Abstract

An uncooled microbolometer-array thermal infrared camera has been incorporated into a remote sensing system for radiometric sky imaging. The radiometric calibration is validated and improved through direct comparison with spectrally integrated data from the Atmospheric Emitted Radiance Interferometer (AERI). With the improved calibration, the Infrared Cloud Imager (ICI) system routinely obtains sky images with radiometric uncertainty less than 0.5 W/(m2 sr) for extended deployments in challenging field environments. We demonstrate the infrared cloud imaging technique with still and time-lapse imagery of clear and cloudy skies, including stratus, cirrus, and wave clouds.

© 2005 Optical Society of America

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References

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  11. R. O. Knuteson, H. E. Revercomb, F. A. Best, N. C. Ciganovich, R. G. Dedecker, T. P. Dirkx, S. C. Ellington, W. F. Feltz, R. K. Garcia, H. B. Howell, W. L. Smith, J. F. Short, and D. C. Tobin, �??Atmospheric Emitted Radiance Interferometer. Pt. II: Instrument Performance,�?? J. Atmos. Oceanic. Technol. 21, 1777-1789 (2004).
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  12. N. L. Seldomridge, �??Dual-polarization cloud lidar design and characterization,�?? M.S. Thesis, Montana State University, Bozeman, Montana (2005)., <a href= "http://www.montana.edu/etd/available/seldomridge_0805.html">http://www.montana.edu/etd/available/seldomridge_0805.html</a>.

Geophys. Res. Let.

J. A. Shaw, H. M. Zorn, J. J. Bates, and J. H. Churnside, �??Observations of downwelling infrared spectral radiance at Mauna Loa, HI during the 1997-1998 ENSO event,�?? Geophys. Res. Let. 26, 1727-1730 (1999).
[CrossRef]

Geophys. Res. Letters

R. D. Cess and P. M. Udelhofen, �??Climate change during 1985-1999: cloud interactions determined from satellite measurements,�?? Geophys. Res. Letters 30, 19-1-4 (2003).
[CrossRef]

IEEE Trans. Geosci. Rem. Sens.

B. Thurairajah and J. A. Shaw, �??Cloud statistics measured with the Infrared Cloud Imager (ICI),�?? IEEE Trans. Geosci. Rem. Sens. 43 (to be published, September 2005).
[CrossRef]

J. Atm. Ocean. Technol.

R. S. Lancaster, J. D. Spinhirne, and K. F. Manizade, �??Combined infrared stereo and laser ranging cloud measurements from shuttle mission STS-85,�?? J. Atm. Ocean. Technol. 20, 67-78 (2003).
[CrossRef]

J. Atmos. Oceanic. Technol.

R. O. Knuteson, H. E. Revercomb, F. A. Best, N. C. Ciganovich, R. G. Dedecker, T. P. Dirkx, S. C. Ellington, W. F. Feltz, R. K. Garcia, H. B. Howell, W. L. Smith, J. F. Short, and D. C. Tobin, �??Atmospheric Emitted Radiance Interferometer. Pt. II: Instrument Performance,�?? J. Atmos. Oceanic. Technol. 21, 1777-1789 (2004).
[CrossRef]

J. Atmos. Sci.

R. F. Cahalan, W. Ridgeway, W. J. Wiscombe, T. L. Bell, and J. B. Snider, �??The albedo of fractal stratocumulus clouds,�?? J. Atmos. Sci. 51, 2434-2455 (1994).
[CrossRef]

J. Solar Energy Eng.

C. H. Whitlock, D. E. Brown, W. S. Chandler, R. C. DiPasquale, N. A. Ritchey, S. K. Gupta, A. C. Wilber, D. P. Kratz, P. W. Stackhouse, �??Global surface solar energy anomalies including El Niño and La Niña years,�?? J. Solar Energy Eng. 123, 211-215 (2001).
[CrossRef]

Mon. Weather Rev.

K.-N. Liou, Influence of cirrus clouds on weather and climate processes: a global perspective,�?? Mon. Weather Rev. 114, 1167-1199 (1986).
[CrossRef]

Opt. Eng.

J. A. Shaw and L. S. Fedor, �??Improved calibration of infrared radiometers for cloud-temperature remote sensing,�?? Opt. Eng. 32, 1002�??1010 (1993).
[CrossRef]

Proc. SPIE

D. M. Erickson, D. H. Tsiang, and M. Jeganathan, �??Upgrade of the Atmospheric Visibility Monitoring system,�?? in Free Space Laser Comm. Technol. XI,G. S. Mecherle, ed., Proc. SPIE 3615, 310-315 (1999).
[CrossRef]

Other

N. L. Seldomridge, �??Dual-polarization cloud lidar design and characterization,�?? M.S. Thesis, Montana State University, Bozeman, Montana (2005)., <a href= "http://www.montana.edu/etd/available/seldomridge_0805.html">http://www.montana.edu/etd/available/seldomridge_0805.html</a>.

P. W. Kruse, Uncooled thermal imaging: Arrays, systems, and applications (SPIE press, 2001), ch. 4.
[CrossRef]

Supplementary Material (10)

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» Media 10: AVI (480 KB)     

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Figures (7)

Fig. 1.
Fig. 1.

Principal components of the ICI optical system. The IR camera alternately views the sky and two blackbody calibration sources (only one shown for convenience).

Fig. 2.
Fig. 2.

FTIR measurements of downwelling atmospheric emitted radiance spectra for a clear, dry atmosphere (bottom), thin cirrus clouds (middle), and stratus clouds (top). The baseline level of window emission also varies with atmospheric water vapor content.

Fig. 3.
Fig. 3.

Time series of mean radiance from ICI images and spectrally integrated radiance from the AERI, using an ideal rectangular bandwidth of 8–14 μm. Only data for relatively uniform clear or cloudy skies were used in the comparison. The ICI data are approximately 1 W/(m2 sr) lower than the AERI data at the cold end and 2.5 – 3 W/(m2 sr) low at the warm end.

Fig. 4.
Fig. 4.

Time series of mean radiance from ICI images and band-integrated radiance from the AERI, using an adjusted rectangular bandwidth of 8.5–14 μm and a nonlinear gain adjustment. By itself, the new bandwidth results in excellent agreement at the cold end but leaves a cold bias at the warm end. The quadratic nonlinearity correction removes the remaining bias.

Fig. 5.
Fig. 5.

ICI radiometric sky images a) radiance image before water vapor correction; b) residual radiance image after water vapor correction; c) cloud-detection image thresholded at 2 W/(m2 sr) showing clouds in red and clear sky in blue. The image was recorded at Lamont, Oklahoma on 2003 April 16, 1643 UTC (precipitable water vapor = 2.3 cm, near-surface air temperature = 13°C). The color bar indicates radiance values for images a) and b) in units of W/(m2 sr).

Fig. 6.
Fig. 6.

Radiometric ICI images (see Table 2 for further information): a) cold, clear sky, NSA, 2004 Mar. 25; b) thin cirrus, NSA, 2004 Mar. 12; c) waves in altocumulus, SGP, 2003 Apr. 5; d) mixed altostratus clouds, MSU, 2005 Mar 8; e) clearing stratus edge, PFRR, 2000 Oct. 1; f) altocumulus, SGP, 2003 Mar. 22; g) birds flying below thick cirrus, SGP, 2003 Apr. 13; h) mixed low and mid-level clouds, PFRR, 2005 May 5; i) low, thick stratus, SGP, 2003 Apr. 16. All images are color coded for brightness temperature (°C) before water vapor correction, with blue = -80 °C and red = +20°C. Click on an image to see a larger version. [Media 1] [Media 2] [Media 3] [Media 4] [Media 5] [Media 6] [Media 7] [Media 8] [Media 9]

Fig. 7.
Fig. 7.

Wave clouds observed with the ICI at Lamont, Oklahoma on 2003 April 5, at 1942 UTC (pwv = 1.24 cm, T a = 14°C). The 13-s 480-kB movie shows ICI residual radiance images (water vapor corrected), obtained over the period 1930-1956 UTC, one frame per minute played back at two frames per second. [Media 10]

Tables (1)

Tables Icon

Table 2. Meteorological conditions, location, date, time, and derived cloud emissivity for ICI images in Fig. 6.

Equations (3)

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L = G ( DN ) + C ,
L c = L + ( 0.0014568 L 2 + 0.14905 L 0.90361 ) [ W / ( m 2 sr ) ] .
ε = L cld L a τ L bb ,

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