US010267686B2(12) United States Patent( 10) Patent No.: US 10 , 267,686 B2(45) Date of Patent:
Apr . 23, 2019

Kester et al.

References Cited
U . S . PATENT DOCUMENTS( 56 )( 54 ) DIVIDED - APERTURE INFRA -RED

SPECTRAL IMAGING SYSTEM( 71 ) Applicant: REBELLION PHOTONICS, INC .,Houston , TX (US)(72 ) Inventors: Robert Timothy Kester, Houston , TX

3 ,841, 763 A
3 ,849 ,005 A(Continued )(US ); Nathan Adrian Hagen ,FOREIGN PATENT DOCUMENTS

Utsunomiya ( JP )( 73 ) Assignee : REBELLION PHOTONICS, INC .,Houston , TX (US)( * ) Notice : Subject to any disclaimer , the term of thispatent is extended or adjusted under 35
U .S .C . 154 (b ) by 0 days.
(22 ) Filed : Jan . 27 , 2017
Prior Publication Data
(65 )US 2017 /0205290 A1 Jul. 20 , 20179 / 2000
7 /2011( Continued )OTHER PUBLICATIONS
Adams, et al., " Advances in Detectors : Hot IR sensors improve IR
camera size , weight, and power” , Laser Focus World , vol. 50 , Issue(Continued )Primary Examiner — Kiho Kim(74 ) Attorney, Agent, or Firm — Knobbe , Martens, Olson& Bear, LLP

Related U . S . Application Data
(63 ) Continuation of application No. 14 /538,827, filed on
Nov . 12 , 2014 , now Pat. No. 9 ,562,849.

ABSTRACT(57 )Various embodiments disclosed herein describe a divided
aperture infrared spectral imaging (DAISI) system that is
adapted to acquire multiple IR images of a scene with asingle - shot (also referred to as a snapshot ). The plurality ofacquired images having different wavelength compositions
that are obtained generally simultaneously . The system
includes at least two optical channels that are spatially andspectrally different from one another. Each ofthe at least two(Continued )GO1J 5 /52

2 365 866
2 787 303

CA

01, Jan . 17 , 2014 , 6 pages. Also available at http ://www .ircameras.
com /articles/advances -detectors-hot-ir -sensors - improve - ir -camera
size-weight-power/.

(21) Appl. No.: 15/418,532(51) Int . CI.
HOIL 25/ 00

10 / 1974 Lewis
11/ 1974 Girard et al .

( 2006 . 01)( 2006 .01)
(Continued )(52) U.S. CI.
CPC .......... GO1J 5/522 (2013.01); G01J 3/0208( 2013 .01 ); GO1J 370232 ( 2013 .01);(Continued )(58 ) Field of Classification Search

CPC .......... HO4N 5 /33; H04N 5/09; HO4N 5 /3655 ;HO4N 5 /3651
See application file for complete search history.

optical channels are configured to transfer IR radiation
incident on the optical system towards an optical FPA unit
comprising at least two detector arrays disposed in the focal

plane of two corresponding focusing lenses . The systemfurther comprises at least one temperature reference sourceor surface that is used to dynamically calibrate the two
detector arrays and compensate for a temperature difference
between the two detector arrays .

22 Claims, 15 Drawing Sheets
Moveabletemperature

400

FiebR

Rete : Lens Arca
440
ence Amay
438

Front Owedive Lens, 424acontrolled shutters
460a , 460b

Filet $ 1784 , 454

Lens Amey , 128

WM

450

met Detector, 456

Tovards Processor , 150

226

wh

SIMU

merancam verwesen
g

450

424

4380 438a
438a 454a 1200

M444

US 10 ,Page
267,2686 B2
Related U .S . Application Data
(60 ) Provisional application No. 61/ 903,075, filed on Nov.
12 , 2013 .
(51) Int. Ci.
GO1J 3/ 02
GOIJ 3 / 12

( 2006 . 01)(2006 .01)
( 2006 .01)

GO1J 3 /28
GO1J 5 /00( 2006 .01 )8 ,653 , 461 B1
8 ,654, 328 B2
9 , 395 ,516 B2
9 , 562, 849 B2

2 /2014 Benson et al.
2 /2014 Tkaczyk et al.
7 /2016 Katsunuma et al .
2 / 2017 Kester et al.

9 , 599, 508 B2
9 ,625,318 B2
9 ,641,772 B2
9 ,644 , 562 B2

3 / 2017 Kester et al.
4 / 2017 Kester et al.
5 / 2017 Yujiri
5 /2017 Fujita

9 ,756 , 263 B2
10 ,084 ,975 B2
2001/0040216 Al

9 /2017 Kester et al.
9 /2018 Kester et al.
11/ 2001 Knauth et al.

2002/0121370 AL

9 /2002 Kurkjian et al.

2002/0015151 AL

2 /2002 Gorin

GO1J 5 /08
GOIN 21/3504( 2014 .01)

2002 /0159101 Al

HO4N 5 /33(2006 . 01)

2003/0134426 A1

7 / 2003 Jiang et al.

2003 /0183756 Al

10 /2003 Huniu(52 ) U .S . CI.
CPC(2006 .01)

2003 /0102435 A1.. ...... GO1J 3 /0297 (2013 .01 ); GOIJ 3 / 12

( 2013 .01) ; GOIJ 3 /2823 (2013 .01); GOIJ
5 /0014 ( 2013 .01 ); GO1J 5 /0806 ( 2013 .01) ;GO1J 5 /0834 (2013 .01) ; G01 ) 5 /0862(2013 . 01 ); GOIN 21/3504 ( 2013 .01); H04N
5 /332 (2013. 01 ); GOIJ 2003/ 283 ( 2013.01);

G01 ) 2003/2826 ( 2013 .01) ; G01 ) 2005 /0048(2013.01 ); GOIJ 2005/0077 (2013 .01 ); GOIN

2201/ 127 (2013 .01)

(56 )U .S . PATENT DOCUMENTS
4 ,464,789 A

1/ 1979 Goetz et al.

5 , 136 ,421 A *5 , 127, 742 A

7 / 1992 Fraden
8 / 1992 Sagan .. .. .. ... .. .. .. .. .

5 , 157, 258 A
5 ,550, 373 A
5 , 559 ,336 A

10 / 1994 MacPherson
8/ 1996 Cole et al.
9 / 1996 Kosai et al.

5 ,354 ,987 A

5 ,604 , 346 A
5 ,822 ,222 A
5 ,877, 500 A

10 / 1992 Gunning , III et al.

6 , 268, 883 B1 7 / 2001 Zehnder et al.
6 ,456 , 261 B1 9 /2002 Zhang
6 ,465, 785 B1 10 / 2002 McManus
6 ,556 , 853 B14 / 2003 Cabib et al .
6 ,680, 778 B21 / 2004 Hinnrichs et al.
6 ,700 ,527 B1
3/ 2004 Martin et al .
7 ,109 ,488 B2 9 /2006 Milton
7 , 119 ,337 B1 10 /2006 Johnson et al.
7 ,242 ,478 B17 / 2007 Dombrowski et al.
7 ,315 , 377 B21 /2008 Holland et al .
7 ,321, 119 B2

1 /2008 King

7 , 364,697 B2
7 ,433, 042 B1
7 ,606 ,484 B1
7 ,634 , 157 B1

4 / 2008 McFarland et al.
10 / 2008 Cavanaugh et al.
10 / 2009 Richards et al .
12 / 2009 Richards et al.

7 ,750, 802 B1
7 ,835, 002 B2
7 ,888,624 B1
8 ,027 ,041 B1
8 ,153,980 B1
8 , 159,568 B2

8 ,212 ,213 B2
8 , 373 ,757 B1

8 ,629 ,930 B2

250 /332

GO2B 5 /04
250 /332

2/ 1997 Hamrelius et al.
10 / 1998 Kaplinsky et al.
3/ 1999 Braig et al.
7 / 1999 DiRenzo et al.
7/ 1999 Hopkins

5 , 920 ,066 A
5 ,926 , 283 A
10 / 1999 Burger
5 ,973 ,844 A
5 ,994, 701 A
11/ 1999 Tsuchimoto et al.
6 ,023,061 A
2 / 2000 Bodkin
6 , 184 ,529 B1 * 2 /2001 Contini ... ... ... ... ... .

2007 /0018105 A1
2007/ 0075888 Al
2007/0108385 Al

1/ 2007 Grimberg
4 / 2007 Kelly et al.
5 /2007 Mantese et al .
7 / 2007 Syllaios et al.
7 /2007 Schimert et al.
7 / 2008 Silver et al.

2006 /0279632 A

G01 ) 1 / 04

250 / 252 . 1

12 /2006 Anderson

2008/0204744 Al

8 / 2008 Mir et al.

2008/0231719 Al

9 / 2008 Benson et al.

2009/0252650 A1

H04N 5 /33

5/ 2004 Braig et al.

6 / 2004 Butler et al.
12 / 2004 Slater2 / 2005 Allen et al.
5 /2005 Watson et al.
3 /2006 Hagene et al.
8 /2006 Lehmann et al.
10 / 2006 Chamberlain et al.

2008 /0251724 Al

8/ 1984 Sternberg

4 ,933, 555 A
6 / 1990 Smith
4 , 963, 963 A * 10 / 1990 Dorman

6 /2003 Myers et al .

2004 /0111232 A1
2004 /0252300 Al
2005/ 0029453 Al
2005 /0103989 Al
2006 /0044562 A1
2006 /0183241 A1
2006 /0232675 A1

2007/0170359 Al
2007/0170363 Al
2008/0170140 A1

References Cited
4 , 134 ,683 A

2004 /0093167 A1

10 / 2002 Alderson et al.

2010 /0162206 Al

10 / 2008 Baliga et al.

10 /2009 Lakshmanan

6 /2010 Roth et al.

2010 /0171866 A1 7 / 2010 Brady et al.
2010 /0211333 A1 8 / 2010 Pruet et al.
2010 /0309467 All 12 /2010 Fox et al.
2011/0176577 A1 7/ 2011 Bandara et al.
2011 /0185048 A1 7/2011 Yew et al.
2011 /0261321 Al 10 / 2011 Ramella -Roman et al.
2012 / 0273680 A1 11/ 2012 Furry

2013 /0181836 AL
2013 /0206990 Al
2013/0228887 A1

7/ 2013 Cardoso et al.
9 /2013 Wehner et al.

2013 / 0235256 A1
2013 /0250124 Al

9 /2013 Kodama
9 /2013 Furry

2013 /0307991 AL

11/2013 Olsen et al .

2015 /0136981 A1
2015 /0138534 Al
2015 /0144770 A1
2015 /0226613 A1

5 / 2015 Kester et al.
5 /2015 Tidhar
5 / 2015 Choi
8 / 2015 Bauer et al.

8 / 2013 Hsu et al.

2013 /0321806 A112/ 2013 Kester et al.
2013/0341509 Al 12/ 2013 Nelson et al.
2013/0342680 Al 12/ 2013 Zeng et al.
2014 /0002639 Al 1/ 2014 Cheben et al.
2014 /0139643 A1 5 /2014 Högasten et al.
2014 /0320843 Al 10 / 2014 Streuber et al.
2015 / 0069239 A1 3 /2015 Kester et al.

2015 /0288894 AL 10 /2015 Geelen et al.
2016 /0037089 Al 2 /2016 Silny et al.
2016 /0041095 A1 2 /2016 Rothberg et al.
2016 /0097713 Al 4 /2016 Kester et al.
2016 /0238454 A1 8 / 2016 Pillans
2016 /0245698 A1 8 /2016 Pau et al.

2015/0316473 AL 11/2015 Kester et al.

2016 /0313181 A1
2016 /0349228 A1
2016 /0356702 A1

10 /2016 Golub et al.
12 /2016 Kester et al.
12/ 2016 Hinnrichs

9 / 2011 Mitchell et al.
4 /2012 Brady et al.
4 / 2012 Ahdoot2017 /0026588 A1
2017 / 0234761 Al

1 /2017 Kester et al .
8/ 2017 Augusto

1/2014 Brueckner et al.

2017 / 0350758 A1 12/ 2017 Kester et al.
2017 /0356802 Al 12 / 2017 Kester et al.

7 / 2010 Parish et al.

11/ 2010 Muhammed et al.
2 / 2011 Murguia et al .

7 / 2012 Myrick et al.
2/2013 Nguyen

2016 /0380014 Al

2017 /0248517 AL

12 /2016 Ganapathi et al.
8/2017 Scherer et al .

US 10 ,Page
267,686
B2
3
References Cited( 56 )U . S . PATENT DOCUMENTS
2018 /0077363 A1 3 /2018 Kester et al.
2018 /0188163 A17 / 2018 Kester et al.
2018 /0191967 A1 7 / 2018 Kester

FOREIGN PATENT DOCUMENTS
CA
EP

EP
EP

EP

EP

GB

GB

JP
WO
WO

WO
WO
WO
WO

WO
WO

WO
WO

WO
WO

wo

WO

2 870 419
0 837 600
2 871 452
2 942 615
2 955 496
3 040 706
101476925182242013 - 128185
WO 2004 /097389
WO 2007/008826
WO 2008/ 109183
WO 2009/094782
WO 2010 /053979
WO 2012 /078417

WO 2012 /082366

WO 2013 / 173541
WO 2015 / 108236
WO 2016 / 196224
WO 2017/201194
WO 2018 /075957

WO 2018 /075964
WO 2018 / 156795

5 /2015
4 / 1998
5 /2015
11 /2015
12 /2015

7 / 2016
12/ 1965

3 / 2015
6 /2013
11 /2004

1 / 2007
9 / 2008
8 / 2009
5 / 2010
6 / 2012
6 / 2012
11 / 20137 /2015
12 /2016

11 / 20174 /2018
4 /2018

8 / 2018

OTHER PUBLICATIONSAllen et al., " Measurements of Methane Emissions at Natural Gas
Production Sites in the United States ” , PNAS , Oct. 29 , 2013 , vol.

110 , No. 44 , pp . 7 .
Alvarez et al., “ Greater Focus Needed on Methane Leakage fromNatural Gas Infrastructure ” , PNAS, Apr. 24 , 2012 , vol. 109 , No. 17 ,pp . 12 .
Bedard et al., “ Image Mapping Spectrometry: Calibration andCharacterization ” , Optical Engineering , Nov . 2012 , vol. 51, No. 11 ,pp. 111711 -1 - 111711 - 13.
Ben -David et al., “ Probability Theory for 3 - Layer Remote Sensing
Radiative Transfer Model: Univariate Case,” Optics Express, Apr.
2012 , vol. 20 , No. 9 , pp . 10004 - 10033.
Ben -David et al., “ Probability Theory for 3 -Layer Remote Sensing
Radiative Transfer Model : Errata ,” Optics Express , May 20 , 2013 ,vol. 21, No. 10 , pp . 11852 .

Brady et al., “ Multiscale Lens Design ” , Optics Express, Jun . 22 ,2009, vol. 17, No. 13 , pp. 10659 - 10674 .
Brochure provided by Lofty Designs to Rebellion Photonics on Oct.
31 , 2012 as noted from the email. Subsequent to that date brochure

was used in connection with potential customers.

Caulton et al., “ Toward a Better Understanding and QuantificationofMethane Emissions from Shale Gas Development ” , PNAS , Apr.

29, 2014 , vol. 111, No. 17 , pp . 7 .
Chen et al., “ Quantitative Sectioning and Noise Analysis for Structured Illumination Microscopy : Erratum ”, Optics Express, Oct. 19 ,2015 , vol. 23, No. 21, pp . 27633 - 27634 .
Chidley et al., “ Flow -Induced Birefringence: The Hidden PSF
Killer in High Performance Injection -Molded Plastic Optics” , Endoscopic Microscopy , Proceedings of SPIE vol. 6082 , 2006 , pp . 11 .
Chu et al., “ The NIST Quantitative Infrared Database ” , Journal of
Research of the National Institute of Standards and Technology ,Jan .- Feb . 1999, vol. 104 , No . 1 , pp . 59 -81 .
DiPietro et al., " Hyperspectral Matched Filter with False - Alarm

Mitigation ” , Optical Engineering, Jan . 2012 , vol. 51 , No . 1, pp .
016202- 1- 016202- 7 .

“ Directed Inspection and Maintenance at Gas Processing Plants andBooster Stations,” United States Environmental Protection Agency

Air and Radiation (6202J), EPA430 - B -03-018, Oct. 2003 available
at https://www3. epa .gov / gasstaridocuments/ II _ dimgasproc .pdf.
Eriksson et al., “ Radiative Cooling Computed for Model Atmo
spheres” , Applied Optics, Dec . 1, 1982, vol. 21, No. 23, pp .
4381- 4388 .

Flanigan , “ Detection of Organic Vapors with Active and Passive
Sensors: A Comparison,” Applied Optics, 1986 , vol. 25 , No. 23 , pp .
4253 -4260 .
Gålfalk et al., “ Making Methane Visable” , Nature Climate Change ,Apr. 2016 , vol. 6 , pp . 426 - 430 .

Gålfalk et al., “Making Methane Visable” , Supplementary Informa
tion , Nature Climate Change, 2015 , pp . 1 - 14 .

Gallagher et al., “ Error Analysis for Estimation of Trace Vapor

Concentration Pathlength in Stack Plumes” , Applied Spectroscopy ,2003 , vol. 57 , No . 6 , pp. 614 -621.

Gallagher et al., " Estimation of Trace Vapor Concentration
Pathlength in Plumes for Remote Sensing Applications from

Hyperspectral Images” , Analytica Chimica Acta , 2003 , vol. 490 , pp .
139 - 152 .
Gao et al., “ Compact Image Slicing Spectrometer ( ISS ) forHyperspectral
Fluorescence Microscopy ” , Optics Express, Jul. 20 , 2009, vol. 17 ,No. 15 , pp . 12293 - 12308.
Gao et al., “ Depth -Resolved Image Mapping Spectrometer (IMS)with Structured Illumination” , Optics Express, Aug . 29 , 2011, vol.
19, No. 18 , pp. 17439 - 17452.
Gao et al., “ Optical Design of a Snapshot High - Sampling Image
Mapping Spectrometer (IMS) for Hyperspectral Microscopy ” , Three
Dimensional and Multidimensional Microscopy:Image Acquisition
and Processing XVII, Proceedings of SPIE vol.7570, 2010 , pp . 1- 7 .
Gao et al., “ Quantitative Comparison Between Full- Spectrum andFilter- Based Imaging in Hyperspectral Fluorescence Microscopy” ,Journal of Microscopy , 2012, vol. 246 , No. 2 , pp . 113 - 123 .
Gao et al.,“ Snapshot Image -Mapping Spectrometer for Hyperspectral
Fluorescence Microscopy ” , Optics and Photonics News,Nov . 2010 ,vol. 21 , No . 12 , p . 50 .
Gao et al., “ Snapshot Image Mapping Spectrometer (IMS) withHigh Sampling Density for Hyperspectral Microscopy” , Optics
Express , Jul. 5 , 2010 , vol. 18 , No . 4 , pp . 14330 - 14344 .

Gerhart et al., “ Detection and Tracking of Gas Plumes in LWIR
Hyperspectral Video Sequence Data ,” Algorithmsand Technologies
for Multispectral, Hyperspectral, and Ultraspectral Imagery XIX ,2013 , SPIE Proceedings vol. 8743, pp . 1 - 14 .

Gittins , Christopher M ., “ Detection and Characterization of Chemi

cal Vapor Fugitive Emissions by Nonlinear Optimal Estimation :Theory and Simulation ” , Applied Optics, Aug. 10 , 2009, vol. 48,

No. 23 , pp . 4545 -4561.

Goldberg et al., “ Dual Band MWIR /LWIR Focal Plane Array Test
Results,” Army Research Lab , Adelphi, MD , Aug . 1999 , pp . 18 .
Golowich et al., “ Performance Limits of LWIR Gaseous Plume
Quantification” , Algorithms and Technologies for Multispectral,Hyperspectral, and Ultraspectral Imagery XVII , 2011, Proceedingsof SPIE vol. 8048 , pp . 1- 12 .

Griffin et al., “ The Herschel — SPIRE 1 - 15 Instrument and its
In - Flight Performance ," Astronomy and Astrophysics, Jul. 1, 2010 ,vol. 518 , pp . 7 .

Gross et al., “ Remote Identification and Quantification of Industrial
Smokestack Effluents via Imaging Fourier- Transform Spectros
copy” , Environmental Science & Technology , 2010 , vol. 44,No. 24 ,pp . 9390 -9397 .
Gupta et al., “Miniature Snapshot Multispectral Imager,” OpticalEngineering, 2011 , vol. 50 , pp . 033203 - 1 -033203 - 9 .

Hadlington , Simon , " New Camera Makes Methane Visible " , Chem

istry World , http ://web .archive.org /web /20160305234907/http ://www .rsc .org /chemistryworld /2015 / 12 /methane -camera -infraredgreenhouse -gas, Dec . 14 , 2015, pp . 2 .
Hagen et al., “ Analysis of Computed Tomographic Imaging Spec
trometers . I. Spatial and Spectral Resolution ” , Applied Optics, Oct .
1 , 2008, vol. 47 , No. 28 , pp. F85 - F95 .
Hagen et al., “ Coded Aperture DUV Spectrometer for Standoff
Raman Spectoscopy” , Next-Generation Spectroscopic Technolo

gies II, Proceedings of SPIE vol. 7319 , 2009 , pp . 1 - 10 .

US 10 ,Page
267,4686 B2
References Cited( 56 )OTHER PUBLICATIONS

Hagen et al ., “ Compound Prism Design Principles, I” , Applied
Optics, Sep . 1, 2011, vol. 50 , No. 25 , pp . 4998 -5011.

Hagen et al., " Compound Prism Design Principles, II : Triplet andJanssen Prisms” , Applied Optics, Sep . 1, 2011, vol. 50 , No. 25 , pp .
5012 -5022 .
Hagen et al., “ Compound Prism Design Principles, III: Linear-in
Wavenumber and Optical Coherence Tomography Prisms” , Applied
Optics, Sep . 1, 2011, vol. 50 , No. 25 , pp . 5023 -5030 .
Hagen et al., “ Fourier Methods of Improving Reconstruction Speed
for CTIS Imaging Spectrometers” , Imagin Spectrometry XII, Pro
ceedings of SPIE vol. 6661, 2007 , pp . 11 .

Hagen et al., “ Foveated Endoscopic Lens” , Journal of Biomedical
Optics, Feb . 2012 , vol. 17 , No. 2 , pp . 021104 - 1 -021104 -6 .

Kester et al., “ High Numerical Aperture Microendoscope Objective
for a Fiber Confocal Reflectance Microscope” , Optics Express,Mar.
5 , 2007, vol. 15 . No. 5 , pp . 2409 - 2420 .

Kester et al., “ Low Cost, High Performance , Self- Aligning Minia
ture Optical Systems” , Applied Optics, Jun . 20 , 2009 , vol. 48, No .
18 , pp . 3375 - 3384 .

Kester et al., “ Real- Time Snapshot Hyperspectral Imaging Endo
scope ” , Journal of Biomedical Optics,May 2011 , vol. 16 , No. 5 , pp .

056005 - 1 -056005 -12.

Kudenov et al., “ Fourier Transform Channeled Spectropolarimetry
in the MWIR ” , Optics Express, Oct. 1, 2007, vol. 15 , No. 20 , pp .
12792- 12805.

Kudenov et al., “ Snapshot Imaging Mueller Matrix Polarimeter
Using Polarization Gratings” , Optics Letters, Apr. 15 , 2012 , vol. 37 ,No. 8 , pp . 1367- 1369 .
Landau et al., “ Design and Evaluation of an Ultra -Slim Objective
for in -vivo Deep Optical Biopsy ” , Optics Express, Mar. 1, 2010 ,Hagen et al., “Gaussian Profile Estimation in One Dimension ” ,Applied Optics, Aug. 1 , 2007, vol. 46 , No. 22, pp . 5374 -5383 .

vol. 18 , No. 5, pp . 4758 -4775 .

Hagen et al., “Gaussian Profile Estimation in Two Dimension " ,Applied Optics, Dec . 20 , 2008 , vol. 47 , No. 36 , pp . 6842-6851.

terization in the Colorado Front Range : A Pilot Study 'by Gabrielle

Hagen et al., “ Quantitative Sectioning and Noise Analysis for
Structured Illumination Microscopy ” , Optics Express, Jan . 2, 2012 ,vol. 20 , No. 1, pp . 403-413 .
Hagen et al., “ Quantitative Sectioning and Noise Analysis for
Structured Illumination Microscopy: Errata ” , Optics Express, Feb .
27 , 2012 , vol. 20 , No . 5 , pp . 5343 .
Hagen et al., “ Real- Time Quantitative Hydrocarbon Gas Imaging
with the Gas Cloud Imager (GCI)” , Proceedings of SPIE , vol. 8358 ,Chemical, Biological,Radiological,Nuclear, and Explosives (CBRNE )Sensing XIII , May 1 , 2012 , pp . 7 .
Hagen et al., “ Review of Snapshot Spectral Imaging Technologies” ,Optical Engineering, Sep . 2013 , vol. 52 , No . 9 , pp . 090901- 1
090901- 23

Hagen et al., “ Snapshot Advantage: A Review of the Light Collec

Levi, Michael A ., “ Comment on ‘ Hydrocarbon Emissions Charac
Pétron et al.” , Journal of Geophysical Research , 2012 , vol. 117 , No .
D21203 , pp . 1 - 5 .

Levi,Michael A ., “ Reply to “ Reply to ‘Comment on Hydrocarbon
Emissions Characterization in the Colorado Front Range - A Pilot

Study ' by Michael A . Levi”” by Gabrielle Pétron et al.” , Journal ofGeophysical Research : Atmospheres, 2013 , vol. 118 , pp . 3044
3046 .

Low et al., “ Remote Sensing and Characterization of Stack Gases byInfrared Spectroscopy . An Approach by Using Multiple -Scan Inter
ferometry " , Environmental Science & Technology , Jan . 1967 , vol.

1, No . 1, pp . 73 - 74 .

Luo et al., “ Fast Processing of Imaging Spectrometer Data Cube
Based on FPGA Design ” , MIPPR 2007 : Multispectral Image Pro

cessing , Proceedings of SPIE vol. 6787, pp. 7 .

tion Improvement for Parallel High - Dimensional Measurement

Manolakis et al., “ Long -Wave Infrared Hyperspectral Remote Sens
ing of Chemical Clouds” , IEEE Signal Processing Magazine, Jul.

Hagen et al., “ Snapshot Mueller Matrix Spectropolarimeter” Optics
Letters , Aug. 1, 2007, vol. 32 , No . 15 , pp . 2100 -2102.
Hagen et al., “ Spectrally -Resolved Imaging of Dynamic Turbid

111702 - 1 -111702 - 7 .

2014 , vol. 31 , No. 4 , pp . 120 - 141.
Mathews, “ Design and Fabrication of a Low -Cost, Multispectral
Imaging System ,” Applied Optics, 2008, pp. F71- F76 , vol. 47 .
Naranjo et al., “ IR Gas Imaging in an Industrial Setting ,” Thermosense

vol. 7892, 2011, pp . 1 - 7 .

XXXII, Published in SPIE Proceedings vol. 7661, May 4 , 2010 , pp .
1-8.

Systems,” Optical Engineering , Jun . 13 , 2012 , vol. 51 , No. 11 , p .

Media ”, Multimodal Biomedical Imaging VI, Proceedings of SPIE

Hagen et al., “ Video - Rate Spectral Imaging of Gas Leaks in the

Nguyen et al., " Snapshot 3D Optical Coherence Tomography Sys

Proceedings vol. 8710 , pp . 7 .

3D Imaging OSA , 2012 , pp . 3 .
Niu et al., “New Approach to Remote Gas - Phase Chemical Quan
tification : Selected -Band Algorithm ” , Optical Engineering, Feb .

Longwave Infrared ,” Chemical, Biological, Radiological, Nuclear,and Explosives (CBRNE ) Sensing XIV , May 29 , 2013 , SPIEHarley et al., “ Remote Quantification of Smokestack Effluent Mass
Flow Rates Using Imaging Fourier Transform Spectrometry,” Chemi
cal, Biological, Radiological, Nuclear, and Explosives (CBRNE )Sensing XII, Apr. 25 - 29, 2011, SPIE Proceedings vol. 8018, pp .

1 - 13.
Hayden et al., “ Determination of Trace -Gas Amounts in Plumes by
the Use of Orthogonal Digital Filtering of Thermal- Emission Spectem using Image Mapping Spectrometer” , Biomedical Optics and2014 , vol. 53 , No. 2 , pp . 021111- 1 - 021111 - 10 .
“ Oil and Natural Gas Sector Leaks” , U .S . EPA Office of Air Quality
Planning and Standards (OAQPS ), Review Panel, Apr. 2014 , pp .63 .
Pétron et al., “ Hydrocarbon Emissions Characterization in the

Colorado Front Range : A Pilot Study ” , Journal of GeophysicalResearch , 2012 , vol. 117 , No. D04304 , pp . 1 - 19 .

Hirsch et al., “ Detection of Gaseous Plumes in IR Hyperspectral

tra” , Applied Optics, Jun . 1, 1996 , vol. 35 , No. 16 , pp . 2802-2809.
Images Using Hierarchical Clustering” , Applied Optics, Sep . 1,

Pétron et al., “ Reply to Comment on ‘Hydrocarbon Emissions
Characterization in the Colorado Front Range A Pilot Study' by
Michael A . Levi” , Journal of Geophysical Research : Atmospheres ,2007 , vol. 46 , No. 25 , pp . 6368 -6374 .

2013 , vol. 118 , pp . 236 - 242.

Johnston et al., “ A Real- Time FPGA Implementation of a BarrelDistortion Correction Aglorithm ” , Projects , 2003, vol. 10 , pp .

91- 96 .
Karion et al., “Methane Emissions Estimate from Airborne Mea

surements Over a Western United States NaturalGas Field ” , Geophysical Research Letters, 2013 , vol. 40 , pp. 4393 -4397 .

Keshava et al., “ A Survey of Spectral Unmixing Algorithms” ,Lincoln Laboratory Journal, 2003 , vol. 14 , No. 1 , pp . 55 - 78 .
Kester et al., " A Real- Time Gas Cloud Imaging Camera for Fugitive
Emission Detection and Monitoring” , Imaging and Applied Optics
Technical Digest, 2012 , pp . 3 .
Kester et al., “ Development of Image Mappers for Hyperspectral
Biomedical Imaging Applications” , Applied Optics, Apr. 1 , 2010 ,vol. 49 , No. 10 , pp . 1886 - 1899 .

Pisano et al., “ Thermal Illuminators for Far-Infrared and Submil
limeter Astronomical Instruments,” Applied Optics , Jun . 1 , 2005,

vol. 44 , No . 16 , pp . 3208 - 3217 .

Polak et al., “ Passive Fourier - Transform Infrared Spectroscopy ofChemical Plumes : An Algorithm for Quantitiative Interpretation
and Real- Time Background Removal” , Applied Optics, Aug . 20 ,1995 , vol. 34 , No . 24 , pp . 5406 -5412 .

Rebellion Photonics , “ Gas Cloud Imaging Camera : A Breakthroughin Leak Monitoring for the Rig & Refinery Safety Market” , Pre

sentation at SPIE Defense Security and Sensing, 28 pages, Apr.
29 -May 3 , 2013 .

Sandsten et al., “ Volume Flow Calculations on Gas Leaks Imaged
with Infrared Gas-Correlation ," Optics Express, 2012 , vol. 20 , No .
18 , pp. 20318 -20329 .

US 10 ,Page
267,686
B2
5( 56 )

References Cited
OTHER PUBLICATIONS

Shogenji et al., “ Multispectral Imaging Using Compact Compound
Optics,” Optics Express, Apr. 19 , 2004, vol. 12 , No. 8 , pp . 1643

1655 .
Telops,“ Hyper -Cam ”, http ://web .archive .org/web /20160608180941/

http ://www . telops.com / en /hyperspectral-cameras/hyper- cam as archived
Jun . 8, 2016 in 2 pages .
Telops, “ Innovative Infrared Imaging ” , http ://web .archive .org/web /20160603212729 /http ://www .telops.com /en / as archived Jun . 3, 2016
in 2 pages.
Walter Jr ., et al., “ Detection of Atmospheric Pollutants : a Correlation Technique ” , Applied Optics, Jun. 1975 , vol. 14 , No. 6 , pp.
1423 - 1428 .
Wikipedia entry https:// en . wikipedia.org/wiki/Mobile _ computing in

Official Communication received in European Application No.
15165877 .0 dated Jan . 3 , 2017 in 9 pages.
Preliminary Amendment as filed in U .S . Appl. No. 14 /700 ,567 dated
Jul. 10 , 2015 in 6 pages .
Publication Request as filed in U . S . Appl. No. 14 /700 ,567 dated
Aug. 24 , 2016 in 237 pages.
Extended European Search Report received in European Application No. EP 15165880 .4 dated Nov. 24 , 2015 in 8 pages.
Preliminary Amendmentas filed in U .S . Appl. No. 14 /792,477 dated
Dec . 21, 2015 in 7 pages .

Preliminary Amendmentas filed in U .S . Appl. No. 15 /166 ,092 dated

Aug. 15 , 2016 in 7 pages.

International Search Report in PCT Application No . PCT/US2016 /

034455 dated Oct. 24 , 2016 in 12 pages.

Preliminary Amendment as filed in U . S . Appl.No. 14 / 538 ,827 dated

TemperatureMeasurements,” SPIE Thermosense Conference XXVIII —Jan . 28 , 2015 in 6 pages.
Office Action received in U .S . Appl. No. 14 /538 ,827 dated Jun. 30 ,2015 in 8 pages.
Non - Final Office Action Response as filed in U .S . Appl. No.
14 /538 , 827 dated Dec . 28 , 2015 in 11 pages.
Notice of Allowance received in U . S . Appl. No. 14 /538 ,827 dated

Young et al., “ An In - Scene Method for Atmospheric Compensation

Feb . 1, 2016 in 18 pages .
Corrected Notice of Allowance received in U . S . Appl. No. 14 /538,827

6 pages , last modified on Dec . 30 , 2016 ; retrieved from the internet
on Feb . 2 , 2017 .

Williamset al., “ Dual- Band MWIR /LWIR Radiometer for Absolute
Manuscript 6205 - 23 , Apr. 18 , 2006 , pp . 13 .

of Thermal Hyperspectral Data ” , Journal ofGeophysical Research ,2002 , vol. 107 , No. D24 , pp . 14 - 1 - 14 - 20 .
Zheng et al., “ A Static Multiplex Fabry -Perot Spectrometer”, Sensors , Cameras, and Systems for Industrial/ Scientific Applications X ,Proceedings of SPIE - IS & T Electronic Imaging, SPIE vol. 7249 ,

2009, pp . 8 .
Zheng et al., “ Analytic -Domain Lens Design with Proximate Ray
Tracing ” , Journal of the Optical Society of America A , Aug. 2010 ,vol. 27 , No. 8, pp . 1791- 1802.

Office Action received in U . S . Appl. No. 14 / 543 ,692 dated Nov . 3 ,2015 in 7 pages .
Interview Summary received in U .S . Appl. No. 14 /543 ,692 dated
Feb . 17 , 2016 in 5 pages .
Response to Office Action as filed in U . S . Appl. No. 14 /543,692
dated May 2 , 2016 in 9 pages .
Office Action received in U .S . Appl. No. 14 /543,692 dated Jun . 1,
2016 in 18 pages.
Response to Final Action as filed in U .S . Appl. No. 14 /543 ,692
dated Nov . 30 , 2016 in 12 pages.
Notice of Allowance received in U . S . Appl. No. 14 /543 ,692 dated
Dec . 9 , 2016 in 12 pages.
Office Action received in U . S . Appl. No . 14 /539 ,899 dated Mar. 26 ,2015 in 6 pages .
Non -Final Office Action Response as filed in U . S . Appl. No .
14 / 539, 899 dated Aug. 26 , 2015 in 8 pages.
Final Office Action received in U . S . Appl. No . 14 / 539 ,899 dated
Dec . 11, 2015 in 9 pages .

Amendment as filed in U . S . Appl. No. 14 / 539, 899 dated Jun . 9 ,2016 in 6 pages .

Notice of Allowance received in U . S . Appl. No. 14 /539 ,899 dated
Jun . 21, 2016 in 17 pages.
Notice of Allowance received in U . S . Appl. No. 14 /539, 899 dated
Oct. 31 , 2016 in 10 pages.
Extended European Search Report received in European Application No. 14192862.2 dated Mar. 30 , 2015 in 10 pages.
Official Communication received in European Application No .
14192862.2 dated Apr. 19 , 2016 in 6 pages.
International Search Report in PCT Application No . PCT /US2013 /
041278 dated Aug. 27 , 2013 in 4 pages.
International Preliminary Report on Patentability in PCT Application No. PCT/US2013 /041278 dated Nov . 27 , 2014 in 10 pages.
Preliminary Amendment as filed in U .S . Appl.No. 14 /700 , 791 dated

Jul. 13 , 2015 in 8 pages.
Notice of Allowance received in U . S . Appl. No. 14 /700 ,791 dated
Jun . 9 , 2016 in 11 pages.

Notice of Allowance received in U . S . Appl. No . 14 /700 ,791 dated
Extended European Search Report received in European Application No. 15165877 .0 dated Oct. 8, 2015 in 12 pages.

Sep . 30 , 2016 in 19 pages.

dated Feb . 10 , 2016 in 4 pages .
Corrected Notice of Allowance received in U . S . Appl. No. 14 /538 ,827
dated Feb . 22, 2016 in 4 pages.
Request for Continued Examination and Response to Correct Application Papers as filed in U .S . Appl. No. 14 /538 ,827 dated Apr. 29 ,2016 in 14 pages.
Notice of Allowance received in U . S . Appl. No. 14 /538 ,827 dated
May 26 , 2016 in 9 pages.
Notice of Allowance received in U .S . Appl. No. 14 /538 ,827 dated
Sep . 19 , 2016 in 9 pages.
Amendment as filed in U .S . Appl. No. 14 /538 ,827 dated Dec . 16 ,2016 in 9 pages.
Amendment after Allowance as filed in U . S . Appl. No. 14 /543 ,692

dated Mar. 3 , 2017 in 6 pages.
Notice of Allowance received in U .S . Appl. No. 14 /543 ,692 dated

Mar. 17, 2017 in 4 pages.

Notice of Allowance received in U .S . Appl. No. 14 / 571, 398 dated
Oct. 18 , 2017 in 8 pages.

Amendment as filed in U . S . Appl. No. 14 /539 ,899 dated Jan . 27,
2017 in 5 pages .

Notice of Allowance received in U . S. Appl . No. 14 /700,791 dated

Feb . 21 , 2017 in 20 pages.
Comments on Allowance received in U .S . Appl. No. 14 /700,791
dated May 19 , 2017 in 2 pages .

Notice of Allowance received in U .S . Appl. No. 14 /700 ,791 dated

Jul. 10 , 2017 in 24 pages .
Official Communication received in U . S . Appl. No. 14 /700 , 567
dated Jun. 14 , 2017 in 29 pages.
Official Communication received in U . S . Appl. No . 14 / 792 ,477
dated Jan . 27 , 2017 in 10 pages.
Response to Restriction Requirement submitted in U .S . Appl. No.
14 /792,477 dated May 8 , 2017 in 6 pages .

Cossel et al., “ Analysis of Trace Impurities in Semiconductor Gas
Via Cavity - Enhanced Direct Frequency Comb Spectroscopy”, Applied
Physics B , Sep . 2010 , vol. 100 , No. 4 , pp . 917 - 924 .

Official Communication received in U . S . Appl. No . 15 / 166 ,092
dated May 15 , 2018 in 30 pages .
Amendment as filed in U .S . Appl. No. 14 /700 , 567 dated Dec . 13 ,2017 in 12 pages .
Amendment as filed in U . S . Appl. No. 14 /792 ,477 dated Jan . 18 ,2018 in 10 pages.
Amendment as filed in U .S . Appl. No. 15 /462,352 dated Feb . 28,
2018 in 5 pages.
International Preliminary Report on Patentability in PCT Application No. PCT /US2016 /034455 dated Dec . 5 , 2017 in 8 pages .
International Search Report in PCT Application No. PCT /US2017 /
057712 dated Mar. 6 , 2018 in 12 pages .

International Search Report in PCT Application No. PCT/US2017 /
057725 dated Feb . 14 , 2018 in 14 pages.

US 10 ,Page
267,6686 B2( 56 )

References Cited

OTHER PUBLICATIONS
Invitation to Pay Additional Fees in PCT Application No. PCT/US2017 /057712 dated Jan . 10 , 2018 in 2 pages.
Invitation to Pay Additional Fees in PCT Application No. PCT/US2017 /057725 dated Dec . 14 , 2017 in 3 pages .
Notice of Allowance received in U . S . Appl. No . 14 /571, 398 dated
Feb . 7 , 2018 in 20 pages .
Notice of Allowance received in U . S . Appl. No. 15 /623, 942 dated
Jan . 24 , 2018 in 22 pages .
Official Communication received in U .S . Appl. No. 14 /700 ,567
dated Mar. 5 , 2018 in 38 pages .
Official Communication received in U . S . Appl. No. 14 /792,477
dated Jul. 19 , 2017 in 20 pages .
Official Communication received in U .S . Appl. No. 15 /462,352
dated Sep . 28 , 2017 in 6 pages.
Preliminary Amendment as filed in U .S . Appl. No . 15 /471, 398 dated
Oct. 6 , 2017 in 6 pages .

Preliminary Amendment as filed in U .S . Appl. No. 15 /623 ,942 dated

Dec . 7 , 2017 in 6 pages .

Preliminary Amendment as filed in U .S . Appl. No. 15 /789 ,811 dated

Sandsten et al., “ Development of Infrared Spectroscopy Techniques
for Environmental Monitoring” , Doctoral Thesis , Aug. 2000, pp .
123 .

Sandsten et al., “ Real- Time Gas-Correlation Imaging Employing
Thermal Background Radiation ” , Optics Express, Feb . 14 , 2000 ,vol. 6 , No. 4 , pp . 92 - 103 .

Official Communication received in U . S . Appl. No . 15 /789 ,829

dated Jun. 5, 2018 in 16 pages.
Notice of Allowance received in U .S . Appl. No. 15 /462 ,352 dated
Jul. 17 , 2018 in 25 pages .
Official Communication received in European Application No.
13732285 .5 dated Jul. 26 , 2018 in 6 pages.
Official Communication received in European Application No.
14192862.2 dated May 2 , 2018 in 3 pages.

Notice of Allowance received in U .S . Appl. No. 14 /792 ,477 dated
Apr. 19 , 2018 in 13 pages .

Notice of Allowance received in U .S . Appl. No. 14 /792,477 dated
Sep . 20 , 2018 in 14 pages.
Official Communication received in U . S . Appl. No . 15 /789 ,811
dated Jul. 27 , 2018 in 22 pages .
International Search Report in PCT Application No. PCT/US2018 /Mar. 20, 2018 in 6 pages .

019271 dated Jun . 27 , 2018 in 15 pages.

Mar. 20, 2018 in 8 pages .

* cited by examiner

Preliminary Amendment as filed in U .S . Appl.No. 15 /789 ,829 datedatentApr. 23 , 2019

US 10 , 267,686 B2

Sheet 1 of 15

128lensaR,erimagainyg 136aDert catoyr

1Towards pro5ces0or

100-,160srMeofvuraebncloe
128a 130

124
,
lans
we

120

l

l

120

120

110 gas

1
.
FIG

120

atentApr. 23 , 2019

US 10 ,267 ,686 B2

Sheet 2 of 15

224
Field Reference 204

-

une

202

W

WWWW

Mit

| 236
M

Kwindo12

224 160

overlapping FOV Region 230
Parallax 228

Gas ar- 226

1226 .. .
200

FIG . 2

Towards
processor 150

atentApr. 23 , 2019

US 10 ,267 ,686 B2

Sheet 3 of 15

Field Reference
338

128

324

ko

300

wo

226

*
2

Object 110

st

Ww ml
LM

:WHENAILKMRUS*

324a 128a

FIG . 3A

324a

wings

O

FIG . 3B

atentApr. 23 , 2019

US 10 ,267 ,686 B2

Sheet 4 of 15

Detedor
456
,

4
.
FIG

128a

FlerAray,454
wwwMoveabl temprauescohnutrlesd

faxrim rip en

.

460a
460b
,

wait

wwwwwwww

128a
!
444

.

ww

bythepiratepapisi*

45348a438asy** * *

ritypridit'

Relay
Lens
Bit
By

bricktret ni ristroplazo14 peti etoise te440

ap ropripiltich

thetitriyor

/Ww w
400

w.

438

,4LOFbrj2eoc4atnisvte

450

424
cm

450

sTsomaotwiarundesn 226
110
,
obed

U.S. Patent Apr 23,2013
atentApr. 23 , 2019

Sheet 5 of 15

US 10 , 267,686 B2

8

DEZ90

7

12
11
10
|
9
6

5B
.
FIG

5

8
7

12
11
10
9
6
5

5A
.
FIG

atentApr. 23 , 2019

US 10 ,267,686 B2

Sheet 6 of 15

filteroa filterla filterza filter3a- .
.

IIIIIIIIIII III III 111111111

I

I

-

13

ZI
TITIIIIIIIIIIIIIIIIIIIIIIIIIILI

11um)(Wavelength
-

-

-

WWI
I
MWmWVVDIULIDIIDIIDIINILIITTIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII

10

ITUTIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII

T

<

70

+
8
.
0

+
2
.
0

transmission

6A
.
FIG

atentApr. 23 , 2019

US 10 ,267,686 B2

Sheet 7 of 15

filterob filterlb filter2b filter3b
R

*

—

13

LI

I

SPL ' JI YUVARLYTATTI(um)Wavel ngth
- - - - - - - - - - IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIITITM

I HT

- -

- -

I-

I

24
.
0

40 [SSIUSuelt

m

6B
.
FIG

atentApr. 23 , 2019

US 10 ,267,686 B2

Sheet 8 of 15

filteroc filteric filter2c filter3c
-

II

HIKH
HARK
.
H

IIIIIIIIIIIII

freed

LIIT

(um)wavel ngth
- - - - - - - - - - - - - - - - - - - -IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII

24
.
0

84
.
0

transmission

Too

6C
.
FIG

atentApr. 23 , 2019

US 10 ,267,686 B2

Sheet 9 of 15

filterod filterld filter2d Filter3d
II
ET

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII

11(um)wavel ngth
ryum

OT

OU
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII

T

WWW
!
"
WX
Y

.
1
OF
4
.
0

2
.
0

100

6D
.
FIG

U . S . Patent

Apr . 23 , 2019

US 10 ,267 ,686 B2

Sheet 10 of 15

???
'
'
???

??????
- ?S S .

;. S .

S

.

..

ITH

SSSSS

Y

=

;
;
'

??????
' '

SWs

ANS

??? ?

.

-

A . ,'- - - -- -

.
.
.
,
'

SSSSS

,

:

???

?
.

.
,

???

?

???

?s

?

????

FIG . 7

Apr . 23 , 2019

U . S . Patent

US 10 ,267, 686 B2

Sheet 11 of 15> > >> >>> >> >>??

.*?????? - ???????

)(CTemplsraiturse

. ???

??

?????
?

==

???? =c?????????
?

S

?
?
?????
??

??
????

?????

??
?
????

i

? werknad
?

?

?

??

?

??

8

Wavelength (microns)??????
FIG . 8A????????

????????????????????????????????????????????????????????????

????????????????????

??????????????????????????????????????????????????????????

?
::)(CTemplsraiturse

Wavelength (microns)

FIG . 8B?

Apr . 23 , 2019

U . S . Patent

US 10 , 267,686 B2

Sheet 12 of 15

900

to object975b

975a -

Mga

M1B

960
928a

thermally
controlled
shutters

block

array

Carta

WO0P

9802
980b
M18

936

9726

camera

INNT
2

wewe

9800

Mga_ 9806

?

?

?

?

M98

?

?

M2A

M
1111111111111111111111

980c

1

1

980f

FIG . 9A

U . S . Patent

Apr . 23 , 2019

US 10 , 267,686 B2

Sheet 13 of 15905

to object- 972b
972a

WW
XXX
w

960

thermally

928acontrolled

11111111111111111

shutters4
camera VW

SHOW

936

W2

7

.

* ** **

00000- 980d

980a
MINN

11

980b

980e
YA

M

9800

VAUVE
980f

FIG . 9B

U . S . Patent

Apr . 23 , 2019

US 10 , 267,686 B2

Sheet 14 of 151000

9 10 11

cameras© mirrors
mirrorsreferencesources

00000
BY

FIG . 10A

1000

X( 8 ) ( 9 ) ( 10 ) ( 11

( 4 ) ( 5 16 ( 7 )
IDE*
*
*

*

FIG . 10B

Apr . 23 , 2019

U . S . Patent

Sheet 15 of 15

US 10 , 267,686 B2

camers reafrencesources
1050

Riia

RIB

RIA

RzB

ICHI
11

Rais
R2oa
R208

R3A

R2B
R2A

. X

Rza

R18

Rab

RLA

Rga

Rob

REA

1002ROB

ROA

10C
.
FIG

US 10 ,267 ,686 B2
DIVIDED -APERTURE INFRA -RED
SPECTRAL IMAGING SYSTEM

are disposed at the focus of one or more lenses . In various
embodiments , the array of photo - sensitive devices can

include a two - dimensional imaging sensor that is sensitive to
CROSS -REFERENCE TO RELATEDAPPLICATIONS

radiation having wavelengths between 1 um and 20 um ( forexample , in mid infra - red wavelength range , long infra - redwavelength range, visible wavelength range , etc .). In various

This application is a continuation of U . S . patent applica
embodiments , the array of photo - sensitive devices cantion Ser. No . 14 / 538, 827 , filed on Nov. 12 , 2014 and titledinclude CCD or CMOS sensors, bolometers or other detec“ DIVIDED - APERTURE INFRA -RED SPECTRAL IMAG - tors that are sensitive to infra -red radiation . The optical
ING SYSTEM ” , which claims benefit under 35 U . S .C . 10 system may include an optical aperture (a boundary of$ 119( e ) of U .S . Provisional Application No. 61/ 903 ,075 , which is defined to circumscribe or encompass the at least
filed on Nov . 12 . 2013 and titled " DIVIDED - APERTURE two or more spatially distinct optical channels ) and one or
INFRA -RED SPECTRAL IMAGING SYSTEM ” . Each of more optical filters . In various implementations, the one or
the above -identified application is incorporated by reference more optical filters can comprise at least two spectrally

herein in its entirety .
TECHNICAL FIELD

15 multiplexed filters . Each of these optical filters can beassociated with one of the at least two or more opticalchannels and configured to transmit a portion of the IRradiation received in the associated optical channel. In
The present invention generally relates to a system and various embodiments , the one or more optical filters can bemethod for gas cloud detection and , in particular, to a system 20 spectrally multiplexed and may include , for example , at leastand method of detecting spectral signatures of chemicalcompositions in a mid - and long-wave infrared spectral

region .

one of a longpass optical filter and a shortpass optical filter ,or a band pass filter (with or without a combination withanother filter such as a notch filter, for example ). The opticalsystem may further include at least two reimaging lenses .
DESCRIPTION OF THE RELATEDTECHNOLOGY

The at least two reimaging lenses, for example each of thereimaging lens,may be disposed to transmit IR radiation (forexample , between about 1 micron and about 20 microns ),Spectral imaging systems and methods have applications that has been transmitted through a corresponding opticalin a variety of fields. Spectral imaging systems and methods
filter towards the optical FPA unit. In one embodiment, theobtain a spectral image of a scene in one or more regions of 30 optical FPA unit is positioned to receive IR radiation fromthe electromagnetic spectrum to detect phenomena , identify

material compositions or characterize processes . The spec
tral image of the scene can be represented as a three

dimensional data cube where two axes of the cube represent

the object through the at least two reimaging lenses to form

respectively - corresponding two or more sets of imaging data
representing the object. The processor or processing elec
tronics is configured to acquire this optical data from the two

two spatial dimensions of the scene and a third axes of the 35 or more sets of imaging data . In various embodiments of theimaging systems, the FPA unit may be devoid of coolingsystems. In various embodiments , two ormore of the arraydata cube represents spectral information of the scene indifferent wavelength regions . The data cube can be pro
cessed using mathematical methods to obtain informationof photo - sensitive devices may be uncooled . In someabout the scene. Some of the existing spectral imaging

temperature - controlled shutters removably positioned toembodiments, the system further comprises two or more
systems generate the data cube by scanning the scene in the 40 block IR radiation incident onto the optical system from thespatial domain ( e. g ., by moving a slit across the horizontal object.
dimensions of the scene) and /or spectral domain ( e. g ., by
Also disclosed herein is an implementation of a method ofscanning a wavelength dispersive element to obtain images
operating an infrared (IR ) imaging system . The methodof the scene in different spectral regions). Such scanning includes receiving IR radiation from an object through at
approaches acquire only a portion of the full data cube at a 45 least two optical channels defined by components of antime. These portions of the full data cube are stored and thenlater processed to generate a full data cube .

optical system of the IR imaging system , which at least two

optical channels are spatially and spectrally different fromone another. The method further includes transmitting thereceived IR radiation towards an optical focal plane array
50 ( FPA ) unit that is not being cooled in the course of normal
The systems, methods and devices of this disclosure each operation . For example , in various embodiments of thehave several innovative aspects, no single one of which is imaging systems, the FPA unit may be devoid of coolingsolely responsible for the desirable attributes disclosed systems. In various embodiments , two ormore of the arrayof photo - sensitive devices may be uncooled . Some embodi
herein .
Various embodiments of the systems described herein sements further comprise removably positioning at least one ofprovide an infrared (IR ) imaging system for determining a at least two temperature - controlled shutters in front of theconcentration of a target chemical species in an object (e . g ., optical system to block IR radiation incident onto the opticala gas plume). The imaging system includes (i) an optical system from the object.
system , having an optical focal plane array (FPA ) unit
Various innovative aspects of the subjectmatter described
configured to receive IR radiation from the object along at in this disclosure can be implemented in the following
least two ormore optical channels defined by components of 60 embodiments :SUMMARY

the optical system , the at least two or more optical channels

Embodiment 1: An infrared ( IR ) imaging system , theoccurrence of data acquisition ( or snapshot ). The optical
FPA unit includes an array of photo -sensitive devices thatand configured to be imaged by the plurality of cam

being spatially and spectrally different from one another; imaging system comprising:and ( ii) a processor or processing electronics configured toa plurality of cameras ;acquire multispectral optical data representing said target
at least one thermal reference source having a known
chemical species from the received IR radiation in a single 65
temperature placed in front of the plurality of cameras
eras ; andUS 10 , 267 ,686 B2
a data -processing unit comprising a processor, the imag Embodiment 19 : The system of any of Embodiments
ing system configured to :1 - 18 , wherein the system includes at least seven opticalacquire with the plurality ofcameras a plurality of frames channels .
having regions that correspond to the image of the
Embodiment 20 : The system of any of Embodiments
5 1- 19, wherein the system includes at least eight opticalreference source ; andapply a dynamic calibration correction to the plurality of channels .
cameras to allow every camera in the plurality of
Embodiment 21: The system of any of Embodiments
cameras to be calibrated to agree with every other 1 -20 , wherein the system includes at least nine opticalcamera in the plurality imaging the reference source .
channels.
Embodiment 2 : The system of Embodiment 1, wherein
Embodiment 22 : The system of any of Embodiments
the plurality of cameras comprises a FPA unit and a plurality 1-21, wherein the system includes at least ten optical chanof lenses .
nels.
Embodiment 3 : The system of any of Embodiments 1 - 2 ,Embodiment 23 : The system of any of Embodiments

wherein the FPA unit comprises one FPA or a plurality of 15 1 - 22 , wherein the system includes at least twelve optical
FPAs.
channels .

Embodiment 4 : The system of any of Embodiments 1 -3 ,Embodiment 24: The system of any of Embodiments
wherein the at least one thermal reference source has a 1- 23 , further comprising one or more sensors configured toknown spectrum .
measure a temperature of the at least one reference source .
Embodiment 5 : The system of any of Embodiments 1 -4 , 20 Embodiment 25 : The system of any of Embodiments
further comprising an additional thermal reference source 1-24 , wherein the plurality ofcameras is configured to image
the same portion of the at least one reference source .
imaged by the plurality of cameras.
Embodiment 6 : The system of any of Embodiments 1 - 5 ,wherein the additional reference source has a temperature

Embodiment 26 : An infrared (IR ) imaging system , theimaging system comprising :and a spectrum different from the known temperature and 25

a plurality of cameras ;the known spectrum of the at least one reference source .

a first temperature - controlled reference source imaged by

Embodiment 7 : The system of any of Embodiments 1 -6 ,wherein the temperature of the additional thermal reference
source is less than the known temperature .
Embodiment 8 : The system of any of Embodiments 1 - 7 , 30

wherein the temperature of the additional thermal reference
source is greater than the known temperature .
Embodiment 9: The system of any of Embodiments 1 -8 ,wherein the at least one reference source is displaced awayfrom a conjugate image plane of the plurality of cameras 35
such that the image of the at least one reference source

captured by the plurality of cameras is blurred .
Embodiment 10 : The system of any of Embodiments 1 - 9,
wherein the at least one reference source is positioned at a
conjugate image plane of the plurality of cameras.
40

the plurality of cameras ;a second temperature-controlled reference source imagedby the plurality of cameras ; andprocessing unit configured to :acquire with the plurality of cameras a plurality of frames
a data -processing unit comprising a processor, said data

having regions that correspond to the image of thereference source ; anddynamically calibrate the plurality of cameras so thatvarious cameras imaging a scene are forced to agree ona temperature estimate of the first and second reference
sources.

Embodiment 27 : The imaging system of any of Embodi

Embodiment 11 : The system of any of Embodiments
1 - 10 , further comprising a plurality of mirrors configured toment 26 , wherein the data -processing unit is configured to
calculate a dynamic calibration correction and apply theimage the at least one reference source onto the plurality ofcorrection to the plurality of cameras for each of the plurality

cameras.
of frames.
Embodiment 12 : The system of any of Embodiments 45 Embodiment 28 : The system of any of Embodiments
1 - 11 , wherein the plurality of mirrors are disposed outside a
26 - 27 , wherein the first reference source is maintained at a
central field of view of the plurality of cameras .
first temperature .
Embodiment 13 : The system of any of Embodiments
Embodiment 29: The system of any of Embodiments
1 - 12 , further comprising a first and a second temperature 26 - 28 . wherein the second reference source is maintained atcontrolled shutter removably positioned to block IR radia - 50 a second temperature.
tion incident on the system from reaching the plurality of
Embodiment 30 : The system of any of Embodiments
cameras .
26-29, wherein the first temperature is greater than the
Embodiment 14 : The system of any of Embodiments second
temperature .
1 - 13 , wherein the system includes at least two spatially and
Embodiment
31: The system of any of Embodiments
55
spectrally different optical channels .
2630,
whereinthefirst temperature is less than the second
Embodiment 15 : The system of any of Embodiments

1 - 14 , wherein the system includes at least three opticaltemperature .

Embodiment 32 : The system of any of Embodiments
channels .
Embodiment 16 : The system of any of Embodiments
26 -31, wherein the first and the second reference sources are
1 - 15 , wherein the system includes at least four optical 60 displaced away from a conjugate image plane of the plural

ity of cameras such that the image of the first and the second
reference sources captured by the plurality of cameras is
1 - 16 , wherein the system includes at least five optical blurred .
channels .
Embodiment 33 : The system of any of Embodiments
Embodiment 18 : The system of any of Embodiments 65 26 -32 , wherein the first and the second reference sources are
1 - 17 , wherein the system includes at least six optical chan - positioned at a conjugate image plane of the plurality ofchannels.

Embodiment 17 : The system of any of Embodiments

nels .

cameras.

US 10 , 267 ,686 B2
Embodiment 34 : The system of any of Embodiments

26 -33, further comprising :a first mirror configured to image the first reference onto
the plurality of cameras ; andEmbodiment 48 : The system of any of Embodiments

44 -47, further comprising a first and a second temperature
controlled shutter removably positioned to block IR radiation incident on the system from reaching the plurality ofa second mirror configured to image the second reference 5 cameras .
Embodiment 49: The system of any of Embodiments
source onto the plurality of cameras.
Embodiment 35 : The system of any of Embodiments 44 - 48 ,wherein the system includes at least two spatially and26 -34 , further comprising a first and a second temperature
spectrally different optical channels.
controlled shutter removably positioned to block IR radia
Embodiment 50: The system of any of Embodimentstion incident on the system from reaching the plurality of " 44-49, wherein the system includes at least three opticalcameras .
channels .
Embodiment 36 : The system of any of Embodiments
Embodiment 51 : The system of any of Embodiments
26 - 35 , wherein the system includes at least two spatially and44 -50 , wherein the system includes at least four optical
spectrally different optical channels .
15 channels.
Embodiment 37 : The system of any of Embodiments
Embodiment 52: The system of any of Embodiments
26 - 36 , wherein the system includes at least four optical 44-51, wherein the system includes at least five opticalchannels .

Embodiment 38 : The system of any of Embodiments

channels.

Embodiment 53 : The system of any of Embodiments

26 -37, wherein the system includes at least six optical 20 44 -52 , wherein the system includes at least six opticalchannels .

channels .

Embodiment 39: The system of any of Embodiments

Embodiment 54 : The system of any of Embodiments

26 - 38 , wherein the system includes at least eight optical

44-52, wherein the system includes at least seven opticalchannels .

Embodiment 40 : The system of any of Embodiments 25channels .
Embodiment 55 : The system of any of Embodiments

26 -39, wherein the system includes at least ten optical 44 -53, wherein the system includes at least eight opticalchannels.
Embodiment 41 : The system of any of Embodiments
56 : The system of any of Embodiments
26 -40, wherein the system includes at least twelve optical 44Embodiment54,
whereinthe system includes at least nine opticalchannels .
30channels.
Embodiment 42 : The system of any of Embodiments
57: The system of any of Embodiments
26 -41, further comprising one ormore sensors configured to 44 -Embodiment55,
whereinthe system includes at least ten opticalmeasure a temperature of the first or the second reference channels .
source .
Embodiment 43 : The system of any of Embodiments 35 Embodiment 58 : The system of any of Embodiments
44 - 56 , wherein the system includes at least twelve optical
26 - 42 , wherein the plurality of cameras is configured toimage the same portion of the first reference source and channels.
Embodiment 59 : The system of any of Embodiments
wherein plurality of cameras is configured to image the same
44 - 57 , wherein the plurality of cameras is configured toportion of the second reference source .
Embodiment 44: An infrared (IR ) imaging system , the 40 image the same portion of the reference .
imaging system comprising :Embodiment 60 : An infrared (IR ) imaging system , thechannels .

a plurality of cameras;a reference having an unknown temperature configured to

be imaged by the plurality of cameras ; andimaging system comprising :an optical system including an optical focal plane arraya data -processing unit comprising a processor , the imag - 45

(FPA ) unit , the optical system includes components
associated with at least two optical channels , said atacquire with the plurality of cameras a plurality of framesdifferent from one another, each of the at least two
optical channels positioned to transfer IR radiation

calculate a dynamic calibration correction using a tem - 50

unit, the optical FPA unit comprising at least two

perature measured by one of the cameras in the plu

detector arrays disposed at a distance from two corre

apply the calibration correction to the other cameras in theat least one thermal reference having a known tempera

plurality of cameras to match the temperature estimate

ture , wherein radiation emitted from the at least one
reference is directed towards the optical FPA unit andimaged by the at least two detector arrays ; anding system configured to :having regions that correspond to the image of thereference ;rality of cameras as a reference temperature ; andof the other cameras in the plurality of cameras with the 55
reference temperature .

Embodiment 45 : The system of any of Embodiment 44 ,wherein the reference is displaced away from a conjugate
image plane of the plurality of cameras such that the imageof the reference source captured by the plurality of cameras 60
is blurred .

Embodiment 46 : The system of any of Embodiments
image plane of the plurality of cameras .

44 - 45 , wherein the reference is positioned at a conjugate

Embodiment 47: The system of any of Embodiments 65

44 - 46 , further comprising a plurality of mirrors configured

to image the reference onto the plurality of cameras .

least two optical channels being spatially and spectrally
incident on the optical system towards the optical FPA

sponding focusing lenses ;a data -processing unit , said data -processing unit config
ured to :acquire a plurality of frames with the at least two detector
arrays having regions in the plurality of image framesthat correspond to the image of the reference ; anddynamically calibrate the at least two detector arrays toaddress a difference in the temperature estimate of thereference between the two detector arrays.
Embodiment 61: The system of any of Embodiment 60 ,wherein the at least one thermal reference has a known
spectrum .

US 10 , 267 ,686 B2
Embodiment 62: The system of any of Embodiments
wherein radiation from the additional reference is directed
towards the optical FPA unit and imaged by the at least two
60 -61, further comprising an additional thermal reference ,detector arrays .

Embodiment 63 : The system of any of Embodiments

Embodiment 78: The system of any of Embodiments
ciated with four optical channels .
Embodiment 79: The system of any of Embodiments
5 60 -78 , wherein the optical system includes components
60 - 77wherein the optical system includes components asso
associated with six optical channels .

60 -62 , wherein the additional reference has a temperature

Embodiment 80 : The system of any of Embodiments

and a spectrum different from the known temperature and60 -79 , wherein the optical system includes components

the known spectrum of the at least one reference source .
associated with eight optical channels .
Embodiment 64 : The system of any of Embodiments 10 Embodiment 81: The system of any of Embodiments
60 -63, wherein the temperature of the additional thermal 60 - 80 , wherein the optical system includes components
associated with ten optical channels.
reference is less than the known temperature .

Embodiment 65 : The system of any of Embodiments
Embodiment 82: The system of any of Embodiments
reference is greater than the known temperature .
associated with twelve optical channels.
Embodiment 66 : The system of any of Embodiments
Embodiment 83 : The system of any of Embodiments
60 -65, wherein the at least one reference is displaced away 60 -82 , wherein the optical system includes components
from a conjugate image plane of the at least two detector associated with sixteen optical channels.
arrays such that the image of the at least one reference 20 Embodiment 84: The system of any of Embodiments
captured by the at least two detector arrays is defocused .
60 -83, wherein the optical system includes components
Embodiment 67 : The system of any of Embodiments associated with twenty four optical channels.
60 -64 , wherein the temperature of the additional thermal 15 60 -81, wherein the optical system includes components

60 -66 , wherein the at least one reference is positioned at a
Embodiment 85 : The system of any of Embodiments
conjugate image plane of the at least two detector arrays 60 - 84 , wherein each of the at least two detector arrays issuch that the image of the at least one reference captured by 25 configured to image the same portion of the at least one
the at least two detector arrays is focused .
reference so as to consistently provide a common reference
Embodiment 68 : The system of any of Embodiments temperature .
60 -67, further comprising at least two reflecting elements
86 : The system of any of Embodiments
configured to direct radiation from the at least one reference 60 Embodiment- 85 , wherein the data - processing unit comprises processsource toward the at least two detector arrays.
Embodiment 69: The system of any of Embodiments

ing electronics.

60 -68, wherein the at least two reflecting elements are

60 - 86 , wherein the data -processing unit comprises a proces

detector arrays .

sor.

between the at least two detector arrays .
Embodiment 71: The system of any of Embodiments
60 -70 , wherein the data -processing unit is configured to :Embodiment 89 : An infrared ( IR ) imaging system , theimaging system comprising :Embodiment 87: The system of any of Embodiments

disposed outside a central field of view of the at least two

88 : The system of any of Embodiments
Embodiment 70 : The system of any of Embodiments 35 60 Embodiment-87 , wherein the data - processing unit comprises one or
60 -69, further comprising a third detector array disposed more
processors.
acquire a plurality of frames using the third detector array ; 40
anddynamically calibrate the third detector array to match atemperature estimate of the third detector array with thetemperature estimates of the at least two detector
arrays .

an optical system including an optical focal plane array(FPA ) unit, the optical system including at least two
optical channels , said at least two optical channels
being spatially and spectrally different from one

another, each of the at least two optical channels
45

Embodiment 72 : The system of any of Embodiments

60 -71, wherein radiation emitted from the at least one
reference source is not imaged by the third detector array.

positioned to transfer IR radiation incident on the

optical system towards the optical FPA unit, the optical
posed at a distance from two corresponding focusing

FPA unit comprising at least two detector arrays dis

Embodiment 73 : The system of any of Embodiments
60 - 72 , wherein the third detector array has a field of view 50
greater than a field of view of the at least two detector arrays .
Embodiment 74 : The system of any of Embodiments
60 - 73 , wherein the at least one reference is imaged by thethird detector array .

lenses ;a first temperature -controlled reference imaged by the atleast two detector arrays ;a second temperature- controlled reference imaged by the

Embodiment 75 : The system of any of Embodiments 55

acquire a plurality of frames with the at least two detector

60-74 , further comprising a third reflecting element disposed

outside the field of view of the at least two detector arrays
and configured to image the at least one reference onto thethird detector array .
Embodiment 76 : The system of any of Embodiments 60

60 -75, further comprising a first and a second temperature
controlled element removably positioned to block IR radiation incident on the optical system from reaching the optical
FPA unit.

Embodiment 77 : The system of any of Embodiments 65
60 - 76 , wherein the optical system includes components

associated with three optical channels .

at least two detector arrays; anda data -processing unit configured to :arrays having regions in the plurality of image framesthat correspond to the image of the first and second
references; anddynamically calibrate the at least two detector arrays toaddress a difference in a temperature estimate of thefirst and second references between the two detector
arrays .

Embodiment 90 : The system of Embodiment 89 , wherein
the first reference is maintained at a first temperature.

Embodiment 91 : The system of any of Embodiments
89 - 90 , wherein the second reference is maintained at asecond temperature .

US 10 , 267 ,686 B2
10
Embodiment 92: The system of any of Embodiments
89 -91, wherein the first temperature is greater than the

Embodiment 107 : The system of any of Embodiments
89 - 106 , wherein the optical system includes components

temperature .
Embodiment 94 : The system of any of Embodiments

associated with five optical channels .
Embodiment 109: The system of any of Embodiments
89- 108 , wherein the optical system includes components

second temperature .

associated with four optical channels.
Embodiment 93 : The system of any of Embodiments
Embodiment 108 : The system of any of Embodiments
89- 92 , wherein the first temperature is less than the second 5 89 - 107, wherein the optical system includes components

89 - 93, wherein the first and the second references arewith six optical channels.
displaced away from a conjugate image plane of the at least 10 associated
Embodiment
The system of any of Embodiments
two detector arrays such that the image of the first and the 89 - 109 , wherein 110the: opticalsystem includes components
second references captured by the at least two detector

associated with seven optical channels.
Embodiment 111 : The system of any of Embodiments
Embodiment 95 : The system of any of Embodiments
diments 8980 -110, wherein the optical system includes components
89- 94 , wherein the first and the second references are 15 associated with eight optical channels.

arrays is defocused .

positioned at a conjugate image plane of the at least two

detector arrays such that the image of the first and the second
references captured by the at least two detector arrays is

Embodiment 112 : The system of any of Embodiments

89 - 111, wherein the optical system includes components
associated with ten optical channels.

focused .

Embodiment 113 : The system of any of Embodiments
Embodiment 96 : The system of any of Embodiments 20 89- 112 , wherein the optical system includes components
89- 95 , further comprising:associated with twelve optical channels.
a first reflecting element configured to direct radiation

Embodiment 114 : The system of any of Embodimentsfrom the first reference toward the at least two detector 89 - 113 , wherein each of the at least two detector arrays is
configured to image the same portion of the first reference
arrays ; anda second reflecting element configured to direct radiation 25 source so as to consistently provide a common first reference
from the second reference toward the at least twoous.
detector arrays

temperature and wherein each of the at least two detector
arrays is configured to image the same portion of the second
reference source so as to consistently provide a common
second reference temperature .

Embodiment 97 : The system of any of Embodiments
89 -96 , wherein the first reflecting element is disposed out 30 Embodiment 115 : The system of any of Embodimentsside a field of view of the at least two detector arrays .
- 114 , further comprising a temperature controller config
Embodiment 98 : The system of any of Embodiments 89
ured
89 -97, wherein the second reflecting element is disposed ence .to control the temperature of the first or second referoutside a field of view of the at least two detector arrays.
116 : The system of any of Embodiments
Embodiment 99 : The system of any of Embodiments$ ,35 89Embodiment115,
furthercomprisingor more sensors configured
89 - 98 , further comprising a third detector array disposed to measure a temperature of one
the first or the second reference .
between the at least two detector arrays .
Embodiment 117 : The system of any of Embodiments
Embodiment 100 : The system of any of Embodiments 89 - 116 , wherein the one or more sensors are configured to89- 99 , wherein the data -processing unit is configured to :communicate the measured temperature of the first or theacquire a plurality of frames using the third detector array ; 40 second reference to a temperature controller.
andEmbodiment 118 : The system of any of Embodiments
dynamically calibrate the third detector array to address a 89 - 117 , wherein the one or more sensors are configured todifference in the temperature estimate of the first andcommunicate the measured temperature of the first or thesecond references between the third detector array andsecond reference to the data -processing unit.

45 Embodiment 119 : The system of any of Embodiments
the two detector arrays .
Embodiment 101: The system of any of Embodiments
89 -118 , wherein the first or the second reference is associ89- 100 , wherein the first and second references are notated with a heater.

Embodiment 120 : The system of any of Embodiments
imaged by the third detector array.
Embodiment 102 : The system of any of Embodiments
89 - 119 , wherein the first or the second reference is associ
89 - 101, wherein the third detector array has a field of view 50 ated with a cooler.

greater than a field of view of the at least two detector arrays .

Embodiment 103: The system of any of Embodiments

Embodiment 121: The system of any of Embodiments

89- 120 ,wherein the data-processing unit comprises process
ing electronics .
Embodiment 122: The system of any of Embodiments

89 - 102, wherein r first and second references are imaged by
the third detector array.
Embodiment 104 : The system of any of Embodiments 55 89 - 121 , wherein the data -processing unit comprises a pro
89 - 103 , further comprising a third reflecting element dis
cessor.
posed outside the field of view of the at least two detector
Embodiment 123: The system of any of Embodiments
arrays and configured to image the first and second refer 89 - 122 , wherein the data - processing unit comprises one ormore processors .
ences onto the third detector array.

Embodiment 105 : The system of any of Embodiments 60

89 - 104 , further comprising a first and a second temperature -Embodiment 124 : An infrared (IR ) imaging system , theimaging system comprising:

controlled element removably positioned to block IR radia

an optical system including components associated withtion incident on the optical system from reaching the opticalat least two optical channels, said at least two optical

FPA unit.

channels being spectrally different from one another,

Embodiment 106 : The system of any of Embodiments 65
89 - 105, wherein the optical system includes components
associated with three optical channels .

each of the at least two optical channels positioned totransfer IR radiation incident on the optical system
towards a plurality of cameras;US 10 , 267,686 B2
11
at least one calibration surface with unknown temperatureand imaged by each of the at least two detectors ; and12spectrally different optical channels comprising at least
one imaging lens configured to image the object on aacquire a plurality of image frames with the plurality of

Focal Plane Array (FPA ) unit ; andprocessing electronics in communication with the FPA

a data -processing unit configured to :cameras including the imaged surface ; andadjust one or more parameters of the cameras in theplurality of cameras such that a temperature estimate ofunit,

wherein said infrared system is configured to :acquire multispectral optical data from the at least four
the calibration surface of the cameras in the plurality ofdifferent optical channels ; andcameras agree with each other.
processthe multispectral optical data to detect one or
Embodiment 125 : The system of Embodiment 124 , 10
moretargetspecies present in the object.
wherein the one or more parameters is associated with a gain
Embodiment142: The system of Embodiment 141, furof the cameras in the plurality of cameras .
thercomprising
twelveoptical channels.
Embodiment 126 : The system of any of Embodiments
Embodiment
143
:
The
system of any of Embodiments
124 - 125 , wherein the one or more parameters is associated 15 141- 142, configured to simultaneously
acquire multispectralwith a gain offset of the cameras in the plurality of cameras . 15 14 .
optical
data
from
the
at
least
four
different
optical channels.
Embodiment 127 : The system of any of Embodiments
Embodiment
144
:
The
systemof
anyof
Embodiments
124 - 126 , wherein the calibration surface is displaced awayfrom a conjugate image plane of the plurality of cameras 141- 143 , further comprising a plurality of optical filterssuch that an image of the surface is defocused .

associated with the optical channels .

Embodiment 128 : The system of any of Embodiments 20 Embodiment 145: The system of any of Embodiments
124 - 127 , wherein the calibration surface is positioned at a141- 144 , wherein a number of optical filters is two .
conjugate image plane of the plurality of cameras such that
Embodiment 146 : The system of any of Embodiments

141- 145 , wherein a number of optical filters is three .
Embodiment 129 : The system of any of Embodiments
Embodiment 147: The system of any of Embodiments
124 - 128 , further comprising at least one reflecting element 25 141 - 146 , wherein a number of optical filters is four.
configured to image the surface onto the plurality of cam Embodiment 148: The system of any of Embodiments
141- 147, wherein the plurality of optical filters comprise ateras.

an image of the surface is focused .

Embodiment 130 : The system of any of Embodiments

124 - 129 , further comprising a first and a second tempera -least one long pass (LP ) filter.

Embodiment 149 : The system of any of Embodiments

ture - controlled element removably positioned to block IR 30 141- 148 , wherein the plurality of optical filters compriseradiation incident on the optical system from reaching theplurality of cameras .

Embodiment 131: The system of any of Embodiments
124 - 130 , wherein the optical system includes components

associated with three optical channels.
Embodiment 132: The system of any of Embodiments
124 -131, wherein the optical system includes components

multiple long pass (LP ) filters.

Embodiment 150 : The system of any of Embodiments

141 - 149, wherein the plurality of optical filters comprise atleast one short pass (SP ) filter.
35 Embodiment 151: The system of any of Embodiments

141- 150 , wherein the plurality of optical filters comprise

multiple short pass ( SP ) filters.
Embodiment 152 : The system of any of Embodiments

associated with four optical channels.
Embodiment 133 : The system of any of Embodiments
141 - 151, wherein the plurality of optical filters comprise at
124 - 132, wherein the optical system includes components 40 least one band pass (BP ) filter.

associated with six optical channels .

Embodiment 134 : The system of any of Embodiments

Embodiment 153 : The system of any of Embodiments

141 - 152, wherein the plurality of optical filters comprise at

124 - 133 , wherein the optical system includes components

one short pass (SP ) filter and one long pass (LP ) filter.

associated with eight optical channels .

Embodiment 154 : The system of any of Embodiments
FPAs.

Embodiment 135 : The system of any of Embodiments 45 141- 153 , wherein the FPA unit comprises a plurality of

124 - 134, wherein the optical system includes components
associated with ten optical channels .

Embodiment 136 : The system of any of Embodiments
124 - 135 , wherein the optical system includes components

Embodiment 155 : The system of any of Embodiments
141- 154 , further comprising first and second temperature
controlled elements removably positioned to block IR radia

50 tion incident on the imaging system from reaching the FPA
associated with twelve optical channels.
Embodiment 137 : The system of any of Embodiments unit.
124 - 136 , wherein the data -processing unit comprises pro
Embodiment 156 : The system of any of Embodiments

141 - 155 , further comprising a field reference configured forcessing electronics .
Embodiment 138 : The system of any of Embodiments
dynamically calibrating a plurality of the FPAs in the FPA
124 - 137 , wherein the data - processing unit comprises a pro - 55 unit.
cessor.
Embodiment 157 : The system of any of Embodiments
Embodiment 139: The system of any of Embodiments
141- 156 , wherein the field reference is configured to obscure
124 - 138 , wherein the data -processing unit comprises one ora peripheral region of an image generated by a plurality ofmore processors .

the FPAs in the FPA unit .
Embodiment 140 : The system of any of Embodiments 60 Embodiment 158: The system of any of Embodiments
124 - 139 , wherein the calibration surface comprises a side141- 157 , configured to compare spectral data in at least one

wall of a housing of the system .

of the four optical channels acquired at a first instant of time

Embodiment 141: An infrared ( IR ) imaging system , the with spectral data in the at least one of the four opticalimaging system comprising :channels acquired at a second instant of time to generate a
at least four spatially and spectrally different optical 65 temporal difference image .
channels configured to receive IR radiation from a
Embodiment 159 : The system of any of Embodiments
common object, each of the at least four spatially and 141- 158 , configured to use a difference between the multiUS 10 , 267 ,686 B2
13

14spectral optical data acquired by the two optical channels to

Embodiment 184 : The system of any of Embodiments

correct parallax -induced imaging errors .

Embodiment 160: The system of any of Embodiments

141 - 159, configured to use a difference between the multi-

141- 183, wherein the thermal reference has a known tem

perature .

Embodiment 185 : The system of any of Embodiments

spectral optical data acquired by the two optical channels to 5 141 - 184 , wherein the thermal reference is a temperature

controlled reference source .
Embodiment 186 : The system of any of Embodiments141- 185 , wherein the temperature -controlled reference
141 - 160 , configured to estimate a size of the object based on source
includes a heater.
the estimated distance and an opticalmagnification factor of 10 Embodiment
187 : The system of any of Embodiments
the two optical channels.

estimate a distance between the system and the object.

Embodiment 161: The system of any of Embodiments

Embodiment 162: The system of any of Embodiments
141 - 161, configured to compare spectral data in one of theat least four optical channels with spectral data in anotherrol

141 - 186 , wherein the temperature-controlled reference

source includes a cooler .
Embodiment 188 : The system of any of Embodiments

141- 187 , further comprising a mirror configured to image

one of the at least four optical channels to generate a spectral 15 the thermal reference onto the FPA unit.
difference image.
Embodiment 189 : The system of any of Embodiments

Embodiment 163: The system of any of Embodiments
141- 162 , further comprising a visible light imaging sensor.
Embodiment 164 : The system of any of Embodiments

141- 188 , wherein a temperature of the thermal reference isunknown.

Embodiment 190 : The system of any of Embodiments

141- 163, configured to use the visible light imaging sensor 20 141 - 189, wherein the thermal reference is a surface .
to compensate for motion - induced imaging errors.
Embodiment 191: The system of any of Embodiments
Embodiment 165 : The system of any of Embodiments 141 - 190 , wherein the surface comprises a wall of a housing
141- 164 , configured to process the multispectral optical data of the system .
by cross -correlating multispectral optical data from at least
Embodiment 192: The system of any of Embodiments
one of the optical channels with a reference spectrum .
25 141 - 191, wherein different optical channels receive IR
Embodiment 166 : The system of any of Embodiments radiation from the same portion of the thermal reference so
141- 165, configured to process the multispectral optical datausing spectral unmixing .

as to consistently provide a common reference temperature .

Embodiment 193 : The system of any of Embodiments

141- 192, wherein a temperature of the same portion of the
Embodiment 167 : The system of any of Embodiments 30 thermalreference is unknown.
141- 166 , further comprising five optical channels.
Embodiment
194 : The system of any of Embodiments
Embodiment 168 : The system of any of Embodiments 141- 193, configured
to acquire the multispectral optical data141- 167 , further comprising six optical channels.
at
a
frame
rate
betweenabout 5 Hz to about 200 Hz.
Embodiment 169: The system of any of Embodiments
Embodiment
195
:
The
system of any of Embodiments
141 - 168 , further comprising seven optical channels .
35
141
194
,
whereinoneor
moreof the at least four optical
Embodiment 170 : The system of any of Embodiments
141- 169, further comprising eight optical channels.
Embodiment 171 : The system of any of Embodiments

channels is configured to collect IR radiation to provide
spectral data corresponding to a discrete spectral band
located in the wavelength range between about 7 . 9 um andabout 8 . 4 um .

141- 170, further comprising nine optical channels .
Embodiment 172: The system of any of Embodiments 40 Embodiment 196 : The system of any of Embodiments
141 - 171, further comprising ten optical channels.
141 - 195 , wherein each optical channel is configured to
Embodiment 173 : The system of any of Embodiments transfer spectrally distinct, two- dimensional image data of
141 - 172 , further comprising eleven optical channels.
the common object to one or more imaging sensors .
Embodiment 174 : The system of any of Embodiments
Embodiment 196 : The system of any of Embodiments
141- 173 , wherein a number of optical filters is five .
45 1 - 24 , wherein the one or more sensors are configured to
Embodiment 175: The system of any of Embodiments
communicate the measured temperature of the at least one
reference source to a temperature controller.
141- 174 , wherein a number of optical filters is six .

Embodiment 176 : The system of any of Embodiments

141- 175 , wherein a number of optical filters is seven .

Embodiment 197 : The system of any of Embodiments

1 -24 , wherein the one or more sensors are configured to
Embodiment 177 : The system of any of Embodiments 50 communicate the measured temperature of the at least one

141- 176 , wherein a number of optical filters is eight.
Embodiment 178 : The system of any of Embodiments

141- 177, wherein a number of optical filters is nine.

reference source to the data -processing unit .
Embodiment 198 : The system of any of Embodiments

26 - 42 , wherein the one or more sensors are configured to
Embodiment 179 : The system of any of Embodiments
communicate measured temperature of the first or the sec
141- 178 , wherein a number of optical filters is ten .
55 ond reference to a temperature controller.
Embodiment 180 : The system of any of Embodiments

Embodiment 199 : The system of any of Embodiments

141- 179, wherein a number of optical filters is eleven .
Embodiment 181: The system of any of Embodiments
141- 180 , wherein a number of optical filters is twelve.

26 - 42 , wherein the one or more sensors are configuredcommunicate the measured temperature of the first or thesecond reference to the data -processing unit.

Embodiment 182: The system of any of Embodiments 60

Embodiment 200 : An infrared ( IR ) imaging system for141- 181, wherein the processing electronics comprises one

imaging a target species in an object, the imaging system

or more processors .

comprising :Embodiment 183 : The system of any of Embodiments
141- 182, further comprising a thermal reference configured

an optical system comprising an optical focal plane array(FPA ) unit and defining a plurality of spatially andto be imaged onto the FPA unit such that a plurality of 65

spectrally different optical channels to transfer IR

image of the thermal reference source .

channel positioned to transfer a portion of the IR

frames of the acquired multispectral optical data has anradiation towards the optical FPA unit, each opticalUS 10 , 267 ,686 B2
15
radiation incident on the optical system from the object
towards the optical FPA unit ; anda programmable processor configured to execute instructions stored in a tangible, non - transitory computerreadable storage medium to process the acquired optical data

rence of data acquisition , multispectral optical datainduced by changes in the object that are not associated with

16

instructions stored in a tangible, non - transitory computer
to compensate for at least one of (i) parallax -induced dif
ferences between the two or more sets of imaging data andreadable storage medium , to acquire , in a single occur- 5 ( ii) difference between the two or more sets of imaging data

representing in spatial (x , y ) and spectral (a ) coordi

the target species.

nates said object and said target species from the IR
Embodiment 217 : The system of any of Embodiments
200 - 216 , wherein the processor is configured to executeradiation received at the optical FPA unit.
Embodiment 201: The system of Embodiment 200 , 10 instructions stored in a tangible, non -transitory computer
wherein the multispectral data comprises a number of spec - readable storage medium to process the acquired optical data
trally different images of the object obtained from IR image
to generate a temporal reference image .
data transferred to the optical FPA unit by a corresponding

Embodiment 218 : The system of any of Embodiments

200 - 217 , wherein the processor is configured to execute
Embodiment 202: The system of any of Embodiments 15 instructions stored in a tangible , non - transitory computer

optical channel.

200 - 201 , further comprising an optical filter corresponding

readable storage medium to use the temporal reference

to a particular optical channel and configured to transmit theimage to generate a temporal difference image .

portion of IR radiation towards the optical FPA unit.

Embodiment 219 : The system of any of Embodiments

Embodiment 203 : The system of any of Embodiments
200 -218 , wherein the processor is configured to execute
200 - 202, wherein the optical filter includes one of a longpass 20 instructions stored in a tangible , non -transitory computerreadable storagemedium to process the acquired optical data
optical filter and a shortpass optical filter.
Embodiment 204: The system of any of Embodiments
to estimate a volume of a gas cloud .

200-203 , further comprising one or more front objective

lenses.

Embodiment 220 : The system of any of Embodiments

200 - 219, wherein IR radiation measured at a pixel com

Embodiment 205: The system of any of Embodiments 25 prises a spectrum comprising a sum of component spectra ,200 - 204 , wherein the optical system comprises a plurality of and wherein the processor is configured to execute instructions stored in a tangible , non -transitory computer-readable
lenses , each lens corresponding to an optical channel .
Embodiment 206 : The system of any of Embodiments
storage medium to unmix the spectrum .

200 - 205, wherein each optical channel is defined at least in

Embodiment 221: The system of any of Embodiments

200 - 206 , wherein the plurality of lenses comprises a lens
Embodiment 208 : The system of any of Embodiments

Embodiment 222: The system of any of Embodiments
cally adjusting data output from the optical FPA unit .

part by a corresponding filter and a corresponding lens. 30 200 -220 , wherein the optical FPA unit includes a bolometer
Embodiment 207 : The system of any of Embodiments
configured to operate without being cooled .
array.

200 -221 , further comprising a field reference for dynami

200 - 207, further comprising a plurality of relay lenses 35 Embodiment 223 : The system of any of Embodiments
configured to relay the IR radiation along the optical chan 200 - 222 , wherein the field reference comprises an array offield stops.
nels .

Embodiment 209 : The system of any of Embodiments

Embodiment 224 : The system of any of Embodiments

200 - 208 , further comprising a plurality of moveable tem -200 -223 , wherein the field reference comprises a uniform

perature -controlled reference source removably positioned 40 temperature across its surface .

to block IR radiation incident onto the optical system fromEmbodiment 225 : The system of any of Embodiments
200 -224 , wherein the field reference is adapted to obscure or
reaching the optical FPA unit .
Embodiment 210 : The system of any of Embodiments block a peripheral portion of the IR radiation propagating
200 - 209 , wherein the multispectral optical data from the from the object towards the optical FPA unit .
plurality of optical channels is captured substantially simul- 45 Embodiment 226 : The system of any of Embodiments
taneously by the optical FPA unit.
200 - 225 , further comprising a visible light imaging sensor.
Embodiment 211 : The system of any of Embodiments
Embodiment 227 : The system of any of Embodiments
200 -210 , wherein the multispectral optical data from the 200 - 226 , wherein the processor is configured to execute
plurality of optical channels is captured during one image instructions stored in a tangible , non - transitory computer
50 readable storage medium to process data received from anframe acquisition by the optical FPA unit.
Embodiment 212: The system of any of Embodiments imaging sensor to compensate for motion - induced imaging
200 - 211 , further comprising first and second temperatureerrors .

controlled moveable shutters removably positioned to block

IR radiation incident onto the optical system from reaching

the optical FPA unit.

Embodiment 213 : The system of any of Embodiments

200 -212 , wherein the optical FPA unit is devoid of a coolingdevice .
Embodiment 214 : The system of any of Embodiments

Embodiment 228 : The system of any of Embodiments

200 - 227, wherein the processor is configured to execute
55 instructions stored in a tangible , non -transitory computerreadable storage medium to process data received from thevisible light imaging sensor to compensate for motion

induced imaging errors.

Embodiment 229: The system of any of Embodiments
60 200 - 228 , wherein the processor is configured to execute
Embodiment 215: The system of any of Embodiments
instructions stored in a tangible, non -transitory computer
200 - 214 , wherein the processor is configured to execute
readable storage medium to construct, in the single occur

200 - 213, further comprising a filter array.

instructions stored in a tangible, non -transitory computerreadable storage medium to acquire said optical data fromthe two or more sets of imaging data .

Embodiment 216 : The system of any of Embodiments

200 -215 , wherein the processor is configured to execute

rence of data acquisition , a multispectral data cube of theobject, the multispectral data cube comprising a number of

65 spectrally different images of the object, each spectrally

different image comprising IR image data transferred to theoptical FPA unit by a corresponding optical channel .

US 10 , 267 ,686 B2
17

18
wherein the system is configured to use a difference
between themultispectral optical data acquired by two
optical channels to estimate a distance between thesystem and the object.
Embodiment 234 : The system of Embodiment 233 ,Embodiment 230 : The system of any of Embodiments
200 - 229, wherein the portion of the IR radiation corresponds

to a region of wavelengths of the spectrum of wavelengths,

the region of wavelengths at least partially overlapping
another region of wavelengths transferred by another optical 5channel.
wherein spectral characteristics of the two optical channels

Embodiment 231: An infrared (IR ) imaging system , theidentical.
imaging system comprising: ed (IR ) Imaging system , the areEmbodiment235: An infrared (IR ) imaging system , thea plurality of spatially and spectrally different optical
ical imaging system comprising :channels , at least some of the plurality of optical 10 a plurality of spatially and spectrally different optical, atchannels configured to receive IR radiation from aleast some of the plurality of optical channels config
common object, each of the plurality of spatially andured to receive IR radiation from a common object,
spectrally different optical channels comprising at least
one imaging lens configured to image the object on a
15
Focal Plane Array (FPA ) unit; andprocessing electronics in communication with the FPA
unit,

wherein said infrared system is configured to :acquire multispectral optical data from the plurality ofdifferent optical channels ; andspectral data in at least one of the plurality of opticalchannels acquired at a first instant of time with spectral 25
data in at least one of the plurality of optical channels
acquired at a second instant of time to generate a

Embodiment 232 : An infrared (IR ) imaging system , the30

a plurality of spatially and spectrally different opticalchannels , at least some of the plurality of opticalchannels configured to receive IR radiation from acommon object, each of the plurality of spatially andspectrally different optical channels comprising at least 35

one imaging lens configured to image the object on a
Focal Plane Array (FPA ) unit; andprocessing electronics in communication with the FPA

acquire multispectral optical data from the plurality ofdifferent optical channels; andprocess the multispectral optical data to detect one ormore target species present in the object , anddifferent optical channels; andprocess the multispectral optical data to detect one ormore target species present in the object.
Embodiment 236 : An infrared (IR ) imaging system , theimaging system comprising :a plurality of spatially and spectrally different optical, atAPtemporal difference image .

unit,

unit ,

wherein said infrared system is configured to :acquire multispectral optical data from the plurality ofwherein the system is further configured to compare

wherein said infrared system is configured to :optical channels comprising at least one imaging lensconfigured to image the object on a Focal Plane Array(FPA ) unit ;a visible light imaging sensor , andprocessing electronics in communication with the FPA

20

process the multispectral optical data to detect one ormore target species present in the object, andimaging system comprising:each of the plurality of spatially and spectrally different

least some of the plurality of optical channels config
ured to receive IR radiation from a common object,
each of the plurality of spatially and spectrally different
optical channels comprising at least one imaging lensconfigured to image the object on a Focal Plane Array(FPA ) unit ; andprocessing electronics in communication with the FPA
unit,

40

wherein said infrared system is configured to :acquire multispectral optical data from the plurality ofdifferent optical channels ; andprocess the multispectral optical data to detect one ormore target species present in the object, andwherein the system is configured to compensate formotion -induced imaging errors .

Embodiment 237: An infrared (IR ) imaging system , thewherein the system is configured to use a difference 45 imaging system comprising :between the multispectral optical data acquired by two
a plurality of spatially and spectrally different, at least
optical channels to correct parallax - induced imaging
Embodiment 232: The system of Embodiment 231 ,ara
errors.

wherein spectral characteristics of the two optical channels 50

are identical.

Embodiment 233: An infrared ( IR ) imaging system , theimaging system comprising:a plurality of spatially and spectrally different opticalchannels , at least some of the plurality of optical 55
channels configured to receive IR radiation from asome of the plurality of optical channels configured toreceive IR radiation from a common object, each of theplurality of spatially and spectrally different opticalchannels comprising at least one imaging lens config

ured to image the object on a Focal Plane Array (FPA )unit; andprocessing electronics in communication with the FPA
unit ,
wherein said infrared system is configured to :acquire multispectral optical data from the plurality ofdifferent optical channels ; andcommon object, each of the plurality of spatially andspectrally different optical channels comprising at least
process the multispectral optical data to detect one or
one imaging lens configured to image the object on amore target species present in the object by cross60
correlating multispectral optical data from at least one
Focal Plane Array (FPA ) unit ; andprocessing electronics in communication with the FPAof the optical channels with a reference spectrum .
Embodiment 238 : An infrared ( IR ) imaging system , theunit,
imaging system comprising :wherein said infrared system is configured to :acquire multispectral optical data from the plurality ofa plurality of spatially and spectrally different optical, atdifferent optical channels ; and65
least some of the plurality of optical channels config
process the multispectral optical data to detect one orured to receive IR radiation from a common object,
each of the plurality of spatially and spectrally different
more target species present in the object, andUS 10 , 267,686 B2
20
FIG . 4 is a diagram of the embodiment employing an
configured to image the object on a Focal Plane Array
array of field references ( e . g ., field stops that can be used as
references for calibration ) and an array of respectively(FPA ) unit; andprocessing electronics in communication with the FPA
corresponding relay lenses.
5 FIG . 5A is a diagram of a 4 -by- 3 pupil array comprisingunit,
circular optical filters ( and IR blocking material between thewherein said infrared system is configured to :acquire multispectral optical data from the plurality of optical filters ) used to spectrally divide an optical wavefront
imaged with an embodiment of the system .
different optical channels ; andFIG . 5B is a diagram of a 4 -by -3 pupil array comprisingprocess the multispectral optical data to detect one or 10 rectangularfilters (and IR blocking materialbetween
more target species present in the object by using the optical opticalfilters)
used to spectrally divide an optical
spectral unmixing.
wavefront
imagedwithan embodiment of the system .
Embodiment 239 : An infrared (IR ) imaging system , theFIG.
6A
depicts
theoreticalplots of transmission charac
imaging system comprising :teristics
ofacombinationofband-pass filters used with anan optical system
includinganoptical
focal
plane
array
ystem including an optical local plane antay 15 embodiment of the system .
optical channels comprising at least one imaging lens

(FPA ) unit, the optical system includes components

FIG . 6B depicts theoretical plots of transmission characassociated with at least two optical channels , said atteristteristics of a spectrally multiplexed notch -pass filter combi

different from one another, each of the at least two

nation used in an embodiment of the system .
FIG . 6C shows theoretical plots of transmission charac

least two optical channels being spatially and spectrally

optical channels positioned to transfer IR radiation 20 teristics of spectrally multiplexed long -pass filter combina
incident on the optical system towards the optical FPA
tion used in an embodiment of the system .
unit, the optical FPA unit comprising at least two
FIG . 6D shows theoretical plots of transmission characdetector arrays disposed at a distance from two corre

teristics of spectrally multiplexed short- pass filter combina

ture , wherein one of the at least two detector arrays is
configured to image the at least one reference ; andan embodiment of the system used for gas detection .

tion used in an embodiment of the system .
sponding focusing lenses;
at least one thermal reference having a known tempera - 25 FIG . 7 is a set of video -frames illustrating operability of

FIGS. 8A and 8B are plots (on axes of wavelength inmicrons versus the object temperature in Celsius represent

a data -processing unit , said data - processing unit config

ing effective optical intensity of the object) illustrating
ured to :acquire a plurality of frames with one of the at least two 30 results of dynamic calibration of an embodiment of thesystem .

detector arrays having regions in the plurality of image
frames that correspond to the image of the reference ;andFIGS. 9A and 9B illustrate a cross-sectional view ofdifferent embodiments of an imaging system comprising an
arrangementof reference sources and mirrors that can be
dynamically calibrate another of the at least two detector 35 used for dynamic
calibration .
array to match a temperature estimate of another of the
FIGS
.
10A
10C
illustrate a plan view of different embodi
at least two detector array with the temperature esti

ments of an imaging system comprising an arrangement ofreference sources and mirrors that can be used for dynamic

mate of one of the at least two detector array .
Embodiment 240: The system of any of Embodiments

1 - 59 , wherein the plurality of cameras are configured to 40

calibration .
Like reference numbers and designations in the various
drawings indicate like elements .

Embodiment 241 : The system of any of Embodiments

DETAILED DESCRIPTION

acquire multispectral image data from an object continu ously for a duration of time.

1 - 59 , comprising at least two spectrally and spatially distinct
optical channels configured to transfer two - dimensional 45 The following description is directed to certain imple
mentations for the purposes of describing the innovative
image data of an object to the plurality of cameras .

Details of one or more implementations of the subject

aspects of this disclosure . However, a person having ordi

matter described in this disclosure are set forth in theaccompanying drawings and the description below . Other

nary skill in the art will readily recognize that the teachings
herein can be applied in a multitude of different ways . The

the description , the drawings and the claims. Note that therelative dimensions of the following figures may not be

device , apparatus, or system that can be configured tooperate as an imaging system such as in an infra -red imaging

features, aspects, and advantages willbecome apparent from 50 described implementations may be implemented in any

drawn to scale .

BRIEF DESCRIPTION OF THE DRAWINGSFIG . 1 shows an embodiment of an imaging system

including a common front objective lens that has a pupil
divided spectrally and re - imaged with a plurality of lenses
onto an infrared FPA .

system . The methods and systems described herein can be

included in or associated with a variety of devices such as ,55 but not limited to devices used for visible and infrared

spectroscopy, multispectral and hyperspectral imaging
devices used in oil and gas exploration, refining, and transportation , agriculture, remote sensing, defense and homeland security , surveillance , astronomy, environmental moni
60 toring, etc . The methods and systems described herein have

FIG . 2 shows an embodiment with a divided front objec - applications in a variety of fields including but not limited toagriculture , biology, physics, chemistry, defense and hometive lens and an array of infrared sensing FPAs.
FIG . 3A represents an embodiment employing an array of land security, environment, oil and gas industry, etc . The
front objective lenses operably matched with the re -imaging teachings are not intended to be limited to the implementa
lens array. FIG . 3B illustrates a two - dimensional array of 65 tions depicted solely in the Figures, but instead have wide
optical components corresponding to the embodiment of applicability as will be readily apparent to one having
FIG . 3A .

ordinary skill in the art.

US 10 , 267 ,686 B2
21
Various embodiments disclosed herein describe a divided
aperture infrared spectral imaging (DAISI) system that is
structured and adapted to provide identification of target
chemical contents of the imaged scene. The system is based

22

cations. For example, in various implementations, the imag
figured to be cooled to a temperature below 300 Kelvin . As

ing systems disclosed herein do not include detectors con

another example, in various implementations, the imaging

on spectrally - resolved imaging and can provide such iden - 5 systems disclosed herein do not include detectors configuredtification with a single - shot (also referred to as a snapshot)
to be cooled to a temperature below 273 Kelvin . As yet
comprising a plurality of images having different wave
another example , in various implementations , the imaging

length compositions that are obtained generally simultane -systems disclosed herein do not include detectors configured

ously . Without any loss of generality , snapshot refers to a
to be cooled to a temperature below 250 Kelvin . As anothersystem in which most of the data elements that are collected 10 example , in various implementations, the imaging systems

are continuously viewing the light emitted from the scene. In

disclosed herein do not include detectors configured to becontrast in scanning systems, at any given time only aminority of data elements are continuously viewing a scene,

cooled to a temperature below 200 Kelvin . Imaging systems
including uncooled detectors can be capable of operating infollowed by a different set of data elements, and so on , until
extremeweather conditions, require less power, are capable
the full dataset is collected . Relatively fast operation can be 15 of operation during day and night, and are less expensive .
achieved in a snapshot system because it does not need touse spectral or spatial scanning for the acquisition of infra red (IR ) spectral signatures of the target chemical contents .

Some embodiments described herein can also be less sus

ceptible to motion artifacts in comparison with spatiallyand /or spectrally scanning systemswhich can cause errors in

Instead , IR detectors ( such as, for example , infrared focal
either the spectral data , spatial data , or both .
plane arrays or FPAs) associated with a plurality of different 20 FIG . 1 provides a diagram schematically illustrating spa
optical channels having different wavelength profiles can be tial and spectral division of incoming light by an embodi
used to form a spectral cube of imaging data . Althoughment 100 of a divided aperture infrared spectral imager

spectral data can be obtained from a single snapshot com
prising multiple simultaneously acquired images corre -(DAISI) system that can image an object 110 possessing IR
spectral signature (s ). The system 100 includes a front objec

be obtained and a portion of these can be selected and

136 can be disposed at the focus of each of the lenses in the

sponding to different wavelength ranges, in various embodi- 25 tive lens 124 , an array of optical filters 130 , an array ofments, multiple snap shots may be obtained . In various reimaging lenses 128 and a detector array 136 . In various
embodiments, these multiple snapshots can be averaged
embodiments , the detector array 136 can include a single
Similarly, in certain embodiments multiple snap shots may
FPA or an array of FPAs. Each detector in the detector arraypossibly averaged . Also , in contrast to commonly used IR 30 array of reimaging lenses 128 . In various embodiments , thespectral imaging systems, the DAISI system does notdetector array 136 can include a plurality of photo -sensitive

require cooling. Accordingly, it can advantageously use devices. In some embodiments, the plurality of photo
uncooled infrared detectors . For example , in various imple - sensitive devices may comprise a two -dimensional imaging
mentations, the imaging systems disclosed herein do not sensor array that is sensitive to radiation having wavelengths
include detectors configured to be cooled to a temperature 35 between 1 um and 20 um ( for example , in near infra - red
below 300 Kelvin . As another example , in various imple - wavelength range, mid infra -red wavelength range , or longmentations, the imaging systems disclosed herein do not infra -red wavelength range ,). In various embodiments , theinclude detectors configured to be cooled to a temperature
below 273 Kelvin . As yet another example , in various

plurality of photo -sensitive devices can include CCD or
CMOS sensors, bolometers , microbolometers or other

implementations, the imaging systems disclosed herein do 40 detectors that are sensitive to infra - red radiation .

not include detectors configured to be cooled to a tempera ture below 250 Kelvin . As another example , in various
implementations , the imaging systems disclosed herein do

An aperture of the system 100 associated with the front
by the combination of the array of optical filters 130 and thetages over existing IR spectral imaging systems, most if notspectrally divided pupil that is disposed forward of theobjective lens system 124 is spatially and spectrally divided

not include detectors configured to be cooled to a tempera - array of reimaging lenses 128 . In various embodiments , the45 combination of the array of optical filters 130 and the array
ture below 200 Kelvin .
Implementations disclosed herein provide several advan - of reimaging lenses 128 can be considered to form a
all ofwhich may require FPAs that are highly sensitive andcooled in order to compensate , during the optical detection ,optical detector array 136 . The spatial and spectral divisionof the aperture into distinct aperture portions forms a plu

for the reduction of the photon flux caused by spectrum - 50 rality of optical channels 120 along which light propagates .

scanning operation . The highly sensitive and cooled FPA
systems are expensive and require a great deal of mainte -In various embodiments , the array 128 of re -imaging lenses
128a and the array of spectral filters 130 which respectively

nance. Since various embodiments disclosed herein are correspond to the distinct optical channels 120 . The plurality
configured to operate in single -shot acquisition mode with - of optical channels 120 can be spatially and /or spectrally
out spatial and/or spectral scanning, the instrument can 55 distinct. The plurality of optical channels 120 can be formed
receive photons from a plurality of points ( e . g., every pointin the object space and/ or image space . In one implemenof the object substantially simultaneously, during the single tation , the distinct channels 120 may include optical chanreading . Accordingly , the embodiments of imaging system
nels that are separated angularly in space . The array ofdescribed herein can collect a substantially greater amount spectral filters 130 may additionally include a filter -holdingof optical power from the imaged scene ( for example , an 60 aperture mask ( comprising, for example , IR light-blocking
order ofmagnitude more photons) at any given moment in materials such as ceramic , metal, or plastic ). Light from thetime especially in comparison with spatial and / or spectral object 110 ( for example a cloud of gas ), the optical prop
scanning systems. Consequently, various embodiments of erties of which in the IR are described by a unique absorp
the imaging systems disclosed herein can be operated using tion , reflection and/ or emission spectrum , is received by the
uncooled detectors ( for example , FPA unit including an 65 aperture of the system 100 . This light propagates througharray of microbolometers ) that are less sensitive to photons
each of the plurality of optical channels 120 and is further
in the IR but are well fit for continuous monitoring appli - imaged onto the optical detector array 136 . In variousUS 10 , 267 ,686 B2
23

24

implementations, the detector array 136 can include at least

whole system . In this specific case , the aperture stop sub

one FPA . In various embodiments, each of the re -imaging

stantially spatially coincides with and /or is about the same

corresponding spectral region . In the illustrated implemen

apertures corresponding to different optical channels 120 . As

lenses 128a can be spatially aligned with a respectively

size or slightly larger , as the plurality of smaller limiting

tation , each filter element from the array of spectral filters 5 a result, the positions for spectral filters of the different

130 corresponds to a different spectral region . Each re -optical channels 120 coincide with the position of theimaging lens 128a and the corresponding filter element of
the array of spectral filter 130 can coincide with ( or form ) a

aperture stop of the whole system , which in this example isshown as a surface between the lens system 124 and the

portion of the divided aperture and therefore with respec -array 128 of the reimaging lenses 128a . In various imple

tively - corresponding spatial channel 120 . Accordingly , in 10 mentations, the lens system 124 can be an objective lensvarious embodiment an imaging lens 128a and a corre -124. However, the objective lens 124 is optional and various

sponding spectral filter can be disposed in the optical path of
one of the plurality of optical channels 120 . Radiation fromembodiments of the system 100 need not include the objec
tive lens 124. In various embodiments, the objective lensarray (e. g., FPA component ) 136 to form a single image

the objective lens 124 is not included . Generally , however,

the object 110 propagating through each of the plurality of
124 can slightly shifts the images obtained by the different
optical channels 120 travels along the optical path of each 15 detectors in the array 136 spatially along a direction per
re -imaging lens 128a and the corresponding filter element of pendicular to optical axis of the lens 124 , thus the function
the array of spectral filter 130 and is incident on the detector
ality of the system 100 is not necessarily compromised when
( e .g ., sub -image ) of the object 110 . The image formed by thethe field apertures corresponding to different optical chandetector array 136 generally includes a plurality of sub - 20 nels may be located in the same or different planes . These
images formed by each of the optical channels 120 . Each offield apertures may be defined by the aperture of the reim

the plurality of sub - images can provide different spatial andaging lens 128a and/ or filters in the divided aperture 130 inspectral information of the object 110 . The different spatial

certain implementations. In one implementation , the field

information results from some parallax because of theapertures corresponding to different optical channels can bedifferent spatial locations of the smaller apertures of the 25 located in different planes and the different planes can bedivided aperture . In various embodiments, adjacent sub

optical conjugates of one another. Similarly , while all of thespectral signatures . The detector array ( e . g ., FPA compo -embodiment 100 are shown to lie in one plane , generally

nent ) 136 is further operably connected with a processor 150

different filter elements of the array of spectral filter 130 can

images can be characterized by close or substantially equal

filter elements in the array of spectral filters 130 of the(not shown ). The processor 150 can be programmed to 30 be disposed in different planes . For example , different filter

aggregate the data acquired with the system 100 into aelements of the array of spectral filters 130 can be disposed

spectral data cube . The data cube represents, in spatial ( x , y )in different planes that are optically conjugate to one

and spectral (a ) coordinates , an overall spectral image of theanother . However, in other embodiments , the different filter

object 110 within the spectral region defined by the combi-

elements can be disposed in non - conjugate planes.

nation of the filter elements in the array of spectral filters 35

In contrast to the embodiment 100 , the front objective lens

130 . Additionally , in various embodiments, the processor or

124 need not be a single optical element, but instead canprocessing electronics 150 may be programmed to deter
mine the unique absorption characteristic of the object 110 .
Also , the processor/processing electronics 150 can , alterna -include a plurality oflenses 224 as shown in an embodiment
200 of the DAISI imaging system in FIG . 2 . These lenses
224 are configured to divide an incoming optical wavefront

tively or in addition , map the overall image data cube into 40 from the object 110 . For example , the array of front objec
a cube of data representing, for example , spatial distribution
tive lenses 224 can be disposed so as to receive an IRof concentrations, c, of targeted chemical components
wavefront emitted by the object that is directed toward thewithin the field of view associated with the object 110 .
Various implementations of the embodiment 100 can

DAISI system . The plurality of front objective lenses 224
divide the wavefront spatially into non -overlapping sections.

ence source 160 including, for example, a shutter systemcomprising one or more reference shutters maintained at

portion of the optical system contributing to the spatial
division of the aperture of the system in this example . Thea heater, a cooler or a temperature - controlled element con -as a two - dimensional (2D ) array of lenses. FIG . 2 presents

include an optional moveable temperature - controlled refer - 45 FIG . 2 shows three objective lenses 224 in a front opticaldifferent temperatures. The reference source 160 can include

plurality of objective lenses 224 , however, can be configured

figured to maintain the reference source 160 at a desired 50 a general view of the imaging system 200 and the resultant

temperature . For example , in various implementations, thefield of view of the imaging system 200 . An exploded view
embodiment 100 can include two reference shutters main 202 of the imaging system 200 is also depicted in greater
tained at different temperatures . The reference source 160 is detail in a figure inset of FIG . 2 . As illustrated in the detailed
removably and, in one implementation , periodically insertedview 202 , the embodiment of the imaging system 200
into an optical path of light traversing the system 100 from 55 includes a field reference 204 at the front end of the system .
the object 110 to the detector array ( e . g ., FPA component)

The field reference 204 can be used to truncate the field of

136 along at least one of the channels 120 . The removableview . The configuration illustrated in FIG . 2 has an opera

reference source 160 thus can block such optical path .

tional advantage over embodiment 100 of FIG . 1 in that theMoreover, this reference source 160 can provide a reference

overall size and/or weight and / or cost of manufacture of the

IR spectrum to recalibrate various components including the 60 embodiment 200 can be greatly reduced because the objec
detector array 136 of the system 100 in real time. The
tive lens is smaller. Each pair of the lenses in the array 224

configuration of the moveable reference source 160 is further discussed below .

and the array 128 is associated with a field of view (FOV) .

Each pair of lenses in the array 224 and the array 128
In the embodiment 100 , the front objective lens system
receives light from the object from a different angle .Accord
124 is shown to include a single front objective lens posi- 65 ingly, the FOV of the different pairs of lenses in the arraytioned to establish a common field - of- view (FOV ) for the
224 and the array 128 do not completely overlap as a result
reimaging lenses 128a and to define an aperture stop for the of parallax . As the distance between the imaging system 200

US 10 , 267 ,686 B2
25(portion 202 ) and the object 110 increases, the overlapping
region 230 between the FOVs of the individual lenses 224

increases while the amount of parallax 228 remains approxi

mately the same, thereby reducing its effect on the system

26

a uniform temperature across its surface and be character
ized by a predetermined spectral curve of radiation emanat

ing therefrom . In various implementations, the field reference 338 can be used as a calibration target to assist in

200 . When the ratio of the parallax - to -object- distance is 5 calibrating or maintaining calibration of the FPA . Accord
substantially equal to the pixel - size - to -system - focal length
ingly , in various implementations , the field reference 338 isratio then the parallax effect may be considered to be

negligible and , for practical purposes, no longer distinguish -used for dynamically adjusting the data output from each

FPA 336 after acquisition of light from the object 110 . This

able . While the lenses 224 are shown to be disposed sub - dynamic calibration process helps provide that output of thestantially in the same plane, optionally different objective 10 different ( e .g ., most, or each of the ) FPA 336 represents
lenses in the array of front objective lenses 224 can becorrect acquired data , with respect to the other FPAs 336 fordisposed in more than one plane. For example , some of theindividual lenses 224 can be displaced with respect to someanalysis, as discussed below in more detail.

other lenses 224. As discussed below , the field reference 204
can be useful in calibrating the multiple detectors 236 .
In one implementation, the front objective lens systemsuch as the array of lenses 224 is configured as an array of

optical components (e .g ., objective lenses 324a , filter ele
ments of the array of spectral filters 130 , re - imaging lenses
128a and FPA units 336 ) are arranged as a 4x3 array. In one
implementation , the 4x3 array 340 of optical components

FIG . 3B illustrates the plan view perpendicular to the axis

other individual lenses 224 along the axis 226 (not shown)226 of an embodiment 300 of the imaging system illustrated
and/ or have different focal lengths as compared to some 15 in FIG . 3A . For the embodiment shown in FIG . 3B , thelenses integrated or molded in association with a monolithic 20 (lenses 324a , 128a; detector elements 336 ) is used behind

substrate . Such an arrangement can reduce the costs andcomplexity otherwise accompanying the optical adjustment

the temperature controlled reference target 160 . The fieldreference aperture 338 can be adapted to obscure and/ orof individual lenses within the system . An individual lens block a peripheral portion of the bundle of light propagatingfrom the object 110 towards the FPA units 336 . As a result ,tion . As one example , a pair of thin and large diameter 25 the field reference 338 obscures and /or blocks the border or

224 can optionally include a lens with varying magnifica -Alvarez plates can be used in at least a portion of the front
objective lens system . Without any loss of generality, theAlvarez plates can produce a change in focal length whentranslated orthogonally with respect to the optical beam

peripheral portion ( s ) of the images of the object 110 formedon the FPA elements located along the perimeter 346 of thedetector system . Generally, two elements of the FPA unit
will produce substantially equal values of digital counts

In further reference to FIG . 1 , the detector array 136 ( e.g ., 30 when they are used to observe the same portion of the scene

FPA component) configured to receive the optical datain the same spectral region using the same optical train . If

representing spectral signature (s ) of the imaged object 110 any of these input parameters ( for example , scene to be
can be configured as a single imaging array ( e . g ., FPA ) 136 .
observed , spectral content of light from the scene, or optical
This single array may be adapted to acquire more than one elements delivering light from the scene to the two detector
image ( formed by more than one optical channel 120 ) 35 elements ) differ, the counts associated with the elements ofsimultaneously . Alternatively , the detector array 136 may the FPA unit will differ as well . Accordingly , and as aninclude a FPA unit . In various implementations, the FPA unit
example , in a case when the two FPAs of the FPA unit 336
can include a plurality of optical FPAs. At least one of these (such as those denoted as # 6 and # 7 in FIG . 3B ) remain
plurality of FPAs can be configured to acquire more than one
substantially un - obscured by the field reference 338, thespectrally distinct image of the imaged object. For example , 40 outputs from these FPAs can be dynamically adjusted to theas shown in the embodiment 200 of FIG . 2 , in various

output from one of the FPAs located along perimeter 346

embodiments , the number of FPAs included in the FPA unit

(such as, for example , the FPA element # 2 or FPA element

may correspond to the number of the front objective lenses
224 . In the embodiment 200 of FIG . 2 , for example , three# 11 ) that processes light having similar spectral character
istics .

lenses 224 . In one implementation of the system , the FPA
unit can include an array of microbolometers . The use ofmultiple microbolometers advantageously allows for anembodiment of an imaging system 400 that contains an array424 of front objective lenses 424a . The array 424 of lenses
424a adapted to receive light from the object 110 and relay

FPAs 236 are provided corresponding to the three objective 45

FIG . 4 illustrates schematically a portion of anotherinexpensive way to increase the total number of detection
the received light to the array 128 of re - imaging lenses 128a
elements ( i.e . pixels ) for recording of the three -dimensional 50 through an array 438 of field references (or field stops ) 438a ,data cube in a single acquisition event (i. e . one snapshot). In

and through an array 440 of the relay lenses . The spectral

various embodiments, an array of microbolometers morecharacteristics of the field references /field stops 438a can be

efficiently utilizes the detector pixels of the array of FPAS

known. The field references 438a are disposed at corre( e. g ., each FPA ) as the number of unused pixels is reduced ,sponding intermediate image planes defined , with respect tominimized and / or eliminated between the images that may 55 the object 110 , by respectively corresponding front objective

exist when using a single microbolometer.

FIG . 3A illustrates schematically an embodiment 300 oflenses 424a . When refractive characteristics of all of thefront objective lenses 424a are substantially the same, all of
the field references 438a are disposed in the same plane . A

the imaging system in which the number of the front
objective lenses 324a in the lens array 324 , the number offield reference 438a of the array 438 obscures ( or casts are - imaging lenses 128a in the lens array 128 , and the number 60 shadow on ) a peripheral region of a corresponding image
of FPAs 336 are the same. So configured , each combination(e . g ., sub - image ) formed at the detector plane 444 throughof respectively corresponding front objective lens 324, re - a respectively corresponding spatial imaging channel 450 ofimaging lens 128a , and FPAs 336 constitutes an individual

the system 400 prior to such image being spectrally pro

imaging channel. Such a channel is associated with acqui-

cessed by the processor 150 . The array 440 of relay lenses

sition of the IR light transmitted from the object 110 through 65 then transmits light along each of the imaging channels 450
an individual filter element of the array of optical filters 130 . through different spectral filters 454a of the filter array 454 ,A field reference 338 of the system 300 is configured to have past the calibration apparatus that includes two temperatureUS 10 , 267 ,686 B2
27

28

controlled shutters 460a , 460b , and then onto the detector

or more coatings that are applied to one or more surfaces ofmodule 456 . In various embodiments, the detector module
456 can include a microbolometer array or some other IR

the reimaging lenses ( such as a lens 128a of FIGS. 1 , 2 , 3 ,and 4 ) or the surfaces of one or more detectors.

FPA .

The optical filtering configuration of various embodi
The embodiment 400 has several operational advantages. 5 ments
disclosed herein may advantageously use a bandpass
It is configured to provide a spectrally known object within filter defining
a specified spectral band . Any of the filters 0aevery image (e.g., sub - image ) and for every snapshot acqui through 3a the transmission curves of which are shown insition which can be calibrated against . Such spectral cer FIG . 6A may, for example , be used . The filters may betainty can be advantageous when using an array of IR FPAS 10 placedin front of the optical FPA (or generally, between thelikemicrobolometers, the detection characteristics of which optical FPA and the object). In particular, and in further
can change from one imaging frame to the next due to , in reference to FIGS . 1, 23, and 4 , when optical detector arrays
part, changes in the scene being imaged as well as thethermal effects caused by neighboring FPAs. In various 136 , 236 , 336 , 456 include microbolometers , the predomi
contribution to noise associated with image acquisition
embodiments , the field reference array 438 of the embodi- 1515 nantisdue
to detector noise . To compensate and /or reduce thement 400 - can be disposed within the Rayleigh range (apnoise,variousembodiments disclosed herein utilize spec
proximately corresponding to the depth of focus) associatedwith the front objective lenses 424 , thereby removing unus trally -multiplexed filters. In various implementations, theable blurred pixels due to having the field reference outside . spectrall -multiplexed filters can comprise a plurality of longp ass filters, a plurality long pass filters, a plurality of bandof this range . Additionally, the embodiment 400 of FIG 4.
can be more compact than , for example , the configuration
300 of FIG . 3A . In the system shown in FIG . 3A , forexample , the field reference 338 may be separated from thepass filters and any combinations thereof. An example of thespectral transmission characteristics of spectrally -multi
plexed filters Ob through 3d for use with various embodi

lens array 324 by a distance greater than several (for 25 ments of imaging systems disclosed herein is depicted in
FIG . 6B . Filters of FIG . 6C can be referred to as longtributed by the field reference to an image formed at a wavelength pass, LP filters. An LP filter generally attenuates
detector plane .
shorter wavelengths and transmits (passes ) longer wave
example , five ) focal lengths to minimize /reduce blur con -In various embodiments , the multi-optical FPA unit of the 20 lengths ( e . g ., over the active range of the target IR portion
IR imaging system can additionally include an FPA config - of the spectrum ). In various embodiments, short-wave

ured to operate in a visible portion of the spectrum . In
reference to FIG . 1 , for example , an image of the scene oflength -pass filters , SP, may also be used . An SP filter
generally attenuates longer wavelengths and transmits

image with the visible - light image . The IR image may beoverlapped virtually , with the use of a processor and spe

the snap -shot/non - scanning mode of operation , embodi

interest formed by such visible - light FPA may be used as a(passes ) shorter wavelengths ( e.g ., over the active range ofbackground to form a composite image by overlapping an IR 35 the target IR portion of the spectrum ). At least in part due tocifically -designed computer program product enabling suchments of the imaging system described herein can use less

4 , and in further reference to FIG . 3B , examples of a 4 -by - 3
array of spectral filters 130 is shown in FIGS. 5A and 5B .

embodiment of the imaging system , filters having spectral
bandwidths greater than those of band -pass filters , thedata processing, or actually , by a viewer. The IR image may sensitive microbolometers without compromising the SNR .
The use of microbolometers , as detector-noise - limited
be created based on the image data acquired by the indi 40 devices, in turn not only benefits from the use of spectrally
vidual FPAs 136 . The so - formed composite image facilitates multiplexed, but also does not require cooling of thethe identification of the precise spatial location of the target imaging systemfiltersduring
normal operation .
species, the spectral signatures of which the system is able
45 Referring again to FIGS. 6A , 6B , 6C , and 6D , each of the45
to detect /recognize .
filters (0b . . . 3d ) transmits light in a substantially wider
Optical Filters.
The optical filters , used with an embodiment of the region of the electromagnetic spectrum as compared to thosesystem , that define spectrally -distinct IR image (e .g., subof the filters (Oa . . . 3a ). Accordingly, when the spectrally
image ) of the object can employ absorption filters, interfer multiplexed set of filters (0b . . . 0d ) is used with anence filters , and Fabry - Perot etalon based filters, to name " embodiment of the imaging system , the overall amount ofjust a few . When interference filters are used , the image light received by the FPAs (for example , 236 , 336 ) is larger
acquisition through an individual imaging channel defined than would be received when using the bandpass filters
by an individual re - imaging lens (such as a lens 128a of (0a . . . 4a ). This added ” transmission of light defined by
FIGS. 1, 2 , 3, and 4 )may be carried out in a single spectral 55 the use of the spectrally -multiplexed LP (or SP) filters
bandwidth or multiple spectral bandwidths. Referring again facilitates an increase of the signal on the FPAs above theto the embodiments 100, 200 , 300, 400 of FIGS . 1 through level of the detector noise . Additionally, by using, in an
Individual filters 1 through 12 are juxtaposed with a sup- 00 uncooled FPAs of the embodiment of the imaging system
porting opto -mechanical element (not shown ) to define aexperience less heating from radiation incident thereon fromfilter-array plane that is oriented , in operation , substantially the imaged scene and from radiation emanating from theperpendicularly to the general optical axis 226 of the imag - FPA in question itself . This reduced heating is due to a
ing system . In various implementations, the individual filters 65 reduction in the back -reflected thermal emission (s ) coming
1 through 12 need not be discrete optical components . from the FPA and reflecting off of the filter from theInstead , the individual filters 1 through 12 can comprise one non -band-pass regions. As the transmission region of theUS 10 , 267 ,686 B2
29

30

multiplexed LP (or SP ) filters is wider, such parasitic effects
are reduced thereby improving the overall performance of
the FPA unit.
In one implementation , the LP and SP filters can bements disclosed herein . An S -matrix approach (which is
restricted to having a number of filters equal to an integerthat is multiple of four minus one ) or a row - doubled Had
amard matrix (requiring a number of filters to be equal to an

combined in a spectrally multiplexed fashion in order to 5 integer multiple of eight) can be used in various embodi
ments . Here, possible numbers of filters using an S -matrix
increase or maximize the spectral extent of the transmission
setup are 3 , 7 , 11, etc and , if a row -doubled Hadamard
region of the filter system of the embodiment.
matrix setup is used , then the possible number of filters is 8 ,The advantage of using spectrally multiplexed filters is

16 . 24 . etc. For example, the goal of the measurem

ayappreciated based on the following derivation , in which a 10 be to measure seven spectral band f; intensities using sevensystem of M filters is examined ( although it is understood measurements g; as follows:that in practice an embodiment of the invention can employ
81 = f1+ 0 +f3 +0 + f3 + 0 + f7+ 11,
any number of filters ). As an illustrative example , the caseof M = 7 is considered . Analysis presented below relates to82= 0 + f2+ f3+ 0 + 0 + f6 +fz+n2
one spatial location in each of the images (e.g ., sub-images ) 15
83= fi +f2+0 + 0 + f3 + 0 +f=+nz
formed by the differing imaging channels (e.g ., different
optical channels 120) in the system . A similar analysis can
84 +0 + 0 + 0 + f4 + fs +f7+ f3 +N4

be performed for each point at an image (e .g ., sub - image ),and thus the analysis can be appropriately extended as 20
required .
The unknown amount of light within each of the M

85= f1 + 0 +f3 + f4 + 0 + f6 + 0 +n5
86 = 0 = f2 + f3+ f4f5 + 0 + 0 +ng

spectral channels (corresponding to these M filters) is
87= fi+f2+ 0 + f4 +0 +0f7+n7
denoted with f1, f , f3, . . . fy , and readings from corre
sponding detector elements receiving light transmitted by 25 Optical transmission characteristics of the filters
described above are depicted in FIG . 6B . Here , a directeach filter is denoted as 81, 82 , 83 . . . Sm , while measurement

estimate of the fi is no longer provided through a relationshiperrors are represented by nj, n2, nz, . . . nm . Then , thesimilar to (g :)= f;. Instead , if a “ hat” notation is used toreadings at the seven FPA pixels each of which is optically denotean estimate of a given value , then a linear combina
filtered by a corresponding band -pass filter of FIG . 6A can 20 tion of themeasurements can be used such as, for example ,be represented by :30
fi=1/ (+81-82+83-84+85-86+87),
81= fi+n1,
f ='/A( - g + g + gy- ga- gs + g% + gy),g2 = 42 +n2,

83= f3+ n3,
84 =f4 +14,

35

fs = 1/ (+ 91- 82+ 83+ 84 - 85+ 86 - 87),

85 =fs+ng,
40

86 =f6 +16 ,87 = f4+ 17,

13= 1/4(+ 81+ 82- 83- 84 + 85 + 86 - 87),
14 = 1/4 (- 81 - 82 - 83 + g4 + gs + g6 + 87),
16 = 1/4( - 81 + g2 + 83 + 84 + 85 - 86 - 87),

L3=14(+81+82-83+84-85-86+ 87 ),These f, are unbiased estimates when the n ; are zero mean

These readings (pixel measurements ) gi are estimates of stochastic variables, so that { f - f; ) = 0 . The measurement
the spectral intensities f;. The estimates g ; are not equal to the 45 variance corresponding to ith measurement is given by thecorresponding f; values because of the measurement errors
equation below :ni. However, if the measurement noise distribution has zero
( 0:-1:)2 )= 1/1602
mean , then the ensemble mean of each individual measure
From
the above equation , it is observed that by employing
ment can be considered to be equal to the true value , i.e .
( g:) = f;. Here, the angle brackets indicate the operation of 50 spectrally -multiplexed system the signal-to -noise ratio
calculating the ensemble mean of a stochastic variable . The (SNR ) of a measurement is improved by a factor ofvariance of the measurement can , therefore , be represented
V16 / 7 = 1 . 51 .
For N channels, the SNR improvement achieved with aas:((83–8,12)= (n=2)= 02

spectrally -multiplexed system can be expressed as ( N + 1 )/( 255 VN ). For example , an embodiment employing 12 spectral
In embodiments utilizing spectrally -multiplexed filters, in channels (N = 12 ) is characterized by a SNR improvement,
comparison with the embodiments utilizing band -pass fil - over a non -spectrally -multiplexed system , comprising aters, the amount of radiant energy transmitted by each of thefactor of up to 1 .88 .
spectrally -multiplexed LP or SP filters towards a given
Two additional examples of related spectrally -multi
detector element can exceed that transmitted through a 60 plexed filter arrangements 0c through 3c and Od through 3d
spectral band of a band -pass filter . In this case , the intensities that can be used in various embodiments of the imagingof light corresponding to the independent spectral bands cansystems described herein are shown in FIGS . 6C and 6D ,be reconstructed by computational means. Such embodi respectively . The spectrally -multiplexed filters shown in
FIGS. 6C and 6D can be used in embodiments of imaging
ments can be referred to as a “ multiplex design ” .
One matrix of such “ multiplexed filter” measurements 65 systems employing uncooled FPAs (such as microbolom
includes a Hadamard matrix requiring “ negative ” filters that eters ). FIG . 6C illustrates a set of spectrally -multiplexed
may not be necessarily appropriate for the optical embodi- long -wavelength pass (LP ) filters used in the system . An LP

US 10 , 267 ,686 B2
31
filter generally attenuates shorter wavelengths and transmits(passes) longer wavelengths (e .g., over the active range ofchannel having a transmission characteristic corresponding

the target IR portion of the spectrum ). A single spectral

32
values of these FPAs. In an alternative embodiment, thesystem having first and second temperature zones may
multi-portion piece may comprise for example a plate . This
include a single or multi -portion piece . This single orto the difference between the spectral transmission curves of 5 piece may be mechanically -movable across the optical axis

at least two of these LP filters can be used to procure
imaging data for the data cube using an embodiment of thesystem described herein . In various implementations , thespectral filters disposed with respect to the different FPAs

with the use of appropriate guides and having a first portion
at a first temperature and a second portion at a second

temperature .
Indeed , the process of calibration of an embodiment of the

can have different spectral characteristics . In various imple - 10 imaging system starts with estimating gain and offset bymentations, the spectral filters may be disposed in front of

performing measurements of radiation emanating , indepen

only some of the FPAs while the remaining FPAs may be
configured to receive unfiltered light. For example , in somedently , from at least two temperature - controlled shutters ofknown and different radiances . The gain and offset can vary

implementations , only 9 of the 12 detectors in the 4x3 arrayfrom detector pixel to detector pixel. Specifically , first theof detectors described above may be associated with a 15 response of the detector unit 456 to radiation emanating
spectral filter while the other 3 detectors may be configured

from one shutter is carried out. For example , the first shutter

to received unfiltered light. Such a system may be config - 160a blocks the FOV of the detectors 456 and the tempera
ured to acquire spectral data in 10 different spectral channels ture T , is measured directly and independently with therm
in a single data acquisition event.
istors . Following such initialmeasurement, the first shutter
The use of microbolometers , as detector-noise- limited 20 160a is removed from the optical path of light traversing thedevices, in turn not only can benefit from the use ofspectrally multiplexed filters , but also does not require

embodiment and another second shutter (for example , 160b )is inserted in its place across the optical axis 226 to prevent

contrast to imaging systems that include highly sensitiveof the second shutter 160b can be different than the firstcooling of the imaging system during normal operation . In

the propagation of light through the system . The temperature

FPA units with reduced noise characteristics , the embodi- 25 shutter ( T , + T ) . The temperature of the second shutter 1606

ments of imaging systemsdescribed herein can employ lesssensitive microbolometers without compromising the SNR .
This result is at least in part due to the snap -shot/non scanning mode of operation .

is also independently measured with thermistors placed incontact with this shutter, and the detector response to radiation emanating from the shutter 160b is also recorded .
Denoting operational response of FPA pixels ( expressed in

As discussed above , an embodiment may optionally , and 30 digital numbers , or “ counts ” ) as g ; to a source of radiance Lig
the readings corresponding to the measurements of the two
example temperature controlled shutters such as shutters shutters can be expressed as:
in addition to a temperature - controlled reference unit ( for

160 ; 160a , 160b , 460a , 460b ), employ a field reference

81 = YL1(71)+goffset
component (e .g., field reference aperture 338 in FIG . 3A ), or
an array of field reference components ( e . g ., filed reference 35
82= yL2(T2)+ g offset
apertures 438 in FIG . 4 ), to enable dynamic calibration .
Such dynamic calibration can be used for spectral acquisi
Here , & offset is the pixel offset value ( in units of counts ),tion of one or more or every data cube . Such dynamic
and y is the pixel gain value ( in units of counts per radiancecalibration can also be used for a spectrally -neutral camera - unit ). The solutions of these two equations with respect toto - camera combination to enable dynamic compensation of 40 the two unknowns goffer
se and y can be obtained if the values

parallax artifacts . The use of the temperature - controlledreference unit ( for example , temperature - controlled shutterof g , and g , and the radiance values L , and L , are available .
These values can , for example , be either measured by asystem 160 ) and field - reference component(s ) facilitates

reference instrument or calculated from the known tempera

maintenance of proper calibration of each of the FPAs tures T , and T , together with the known spectral response of
45 the optical system and FPA . For any subsequent measureindividually and the entire FPA unit as a whole .
In particular, and in further reference to FIGS. 1 , 2 , 3 , andment, one can then invert the equation (s ) above in order to

4 , the temperature - controlled unit generally employs a sys tem having first and second temperature zones maintained at

estimate the radiance value of the object from the detector
measurement, and this can be done for each pixel in eachfirst and second different temperatures . For example, shutter FPA within the system .
system of each of the embodiments 100 , 200 , 300 and 400 50 As already discussed , and in reference to FIGS. 1 throughcan employ not one but at least two temperature -controlled

4 , the field -reference apertures may be disposed in an object

shutters that are substantially parallel to one another andspace or image space of the optical system , and dimensioned

transverse to the general optical axis 226 of the embodi-

to block a particular portion of the IR radiation receivedment(s ) 100 , 200 , 300 , 400 . Two shutters at two different

from the object . In various implementations, the field

temperatures may be employed to providemore information 55 reference aperture , the opening of which can be substantiallyfor calibration ; for example , the absolute value of thesimilar in shape to the boundary of the filter array (fordifference between FPAs at one temperature as well as theexample , and in reference to a filter array of FIGS. 3B ,change in that difference with temperature change can be

5B - e . g ., rectangular ). The field - reference aperture can berecorded . Referring , for example , to FIG . 4 , in which suchplaced in front of the objective lens ( 124 , 224 , 324, 424 ) at

multi- shutter structure is shown, the use of multiple shutters 60 a distance that is at least several times in one implemen
enables the user to create a known reference temperaturetation - at least five times ) larger than the focal length of thedifference perceived by the FPAs 456 . This reference tem -lens such that the field -reference aperture is placed closer toperature difference is provided by the IR radiation emitted

the object. Placing the field - reference aperture closer to theby the shutter (s ) 160a , 160b when these shutters are posi-

object can reduce the blurriness of the image. In the embodi

tioned to block the radiation from the object 110 . As a result , 65 ment 400 of FIG . 4 , the field -reference aperture can be
not only the offset values corresponding to each of theplaced within the depth of focus of an image conjugate plane
individual FPAs pixels can be adjusted but also the gain
formed by the front objective lens 424 . The field reference ,US 10 , 267 ,686 B2

33

generally, can facilitate , effectuates and /or enable dynamic

compensation in the system by providing a spectrally known
and stabilize the output from the different FPAs in the array.

and temporally -stable object within every scene to reference

34
perature or radiance units , etc.). Moreover , the calibration

process can also allow the FPAs (e.g ., each of the FPAs) to
pixel of a particular FPA can be optically re -mapped throughbe spatially co -registered with one another so that a given

Because each FPA 's offset value is generally adjusted 5 the optical system to the same location at the object as thefrom each frame to the next frame by the hardware , com -corresponding pixel of another FPA .

that is not compensated for by the static calibration param

encing method may be employed . The method involves

eters goffser and y established , for example , by the movable

forming a difference image from various combinations ofparing the outputs ofone FPA with another can have an error

To achieve at least some of these goals, a spectral differ

shutters 160 . In order to ensure that FPAs operate in radio - 10 the images from different channels . In particular , the images

metric agreement over time, it is advantageous for a portionof each detector array to view a reference source ( such as theused to form difference images can be registered by two or
more different FPAs in spectrally distinct channels having

field reference 338 in FIG . 3A , for example ) over a plurality

different spectral filters with different spectral characterisof frames obtained over time. If the reference source spec -tics . Images from different channels having different spectral

trum is known a priori (such as a blackbody source at a 15 characteristics will provide different spectral information .

known temperature ), one can measure the response of each
FPA to the reference source in order to estimate changes toComparing ( e. g., subtracting ) these images, can therefore

yield valuable spectral based information . For example , if

the pixel offset value . However, the temperature of thethe filter element of the array of spectral filters 130 correreference source need not be known . In such implementa -sponding to a particular FPA 336 transmits light from thetions, dynamic calibration of the different detectors can be 20 object 110 including a cloud of gas, for example , with aperformed by monitoring the change in the gain and theoffset for the various detectors from the time the movable
shutters used for static calibration are removed . An example

certain spectrum that contains the gas absorption peak or agas emission peak while another filter element of the arrayof spectral filters 130 corresponding to another FPA 336

calculation of the dynamic offset proceeds as follows.
does not transmit such spectrum , then the difference between
Among the FPA elements in an array of FPAs in an 25 the images formed by the two FPAs at issue will highlightembodimentof the imaging system , one FPA can be selected the presence of gas in the difference image.
to be the “ reference FPA ” . The field reference temperature
A shortcoming of the spectral differencing method is thatmeasured by all the other FPAs can be adjusted to agree with
contributions of some auxiliary features associated withthe field reference temperature measured by the reference as imaging ( not just the target species such as gas itself) can

discussed below . The image obtained by each FPA includes 30 also be highlighted in and contribute to the difference image.
a set of pixels obscured by the field reference 338 . Using the Such contributing effects include , to name just a few , parpreviously obtained calibration parameters goffset and y ( the allax -induced imaging of edges of the object, influence of
pixel offset and gain ), the effective blackbody temperature T , magnification differences between the two or more opticalof the field reference as measured by each FPA is estimated channels , and differences in rotational positioning and ori
35 entation between the FPAs. While magnification -relatedusing the equation below :,errors and FPA - rotation -caused errors can be compensated
T;=mean {(g+ Ag :+8osedy }=mean{(8 -& offse )/Y} +AT;
for by increasing the accuracy of the instrument construction
Using the equation above, the mean value over all pixels as well as by post-processing of the acquired imaging,that are obscured by the field reference is obtained. In the parallax is scene -induced and is not so easily correctable . In
above equation Ag; is the difference in offset value of the 40 addition , the spectral differencing method is vulnerable tocurrent frame from Agoffset obtained during the calibration
step . For the reference FPA , Ag, can be simply set to zero .
Then , using the temperature differences measured by each

FPA , one obtains
T;- Tref=mean {(g + Agi+ goffser/Y} + AT;
mean {(8 - 8offset)/Y } = 47;
Once AT; for each FPA is measured , its value can beradiance calibration errors . Specifically, if one FPA registers
radiance of light from a given feature of the object as thathaving a temperature of 40° C ., for example , while the datafrom another FPA represents the temperature of the same

45 object feature as being 39° C ., then such feature of the object

will be enhanced or highlighted in the difference image( formed at least in part based on the images provided bythese two FPAs) due to such radiance -calibration error.

subtracted from each image in order to force operational
One solution to some of such problems is to compare
agreement between such FPA and the reference FPA . While 50 ( e .g ., subtract) images from the same FPA obtained at
the calibration procedure has been discussed above in refdifferent instances in time. For example , images can beerence to calibration of temperature , a procedurally similar
compared to or subtracted from a reference image obtained
methodology of calibration with respect to radiance value

at another time. Such reference image , which is subtracted

can also be implemented .
Examples of Methodology ofMeasurements .

from other later obtained images , may be referred to as a
55 temporal reference image . This solution can be applied toPrior to optical data acquisition using an embodiment of spectral difference images as well . For example , the image
the IR imaging system as described herein , one or more, data resulting from spectral difference images can be nor

most, or potentially all the FPAs of the system can be

malized by the data corresponding to a temporal reference

calibrated . For example, greater than 50 % , 60 % , 70 % , 80 %image. For instance , the temporal reference images can beor 90 % or the FPAs 336 can be initially calibrated . As shown 60 subtracted from the spectral difference image to obtain thein FIG . 3 , these FPAs 336 may form separate images of thetemporal difference image . This process is referred to , forobject using light delivered in a corresponding optical the purposes of this disclosure , as a temporal differencing
channel that may include the combination of the correspond algorithm or method and the resultant image from subtract
ing front objective and re - imaging lenses 324 , 128 . The ing the temporal reference image from another image (suchcalibration procedure can allow formation of individual 65 as the spectral difference image ) is referred to as the tem
images in equivalent units (so that, for example , the reading poral difference image . In some embodiments where specfrom the FPA pixels can be re-calculated in units of tem -tral differencing is employed , a temporal reference image

US 10 , 267 ,686 B2
35

36

may be formed , for example , by creating a spectral differ ence image from the two or more images registered by theby comparing the images from two different FPAswhere theposition between the FPAs is known. The parallax can be

be useful in subtracting out or removing various errors ordeleterious effects . For example , the result of the algorithm

filter or both have no spectral filters . Parallax error correc
tion , however, can still be obtained from two FPAs that have

two or more FPAs at a single instance in time. This spectral
difference image is then used as a temporal reference image .
The temporal reference image can then be subtracted from 5
other later obtained images to provide normalization that can

is not affected by a prior knowledge of whether the object or

calculated from the known relative position difference . Dif
ferences between the images from these two FPAs can be
attributed to parallax , especially, if the FPA have the same
spectral characteristics , for example have the same spectral

different spectral characteristics or spectral filters , especiallyscene contains a target species ( such as gas of interest ), 10 if the different spectral characteristics , e . g ., the transmission

because the algorithm can highlight changes in the scenecharacteristics . Thus, a spectral difference image can becalculated from multiple spectral channels as discussed

above based on a snap -shot image acquisition at any later

spectra of the respective filters are known and/ or negligible .
Use ofmore than two FPAs or FPAs of different locations
such as FPAs spaced farther apart can be useful. For

example, when the spectral differencing of the image data is

time and can be subtracted from the temporal reference 15 performed with the use of the difference between the images
image to form a temporal difference image. This temporalcollected by the outermost two cameras in the array ( such as,

difference image is thus a normalized difference image . The
for example , the FPAs corresponding to filters 2 and 3 of thedifference between the two images (the temporal difference
array of filters of FIG . 5A ), a difference image referred to as
image ) can highlight the target species ( gas ) within thea " difference image 2 - 3 ” is formed . In this case , the alter
normalized difference image , since this species was not 20 native “ difference image 1 - 4 ” is additionally formed frompresent in the temporal reference frame. In various embodi- the image data acquired by, for example, the alternativements, more than two FPAs can be used both for registering FPAs corresponding to filters 1 and 4 of FIG . 5A . Assuming

the temporal reference image and a later- acquired differenceor ensuring that both of these two alternative FPAs havesame spectral characteristic , then the images obtained by the

pixels corresponding to parallax -induced features in the

two FPAs can be combined after they have been registeredimage . Accordingly , based on positive determination that theimage to obtain a better SNR figure ofmerit. For example ,approximately the same spectral sensitivity to the target
if two FPAs are associated with spectral filters having the 25 species , the alternative " difference image 1 - 4 ” will highlightto get a better SNR figure .

samepixels are highlighted in the spectral “ difference image

While the temporal differencing method can be used to
2 - 3 ” used for target species detection , a conclusion can be
reduce or eliminate some of the shortcomings of the spectral 30 made that the image features corresponding to these pixels
differencing , it can introduce unwanted problems of its own .
are likely to be induced by parallax and not the presence ofFor example, temporal differencing of imaging data is less target species in the imaged scene. It should be noted thatsensitive to calibration and parallax induced errors than thecompensation of parallax can also be performed using
spectral differencing of imaging data . However, any change images created by individual re -imaging lenses, 128a, whenin the imaged scene that is not related to the target species 35 using a single FPA or multiple FPA 's as discussed above .
of interest (such as particular gas, for example ) is high - FPAs spaced apart from each other in different directions canlighted in a temporally -differenced image. Thus such change also be useful. Greater than 2, for example, 3 or 4 , or morein the imaged scene may be erroneously perceived as a
FPAs can be used to establish parallax for parallax correc
location of the target species triggering, therefore, an error tion . In certain embodiments two central FPAs and one
in detection of target species . For example , if the tempera - 40 corner FPA are used for parallax correction . These FPA may,ture of the background against which the gas is being
detected changes (due to natural cooling down as the day
progresses , or increases due to a person or animal or anotherobject passing through the FOV of the IR imaging system ),in certain embodiments , have substantially similar or thesame spectral characteristics, for example, have filters hav
ing similar or the same transmission spectrum or have nofilter at all.

then such temperature change produces a signal difference 45 Another capability of the embodiments described herein
as compared to the measurement taken earlier in time. is the ability to perform the volumetric estimation of a gas
Accordingly , the cause of the scenic temperature change thecloud . This can be accomplished by using (instead ofcooling object, the person walking, etc .) may appear as thecompensating or negating ) the parallax induced effects
detected target species ( such as gas ). It follows, therefore , described above . In this case , the measured parallax between
that an attempt to compensate for operational differences 50 two or more similar spectral response images ( e . g ., two oramong the individual FPAs of a multi-FPA IR imaging
system with the use of methods that turn on spectral ormore channels or FPAs) can be used to estimate a distance
between the imaging system and the gas cloud or between

temporal differencing can cause additionalproblems leading

the imaging system and an object in the field of view of theto false detection of target species. Among these problems

system . The parallax induced transverse image shift , d ,are scene -motion - induced detection errors and parallax - 55 between two images is related to the distance , z , between thecaused errors that are not readily correctable and /or com cloud or object 110 and the imaging system according to thepensatable . Accordingly , there is a need to compensate forequation z = - sz'/d . Here , s , is the separation between two

image data acquisition and processing errors caused bysimilar spectral response images , and z ' is the distance to the

motion of elements within the scene being imaged . Various

image plane from the back lens . The value for z ' is typicallyembodiments of data processing algorithmsdescribed herein 60 approximately equal to the focal length f of the lens of theaddress and fulfill the need to compensate for such motion - imaging system . Once the distance z between the cloud andthe imaging system is calculated , the size of the gas cloud
induced and parallax -induced image detection errors.
In particular, to reduce or minimize parallax -induced can be determined based on the magnification , m = f/z , where
differences between the images produced with two or moreeach image pixel on the gas cloud , Ax', corresponds to apredetermined FPAs, another difference image can be used 65 physical size in object space Ax = Ax '/m . To estimate thethat is formed from the images of at least two different FPAS

volume of the gas cloud, a particular symmetry in theto estimate parallax effects. Parallax error can be determined

thickness of the cloud based on the physical size of the cloudUS 10 ,267,686 B2
37
can be assumed . For example , the cloud image can berotated about a central axis running through the cloud image
to create a three dimensional volume estimate of the gas
cloud size . It is worth noting that in the embodiments

38
expected brightness . The spectral unmixing methodology
can also benefit from temporal, parallax , and motion com
pensation techniques.

In various embodiments, a method of identifying thedescribed herein only a single imaging system is required for 5 presence of a target species in the object includes obtaining

such volume estimation . Indeed , due to the fact that thethe radiance spectrum (or the absorption spectrum ) from theinformation about the angle at which the gas cloud is seen

object in a spectral region indicative of the presence of thedata includes the information about the imaged scenetion coefficient) by correlating the obtained radiance specby the system is decoded in the parallax effect, the image

target species and calculating a correlation ( e . g ., a correla

viewed by the system in association with at least two angles . 10 trum (or the absorption spectrum ) with a reference spectrum

When the temporal differencing algorithm is used forfor the target species. The presence or absence of the target

processing the acquired imaging data, a change in the scene

species can be determined based on an amount of correlationthat is not caused by the target species can inadvertently be( e . g ., a value of correlation coefficient) . For example , thehighlighted in the resulting image . In various embodiments,

presence of the target species in the object can be confirmed

compensation for this error makes use of the temporal 15 if the amount of correlation or the value of correlationdifferencing between two FPAs that are substantially equallycoefficient is greater than a threshold . In various implemen

spectrally sensitive to the target species . In this case , thetations , the radiance spectrum (or the absorption spectrum )temporal difference image will highlight those pixels thecan be obtained by obtaining a spectral difference image

these pixels on both FPAs, which are substantially equally
spectrally sensitive to the target species, to form the result-tions thereof.
For example , an embodiment of the system configured toing image , excludes the contribution of the target species todetect the presence of methane in a gas cloud comprises

intensity of which have changed in time ( and not in wave - between a filtered optical channel and /or another filteredlength ). Therefore , subtracting the data corresponding to 20 optical channel/ unfiltered optical channel or any combina

the resulting image. The differentiation between ( i ) changes
optical components such that one or more of the plurality ofin the scene due to the presence of target species and (ii ) 25 optical channels is configured to collect IR radiation tochanges in the scene caused by changes in the background provide spectral data corresponding to a discrete spectral
not associated with the target species is, therefore , possible . band located in the wavelength range between about 7 .9 um
In some embodiments , these two channels having the same and about 8 . 4 um corresponding to an absorption peak ofor substantially similar spectral response so as be substan - methane . The multispectral data obtained in the one or more
tially equally spectrally sensitive to the target species may 30 optical channels can be correlated with a predetermined
comprise FPAs that operate using visible light. It should also
absorption spectrum of methane in the wavelength range

be noted that , the data acquired with a visible light FPA

between about 7.9 um and 8 .4 um . In various implementa

can also be used to facilitate such differentiation and com

can be saved in a database or a reference library accessible(when present as part of the otherwise IR imaging system )tions, the predetermined absorption spectrum of methane

pensation of the motion -caused imaging errors . Visible 35 by the system . Based on an amount of correlation ( e . g ., acameras generally have much lower noise figure than IR

value of correlation coefficient), the presence or absence of

cameras (at least during daytime). Consequently , the tem poral difference image obtained with the use of image datafrom the visible light FPA can be quite accurate . The visible

methane in the gas cloud can be detected .
Examples of Practical Embodiments and Operation
The embodiment 300 of FIG . 3 is configured to employ 12

well as many potential false -alarms in the scene due tomotion caused by people , vehicles, birds, and steam , for

FPAs 336 to capture a video sequence substantially imme
diately after performing calibration measurements. The

example , as long as the moving object can be observed in thevideo sequence corresponds to images of a standard labo

visible region of the spectra . This has the added benefit ofratory scene and the calibration measurements are perwithout reducing the sensitivity of the system since manytargets such as gas clouds cannot be observed in the visible

shutters, as discussed above, one at room temperature andone 5º C . above room temperature . The use of 12 FPAS

spectral region . In various implementations, an IR camera

allows increased chance of simultaneous detection and esti

FPA can be used to compensate for motion in the system as 40 optical channels and 12 corresponding microbolometer

providing an additional level of false alarm suppression 45 formed with the use of a reference source including two

mation of the concentrations of about 8 or 9 gases present at
can be used to compensate for motion artifacts.
Another method for detection of the gases is to use a 50 the scene. In various embodiments , the number of FPAs 336
spectral unmixing approach . A spectral unmixing approach
can vary, depending on the balance between the operational
assumes that the spectrum measured at a detector pixel isrequirements and consideration of cost.

composed of a sum of component spectra ( e . g ., methane andDue to the specifics of operation in the IR range of theother gases ). This approach attempts to estimate the relative

spectrum , the use of the so -called noise - equivalent tempera

weights of these components needed to derive the measure - 55 ture difference (or NETD ) is preferred and is analogous toment spectrum . The component spectra are generally takenfrom a predetermined spectral library ( for example , fromdata collection that has been empirically assembled ), thoughsometimes one can use the scene to estimate these as well

the SNR commonly used in visible spectrum instruments .
The array ofmicrobolometer FPAs 336 is characterized toperform at NETD 572 mK at an f-number of 1.2 . Eachmeasurement was carried out by summing four consecutive( often called " endmember determination ” ). In various 60 frames, and the reduction in the NETD value expected due
embodiments , the image obtained by the detector pixel is a
to such summation would be described by corresponding
radiance spectrum and provides information about thefactor of V4 = 2 . Under ideal measurement conditions, therebrightness of the object. To identify the contents of a gas

fore, the FPA NETD should be about 36 mK .

comparing the measured brightness with an estimate of theembodiments including a single large format microbolom

cloud in the scene and/ or to estimate the concentration of the
It is worth noting that the use of optically - filtered FPAs invarious gases in the gas cloud , an absorption / emission 65 various embodiments of the system described herein can
spectrum of the various gases of interest can be obtained byprovide a system with higher number of pixels. For example ,US 10 , 267 ,686 B2

39

40

eter FPA array can provide a system with large number ofpixels. Various embodiments of the systems described

menting the dynamic correction procedure is shown in
FIGS. 8A , 8B , where the curves labeled “ obj” (or “ A ” )advantage of the compensation algorithms such as theperature perceived by different detector elements is as highget-species related data , the compensation algorithms arecarried out with respect to target-species related data and notof the temperature of the aperture 338 of the embodiment
300 of FIG . 3A . The results of detection of radiation carriedherein can also offer a high optical throughput for a sub
represent temperature estimates of an identified region in the
stantially low number of optical channels. For example, the scene . The abscissa in each of the plots of FIGS. 8A , 8B
systemsdescribed herein can provide a high optical through - 5 indicates the number of a FPA , while the ordinate corre
put for a number of optical channels between 4 and 50 . By sponds to temperature (in degrees C .). Accordingly, it ishaving a lower number of optical channels ( e.g ., between 4 expected that when all detector elements receive radiant data
and 50 optical channels ), the systemsdescribed herein have that, when interpreted as the object's temperature , indicateswider spectral bins which allows the signals acquired withinthat the object’ s temperature perceived by all detector ele
each spectral bin to have a greater integrated intensity . 10 ments
same, any given curve would be a substantiallyAn advantage of the embodiments described herein over flat lineis. theDatacorresponding to each of the multiple “ obj”
various scanning based hyperspectral systems that are con
curves are taken from a stream of video frames separated
figured for target species detection (for example , gas cloudfrom one another by about 0 . 5 seconds ( for a total of 50
detection ) is that , the entire spectrum can be resolved in a frames). The recorded “ obj” curves shown in FIG . 8A
snapshot mode (for example , during one image frame acqui- 15
sition by the FPA array ). This feature enables the embodi indicate that the detector elements disagree about thements of the imaging systems described herein to take object's temperature, and that difference in object's tem
parallax and motion compensation algorithms mentioned
as about 2 . 5° C . In addition , all of the temperature estimates
above . Indeed , as the imaging data required to implement 20 are steadily drifting in time, from frame to frame. The curves
these algorithms are collected simultaneously with the tar - labeled “ ref” ( or “ C ” ) correspond to the detectors ' estimateswith respect to data acquired at another time interval. Thisout after each detector pixel has been subjected to therapid data collection thus improves the accuracy of the data 25 dynamic calibration procedure described above arecompensation process. In addition , the frame rate of dataacquisition is much higher. For example , embodiments of
the imaging system described herein can operate at video
rates from about 5 Hz and higher. For example, various

expressed with the curved labeled “ obj corr” (or “ B ” ). Now ,the difference in estimated temperature of the object among
the detector elements is reduced to about 0 .5° C . (thereby
improving the original reading at least by a factor of 5 ) .

embodiments described herein can operate at frame rates 30

FIG . 8B represents the results of similar measurementsfrom about 5 Hz to about 60 Hz or 200 Hz. Thus, the usercorresponding to a different location in the scene (a location

is able to recognize in the images the wisps and swirls

typical of gas mixing without blurring out of these dynamic

which is at a temperature about 9° C . above the estimatedtemperature of the aperture 338 of FIG . 3A ). As shown , theimage features and other artifacts caused by the change of correction algorithm discussed above is operable and effec
scene (whether spatial or spectral) during the lengthy mea - 35 tive and applicable to objects kept at different temperature .
surements . In contradistinction , scanning based imaging

systems involve image data acquisition over a period of timeexceeding a single - snap -shot time and can , therefore , blur
the target gas features in the image and inevitably reduce theAccordingly , the algorithm is substantially temperature

independent.

Dynamic Calibration Elements and References
FIGS . 9A and 9B illustrates schematically different imple

otherwise achievable sensitivity of the detection . This result 40 mentations 900 and 905 respectively of the imaging system

is in contrast to embodiments of the imaging systemdescribed herein that are capable of detecting the localized
concentrations of gas without it being smeared out with thethat include a variety of temperature calibration elements tofacilitate dynamic calibration of the FPAs. The temperature
calibration elements can include mirrors 975a, 975b ( repareas of thinner gas concentrations. In addition , the higher

resented as Ma, Mga , etc .) as well as reference sources

an alarm can trigger within fractions of a second rather thanfront objective lens, a divided aperture , one or more spectral

several seconds.

filters , an array of imaging lenses 928a and an imaging
element 936 . In various implementations , the imaging ele

frame rate also enables a much faster response rate to a leak 45 972a and 972b . The implementation 900 can be similarlyof gas (when detecting such leak is the goal). For example ,configured as the embodiment 300 and include one ormore

To demonstrate the operation and gas detection capabilityof the imaging systems described herein , a prototype was 50 ment 936 ( e . g ., camera block ) can include an array ofconstructed in accordance with the embodiment 300 of FIG .
3A and used to detect a hydrocarbon gas cloud of propylene
at a distance of approximately 10 feet. FIG . 7 illustrates

cameras . In various implementations , the array of cameras
can comprise an optical FPA unit . The optical FPA unit cancomprise a single FPA , an array of FPAs. In various imple

video frames 1 through 12 representing gas -cloud- detection
to t= 12 . The images 1 through 12 are selected frames taken

mentations, the array of cameras can include one or more
5 , detector array 9 in FIGS. 9A and 9B . In various embodi

output 710 ( seen as a streak of light) in a sequence from t = 1 55 detector arrays represented as detector array 1 , detector arrayfrom a video -data sequence captured at a video -rate of 15

ments , the FOV of each of the detector arrays 1 , 5 , 9 can beframes /sec . The detected propylene gas is shown as a streak

divided into a central region and a peripheral region . Withof light 710 (highlighted in red ) near the center of eachout any loss of generality, the central region of the FOV ofimage . The first image is taken just prior to the gas emerging 60 each of the detector arrays 1 , 5 , 9 can include the region
from the nozzle of a gas- contained , while the last image
where the FOV of all the detector arrays 1 , 5 , 9 overlap . In

represents the system output shortly after the nozzle has

been turned off
The same prototype of the system can also demonstrate

the embodiment illustrated in FIG . 9A , some temperature
calibration elements, namely , reference sources 972a and972b are placed at a distance from the detector arrays 1, 5 ,the dynamic calibration improvement described above by 65 9 , for example , and mirrors to image them onto the detector
imaging the scene surrounding the system (the laboratory )arrays are then placed at the location of the scene referencewith known temperature differences . The result of imple
aperture (e .g ., 338 of FIG . 3A ).

US 10 , 267 ,686 B2
41

In FIG . 9A , the temperature -calibration elements 975a

and 975b comprise mirrors that reflect radiation from the42
In FIG . 9B , the temperature-calibration elements com

prise temperature -controlled elements 972a and 972b ( e. g .,reference sources 972a and 972b ( represented as ref A anda thermally controlled emitter, a heating strip , a heater or a

ref B ). The mirrors 975a and 975b can be disposed away

cooler ) disposed a distance from the detector arrays 1 , 5 , 9 .

the central FOV is not blocked or obscured by the image ofments 972a and 972b can be disposed away from the central

the reference source 972a and 972b . In various implemen -FOV of the detector arrays 1 , 5 , 9 such that the central FOVfrom the central FOV of the detector arrays 1 , 5 , 9 such that 5 In various embodiments, the temperature - controlled ele

tations, the FOV of the detector array 5 could be greater thanthe FOV of the detector arrays 1 and 9 . In such implemen -is not blocked or obscured by the image of the reference

source 972a and 972b . The radiation emitted from thetations, the mirrors 9750 and 975b can be disposed away 10 reference sources 972a and 972b is also imaged by thefrom the central FOV of the detector array 5 at a locationsuch that the reference source 972a and 972b is imaged bydetector array 936 along with the radiation incident from theobject. Depending on the position of the reference sources

the detector array 5 . The mirrors 975a and 975b may 972a and 972b the image obtained by the detector array ofcomprise imaging optical elements having optical power the reference sources can be blurred (or defocused ) or sharpthat image the reference sources 972a and 972b onto the 15 (or focused ). The images 980a , 9806 , 980c, 980d , 980e anddetector arrays 1 and 9 . In this example, the reference
sources 972a and 972b can be disposed in the same plane as
the re -imaging lenses 928a , however , the reference sources
972a and 972b can be disposed in a different plane or in

980f of the temperature - controlled elements 972a and 972b
can be used as a reference to dynamically calibrate the one
or more cameras in the array of cameras.

In the implementations depicted in FIGS. 9A and 9b , thedifferent locations. For example , the reference sources 972a 20 detector arrays 1 , 5 and 9 are configured to view (or image )and 972b can be disposed in a plane that is conjugate to theplane in which the detector array 1, detector array 5 , anddetector array 9 are disposed such that a focused image ofboth the reference sources 972a and 972b . Accordingly ,multiple frames (e . g ., every or substantially every frame)
within a sequence of images contains one or more regions in

the reference sources 972a and 972b is formed by thethe image in which the object image has known thermal anddetector arrays. In some implementations, the reference 25 spectral properties . This allowsmultiple ( e . g ., most or each )sources 972a and 972b can be disposed in a plane that isspaced apart from the conjugate plane such that a defocused

image of the reference sources 972a and 972b is formed by

the detector arrays. In various implementations, the refercameras within the array of cameras to be calibrated to agreewith other ( e. g ., most or every other ) camera imaging thesame reference source (s ) or surface (s ). For example , detec

tor arrays 1 and 9 can be calibrated to agree with each other.

ence sources 972a and 972b need not be disposed in the 30 As another example , detector arrays 1 , 5 and 9 can besame plane .
calibrated to agree with each other . In various embodiments ,As discussed above , in some embodiments , the reference
the lenses 928a provide blurred (or defocused ) images of thesources 972a and 972b are imaged onto the detector array 1
reference sources 972a, 972b on the detector arrays 1 and 9
and detector array 9 , without much blur such that the because the location of the reference sources are not exactly
reference sources 972a and 972b are focused . In contrast , in 35 in a conjugate planes of the detector arrays 1 and 9 . Althoughother embodiments , the image of the formed of reference

the lenses 928a are described as providing blurred or defo

array 9 are blurred such that the reference sources 972a andsurfaces are imaged on the detectors arrays 1 , 5 , 9 without

sources 972a and 972b on the detector array 1 , and detector

cused images, in various embodiments, reference sources or972b are defocused , and thereby provide some averaging ,such blur and defocus and instead are focused images .
smoothing , and /or low pass filtering. The reference sources 40 Additionally optical elements may be used , such as for
972a and 972b may comprise a surface of known tempera example , the mirrors shown in FIG . 9A to provide such
ture and may or may not include a heater or cooler attachedthereto or in thermal communication therewith . For

focused images .
The temperature of the reference sources 972b , 972a can

example , the reference source 972a and 972b may comprises
with a temperature sensor and a heater and sensor respec

be different. For example , the reference source 972a can bea temperature Tg lower than the temperature Tg . A heater can

the temperature of the reference surface . In various imple

to maintain it at a temperature T2, and a cooler can beheaters and coolers respectively or may comprise a surface 45 at a temperature T4, and the reference source 972b can be attively in direct thermal communication therewith to control

be provided under the temperature -controlled element 972a

mentations, the reference sources 972a and 972b can include provided underneath the temperature - controlled elementa temperature controller configured to maintain the reference 50 972b to maintain it at a temperature TR. In various imple
sources 972a and 972b at a known temperature . In some mentations, the embodiments illustrated in FIGS. 9A and 9B
implementations , the reference sources 972a and 972b can
can be configured to image a single reference source 972
be associated with one or more sensors that measure the instead of two references sources 972a and 972b maintained
temperature of the reference sources 972a and 972b andat different temperatures . It is understood that the single
communicate the measured temperature to the temperature 55 reference source need not be thermally controlled . For

controller. In some implementations , the one or more sen sors can communicate the measured temperature to thedata - processing unit. In various implementations, the refer ence sources 972a and 972b may comprise a surface of

example , in various implementations, a plurality of detectors
in the detector array can be configured to image a same
surface of at least one calibration element whose thermaland spectral properties are unknown. In such implementa

unknown temperature . For example , the reference sources 60 tions, one of the plurality of detectors can be configured as

may comprise a wall of a housing comprising the imaging
system . In some implementations, the reference sources
972a and 972b comprising a surface need not be associateda reference detector and the temperature of the surface of thedetectors can be estimated using the radiance spectrum

controllers .

detector. For example , detector arrays 1 and 9 can beat least one calibration element imaged by the plurality ofwith sensors , temperature controllers . However, in other obtained by the reference detector. The remaining plurality
implementations , the reference sources 972a and 972b com - 65 of detectors can be calibrated such that their temperature
prising a surface can be associated with sensors, temperature
and /or spectral measurements agree with the referenceUS 10 , 267 ,686 B2

43

44

calibrated to agree with each other. As another example,

the scene) immediately after the calibration is complete . It

detector arrays 1 , 5 and 9 can be calibrated to agree witheach other.
The reference sources 972a and 972b can be coated withcannot, however, prevent the cameras ' estimates from drift

ing away from one another during the process of imaging an

unknown scene. The dynamic calibration can be used toa material to make it behave substantially as a blackbody 5 reduce or prevent this drift, so that all cameras imaging a(for which the emission spectrum is known for any given

scene can be forced to agree on the temperature estimate ofcamera ) so operated agrees, operationally, with most or

an outer ring of cameras including cameras 0 , 1 , 2 , 3, 7 , 11,temperature ). If a temperature sensor is used at the location
the reference sources /surfaces, and adjust this correctionof each reference source , then the temperature can beduring every frame.
tracked at these locations. As a result, the regions in the
FIG . 10A illustrates schematically a related embodimentimage of each camera ( e . g ., on the detector arrays 1 and 9 ) 10 1000 of the imaging system , in which one ormore mirrors
in which the object has such known temperature ( and, MA, . . . M114 and Mob , . . . Mu are placed within the fields
therefore , spectrum ) can be defined . A calibration procedureof view of one or more cameras 0 , . . . , 11 , partially blocking
can thus be used so thatmost of the cameras (if not every
the field of view . The cameras 0 , . . . , 11 are arranged to form
every other camera , for objects at the temperatures repre - 15 10 , 9 , 8 and 4 surrounding the central cameras 5 and 6 . In

sented by those two sources . Calibrating infrared cameras

various implementations , the FOV of the central cameras 5

using sources at two different temperatures is known as aand 6 can be less than or equal to the FOV of the outer ring

" two -point” calibration , and assumes that the measured of cameras 0 , 1, 2 , 3 , 7, 11, 10 , 9, 8 and 4 . In suchsignal at a given pixel is linearly related to the incident implementations, the one ormore mirrors MOA , . . .M114 andirradiance . Since this calibration can be performed during 20 Mob , . . . MUR can be placed outside the central FOV of themultiple , more , or even every frame of a sequence , it iscameras 5 and 6 and is placed in a peripheral FOV of thereferred to as a " dynamic calibration” .
cameras outer ring of cameras 0 , 1, 2, 3 , 7 , 11 , 10 , 9 , 8 andAn example of the dynamic calibration procedure is as 4 which does not overlap with the central FOV of thefollows. If there is a temperature sensor on the reference

cameras 5 and 6 such that the reference sources A and B are

sources or reference surface , then the temperature measure - 25 not imaged by the cameras 5 and 6 . In various implemenments obtained by these temperature sensors can be used todetermine their expected emission spectra . These tempera
ture measurements are labeled as T [R ], T ][ R ], and Tc[ R ]tations , the FOV of the central cameras 5 and 6 can begreater than the FOV of the outer ring of cameras 0 , 1, 2 , 3 ,7 , 11 , 10 , 9 , 8 and 4 . In such implementations, the one orfor the " reference temperatures ” of sources/surfaces A , B , more mirrors Mox, . . . M , 14 and Mor ,M R can be placed
and C . These temperature measurements can be used as 30 in a peripheral FOV of the cameras 5 and 6 which does
scalar correction factors to apply to the entire image of aoverlap with the central FOV of the outer ring of cameras 0 ,given camera , forcing it to agree with the reference tem -1, 2 , 3 , 7 , 11 , 10 , 9 , 8 and 4 such that the reference sources

can be used instead . This camera can be referred to as the" reference camera ” . In this case , the same formulae as thosemirrors, for example ) is installed at a distance from theFPAs, for example , in the plane of the reference aperture 160

provided below can be used , but with T [R ] and T [ R ]shown in FIG . 3A . These elements (mirror or imaging

peratures. Correcting the temperature estimate of a given
A and B are imaged by the cameras 5 and 6 .
pixel from T to T ' can use formulae analogous to thoseThis design is an enhancement to the systems 300 and 400
discussed below in reference to FIGS. 10A , 10B , 10C . If no 35 shown in FIGS. 3A and 4A . In the system 1000 shown in
direct temperature sensor is used , then one of the cameras
FIG . 10A , an array of two or more imaging elements ( curved

representing the temperatures of the reference sources / sur- 40 elements ) are used to image one or more temperature

faces A and B as estimated by the reference camera . By

controlled reference sources A and B onto the detector

applying the dynamic calibration correction formulae, all of

elements of two or more of the cameras . The primary

the other cameras are forced to match the temperature

difference between embodiment 1000 and embodiment 300

or 400 is that now a plurality or most or all of the outer ring
In the configuration illustrated in FIG . 9B , the reference 45 of cameras in the array can image both the reference sources
sources 972a and 972b are placed such that the images of the A and B instead of imaging one of the two reference source
estimates of the reference camera .

sources on the detector arrays are blurred . The configuration
illustrated in FIG . 9A is similar to the system 400 illustrated
in FIG . 4 where the reference sources are placed at an

A and B . Accordingly, most or all of the outer ring ofcameras image an identical reference source or an identicalset of reference sources ( e .g ., both the reference sources Aintermediate image plane ( e . g ., a conjugate image plane ). In 50 and B ) rather than using different reference sources forthis configuration , the array of reference apertures, similar toreference apertures 438a in FIG . 4 , will have an accompa nying array of reference sources or reference surfaces suchdifferent cameras or imaging different portions of the reference sources as shown in FIGS. 3A and 4A . Thus , thisapproach improves the robustness of the calibration , as itthat the reference sources or surfaces ( e . g ., each reference

eliminates potential failures and errors due to the having

source or surface ) are imaged onto a camera or a detector 55 additional thermal sensors estimating each reference source .
array such as FPAs 1 , 5 , 9 . With this approach , the reference
The imaging elements in the system 1000 (shown assource or surface images are at a conjugate image plane and mirrors in FIGS. 10A and 10B ) image one or more conthus are not appreciably blurred , so that their images can betrolled -temperature reference sources or a surface of amade to block a smaller portion of each camera ' s field of calibration element (shown as A and B in FIGS . 10A and
60 10B ) into the blocked region of the cameras ' fields of view .
view .

A " static” calibration (a procedure in which the scene is

FIG . 10B shows an example in which mirror Mo, images

or each camera ) to accurately estimate the temperature of adetector array of a camera , so that many, most, or everylargely blocked with a reference source such as the moving reference source /surface A onto camera 0 , and mirror Mob
shutters 960 in FIGS. 9A and 9B , so that imaging of aimages reference source /surface B onto camera 0 , andunknown scene cannot be performed in parallel with cali - likewise for cameras 1 , 2 , and 3 . This way, each of thebration allows a plurality of the cameras (for example ,most 65 mirrors is used to image a reference source /surface onto aplurality of elements ( for example, most or each element inframe within a sequence of images contains one or moreUS 10 ,267,686 B2

45

46

regions in the image in which the object image has known
thermal and spectral properties . This approach allowsmost

array of cameras images both of references A and B , so that
there are known regions in the image of these cameras inof the camera , if not each camera , within the array ofwhich the object has a known temperature (and therefore

cameras to be calibrated to agree with most or every otherspectrum ). Then one can perform a calibration procedure .

example , cameras 0 , 1 , 2 , 3 , 7 , 11 , 10 , 9, 8 and 4 can becalibrated to agree with each other. As another example ,cameras 0 , 1 , 2 and 3 can be calibrated to agree with eachso operated agrees with various , most, or every other cam
era , for objects at the temperatures represented by those twosources. For example , two, three, four, five , six , seven , eight,

camera imaging the same reference source or sources. For 5 This procedure can provide that many, most or every camera

other. As yet another example , cameras 0 , 1 , 2 , 3 , 7 , 11, 10 ,nine , ten , eleven or twelve cameras can be calibrated to
9 , 8 , 4 , 5 and 6 can be calibrated to agree with each other. 10 agree with each other. In certain embodiments , however , not

Accordingly , in various implementations, two, three , four,

all the cameras are calibrated to agree with each other. For

five, six , seven , eight, nine , ten , eleven or twelve cameras

example , one, two, or more cameras may not be calibrated

can be calibrated to agree with each other. In certain
embodiments, however, not all the cameras are calibrated toto agree with each other while others may be calibrated toagree with each other. As discussed above , calibration ofagree with each other. For example, one, two, or more 15 infrared cameras using sources at two different temperatures

cameras may notbe calibrated to agree with each other whileothers may be calibrated to agree with each other. In various
embodiments, these mirrors may be configured to image thereference sources/surfaces A and B onto different respective

is known as a “ two-point” calibration , and assumes that themeasured signal at a given pixel is linearly related to theincident irradiance .
The dynamic calibration is used to obtain a correctedin FIG . 9A .

T"[x,y,c,] = (7 [x,y,c]- TA[R ])G [c]+ T [R ]where is T [R ] is a dynamic offset correction factor, and,pixels a given FPA . Without any loss of generality , FIGS. 20 temperature T ' from the initial temperature T estimated at
10A and 10B represent a top view of the embodiment shown each pixel in a camera using the following formulae :FIG . 10C illustrates schematically a related embodiment1050 of the imaging system , in which one ormore ' reference

sources Roa , . . . , R114 and Rob , . . . , RUB are disposed 25
around the array of detectors 0 , . . . , 11 . In various

implementations, the one or more reference sources
ROA , . . . R114 and Rob , . . , Rus can be a single reference

TB [ R ] – TA [R ]G [c] = Te?c] – TA[c] 'source that is images by the detectors 0 , . . . , 11 . In various

implementations , central detector arrays 5 and 6 can have a 30 is a dynamic gain correction factor. The term c discussed

FOV that is equal to or lesser than the FOV of the outer ringof the detectors 0 , 1 , 2 , 3 , 7 , 11 , 10 , 9 , 8 and 4 . In such

implementations, the reference sources ROA . . . , R114 canabove is a camera index that identifies the camera whose
data is being corrected .

References throughout this specification to “ one embodi

be disposed away from the central FOV of the detector

ment," " an embodiment," " a related embodiment,” or simi

sources Ro4 , . . , Ruis imaged only by the outer ring ofdetectors 0 , 1 , 2, 3 , 7 , 11 , 10 , 9 , 8 and 4 . In various

characteristic described in connection with the referred to" embodiment” is included in at least one embodiment of thearrays 5 and 6 such that the radiation from the reference 35 lar language mean that a particular feature , structure , or
implementations, central detector arrays 5 and 6 can have apresent invention . Thus , appearances of the phrases “ in one

FOV that is greater than the FOV of the outer ring of theembodiment,” “ in an embodiment,” and similar language
detectors 0 , 1 , 2 , 3 , 7 , 11 , 10 , 9 , 8 and 4 . In such imple - 40 throughout this specification may , but do not necessarily, allmentations, the reference sources Roa , . . ., Ru4 can be refer to the same embodiment. It is to be understood that nodisposed in the peripheral FOV of the detector arrays 5 and portion of disclosure , taken on its own and in possible
6 such that the radiation from the reference sources
connection with a figure , is intended to provide a complete

ROA, . . . ,R114 is imaged only by the outer ring of detectors

description of all features of the invention .

reference sources Ro4 , . . . ,R1, is therefore imaged by theouter ring of detectors 0 , 1, 2 , 3 , 7, 11, 10 , 9 , 8 and 4 as wellsame or similar elements wherever possible . The depictedstructural elements are generally not to scale , and certain

as central cameras 5 and 6 . Without any loss of generality ,components are enlarged relative to the other components

0 , 1 , 2 , 3 , 7 , 11, 10 , 9 , 8 and 4 . The radiation from the 45

In the drawings like numbers are used to represent the

FIG . 10C represents a top view of the embodiment shown infor purposes of emphasis and understanding . It is to be
50 understood that no single drawing is intended to support a
FIG . 9B .
In various implementations, one can use a heater under complete description of all features of the invention . In otherneath , adjacent to , or in thermal communication with referwords, a given drawing is generally descriptive of only

a cooler underneath , adjacent to , or in thermal communica -given drawing and an associated portion of the disclosure

ence source /surface A to give it a higher temperature T4 , andsome, and generally not all, features of the invention . Ation with reference source B to give it a lower temperature 55 containing a description referencing such drawing do not,TR . In various implementations, the embodiments illustrated
generally , contain all elements of a particular view or all

in FIGS . 10A , 10B and 10C can be configured to image afeatures that can be presented is this view , for purposes ofsingle reference source A instead of two references sources

simplifying the given drawing and discussion , and to direct

A and B maintained at different temperatures. As discussed

the discussion to particular elements that are featured in this

above , the embodiments illustrated in FIGS. 10A , 10B and 60 drawing . A skilled artisan will recognize that the invention

10C can be configured to image a same surface of amay possibly be practiced without one or more of thecalibration element . In such implementations, the tempera -specific features , elements , components , structures , details ,ture of the surface of the calibration element need not be

or characteristics , or with the use of other methods , com

known . Many, most or each reference source / surface can beponents , materials , and so forth . Therefore , although a
coated with a material to make it behave approximately as 65 particular detail of an embodiment of the invention may nota blackbody , for which the emission spectrum is known forbe necessarily shown in each and every drawing describing

any given temperature . If many, most, or each camera in thesuch embodiment, the presence of this detail in the drawing

US 10 , 267 ,686 B2
47

48

may be implied unless the context ofthe description requires

computer -readable medium . Computer-readable media

otherwise . In other instances , well known structures, details,
materials , or operations may be not shown in a given

includes both computer storage media and communication
media including any medium that can be enabled to transfer

drawing or described in detail to avoid obscuring aspects ofa computer program from one place to another. A storage

an embodiment of the invention that are being discussed . 5 media may be any available media that may be accessed by

Furthermore , the described single features, structures , orcharacteristics of the invention may be combined in any
suitable manner in one or more further embodiments .
The features recited in claims appended to this disclosure

a computer . By way of example , and not limitation , suchcomputer- readable media may include RAM , ROM ,EEPROM , CD -ROM or other optical disk storage ,magnetic
disk storage or other magnetic storage devices , or any otherare intended to be assessed in light of the disclosure as a 10 medium that may be used to store desired program code inwhole , including features disclosed in prior art to which
the form of instructions or data structures and that may bereference is made.
Atleast some elements of a device of the invention can beaccessed by a computer . Also , any connection can be prop
erly termed a computer - readable medium . Disk and disc , ascontrolled -and at least some steps of a method of theused herein , includes compact disc (CD ), laser disc , opticalinvention can be effectuated , in operation -with a program - 15 disc , digital versatile disc (DVD ), floppy disk , and blu -raymable processor governed by instructions stored in amemory. The memory may be random access memory(RAM ), read -only memory (ROM ), flash memory or any

other memory, or combination thereof, suitable for storing

disc where disks usually reproduce data magnetically , whilediscs reproduce data optically with lasers . Combinations of

the above also may be included within the scope of com

puter -readable media . Additionally , the operations of acontrol software or other instructions and data . Those skilled 20 method or algorithm may reside as one or any combinationin the art should also readily appreciate that instructions or or set of codes and instructions on a machine readable
programs defining the functions of the present invention
medium and computer -readable medium , which may be
may be delivered to a processor in many forms, including ,incorporated into a computer program product.
but not limited to , information permanently stored on non
Variousmodifications to the implementations described inwritable storage media ( e .g . read -only memory devices 25 this disclosure may be readily apparent to those skilled in thewithin a computer, such as ROM , or devices readable by aart, and the generic principles defined herein may be appliedcomputer I/O attachment, such as CD -ROM or DVD disks ), to other implementations without departing from the spirit orinformation alterably stored on writable storage media ( e .g .
scope of this disclosure . Thus , the claims are not intended to
floppy disks , removable flash memory and hard drives ) or be limited to the implementations shown herein , but are to
information conveyed to a computer through communica - 30 be accorded the widest scope consistent with this disclosure ,tion media , including wired or wireless computer networks. the principles and the novel features disclosed herein .

In addition , while the invention may be embodied in soft
may optionally or alternatively be embodied in part or in

Certain features that are described in this specification in
mented in combination in a single implementation . Con

other hardware or some combination of hardware , softwaretion .Moreover, although features may be described above as

ware , the functions necessary to implement the invention

the context of separate implementations also can be imple

whole using firmware and /or hardware components, such as 35 versely , various features that are described in the context of
combinatorial logic , Application Specific Integrated Circuits
a single implementation also can be implemented in multiple( ASICs), Field -Programmable Gate Arrays ( FPGAs) or implementations separately or in any suitable subcombina

and/ or firmware components .
acting in certain combinations and even initially claimed as
While examples of embodiments of the system and 40 such , one or more features from a claimed combination canmethod of the invention have been discussed in reference toin some cases be excised from the combination , and thethe gas- cloud detection , monitoring , and quantification ( in cluding but not limited to greenhouse gases such as Carbon

claimed combination may be directed to a subcombination
or variation of a subcombination .

Dioxide, Carbon Monoxide, Nitrogen Oxide as well as

What is claimed is:

Hydrogen Sulfide, Sulfur Hexafluoride , Ammonia , Benzene ,p -and m -Xylene, Vinyl chloride, Toluene, Propylene oxide ,an optical system comprising an optical focal plane array

Propylene, Methanol, Hydrazine , Ethanol, 1 ,2 - dichloroeth
ane , 1 , 1 -dichloroethane, Dichlorobenzene, Chlorobenzene, 50(FPA ) unit, the optical system including components
associated with at least two optical channels, said atleast two optical channels being spatially and spectrally

readily adapted for other chemical detection applications.

to name just a few ), embodiments of the inventon can be
For example , detection of liquid and solid chemical spills ,biological weapons, tracking targets based on their chemicaldifferent from one another, the at least two opticalthe optical system towards the optical FPA unit, theoptical FPA unit comprising at least two groups ofcomposition , identification of satellites and space debris, 55

detector pixels disposed at a distance from at least two

ing , endoscopy , mold detection , fire and flame detection , andpesticide detection are within the scope of the invention .

a first thermal reference at a first temperature ;a second thermal reference at a second temperature difhydrocarbon gases such as Methane, Ethane, Propane, n - Bu - 45 1 . An infrared (IR ) imaging system , the imaging systemtane, iso -Butane, n -Pentane, iso -Pentane , neo -Pentane ,comprising:ophthalmological imaging , microscopy and cellular imag

As used herein , a phrase referring to " at least one of” a listof items refers to any combination of those items, including 60

channels positioned to transfer IR radiation incident on
corresponding focusing lenses ;ferent from the first temperature , wherein radiation

emitted from the first and the second thermal references

is directed to at least one of the at least two groups of

single members . As an example , " at least one of: a , b , or c "is intended to cover : a , b , c , a - b , a - c , b - c , and a - b - c .

detector pixels simultaneously with radiation emitted

on or transmitted over as one or more instructions or code on
a computer - readable medium . The steps of a method or 65
algorithm disclosed herein may be implemented in a pro

electronics configured to :dynamically calibrate the at least two groups of detec
tor pixels to reduce a difference in measurements
obtained using light from the first and the second

If implemented in software, the functions may be stored

cessor -executable software module which may reside on afrom a scene viewed by the imaging system ; andUS 10 , 267,686 B2

50

49
thermal references received by at least one of the atleast two groups of detector pixels.
2. The system of claim 1 , wherein at least one of the firstor the second thermal references has a known spectrum .

a thermal reference comprising a first portion at a first
temperature and a second portion at a second tempera

ture different from the first temperature , wherein radiation emitted from the first and the second portions of
the thermal reference is directed to at least one of theat least two groups of detector pixels simultaneouslywith radiation emitted from a scene viewed by the

3 . The system of claim 1 , wherein at least one of the first 5

or the second temperatures is unknown.

4 . The system of claim 1 , wherein at least one of the firstor the second thermal references is displaced away from a
conjugate image plane of optical FPA unit such that animage of at least one of the first or the second thermal 10

imaging system ; andconfigured to :a data -processing system , said data - processing systemreferences on at least one of the at least two groups ofdynamically calibrate the at least two groups of detec

detector pixels is blurred .

tor pixels to reduce a difference in measurements

5 . The system of claim 1, wherein at least one of the firstor the second thermal references is positioned at a conjugate
15
image plane of the optical FPA unit.

portions of the thermal reference obtained by at least
one of the at least two groups of detector pixels .

6 . The system of claim 1 , wherein at least one of the firstor the second thermal references is disposed outside aobtained using light from of the first and the second

13 . The system of claim 12 , wherein the first or the second

temperatures is unknown.
14 . The system of claim 12 , wherein the thermal reference

central field of view of the optical FPA unit.

is displaced away from a conjugate image plane of the
7 . The system of claim 1 , further comprising at least one
incident 2020 optical
FPA unit such that an image of at leastone of the first
shutter removably positioned to block IR radiationIn incident
opusthe second
or
portions of the thermal reference is blurred .
on the system from reaching the optical FPA unit.
15 . The system ofclaim 12 , wherein the thermal reference
8 . The system of claim 1, wherein the optical system
is positioned at a conjugate image plane of the optical FPA
includes at least three optical channels.
9 . The system of claim 1, wherein the optical system

includes at least four optical channels .

10 . The system of claim 1 , wherein the measurements

obtained by the at least two groups of detector pixels using

the light received from the thermal references are tempera
ture measurements of the first and second thermal refer

25

unit.

16 . The system ofclaim 12 ,wherein the first or the second

portion of the thermal reference is disposed outside a central

field of view of the optical FPA unit.
17 . The system of claim 12 , further comprising at least

one shutter removably positioned to block IR radiation
3030 mioincident on the system from reaching the optical FPA unit .
18 . The system of claim 12 , wherein the optical system
11 . The system of claim 1, wherein one of the at least two
at least three optical channels .
groups of detector pixels comprises a first focal plane array includes
19.
Theof claim 12 , wherein the optical system
and another of the at least two groups of detector pixels includes at system
least four optical channels .
comprises a second focal plane array.
ng system
system 3535 20. The system of claim 12, wherein the optical system
12 . An infrared (IR ) imaging system , the imaging
includes at least five optical channels .
comprising:
21 . The system of claim 12 , wherein the measurements
an optical system including an optical focal plane array obtainedby the at least two groups of detector pixels using(FPA ) unit , the optical system including components
the
light
received from the first and second portions of theassociated with at least two optical channels, said at 40 thermal reference
measurements of the firstleast two optical channels being spatially and spectrally 40 and second portionsareoftemperaturethethermalreference .
different from one another , the at least two optical. The system of claim 12 , wherein one of the at least
channels positioned to transfer IR radiation incident on two22 groupsof detector pixels comprises a first focal plane
the optical system towards the optical FPA unit, theandanotherofthe at least two groups of detector pixels
optical FPA unit comprising at least two groups of arrayarra

ences.

detector pixels disposed at a distance from at least two 45 comprises a second focal plane array.

corresponding focusing lenses ;***