, sensor 2 km below cloud base).

Equations (4)

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

σ e = 0.14 L ,
τ = exp [ - ( 0.14 L ) L ] ,
I λ ( z 1 ) = z 1 B λ [ T ( z ) ] exp [ - τ ( z 1 , ) ] σ e λ d z ,
σ e λ = - cos θ δ z ln τ λ ,

Metrics