Abstract

A hand-held, battery-powered Fourier transform infrared spectroradiometer weighing 12.5 kg has been developed for the field measurement of spectral radiance from the Earth's surface and atmosphere in the 3−5-μm and 8−14-μm atmospheric windows, with a 6-cm−1 spectral resolution. Other versions of this instrument measure spectral radiance between 0.4 and 20 μm, using different optical materials and detectors, with maximum spectral resolutions of 1 cm−1. The instrument tested here has a measured noise-equivalent delta T of 0.01 °C, and it measures surface emissivities, in the field, with an accuracy of 0.02 or better in the 8−14-μm window (depending on atmospheric conditions), and within 0.04 in accessible regions of the 3−5-μm window. The unique, patented design of the interferometer has permitted operation in weather ranging from 0 to 45 °C and 0 to 100% relative humidity, and in vibration-intensive environments such as moving helicopters. The instrument has made field measurements of radiance and emissivity for 3 yr without loss of optical alignment. We describe the design of the instrument and discuss methods used to calibrate spectral radiance and calculate spectral emissivity from radiance measurements. Examples of emissivity spectra are shown for both the 3−5-μm and 8−14-μm atmospheric windows.

© 1996 Optical Society of America

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References

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  1. S. Hook, A. B. Kahle, “μFTIR—a new field spectrometer for validation of infrared data,,” Remote Sensing Environ. (to be published).
  2. M21—remote sensing chemical agent alarm (RSCAAL) (Brunswick Defense, Deland, Fla., 1992), pp. 1–24.
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    [CrossRef]
  6. R. A. Hanel, B. Schlachman, F. D. Clark, C. H. Prokesh, J. B. Taylor, W. M. Wilson, L. Chaney, “The Nimbus III Michelson interferometer,” Appl. Opt. 9, 1767–1774 (1970).
    [CrossRef] [PubMed]
  7. R. A. Hanel, D. Crosby, L. Herath, D. Vanous, D. Collins, H. Creswick, C. Harris, D. Rhodes, “Infrared spectrometer for Voyager,” Appl. Opt. 19, 1391–1400 (1980).
    [CrossRef] [PubMed]
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    [CrossRef]
  9. F. M. Luther, R. G. Ellingson, Y. Fouquart, S. Fels, N. A. Scott, W. J. Wiscombe, “Intercomparison of radiation codes in climate models (ICRCCM): longwave clearsky results—a workshop summary,” Am. Meterol. Soc. Bull. 69, 40–48 (1988).
  10. S. A. Ackerman, W. L. Smith, J. D. Spinhirne, H. E. Revercomb, “The 27–28 October 1986 FIRE IFO cirrus case study: spectral properties of cirrus clouds in the 8–12 μm window,” Mon. Weather Rev. 118, 2377–2388 (1990).
    [CrossRef]
  11. D. Lubin, “The role of the tropical super greenhouse effect in heating the ocean surface,” Science 265, 224–227 (1994).
    [CrossRef] [PubMed]
  12. R. J. Bell, Introductory Fourier Transfer Spectroscopy (Academic, New York, 1972), Chap. 1.
  13. H. E. Revercomb, H. Buijs, H. B. Howell, D. D. LaPorte, W. L. Smith, L. A. Sromovsky, “Radiometric calibration of IR Fourier transform spectrometers: solution to a problem with the high-resolution interferometer sounder,” Appl. Opt. 27, 3210–3218 (1988).
    [CrossRef] [PubMed]
  14. H. L. Buijs, “A class of high resolution ruggedized Fourier transform spectrometers,” in Multiple and/or High Throughput Spectroscopy, G. A. Vanasse, ed., Proc. Soc. Photo-Opt. Instrum. Eng.191, 116 (1979).
  15. H. L. Buijs, D. J. W. Kendall, G. Vail, J. N. Berube, “Fourier transform infrared hardware developments,” in 1981 International Conference on Fourier Transform Infrared Spectroscopy, H. Sakai, ed., Proc. Soc. Photo-Opt. Instrum. Eng.289, 322 (1981).
  16. Bomem FT-IR Spectroradiometer Catalog, (Bomen, Inc., Québec, Canada, 1993), p. 29.
  17. H. E. Revercomb, H. Buijs, H. B. Howell, R. O. Knuteson, D. D. LaPorte, W. L. Smith, L. A. Sromovsky, H. W. Wolf, “Radiometric calibration of IR interferometers: experience from the high-resolution interferometer sounder (HIS) aircraft instrument,” in RSRM 87: Advances in Remote Sensing Retrieval Methods, A. Deepak, H. E. Fleming, J. S. Theon, eds., (Deepak Publishing, Hampton, Va., 1989), pp. 89–102.
  18. J. W. Salisbury, D. M. D’Aria, “Emissivity of terrestrial materials in the 8–14μm atmospheric window,” Remote Sensing Environ. 42, 83–106 (1992).
    [CrossRef]
  19. A. B. Kahle, R. E. Alley, “Separation of temperature and emittance in remotely sensed radiance measurements,” Remote Sensing Environ. 42, 107–111 (1992).
    [CrossRef]
  20. J. W. Salisbury, D. M. D’Aria, “Emissivity of terrestrial materials in the 3–5 μm atmospheric window,” Remote Sensing Environ. 47, 345–361 (1994).
    [CrossRef]
  21. J. W. Salisbury, A. E. Wald, D. M. D’Aria, “Thermal-infrared remote sensing and Kirchhoff's law 1. Laboratory measurements,” J. Geophys. Res. 99, 11,897–11,911 (1994).
    [CrossRef]

1994 (3)

D. Lubin, “The role of the tropical super greenhouse effect in heating the ocean surface,” Science 265, 224–227 (1994).
[CrossRef] [PubMed]

J. W. Salisbury, D. M. D’Aria, “Emissivity of terrestrial materials in the 3–5 μm atmospheric window,” Remote Sensing Environ. 47, 345–361 (1994).
[CrossRef]

J. W. Salisbury, A. E. Wald, D. M. D’Aria, “Thermal-infrared remote sensing and Kirchhoff's law 1. Laboratory measurements,” J. Geophys. Res. 99, 11,897–11,911 (1994).
[CrossRef]

1992 (2)

J. W. Salisbury, D. M. D’Aria, “Emissivity of terrestrial materials in the 8–14μm atmospheric window,” Remote Sensing Environ. 42, 83–106 (1992).
[CrossRef]

A. B. Kahle, R. E. Alley, “Separation of temperature and emittance in remotely sensed radiance measurements,” Remote Sensing Environ. 42, 107–111 (1992).
[CrossRef]

1990 (1)

S. A. Ackerman, W. L. Smith, J. D. Spinhirne, H. E. Revercomb, “The 27–28 October 1986 FIRE IFO cirrus case study: spectral properties of cirrus clouds in the 8–12 μm window,” Mon. Weather Rev. 118, 2377–2388 (1990).
[CrossRef]

1988 (4)

1980 (1)

1970 (1)

1964 (1)

Ackerman, S. A.

S. A. Ackerman, W. L. Smith, J. D. Spinhirne, H. E. Revercomb, “The 27–28 October 1986 FIRE IFO cirrus case study: spectral properties of cirrus clouds in the 8–12 μm window,” Mon. Weather Rev. 118, 2377–2388 (1990).
[CrossRef]

Alley, R. E.

A. B. Kahle, R. E. Alley, “Separation of temperature and emittance in remotely sensed radiance measurements,” Remote Sensing Environ. 42, 107–111 (1992).
[CrossRef]

Bell, R. J.

R. J. Bell, Introductory Fourier Transfer Spectroscopy (Academic, New York, 1972), Chap. 1.

Berube, J. N.

H. L. Buijs, D. J. W. Kendall, G. Vail, J. N. Berube, “Fourier transform infrared hardware developments,” in 1981 International Conference on Fourier Transform Infrared Spectroscopy, H. Sakai, ed., Proc. Soc. Photo-Opt. Instrum. Eng.289, 322 (1981).

Block, L. C.

Brasunas, J. C.

Buijs, H.

H. E. Revercomb, H. Buijs, H. B. Howell, D. D. LaPorte, W. L. Smith, L. A. Sromovsky, “Radiometric calibration of IR Fourier transform spectrometers: solution to a problem with the high-resolution interferometer sounder,” Appl. Opt. 27, 3210–3218 (1988).
[CrossRef] [PubMed]

H. E. Revercomb, H. Buijs, H. B. Howell, R. O. Knuteson, D. D. LaPorte, W. L. Smith, L. A. Sromovsky, H. W. Wolf, “Radiometric calibration of IR interferometers: experience from the high-resolution interferometer sounder (HIS) aircraft instrument,” in RSRM 87: Advances in Remote Sensing Retrieval Methods, A. Deepak, H. E. Fleming, J. S. Theon, eds., (Deepak Publishing, Hampton, Va., 1989), pp. 89–102.

Buijs, H. L.

H. L. Buijs, “A class of high resolution ruggedized Fourier transform spectrometers,” in Multiple and/or High Throughput Spectroscopy, G. A. Vanasse, ed., Proc. Soc. Photo-Opt. Instrum. Eng.191, 116 (1979).

H. L. Buijs, D. J. W. Kendall, G. Vail, J. N. Berube, “Fourier transform infrared hardware developments,” in 1981 International Conference on Fourier Transform Infrared Spectroscopy, H. Sakai, ed., Proc. Soc. Photo-Opt. Instrum. Eng.289, 322 (1981).

Carlson, R. C.

Chaney, L.

Clark, F. D.

Collins, D.

Creswick, H.

Crosby, D.

D’Aria, D. M.

J. W. Salisbury, D. M. D’Aria, “Emissivity of terrestrial materials in the 3–5 μm atmospheric window,” Remote Sensing Environ. 47, 345–361 (1994).
[CrossRef]

J. W. Salisbury, A. E. Wald, D. M. D’Aria, “Thermal-infrared remote sensing and Kirchhoff's law 1. Laboratory measurements,” J. Geophys. Res. 99, 11,897–11,911 (1994).
[CrossRef]

J. W. Salisbury, D. M. D’Aria, “Emissivity of terrestrial materials in the 8–14μm atmospheric window,” Remote Sensing Environ. 42, 83–106 (1992).
[CrossRef]

Ellingson, R. G.

F. M. Luther, R. G. Ellingson, Y. Fouquart, S. Fels, N. A. Scott, W. J. Wiscombe, “Intercomparison of radiation codes in climate models (ICRCCM): longwave clearsky results—a workshop summary,” Am. Meterol. Soc. Bull. 69, 40–48 (1988).

Fels, S.

F. M. Luther, R. G. Ellingson, Y. Fouquart, S. Fels, N. A. Scott, W. J. Wiscombe, “Intercomparison of radiation codes in climate models (ICRCCM): longwave clearsky results—a workshop summary,” Am. Meterol. Soc. Bull. 69, 40–48 (1988).

Fouquart, Y.

F. M. Luther, R. G. Ellingson, Y. Fouquart, S. Fels, N. A. Scott, W. J. Wiscombe, “Intercomparison of radiation codes in climate models (ICRCCM): longwave clearsky results—a workshop summary,” Am. Meterol. Soc. Bull. 69, 40–48 (1988).

Hanel, R. A.

Harris, C.

Hayden, A. F.

Herath, L.

Herath, L. W.

Hook, S.

S. Hook, A. B. Kahle, “μFTIR—a new field spectrometer for validation of infrared data,,” Remote Sensing Environ. (to be published).

Howell, H. B.

H. E. Revercomb, H. Buijs, H. B. Howell, D. D. LaPorte, W. L. Smith, L. A. Sromovsky, “Radiometric calibration of IR Fourier transform spectrometers: solution to a problem with the high-resolution interferometer sounder,” Appl. Opt. 27, 3210–3218 (1988).
[CrossRef] [PubMed]

H. E. Revercomb, H. Buijs, H. B. Howell, R. O. Knuteson, D. D. LaPorte, W. L. Smith, L. A. Sromovsky, H. W. Wolf, “Radiometric calibration of IR interferometers: experience from the high-resolution interferometer sounder (HIS) aircraft instrument,” in RSRM 87: Advances in Remote Sensing Retrieval Methods, A. Deepak, H. E. Fleming, J. S. Theon, eds., (Deepak Publishing, Hampton, Va., 1989), pp. 89–102.

Kahle, A. B.

A. B. Kahle, R. E. Alley, “Separation of temperature and emittance in remotely sensed radiance measurements,” Remote Sensing Environ. 42, 107–111 (1992).
[CrossRef]

S. Hook, A. B. Kahle, “μFTIR—a new field spectrometer for validation of infrared data,,” Remote Sensing Environ. (to be published).

Kendall, D. J. W.

H. L. Buijs, D. J. W. Kendall, G. Vail, J. N. Berube, “Fourier transform infrared hardware developments,” in 1981 International Conference on Fourier Transform Infrared Spectroscopy, H. Sakai, ed., Proc. Soc. Photo-Opt. Instrum. Eng.289, 322 (1981).

Knuteson, R. O.

H. E. Revercomb, H. Buijs, H. B. Howell, R. O. Knuteson, D. D. LaPorte, W. L. Smith, L. A. Sromovsky, H. W. Wolf, “Radiometric calibration of IR interferometers: experience from the high-resolution interferometer sounder (HIS) aircraft instrument,” in RSRM 87: Advances in Remote Sensing Retrieval Methods, A. Deepak, H. E. Fleming, J. S. Theon, eds., (Deepak Publishing, Hampton, Va., 1989), pp. 89–102.

Kunde, V. G.

LaPorte, D. D.

H. E. Revercomb, H. Buijs, H. B. Howell, D. D. LaPorte, W. L. Smith, L. A. Sromovsky, “Radiometric calibration of IR Fourier transform spectrometers: solution to a problem with the high-resolution interferometer sounder,” Appl. Opt. 27, 3210–3218 (1988).
[CrossRef] [PubMed]

H. E. Revercomb, H. Buijs, H. B. Howell, R. O. Knuteson, D. D. LaPorte, W. L. Smith, L. A. Sromovsky, H. W. Wolf, “Radiometric calibration of IR interferometers: experience from the high-resolution interferometer sounder (HIS) aircraft instrument,” in RSRM 87: Advances in Remote Sensing Retrieval Methods, A. Deepak, H. E. Fleming, J. S. Theon, eds., (Deepak Publishing, Hampton, Va., 1989), pp. 89–102.

Lubin, D.

D. Lubin, “The role of the tropical super greenhouse effect in heating the ocean surface,” Science 265, 224–227 (1994).
[CrossRef] [PubMed]

Luther, F. M.

F. M. Luther, R. G. Ellingson, Y. Fouquart, S. Fels, N. A. Scott, W. J. Wiscombe, “Intercomparison of radiation codes in climate models (ICRCCM): longwave clearsky results—a workshop summary,” Am. Meterol. Soc. Bull. 69, 40–48 (1988).

Prokesh, C. H.

Revercomb, H. E.

S. A. Ackerman, W. L. Smith, J. D. Spinhirne, H. E. Revercomb, “The 27–28 October 1986 FIRE IFO cirrus case study: spectral properties of cirrus clouds in the 8–12 μm window,” Mon. Weather Rev. 118, 2377–2388 (1990).
[CrossRef]

H. E. Revercomb, H. Buijs, H. B. Howell, D. D. LaPorte, W. L. Smith, L. A. Sromovsky, “Radiometric calibration of IR Fourier transform spectrometers: solution to a problem with the high-resolution interferometer sounder,” Appl. Opt. 27, 3210–3218 (1988).
[CrossRef] [PubMed]

H. E. Revercomb, H. Buijs, H. B. Howell, R. O. Knuteson, D. D. LaPorte, W. L. Smith, L. A. Sromovsky, H. W. Wolf, “Radiometric calibration of IR interferometers: experience from the high-resolution interferometer sounder (HIS) aircraft instrument,” in RSRM 87: Advances in Remote Sensing Retrieval Methods, A. Deepak, H. E. Fleming, J. S. Theon, eds., (Deepak Publishing, Hampton, Va., 1989), pp. 89–102.

Rhodes, D.

Salisbury, J. W.

J. W. Salisbury, D. M. D’Aria, “Emissivity of terrestrial materials in the 3–5 μm atmospheric window,” Remote Sensing Environ. 47, 345–361 (1994).
[CrossRef]

J. W. Salisbury, A. E. Wald, D. M. D’Aria, “Thermal-infrared remote sensing and Kirchhoff's law 1. Laboratory measurements,” J. Geophys. Res. 99, 11,897–11,911 (1994).
[CrossRef]

J. W. Salisbury, D. M. D’Aria, “Emissivity of terrestrial materials in the 8–14μm atmospheric window,” Remote Sensing Environ. 42, 83–106 (1992).
[CrossRef]

J. W. Salisbury, “First use of a new portable thermal infrared spectrometer,” in Proceedings of the Tenth Annual IEEE International Geoscience and Remote Sensing Symposium (Institute of Electrical and Electronics Engineers, New York, 1990), pp. 1775–1778.
[CrossRef]

Schlachman, B.

Scott, N. A.

F. M. Luther, R. G. Ellingson, Y. Fouquart, S. Fels, N. A. Scott, W. J. Wiscombe, “Intercomparison of radiation codes in climate models (ICRCCM): longwave clearsky results—a workshop summary,” Am. Meterol. Soc. Bull. 69, 40–48 (1988).

Smith, W. L.

S. A. Ackerman, W. L. Smith, J. D. Spinhirne, H. E. Revercomb, “The 27–28 October 1986 FIRE IFO cirrus case study: spectral properties of cirrus clouds in the 8–12 μm window,” Mon. Weather Rev. 118, 2377–2388 (1990).
[CrossRef]

H. E. Revercomb, H. Buijs, H. B. Howell, D. D. LaPorte, W. L. Smith, L. A. Sromovsky, “Radiometric calibration of IR Fourier transform spectrometers: solution to a problem with the high-resolution interferometer sounder,” Appl. Opt. 27, 3210–3218 (1988).
[CrossRef] [PubMed]

H. E. Revercomb, H. Buijs, H. B. Howell, R. O. Knuteson, D. D. LaPorte, W. L. Smith, L. A. Sromovsky, H. W. Wolf, “Radiometric calibration of IR interferometers: experience from the high-resolution interferometer sounder (HIS) aircraft instrument,” in RSRM 87: Advances in Remote Sensing Retrieval Methods, A. Deepak, H. E. Fleming, J. S. Theon, eds., (Deepak Publishing, Hampton, Va., 1989), pp. 89–102.

Spinhirne, J. D.

S. A. Ackerman, W. L. Smith, J. D. Spinhirne, H. E. Revercomb, “The 27–28 October 1986 FIRE IFO cirrus case study: spectral properties of cirrus clouds in the 8–12 μm window,” Mon. Weather Rev. 118, 2377–2388 (1990).
[CrossRef]

Sromovsky, L. A.

H. E. Revercomb, H. Buijs, H. B. Howell, D. D. LaPorte, W. L. Smith, L. A. Sromovsky, “Radiometric calibration of IR Fourier transform spectrometers: solution to a problem with the high-resolution interferometer sounder,” Appl. Opt. 27, 3210–3218 (1988).
[CrossRef] [PubMed]

H. E. Revercomb, H. Buijs, H. B. Howell, R. O. Knuteson, D. D. LaPorte, W. L. Smith, L. A. Sromovsky, H. W. Wolf, “Radiometric calibration of IR interferometers: experience from the high-resolution interferometer sounder (HIS) aircraft instrument,” in RSRM 87: Advances in Remote Sensing Retrieval Methods, A. Deepak, H. E. Fleming, J. S. Theon, eds., (Deepak Publishing, Hampton, Va., 1989), pp. 89–102.

Taylor, J. B.

Telfair, W. B.

Vail, G.

H. L. Buijs, D. J. W. Kendall, G. Vail, J. N. Berube, “Fourier transform infrared hardware developments,” in 1981 International Conference on Fourier Transform Infrared Spectroscopy, H. Sakai, ed., Proc. Soc. Photo-Opt. Instrum. Eng.289, 322 (1981).

Vanous, D.

Wald, A. E.

J. W. Salisbury, A. E. Wald, D. M. D’Aria, “Thermal-infrared remote sensing and Kirchhoff's law 1. Laboratory measurements,” J. Geophys. Res. 99, 11,897–11,911 (1994).
[CrossRef]

Wilson, W. M.

Wiscombe, W. J.

F. M. Luther, R. G. Ellingson, Y. Fouquart, S. Fels, N. A. Scott, W. J. Wiscombe, “Intercomparison of radiation codes in climate models (ICRCCM): longwave clearsky results—a workshop summary,” Am. Meterol. Soc. Bull. 69, 40–48 (1988).

Wolf, H. W.

H. E. Revercomb, H. Buijs, H. B. Howell, R. O. Knuteson, D. D. LaPorte, W. L. Smith, L. A. Sromovsky, H. W. Wolf, “Radiometric calibration of IR interferometers: experience from the high-resolution interferometer sounder (HIS) aircraft instrument,” in RSRM 87: Advances in Remote Sensing Retrieval Methods, A. Deepak, H. E. Fleming, J. S. Theon, eds., (Deepak Publishing, Hampton, Va., 1989), pp. 89–102.

Zachor, A. S.

Am. Meterol. Soc. Bull. (1)

F. M. Luther, R. G. Ellingson, Y. Fouquart, S. Fels, N. A. Scott, W. J. Wiscombe, “Intercomparison of radiation codes in climate models (ICRCCM): longwave clearsky results—a workshop summary,” Am. Meterol. Soc. Bull. 69, 40–48 (1988).

Appl. Opt. (6)

J. Geophys. Res. (1)

J. W. Salisbury, A. E. Wald, D. M. D’Aria, “Thermal-infrared remote sensing and Kirchhoff's law 1. Laboratory measurements,” J. Geophys. Res. 99, 11,897–11,911 (1994).
[CrossRef]

Mon. Weather Rev. (1)

S. A. Ackerman, W. L. Smith, J. D. Spinhirne, H. E. Revercomb, “The 27–28 October 1986 FIRE IFO cirrus case study: spectral properties of cirrus clouds in the 8–12 μm window,” Mon. Weather Rev. 118, 2377–2388 (1990).
[CrossRef]

Remote Sensing Environ. (3)

J. W. Salisbury, D. M. D’Aria, “Emissivity of terrestrial materials in the 8–14μm atmospheric window,” Remote Sensing Environ. 42, 83–106 (1992).
[CrossRef]

A. B. Kahle, R. E. Alley, “Separation of temperature and emittance in remotely sensed radiance measurements,” Remote Sensing Environ. 42, 107–111 (1992).
[CrossRef]

J. W. Salisbury, D. M. D’Aria, “Emissivity of terrestrial materials in the 3–5 μm atmospheric window,” Remote Sensing Environ. 47, 345–361 (1994).
[CrossRef]

Science (1)

D. Lubin, “The role of the tropical super greenhouse effect in heating the ocean surface,” Science 265, 224–227 (1994).
[CrossRef] [PubMed]

Other (8)

R. J. Bell, Introductory Fourier Transfer Spectroscopy (Academic, New York, 1972), Chap. 1.

J. W. Salisbury, “First use of a new portable thermal infrared spectrometer,” in Proceedings of the Tenth Annual IEEE International Geoscience and Remote Sensing Symposium (Institute of Electrical and Electronics Engineers, New York, 1990), pp. 1775–1778.
[CrossRef]

S. Hook, A. B. Kahle, “μFTIR—a new field spectrometer for validation of infrared data,,” Remote Sensing Environ. (to be published).

M21—remote sensing chemical agent alarm (RSCAAL) (Brunswick Defense, Deland, Fla., 1992), pp. 1–24.

H. L. Buijs, “A class of high resolution ruggedized Fourier transform spectrometers,” in Multiple and/or High Throughput Spectroscopy, G. A. Vanasse, ed., Proc. Soc. Photo-Opt. Instrum. Eng.191, 116 (1979).

H. L. Buijs, D. J. W. Kendall, G. Vail, J. N. Berube, “Fourier transform infrared hardware developments,” in 1981 International Conference on Fourier Transform Infrared Spectroscopy, H. Sakai, ed., Proc. Soc. Photo-Opt. Instrum. Eng.289, 322 (1981).

Bomem FT-IR Spectroradiometer Catalog, (Bomen, Inc., Québec, Canada, 1993), p. 29.

H. E. Revercomb, H. Buijs, H. B. Howell, R. O. Knuteson, D. D. LaPorte, W. L. Smith, L. A. Sromovsky, H. W. Wolf, “Radiometric calibration of IR interferometers: experience from the high-resolution interferometer sounder (HIS) aircraft instrument,” in RSRM 87: Advances in Remote Sensing Retrieval Methods, A. Deepak, H. E. Fleming, J. S. Theon, eds., (Deepak Publishing, Hampton, Va., 1989), pp. 89–102.

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Figures (13)

Fig. 1.
Fig. 1.

(a) Schematic of the μFTIR interferometer showing the path difference achieved by the offset of one of the KBr prisms by distance S (in centimeters). In practice, both prisms are offset by distance S in opposite directions to increase the path length difference. The resolution of the interferometer (in inverse centimeters) is 1/4Sn sin(θ), where n is the index of refraction of KBr and θ is the angle between the direction of motion and the mirrored sides of the prisms. (b) Diagram showing the μFTIR optical module. The thermoelectric enclosure is indicated by the dashed lines; MCT, mercury cadmium telluride.

Fig. 2.
Fig. 2.

Uncalibrated instrument radiances of quartz sand, DWR, and blackbody measurements at 25 °C and 40 °C, measured in Florida at an air temperature of 40 °C and at 95% relative humidity, under partly cloudy skies; WBB, warm blackbody; CBB, cold blackbody.

Fig. 3.
Fig. 3.

(a) Calibrated radiances of 75−250 μm quartz sand (solid curves) and DWR's (dashed curves) measured in Nevada at an air temperature of 29 °C and at 9% relative humidity, under clear skies. The DWR spectra were corrected for emission from the diffuse gold plate. The smooth portions of quartz spectra are regions of high emissivity (low reflectance) characterized primarily by the Planck function representing the quartz temperature. The two broad quartz radiance minima between 8 and 9.5 μm are fundamental molecular vibration bands (reststrahlen bands) of quartz combined with reflected DWR emission lines from atmospheric water vapor. The DWR spectra show water vapor line emission features in the 7−9-μm region, the ozone doublet bands near 9.6 μm, and continuum emission with line emission features superimposed from 10 μm to the 14-μm band of CO2 emission lines. This spectral region contains a calibration artifact caused by the nonlinear response to cold targets that peaks at 11.8 μm (see Subsection 4.D). (b) Four calibrated radiance curves for the same quartz sand measured in Florida at an air temperature of 40 °C and at 95% relative humidity, under partly cloudy skies. The quartz radiances (solid curves) show more structure because of reflection of stronger water vapor line emission features than those in (a). The three DWR spectra (dashed curves) vary considerably as a result of meteorological conditions changing over a time period of 30 min. The calibration artifact from nonlinear response to low-radiance targets is not observed in these spectra, because increased emission from water vapor raises the DWR above the nonlinear threshold.

Fig. 4.
Fig. 4.

Spectral signal-to-noise ratio from a single 1-s scan of a 25 °C blackbody for InSb and HgCdTe detectors. The signal-to-noise ratio was calculated when the uncalibrated instrument response to the blackbody at each wavelength was divided by the rms variation of instrument response over 462 spectral points between 1.55 and 2.0 μm, where the variation is only from noise.

Fig. 5.
Fig. 5.

Plot of noise-equivalent delta T (NEΔT) for the InSb and HgCdTe detectors, observing a 25 °C blackbody for 1 s. The spectra were calculated when the difference in brightness temperatures between a 25 °C blackbody spectrum and a 25 °C blackbody spectrum with the rms noise subtracted was found.

Fig. 6.
Fig. 6.

Plot showing the relative contributions to the IR field of view of the instrument averaged over the 8−14-μm instrument bandpass. This plot was constructed from measurements of the peak-to-peak height of interferograms from a hot soldering iron at a distance of 110 cm, as a function of position relative to the 9-cm diameter of the circular, visible field of view. The background response far outside the field of view was subtracted, and the difference was normalized when it was divided by the response difference in the center of the field of view. The normalized values were divided into ten levels of equal response, shown in the plot. The X axis is parallel to the long side of the instrument enclosure, and the Y axis is parallel to the short side of the instrument enclosure.

Fig. 7.
Fig. 7.

Blackbody emissivity spectrum calculated from the measurement of DHR.

Fig. 8.
Fig. 8.

Instrument responsivity calculation over 5° intervals at 10 and 12 μm, as a function of source brightness temperature. Instrument responsivity was calculated with responsivity Eq. (4).

Fig. 9.
Fig. 9.

Radiances from aluminum at liquid-nitrogen (LN2) temperature calibrated with two different calibration sets.

Fig. 10.
Fig. 10.

Four emissivity spectra calculated from the quartz and DWR spectra shown in (a) Fig. 3(a), (b) Fig. 3(b).

Fig. 11.
Fig. 11.

Comparison of average quartz sand emissivity measured under (a) stable atmospheric conditions with low water vapor content to an emissivity calculated from laboratory measurements of DHR, (b) unstable atmospheric conditions with high water vapor content to an emissivity calculated from laboratory measurements of DHR.

Fig. 12.
Fig. 12.

Average emissivity calculated from four measurements of fine (<75 μm) quartz powder, compared with an emissivity calculated from laboratory measurements of DHR.

Fig. 13.
Fig. 13.

Measurements of emission from an air path at ambient temperature by the μFTIR mounted in a van driving down a dirt road at 56 kph, compared with a stationary measurement.

Tables (1)

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Table 1. Instrument Components Listed with Weight, Dimensions, and the Time-Averaged Power Requirements

Equations (11)

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V S ( λ ) = r ( λ ) L S , meas ( λ ) r ( λ ) L ( λ , T inst ) ,
S ( λ ) = 1 R S ( λ ) .
L S ( λ) = S ( λ ) B ( λ , T S ) + [ 1 S ( λ ) ] L DWR ( λ ) ,
r ( λ ) = V H ( λ ) V A ( λ ) B ( T H , λ ) B ( T A , λ ) .
L 0 ( λ , T inst ) = B ( T A , λ ) [ V A ( λ ) / r ( λ ) ] .
L S ( λ ) = V S ( λ ) / r ( λ ) + L 0 ( λ , T inst ) .
L DWR, meas ( λ ) = L DWR ( λ ) [ 1 G ( λ ) ] + G ( λ ) B ( T G , λ ) ,
L DWR ( λ ) = L DWR, meas ( λ ) G ( λ ) B ( T G , λ ) [ 1 G ( λ ) ] .
S ( λ ) = L S ( λ ) L DWR ( λ ) B ( λ , T S ) L DWR ( λ ) ,
T ( λ ) = 14387.9 λ    × 1 ln ( { 3.7418 × 10 8 / [ λ 5 × L S ( λ ) ] } + 1 ) .
B ( λ max , T ) = L S ( λ ) L DWR ( λ ) max ( λ ) + L DWR ( λ ) .

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