Abstract

We discuss and evaluate a long wave infrared imaging spectrometer in terms of its opto-mechanical design and analysis, alignment, testing, and calibration. The instrument is a practical airborne sensor achieving high spectral resolution and sensitive noise equivalent delta temperature. The instrument operates in the 8 to 12.5 μm spectral region with 28.85 nm spectral sampling, 1 mrad instantaneous field of view, and >40° cross track field. The instrument comprises three uniform sub-modules with identical design parameters and performances. The sub-module design is based on a refractive foreoptics feeding an all-reflective spectrometer. The optical form of the spectrometer is a double-pass reflective triplet with a flat grating, which has a fast f/2 and high optical throughput. Cryogenic optics of 100 K is implemented only for the spectrometer. Assembly and thermal deformation and focusing adjustment design are particularly considered for this low temperature. All the mirrors of the spectrometer are opto-mechanical-integrated designed and manufactured by single-point diamond turning technology. We consider the center sub-module as an example, and we present its laboratory testing results and calibration; the results indicate the instrument’s potential value in airborne sensing.

© 2017 Optical Society of America

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References

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  1. W. R. Johnson, S. J. Hook, P. Z. Mouroulis, D. W. Wilson, S. D. Gunapala, C. J. Hill, J. M. Mumolo, and B. T. Eng, “QWEST: Quantum well infrared earth science testbed,” Proc. SPIE 7086, 708606 (2008).
    [Crossref]
  2. J. L. Hall, R. H. Boucher, D. J. Gutierrez, S. J. Hansel, B. P. Kasper, E. R. Keim, N. M. Moreno, M. L. Polak, M. G. Sivjee, D. M. Tratt, and D. W. Warren, “First flights of a new airborne thermal infrared imaging spectrometer with high area coverage,” Proc. SPIE 8012, 801203 (2011).
    [Crossref]
  3. W. R. Johnson, G. Hulley, and S. J. Hook, “Remote gas plume sensing and imaging with NASA’s Hyperspectral Thermal Emission Spectrometer (HyTES),” Proc. SPIE 9101, 91010V (2014).
    [Crossref]
  4. P. Mouroulis, R. O. Green, and T. G. Chrien, “Design of pushbroom imaging spectrometers for optimum recovery of spectroscopic and spatial information,” Appl. Opt. 39(13), 2210–2220 (2000).
    [Crossref] [PubMed]
  5. P. Mouroulis, R. O. Green, and D. W. Wilson, “Optical design of a coastal ocean imaging spectrometer,” Opt. Express 16(12), 9087–9096 (2008).
    [Crossref] [PubMed]
  6. P. Mouroulis, B. Van Gorp, R. O. Green, H. Dierssen, D. W. Wilson, M. Eastwood, J. Boardman, B. C. Gao, D. Cohen, B. Franklin, F. Loya, S. Lundeen, A. Mazer, I. McCubbin, D. Randall, B. Richardson, J. I. Rodriguez, C. Sarture, E. Urquiza, R. Vargas, V. White, and K. Yee, “Portable remote imaging spectrometer coastal ocean sensor: design, characteristics, and first flight results,” Appl. Opt. 53(7), 1363–1380 (2014).
    [Crossref] [PubMed]
  7. D. W. Warren, D. J. Gutierrez, and E. R. Keim, “Dyson spectrometers for high-performance infrared applications,” Opt. Eng. 47(10), 103601 (2008).
    [Crossref]
  8. L. G. Cook, “Reflective optical triplet having a real entrance pupil,” United States Patent 4,733,955 (1988).
  9. L. G. Cook, “Compact all-reflective imaging spectrometer,” United States Patent 5,260,767 (1993).
  10. L. G. Cook, “High-resolution, all-reflective imaging spectrometer,” United States Patent 6,886,953 (2005).
  11. L. G. Cook, “High-resolution, all-reflective imaging spectrometer,” United States Patent 7,080,912 (2006).
  12. L. G. Cook, “Two-channel imaging spectrometer utilizing shared objective, collimating, and imaging optics,” United States Patent 7,382,498 (2008).
  13. J. Pan, The design, manufacture and test of the aspherical optical surfaces (Suzhou University, 2004), Chap. 5.
  14. L. G. Cook and J. F. Silny, “Imaging spectrometer trade studies: a detailed comparison of the Offner-Chrisp and reflective triplet optical design forms,” Proc. SPIE 7813, 78130F (2010).
    [Crossref]
  15. E. Liu, Y. Wu, Y. Wang, J. Wen, G. Lv, C. Li, J. Hou, and L. Yuan, “The development of a cryogenic integrated system with the working temperature of 100K,” Proc. SPIE 9821, 98210B (2016).
  16. L. Yuan, Z. He, Y. Wang, and G. Lv, “Manufacture, alignment and measurement for a reflective triplet optics in imaging spectrometer,” Proc. SPIE 9684, 96840B (2016).

2016 (2)

E. Liu, Y. Wu, Y. Wang, J. Wen, G. Lv, C. Li, J. Hou, and L. Yuan, “The development of a cryogenic integrated system with the working temperature of 100K,” Proc. SPIE 9821, 98210B (2016).

L. Yuan, Z. He, Y. Wang, and G. Lv, “Manufacture, alignment and measurement for a reflective triplet optics in imaging spectrometer,” Proc. SPIE 9684, 96840B (2016).

2014 (2)

2011 (1)

J. L. Hall, R. H. Boucher, D. J. Gutierrez, S. J. Hansel, B. P. Kasper, E. R. Keim, N. M. Moreno, M. L. Polak, M. G. Sivjee, D. M. Tratt, and D. W. Warren, “First flights of a new airborne thermal infrared imaging spectrometer with high area coverage,” Proc. SPIE 8012, 801203 (2011).
[Crossref]

2010 (1)

L. G. Cook and J. F. Silny, “Imaging spectrometer trade studies: a detailed comparison of the Offner-Chrisp and reflective triplet optical design forms,” Proc. SPIE 7813, 78130F (2010).
[Crossref]

2008 (3)

P. Mouroulis, R. O. Green, and D. W. Wilson, “Optical design of a coastal ocean imaging spectrometer,” Opt. Express 16(12), 9087–9096 (2008).
[Crossref] [PubMed]

D. W. Warren, D. J. Gutierrez, and E. R. Keim, “Dyson spectrometers for high-performance infrared applications,” Opt. Eng. 47(10), 103601 (2008).
[Crossref]

W. R. Johnson, S. J. Hook, P. Z. Mouroulis, D. W. Wilson, S. D. Gunapala, C. J. Hill, J. M. Mumolo, and B. T. Eng, “QWEST: Quantum well infrared earth science testbed,” Proc. SPIE 7086, 708606 (2008).
[Crossref]

2000 (1)

Boardman, J.

Boucher, R. H.

J. L. Hall, R. H. Boucher, D. J. Gutierrez, S. J. Hansel, B. P. Kasper, E. R. Keim, N. M. Moreno, M. L. Polak, M. G. Sivjee, D. M. Tratt, and D. W. Warren, “First flights of a new airborne thermal infrared imaging spectrometer with high area coverage,” Proc. SPIE 8012, 801203 (2011).
[Crossref]

Chrien, T. G.

Cohen, D.

Cook, L. G.

L. G. Cook and J. F. Silny, “Imaging spectrometer trade studies: a detailed comparison of the Offner-Chrisp and reflective triplet optical design forms,” Proc. SPIE 7813, 78130F (2010).
[Crossref]

Dierssen, H.

Eastwood, M.

Eng, B. T.

W. R. Johnson, S. J. Hook, P. Z. Mouroulis, D. W. Wilson, S. D. Gunapala, C. J. Hill, J. M. Mumolo, and B. T. Eng, “QWEST: Quantum well infrared earth science testbed,” Proc. SPIE 7086, 708606 (2008).
[Crossref]

Franklin, B.

Gao, B. C.

Green, R. O.

Gunapala, S. D.

W. R. Johnson, S. J. Hook, P. Z. Mouroulis, D. W. Wilson, S. D. Gunapala, C. J. Hill, J. M. Mumolo, and B. T. Eng, “QWEST: Quantum well infrared earth science testbed,” Proc. SPIE 7086, 708606 (2008).
[Crossref]

Gutierrez, D. J.

J. L. Hall, R. H. Boucher, D. J. Gutierrez, S. J. Hansel, B. P. Kasper, E. R. Keim, N. M. Moreno, M. L. Polak, M. G. Sivjee, D. M. Tratt, and D. W. Warren, “First flights of a new airborne thermal infrared imaging spectrometer with high area coverage,” Proc. SPIE 8012, 801203 (2011).
[Crossref]

D. W. Warren, D. J. Gutierrez, and E. R. Keim, “Dyson spectrometers for high-performance infrared applications,” Opt. Eng. 47(10), 103601 (2008).
[Crossref]

Hall, J. L.

J. L. Hall, R. H. Boucher, D. J. Gutierrez, S. J. Hansel, B. P. Kasper, E. R. Keim, N. M. Moreno, M. L. Polak, M. G. Sivjee, D. M. Tratt, and D. W. Warren, “First flights of a new airborne thermal infrared imaging spectrometer with high area coverage,” Proc. SPIE 8012, 801203 (2011).
[Crossref]

Hansel, S. J.

J. L. Hall, R. H. Boucher, D. J. Gutierrez, S. J. Hansel, B. P. Kasper, E. R. Keim, N. M. Moreno, M. L. Polak, M. G. Sivjee, D. M. Tratt, and D. W. Warren, “First flights of a new airborne thermal infrared imaging spectrometer with high area coverage,” Proc. SPIE 8012, 801203 (2011).
[Crossref]

He, Z.

L. Yuan, Z. He, Y. Wang, and G. Lv, “Manufacture, alignment and measurement for a reflective triplet optics in imaging spectrometer,” Proc. SPIE 9684, 96840B (2016).

Hill, C. J.

W. R. Johnson, S. J. Hook, P. Z. Mouroulis, D. W. Wilson, S. D. Gunapala, C. J. Hill, J. M. Mumolo, and B. T. Eng, “QWEST: Quantum well infrared earth science testbed,” Proc. SPIE 7086, 708606 (2008).
[Crossref]

Hook, S. J.

W. R. Johnson, G. Hulley, and S. J. Hook, “Remote gas plume sensing and imaging with NASA’s Hyperspectral Thermal Emission Spectrometer (HyTES),” Proc. SPIE 9101, 91010V (2014).
[Crossref]

W. R. Johnson, S. J. Hook, P. Z. Mouroulis, D. W. Wilson, S. D. Gunapala, C. J. Hill, J. M. Mumolo, and B. T. Eng, “QWEST: Quantum well infrared earth science testbed,” Proc. SPIE 7086, 708606 (2008).
[Crossref]

Hou, J.

E. Liu, Y. Wu, Y. Wang, J. Wen, G. Lv, C. Li, J. Hou, and L. Yuan, “The development of a cryogenic integrated system with the working temperature of 100K,” Proc. SPIE 9821, 98210B (2016).

Hulley, G.

W. R. Johnson, G. Hulley, and S. J. Hook, “Remote gas plume sensing and imaging with NASA’s Hyperspectral Thermal Emission Spectrometer (HyTES),” Proc. SPIE 9101, 91010V (2014).
[Crossref]

Johnson, W. R.

W. R. Johnson, G. Hulley, and S. J. Hook, “Remote gas plume sensing and imaging with NASA’s Hyperspectral Thermal Emission Spectrometer (HyTES),” Proc. SPIE 9101, 91010V (2014).
[Crossref]

W. R. Johnson, S. J. Hook, P. Z. Mouroulis, D. W. Wilson, S. D. Gunapala, C. J. Hill, J. M. Mumolo, and B. T. Eng, “QWEST: Quantum well infrared earth science testbed,” Proc. SPIE 7086, 708606 (2008).
[Crossref]

Kasper, B. P.

J. L. Hall, R. H. Boucher, D. J. Gutierrez, S. J. Hansel, B. P. Kasper, E. R. Keim, N. M. Moreno, M. L. Polak, M. G. Sivjee, D. M. Tratt, and D. W. Warren, “First flights of a new airborne thermal infrared imaging spectrometer with high area coverage,” Proc. SPIE 8012, 801203 (2011).
[Crossref]

Keim, E. R.

J. L. Hall, R. H. Boucher, D. J. Gutierrez, S. J. Hansel, B. P. Kasper, E. R. Keim, N. M. Moreno, M. L. Polak, M. G. Sivjee, D. M. Tratt, and D. W. Warren, “First flights of a new airborne thermal infrared imaging spectrometer with high area coverage,” Proc. SPIE 8012, 801203 (2011).
[Crossref]

D. W. Warren, D. J. Gutierrez, and E. R. Keim, “Dyson spectrometers for high-performance infrared applications,” Opt. Eng. 47(10), 103601 (2008).
[Crossref]

Li, C.

E. Liu, Y. Wu, Y. Wang, J. Wen, G. Lv, C. Li, J. Hou, and L. Yuan, “The development of a cryogenic integrated system with the working temperature of 100K,” Proc. SPIE 9821, 98210B (2016).

Liu, E.

E. Liu, Y. Wu, Y. Wang, J. Wen, G. Lv, C. Li, J. Hou, and L. Yuan, “The development of a cryogenic integrated system with the working temperature of 100K,” Proc. SPIE 9821, 98210B (2016).

Loya, F.

Lundeen, S.

Lv, G.

L. Yuan, Z. He, Y. Wang, and G. Lv, “Manufacture, alignment and measurement for a reflective triplet optics in imaging spectrometer,” Proc. SPIE 9684, 96840B (2016).

E. Liu, Y. Wu, Y. Wang, J. Wen, G. Lv, C. Li, J. Hou, and L. Yuan, “The development of a cryogenic integrated system with the working temperature of 100K,” Proc. SPIE 9821, 98210B (2016).

Mazer, A.

McCubbin, I.

Moreno, N. M.

J. L. Hall, R. H. Boucher, D. J. Gutierrez, S. J. Hansel, B. P. Kasper, E. R. Keim, N. M. Moreno, M. L. Polak, M. G. Sivjee, D. M. Tratt, and D. W. Warren, “First flights of a new airborne thermal infrared imaging spectrometer with high area coverage,” Proc. SPIE 8012, 801203 (2011).
[Crossref]

Mouroulis, P.

Mouroulis, P. Z.

W. R. Johnson, S. J. Hook, P. Z. Mouroulis, D. W. Wilson, S. D. Gunapala, C. J. Hill, J. M. Mumolo, and B. T. Eng, “QWEST: Quantum well infrared earth science testbed,” Proc. SPIE 7086, 708606 (2008).
[Crossref]

Mumolo, J. M.

W. R. Johnson, S. J. Hook, P. Z. Mouroulis, D. W. Wilson, S. D. Gunapala, C. J. Hill, J. M. Mumolo, and B. T. Eng, “QWEST: Quantum well infrared earth science testbed,” Proc. SPIE 7086, 708606 (2008).
[Crossref]

Polak, M. L.

J. L. Hall, R. H. Boucher, D. J. Gutierrez, S. J. Hansel, B. P. Kasper, E. R. Keim, N. M. Moreno, M. L. Polak, M. G. Sivjee, D. M. Tratt, and D. W. Warren, “First flights of a new airborne thermal infrared imaging spectrometer with high area coverage,” Proc. SPIE 8012, 801203 (2011).
[Crossref]

Randall, D.

Richardson, B.

Rodriguez, J. I.

Sarture, C.

Silny, J. F.

L. G. Cook and J. F. Silny, “Imaging spectrometer trade studies: a detailed comparison of the Offner-Chrisp and reflective triplet optical design forms,” Proc. SPIE 7813, 78130F (2010).
[Crossref]

Sivjee, M. G.

J. L. Hall, R. H. Boucher, D. J. Gutierrez, S. J. Hansel, B. P. Kasper, E. R. Keim, N. M. Moreno, M. L. Polak, M. G. Sivjee, D. M. Tratt, and D. W. Warren, “First flights of a new airborne thermal infrared imaging spectrometer with high area coverage,” Proc. SPIE 8012, 801203 (2011).
[Crossref]

Tratt, D. M.

J. L. Hall, R. H. Boucher, D. J. Gutierrez, S. J. Hansel, B. P. Kasper, E. R. Keim, N. M. Moreno, M. L. Polak, M. G. Sivjee, D. M. Tratt, and D. W. Warren, “First flights of a new airborne thermal infrared imaging spectrometer with high area coverage,” Proc. SPIE 8012, 801203 (2011).
[Crossref]

Urquiza, E.

Van Gorp, B.

Vargas, R.

Wang, Y.

E. Liu, Y. Wu, Y. Wang, J. Wen, G. Lv, C. Li, J. Hou, and L. Yuan, “The development of a cryogenic integrated system with the working temperature of 100K,” Proc. SPIE 9821, 98210B (2016).

L. Yuan, Z. He, Y. Wang, and G. Lv, “Manufacture, alignment and measurement for a reflective triplet optics in imaging spectrometer,” Proc. SPIE 9684, 96840B (2016).

Warren, D. W.

J. L. Hall, R. H. Boucher, D. J. Gutierrez, S. J. Hansel, B. P. Kasper, E. R. Keim, N. M. Moreno, M. L. Polak, M. G. Sivjee, D. M. Tratt, and D. W. Warren, “First flights of a new airborne thermal infrared imaging spectrometer with high area coverage,” Proc. SPIE 8012, 801203 (2011).
[Crossref]

D. W. Warren, D. J. Gutierrez, and E. R. Keim, “Dyson spectrometers for high-performance infrared applications,” Opt. Eng. 47(10), 103601 (2008).
[Crossref]

Wen, J.

E. Liu, Y. Wu, Y. Wang, J. Wen, G. Lv, C. Li, J. Hou, and L. Yuan, “The development of a cryogenic integrated system with the working temperature of 100K,” Proc. SPIE 9821, 98210B (2016).

White, V.

Wilson, D. W.

Wu, Y.

E. Liu, Y. Wu, Y. Wang, J. Wen, G. Lv, C. Li, J. Hou, and L. Yuan, “The development of a cryogenic integrated system with the working temperature of 100K,” Proc. SPIE 9821, 98210B (2016).

Yee, K.

Yuan, L.

E. Liu, Y. Wu, Y. Wang, J. Wen, G. Lv, C. Li, J. Hou, and L. Yuan, “The development of a cryogenic integrated system with the working temperature of 100K,” Proc. SPIE 9821, 98210B (2016).

L. Yuan, Z. He, Y. Wang, and G. Lv, “Manufacture, alignment and measurement for a reflective triplet optics in imaging spectrometer,” Proc. SPIE 9684, 96840B (2016).

Appl. Opt. (2)

Opt. Eng. (1)

D. W. Warren, D. J. Gutierrez, and E. R. Keim, “Dyson spectrometers for high-performance infrared applications,” Opt. Eng. 47(10), 103601 (2008).
[Crossref]

Opt. Express (1)

Proc. SPIE (6)

W. R. Johnson, S. J. Hook, P. Z. Mouroulis, D. W. Wilson, S. D. Gunapala, C. J. Hill, J. M. Mumolo, and B. T. Eng, “QWEST: Quantum well infrared earth science testbed,” Proc. SPIE 7086, 708606 (2008).
[Crossref]

J. L. Hall, R. H. Boucher, D. J. Gutierrez, S. J. Hansel, B. P. Kasper, E. R. Keim, N. M. Moreno, M. L. Polak, M. G. Sivjee, D. M. Tratt, and D. W. Warren, “First flights of a new airborne thermal infrared imaging spectrometer with high area coverage,” Proc. SPIE 8012, 801203 (2011).
[Crossref]

W. R. Johnson, G. Hulley, and S. J. Hook, “Remote gas plume sensing and imaging with NASA’s Hyperspectral Thermal Emission Spectrometer (HyTES),” Proc. SPIE 9101, 91010V (2014).
[Crossref]

L. G. Cook and J. F. Silny, “Imaging spectrometer trade studies: a detailed comparison of the Offner-Chrisp and reflective triplet optical design forms,” Proc. SPIE 7813, 78130F (2010).
[Crossref]

E. Liu, Y. Wu, Y. Wang, J. Wen, G. Lv, C. Li, J. Hou, and L. Yuan, “The development of a cryogenic integrated system with the working temperature of 100K,” Proc. SPIE 9821, 98210B (2016).

L. Yuan, Z. He, Y. Wang, and G. Lv, “Manufacture, alignment and measurement for a reflective triplet optics in imaging spectrometer,” Proc. SPIE 9684, 96840B (2016).

Other (6)

L. G. Cook, “Reflective optical triplet having a real entrance pupil,” United States Patent 4,733,955 (1988).

L. G. Cook, “Compact all-reflective imaging spectrometer,” United States Patent 5,260,767 (1993).

L. G. Cook, “High-resolution, all-reflective imaging spectrometer,” United States Patent 6,886,953 (2005).

L. G. Cook, “High-resolution, all-reflective imaging spectrometer,” United States Patent 7,080,912 (2006).

L. G. Cook, “Two-channel imaging spectrometer utilizing shared objective, collimating, and imaging optics,” United States Patent 7,382,498 (2008).

J. Pan, The design, manufacture and test of the aspherical optical surfaces (Suzhou University, 2004), Chap. 5.

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Figures (16)

Fig. 1
Fig. 1 (a) Schematic of the long wave infrared imaging spectrometer. (b) Field combination design of three uniform sub-modules. Here, ω denotes the field of view of the sub-module, θ the intersection angle of two adjacent sub-modules, and ωtotal the total integrated field.
Fig. 2
Fig. 2 Design procedure for reflective triplet spectrometer.
Fig. 3
Fig. 3 Raytrace of the on-axis three-mirror system. M1, M2, and M3 denote the primary, secondary, and tertiary mirrors, respectively. Parameters h 1 , h 2 , and h 3 denote the marginal ray heights on the primary, secondary, and tertiary mirrors, respectively. Parameters l 2 and l 2 ' denote, respectively, the objective and image distances of the secondary, and l 3 and l 3 ' , respectively, the objective and image distances of the tertiary. Further, d 1 , d 2 denote, respectively, the distances between the primary and secondary, and secondary and tertiary. Finally, f 1 ' denotes the image focal length of the primary.
Fig. 4
Fig. 4 Spot diagrams of the reflective triplet (RT) spectrometer for the four fields (0, 0.5, 0.707, and 1 normalized) along the slit for the two extreme wavelengths of (a) 8 μm and (b) 12.5 μm. The size of the scale box equals that of one detector pixel (30 μm × 30 μm).
Fig. 5
Fig. 5 Spectral distortions of the reflective triplet (RT) spectrometer. (a) Smile corresponding to wavelengths of 8 μm, 10.25 μm, and 12.5 μm. The maximum smile occurs at the end of the slit at the wavelength of 8 μm, which is about one-eighth of a pixel. (b) Keystone of the 0, 0.5, 0.707, and 1 normalized fields of view, spanning the length of the slit. The maximum keystone occurs at the end of the slit at 12.5 μm, which is less than one-tenth of a pixel.
Fig. 6
Fig. 6 Simulation of diffraction efficiency of the flat grating for different grooving depths.
Fig. 7
Fig. 7 Raytrace of the integrated system in the spectral dimension view. M0, M1, M2, and M3 denote the plane reflector, primary, secondary, and tertiary mirrors, respectively. BSF denotes the background radiation suppressed filter.
Fig. 8
Fig. 8 Spot diagrams of the integrated system for the four fields (0, 0.5, 0.707, and 1 normalized) along the slit of the two extreme wavelengths of (a) 8 μm and (b) 12.5 μm. The size of the scale box equals that of one detector pixel (30 μm × 30 μm).
Fig. 9
Fig. 9 Cryogenic design of the instrument: (a) front view and (b) rear view.
Fig. 10
Fig. 10 Opto-mechanical design of the tertiary mirror. All the surfaces are blackened except for the assembly and optical surfaces. The optical surface is gold-coated.
Fig. 11
Fig. 11 Responses of the center sub-module RT spectrometer for the three narrow band filters.
Fig. 12
Fig. 12 (a) Measured cross-track spatial response functions (CRFs) of spatial pixels in the center field point and for the 8, 10.02 and 11.17 μm wavelengths. (b) Measured along-track spatial response functions (ARFs) in the center field point and for the 8 and 10.6 μm wavelengths.
Fig. 13
Fig. 13 (a) Sample spectral response functions (SRFs) in the range of 8150 to 8350 nm for the center sub-module at the center field, demonstrating 28.85 nm spectral sampling and average 41.5 nm FWHM resolution. The “coarse” curves indicate test results while the smooth curves are the results of curve fitting. (b) SRF FWHM curve for the center field in the range of 8 to 12.5 μm (spectral channels 1 to 156 or FPA rows 50 to 205) of the center sub-module.
Fig. 14
Fig. 14 Measured spectra for ammonia gas compared with the standard spectrometer.
Fig. 15
Fig. 15 (a) Smile for the 8.155 and 10.604 μm wavelengths spanning the slit. The curves are obtained with a 2nd polynomial order curve fitting. The horizontal axis represents spatial pixels. (b) Keystone for four field points of the 0, 0.5, 0.707, and 1 normalized fields of view, spanning the length of the slit. The horizontal axis represents spectral channels. The curves are obtained with a 2nd polynomial order curve fitting. It is noted that due to the region-segmented filter set in front of the FPA, the response become weak after 10.5 μm. Thus, measured results of the spectral channels after 160 are not very accuracy and are not shown here. The upper area of the filter corresponds to 8 to 11.6 μm band pass, and the bottom area to the 11.6 to 12.5 μm band pass. However, the test result shows that the transmission of the 10.5 to 12.5 μm region is lower than the designed value. The filter suppresses background radiations but also lowers a greater number of signals in the 10.5 to 12.5 μm range. The filter is not perfect and should be replaced in future.
Fig. 16
Fig. 16 Noise equivalent delta temperature (NEdT) performance corresponding to the spectral range of 8 to 10.5 μm (spectral channels 1 to 87 or FPA rows 50 to 136) of the center sub-module. It is noted that due to the abovementioned region-segmented filter set in front of the FPA, the data become large after 10.5 μm. The NEdT values are 0.18 K, 0.19 K, 0.23 K, and 0.30 K for ranges of 10.5 to 11 μm, 11 to 11.5 μm, 11.5 to 12 μm, and 12 to 12.5 μm, respectively.

Tables (5)

Tables Icon

Table 1 Sub-module system specifications and performances

Tables Icon

Table 2 Analysis results of radiation simulation

Tables Icon

Table 3 Results of the center sub-module RT optics via use of long wave infrared interferometer

Tables Icon

Table 4 Comparison of FWHMs acquired with center sub-module RT spectrometer and standard equipment

Tables Icon

Table 5 Modulation transfer functions (MTFs) of the center sub-module imaging spectrometer

Equations (4)

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

α 1 = l 2 f 1 ' h 2 h 1 , α 2 = l 3 l 2 ' h 3 h 2 , β 1 = l 2 ' l 2 , β 2 = l 3 ' l 3 .
{ S I = f 1 ( k 1 , k 2 , k 3 , α 1 , α 2 , β 1 , β 2 ) S II = f 2 ( k 2 , k 3 , α 1 , α 2 , β 1 , β 2 ) S III = f 3 ( k 2 , k 3 , α 1 , α 2 , β 1 , β 2 ) .
{ ( λ l λ s ) Δ λ ' p = f ' tan ( θ l θ s ) Δ λ ' Δ λ / ( 1.1 ~ 1.5 ) d ( sin θ s sin θ 0 ) = m λ s d ( sin θ l sin θ 0 ) = m λ l ,
NEdT = ( T 2 T 1 ) RMS ( T 1 , λ i ) DN ( T 2 , λ i ) DN ( T 1 , λ i ) ,

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