US010444070B2(12) United States Patent(10) Patent No.: US 10 ,444,070 B2(45) Date of Patent:

Kester et al.

(54 ) DIVIDED -APERTURE INFRA -RED
SPECTRAL IMAGING SYSTEM

References Cited
U . S . PATENT DOCUMENTS( 56 )(71) Applicant: Rebellion Photonics, Inc., Houston , TX

3 ,841, 763 A(US)

3 , 849 ,005 A(72 ) Inventors : Robert Timothy Kester, Pearland , TX
(US) ; Nathan Adrian Hagen ,Utsunomiya (JP )(73 ) Assignee : Rebellion Photonics, Inc., Houston , TX

(65 )Subject to any disclaimer, the term of thispatent is extended or adjusted under 35
U .S .C . 154 (b ) by 0 days.

FOREIGN PATENT DOCUMENTS
2 365 866
2 787 303CA

US 2017 /0350758 A1 Dec . 7 , 2017
Related U .S . Application Data
(63 ) Continuation of application No. 14 /539 ,899, filed on

Nov . 12 , 2014 , now Pat. No. 9,599 ,508 , which is a(Continued )(52 ) U .S . CI.

9 / 2000
7 /2011

OTHER PUBLICATIONSUS 10, 113,914 B2 , 10 /2018 , Kester et al. (withdrawn )(Continued )Primary Examiner – David P Porta
Assistant Examiner — Faye Boosalis(74 ) Attorney, Agent, or Firm — Knobbe, Martens, Olson

Mar. 17 , 2017
Prior Publication Data

(51) Int. CI.
GOIN 21/ 3504
GO1J 3 /02

11/ 1974 Girard et al.

(Continued )(21) Appl. No.: 15/462,350(22) Filed :10 / 1974 Lewis(Continued )(US)( * ) Notice :Oct. 15, 2019

& Bear, LLP(57)
ABSTRACT
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 and( 2014.01)(2006 .01 )(Continued )spectrally different from one another . Each of the at least two
optical channels are configured to transfer IR radiation

CPC ........... GO1J 3/ 0232 ( 2013 .01); GOIJ 3 /0229(2013 .01 ); GOIJ 3 /28 (2013.01); GOIJ 3 /2823(2013. 01);

(Continued )(58 ) Field of Classification Search
CPC .......... GO1J 3 /0232 ; G01J 3 /0229 ; G01J 3 /28;
G01J 3 /36 ; G01J 3 /2823 ; GOIN 21 /3504
See application file for complete search history .

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 .

16 Claims, 15 Drawing Sheets

wishessace 204
202
7

224

0

expers vrugot 230

Pili 228- - 226200

Towards
processor 150

US 10 ,Page
444,2070 B2
Related U .S . Application Data
continuation - in -part of application No. PCT/US2013 /
041278 , filed on May 16 , 2013 .

9 ,644 , 562 B2
9 ,756 , 263 B2
10 ,084, 975 B2
10 ,254 , 166 B2
10 ,267,686 B2

4 /2019 Kester et al.

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

(52 ) U .S . CI.

CPC ............ GO1J 3 /36 ( 2013 .01); GOIN 21/ 3504
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DIVIDED -APERTURE INFRA -RED
SPECTRAL IMAGING SYSTEM

the optical system , the at least two or more optical channels
being spatially and spectrally different from one another;and (ii ) a processor or processing electronics configured to

CROSS -REFERENCE TO RELATEDAPPLICATIONS

acquire multispectral optical data representing said target

5 chemical species from the received IR radiation in a single
occurrence of data acquisition (or snapshot). The optical

This application is a continuation of U . S . patent applica

FPA unit includes an array of photo - sensitive devices thattion Ser. No . 14 /539,899, filed on Nov. 12 , 2014 , which

are disposed at the focus of one or more lenses. In various

titled “ DIVIDED -APERTURE INFRA -RED SPECTRAL

radiation having wavelengths between 1 um and 20 um (forCHEMICAL DETECTION ,” which claimsbenefit under 35
U .S .C . $ 119(e ) of U . S . Provisional Application No . 61/688 ,
630 , filed on May 18 , 2012 and of U . S . Provisional Applitors that are sensitive to infra -red radiation . The opticalsystem may include an optical aperture (a boundary ofincorporated by reference herein in its entirety .

more optical filters . In various implementations, the one or

and method of detecting spectral signatures of chemicalcompositions in a mid - and long -wave infrared spectral

various embodiments, the one or more optical filters can bespectrally multiplexed and may include, for example, at leastclaims benefit under 35 U .S . C . $ 119 (e ) of U . S . Provisional embodiments , the array of photo -sensitive devices canApplication No . 61/ 903 ,075 , filed on Nov . 12 , 2013 and 10 include a two - dimensional imaging sensor that is sensitive to

IMAGING SYSTEM ” and which is also a continuation - inexample , in mid infra - red wavelength range , long infra -redpart of International Application No. PCT /US /2013 / 041278 , wavelength range, visible wavelength range, etc . ). In various
filed on May 16 , 2013 and titled “ DIVIDED - APERTURE, the array of photo -sensitive devices can
INFRA -RED SPECTRAL IMAGING SYSTEM FOR 15 embodiments
include CCD or CMOS sensors, bolometers or other detec

cation No . 61/ 764 ,776 , filed on Feb . 14 , 2013. The disclo which is defined to circumscribe or encompass the at least
sure of each of the above identified application is 20 two or more spatially distinct optical channels ) and one ormore optical filters can comprise at least two spectrally
multiplexed filters . Each of these optical filters can be
TECHNICAL FIELD
associated with one of the at least two or more optical
The present invention generally relates to a system and 25 channels and configured to transmit a portion of the IR
method for gas cloud detection and , in particular, to a systemradiation received in the associated optical channel. In
region .
DESCRIPTION OF THE RELATEDTECHNOLOGY

one of a longpass optical filter and a shortpass optical filter ,30 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 .

The at least two reimaging lenses, for example each of theSpectral imaging systems and methods have applications reimaging lens, may be disposed to transmit IR radiation (forin a variety of fields. Spectral imaging systemsand methods 35 example, between about 1 micron and about 20 microns ),obtain a spectral image of a scene in one or more regions ofthat has been transmitted through a corresponding opticalmaterial compositions or characterize processes . The spec
tral image of the scene can be represented as a three

optical FPA unit is positioned to receive IR radiation fromthe object through the at least two reimaging lenses to form

two spatial dimensions of the scene and a third axes of therepresenting the object. The processor or processing elec

the electromagnetic spectrum to detect phenomena , identify

filter towards the optical FPA unit . In one embodiment, thedimensional data cube where two axes of the cube represent 40 respectively -corresponding two or more sets of imaging data

data cube represents spectral information of the scene indifferent wavelength regions . The data cube can be pro cessed using mathematical methods to obtain information

tronics is configured to acquire this optical data from the two
or more sets of imaging data . In various embodiments of theimaging systems, the FPA unit may be devoid of coolingabout the scene. Some of the existing spectral imaging 45 systems. In various embodiments, two or more of the arraysystems generate the data cube by scanning the scene in the of photo -sensitive devices may be uncooled . In somespatial domain (e . g ., by moving a slit across the horizontal embodiments , the system further comprises two or moredimensions of the scene) and /or spectral domain (e . g ., bytemperature - controlled shutters removably positioned toscanning a wavelength dispersive element to obtain images block IR radiation incident onto the optical system from theof the scene in different spectral regions). Such scanning 50 object.

approaches acquire only a portion of the full data cube at a

Also disclosed herein is an implementation of a method oftime. These portions of the full data cube are stored and thenlater processed to generate a full data cube .

operating an infrared (IR ) imaging system . The method
includes receiving IR radiation from an object through at
least two optical channels defined by components of an

SUMMARY

55 optical system of the IR imaging system , which at least two
optical channels are spatially and spectrally different fromThe systems, methods and devices of this disclosure eachone another. The method further includes transmitting thehave several innovative aspects , no single one of which isreceived IR radiation towards an optical focal plane arraysolely responsible for the desirable attributes disclosed
herein .

Various embodiments of the systems described hereinconcentration of a target chemical species in an object (e .g .,a gas plume). The imaging system includes (i) an opticalprovide an infrared (IR ) imaging system for determining a(FPA ) unit that is not being cooled in the course of normal
60 Operation . For example , in various embodiments of theimaging systems, the FPA unit may be devoid of coolingof photo - sensitive devices may be uncooled . Some embodi
ments further comprise removably positioning at least one ofsystems. In various embodiments, two or more of the arraysystem , having an optical focal plane array (FPA ) unit 65 at least two temperature -controlled shutters in front of theconfigured to receive IR radiation from the object along at optical system to block IR radiation incident onto the opticalleast two ormore optical channels defined by components ofsystem from the object.

US 10 ,444 ,070 B2gate image plane of the plurality of cameras such that theimage of the at least one reference source captured by the

Various innovative aspects of the subjectmatter describedin this disclosure can be implemented in the following

plurality of cameras is blurred.

embodiments :Embodiment 1

Embodiment 10

An infrared (IR ) imaging system , the imaging system
The system of any of Embodiments 1- 9 , wherein the atleast one reference source is positioned at a conjugate image
plane of the plurality of cameras.
a plurality of cameras ;at least one thermal reference source having a known 10
Embodiment 11
temperature placed in front of the plurality of cameras

comprising:and configured to be imaged by the plurality of cam
eras ; anda data -processing unit comprising a processor, the imag ing system configured to :acquire with the plurality of cameras a plurality of frames
having regions that correspond to the image of thereference source; andThe system of any of Embodiments 1 - 10 , further com

prising a plurality ofmirrors configured to image the at least

one reference source onto the plurality of cameras .
Embodiment 12

apply a dynamic calibration correction to the plurality of 20

The system of any of Embodiments 1- 11 , wherein thecameras to allow every camera in the plurality ofplurality of mirrors are disposed outside a central field ofcamera in the plurality imaging the reference source .
Embodiment 2
25

Embodiment 13

view of the plurality of cameras.

cameras to be calibrated to agree with every otherThe system of Embodiment 1 , wherein the plurality ofcameras comprises a FPA unit and a plurality of lenses .

Embodiment 3

The system of any of Embodiments 1 - 12 , further com

prising a first and a second temperature - controlled shutter

removably positioned to block IR radiation incident on thesystem from reaching the plurality of cameras.
30

The system of any of Embodiments 1-2 ,wherein the FPA

unit comprises one FPA or a plurality of FPAs.

Embodiment 14
The system of any of Embodiments 1 - 13 , wherein thesystem includes at leasttwo spatially and spectrally different
Embodiment 4
35 optical channels.
The system of any of Embodiments 1 -3 , wherein the at
Embodiment 15
least one thermal reference source has a known spectrum .
Embodiment 5
The system of any of Embodiments 1 - 14 , wherein the
40tu system
includes at least three optical channels.
The system of any of Embodiments 1 -4 , further compris
ing an additional thermal reference source imaged by the
Embodiment 16
plurality of cameras.
45 The system of any of Embodiments 1- 15 , wherein the
Embodiment 6
system includes at least four optical channels .
theThe system of any of Embodiments 1- 5, whereinn the
Embodiment 17

additional reference source has a temperature and a spec

trum different from the known temperature and the known
50
spectrum of the at least one reference source .

Embodiment 7

The system of any of Embodiments 1 - 16 , wherein thesystem includes at least five optical channels.
Embodiment 18

The system of any of Embodiments 1 -6 , wherein thetemperature of the additional thermal reference source is less 55 The system of any of Embodiments 1- 17 , wherein thethan the known temperature .
system includes at least six optical channels .
Embodiment 8
Embodiment 19
The system of any of Embodiments 1- 7 , wherein the 60 The system of any of Embodiments 1 -18 , wherein thetemperature of the additional thermal reference source isgreater than the known temperature .

Embodiment 9
65
The system of any of Embodiments 1 -8 , wherein the atleast one reference source is displaced away from a conju

system includes at least seven optical channels .

Embodiment 20

The system of any of Embodiments 1 - 19 , wherein thesystem includes at least eight optical channels.

US 10 ,444 ,070 B2
Embodiment 30
The system of any of Embodiments 26 -29, wherein thefirst temperature is greater than the second temperature .

Embodiment 21

The system of any of Embodiments 1- 20 , wherein thesystem includes at least nine optical channels.

Embodiment 31

Embodiment 22

system of any of Embodiments 26 -30 , wherein the
The system of any of Embodiments 1- 21 , wherein the firstThetemperatureis less than the second temperature .
system includes at least ten optical channels .
10
Embodiment 32
Embodiment 23
of any of Embodiments 26 -31 , wherein the
The system of any of Embodiments 1 -22 , wherein the firstTheandsystemthesecondreference sources are displaced awaysystem includes at least twelve optical channels.
15 from a conjugate image plane of the plurality of cameras
such that the image of the first and the second reference
Embodiment 24
sources captured by the plurality of cameras is blurred .
The system of any of Embodiments 1 -23 , further com
Embodiment 33
prising one or more sensors configured to measure a tem - 20
perature of the at least one reference source .
The system of any of Embodiments 26 -32 , wherein thefirst and the second reference sources are positioned at a
conjugate image plane of the plurality of cameras .
Embodiment 25

The system of any of Embodiments 1 -24 , wherein the25

Embodiment 34

plurality of cameras is configured to image the sameportion

The system of any of Embodiments 26 - 33 , further com
prising:
30 a firstmirror configured to image the first reference onto
Embodiment 26
the plurality of cameras ; andAn infrared (IR ) imaging system , the imaging systema second mirror configured to image the second reference
source onto the plurality of cameras.
comprising:a plurality of cameras;
Embodiment 35
a first temperature -controlled reference source imaged by 35
the plurality of cameras;
The system of any of Embodiments 26 - 34 , further com
a second temperature -controlled reference source imaged prisinga first and a second temperature - controlled shutter
by the plurality of cameras ; andremovablyto block IR radiation incident on thea data -processing unit comprising a processor, said data4 40 system frompositioned
reaching
the plurality of cameras.
processing unit configured to :acquire with the plurality of cameras a plurality of frames
Embodiment 36
having regions that correspond to the image of thereference source; andThe system of any of Embodiments 26 -35 , wherein the
dynamically calibrate the plurality of cameras so that 4545 system
includes at least two spatially and spectrally different
various cameras imaging a scene are forced to agree on
opticalchannels .
a temperature estimate of the first and second referenceof the at least one reference source .

sources .

Embodiment 37
Embodiment 27

50

0

The imaging system of any of Embodiment 26 , wherein

the data - processing unit is configured to calculate a dynamic

Embodiment 38

calibration correction and apply the correction to the plu

rality of cameras for each of the plurality of frames.

The system of any of Embodiments 26 -36 , wherein thesystem includes at least four optical channels.

55

Embodiment 28

The system of any of Embodiments 26 - 27 , wherein thefirst reference source is maintained at a first temperature.

The system of any of Embodiments 26 -37 , wherein thesystem includes at least six optical channels.
Embodiment 39

The system of any of Embodiments 26 -38 , wherein thesystem includes at least eight optical channels .
Embodiment 29

Embodiment 40
The system of any of Embodiments 26 - 28 , wherein the 65

second reference source is maintained at a second tempera
ture .

The system of any of Embodiments 26 - 39, wherein thesystem includes at least ten optical channels.

US 10 ,444 ,070 B2
Embodiment 41

removably positioned to block IR radiation incident on the

The system of any of Embodiments 26 -40 , wherein thesystem includes at least twelve optical channels.

Embodiment 49
EM

Embodiment 42

The system of any of Embodiments 44 -48, wherein thesystem includes at least two spatially and spectrally different

system from reaching the plurality of cameras .

optical channels.

The system of any of Embodiments 26 -41, further com

prising one or more sensors configured to measure a tem - 10
perature of the first or the second reference source .

The system of any of Embodiments 44 -49 , wherein the

Embodiment 43

system includes at least three optical channels.

The system of any of Embodiments 26 -42 , wherein the 15

plurality of cameras is configured to image the sameportion

ofthe firstreference source and wherein plurality of cameras
is configured to image the same portion of the second
reference source .

Embodiment 50

Embodiment 51
The system of any of Embodiments 44 -50 , wherein thesystem includes at least four optical channels .

Embodiment 52
Embodiment 44
The system of any of Embodiments 44 -51, wherein thesystem includes at least five optical channels .
An infrared ( IR ) imaging system , the imaging systemcomprising:
Embodiment 53
25
a plurality of cameras ;The system of any of Embodiments 44-52 , wherein thea reference having an unknown temperature configured to system
includes at least six optical channels .
be imaged by the plurality of cameras; anda data -processing unit comprising a processor, the ima
imag
Embodiment 54
30
ing system configured to :acquire with the plurality of cameras a plurality of frames
The system of any of Embodiments 44 -52, wherein thehaving regions that correspond to the image of thesystem includes at least seven optical channels.
reference ;20

calculate a dynamic calibration correction using a tem - 35
perature measured by one of the cameras in the plu

rality of cameras as a reference temperature; andapply the calibration correction to the other cameras in theplurality of cameras to match the temperature estimate

Embodiment 55

The system of any of Embodiments 44 -53 , wherein thesystem includes at least eight optical channels .
Embodiment 56of the other cameras in the plurality of cameraswith the 40
reference temperature .
The system of any of Embodiments 44 -54 , wherein thesystem includes at least nine optical channels.

Embodiment 45

Embodiment 57

The system of any of Embodiment 44 , wherein the 45

reference is displaced away from a conjugate image plane ofthe plurality of cameras such that the image of the reference
source captured by the plurality of cameras is blurred .

The system of any of Embodiments 44 -55 , wherein thesystem includes at least ten optical channels.

Embodiment 58
Embodiment 46
The system of any of Embodiments 44 -56 , wherein thesystem includes at least twelve optical channels.
The system of any of Embodiments 44 -45, wherein thereference is positioned at a conjugate image plane of the
Embodiment 59
plurality of cameras.
55
The system of any of Embodiments 44 -57 , wherein theplurality of cameras is configured to image the same portion
Embodiment 47of the reference .
The system of any of Embodiments 44 -46 , further com
Embodiment 60
prising a plurality of mirrors configured to image the refer - 60
ence onto the plurality of cameras.
An infrared (IR ) imaging system , the imaging systemcomprising:
50

Embodiment 48

The system of any of Embodiments 44 -47, further com

prising a first and a second temperature -controlled shutter

65

an optical system including an optical focal plane array(FPA ) unit, the optical system includes components
associated with at least two optical channels , said atleast two optical channels being spatially and spectrallyUS 10,444 ,070 B2
10
Embodiment 68
The system of any of Embodiments 60 -67, further com
unit, the optical FPA unit comprising at least two prising at least two reflecting elements configured to direct
detector arrays disposed at a distance from two corre- 5 radiation from the at least one reference source toward thesponding focusing lenses;
at least two detector arrays.
at least one thermal reference having a known tempera
Embodiment 69
ture , wherein radiation emitted from the at least one
different from one another, each of the at least two
optical channels positioned to transfer IR radiation
incident on the optical system towards the optical FPA

reference is directed towards the optical FPA unit andimaged by the at least two detector arrays ; and10

The system of any of Embodiments 60 -68, wherein the at

a data -processing unit, said data -processing unit config ured to :least two reflecting elements are disposed outside a central
field of view of the at least two detector arrays .
acquire a plurality of frames with the at least two detector
Embodiment 70
arrays having regions in the plurality of image frames 15

that correspond to the image of the reference ; andThe system of any of Embodiments 60 -69, further com

dynamically calibrate the at least two detector arrays toaddress a difference in the temperature estimate of theprising a third detector array disposed between the at least
two detector arrays .

reference between the two detector arrays .
20

Embodiment 61

Embodiment 71

The system of any of Embodiment60 ,wherein the at least

The system of any of Embodiments 60 -70 , wherein thedata -processing unit is configured to :one thermal reference has a known spectrum .

25

Embodiment 62

acquire a plurality of frames using the third detector array ;anddynamically calibrate the third detector array to match a

The system of any of Embodiments 60 -61, further com
prising an additional thermal reference, wherein radiation

temperature estimate of the third detector array with thefrom the additional reference is directed towards the optical 30

arrays .

FPA unit and imaged by the at least two detector arrays .
Embodiment 63

temperature estimates of the at least two detector

Embodiment 72
The system of any of Embodiments 60 -71, wherein radia

The system of any of Embodiments 60 -62 , wherein the 35 tion emitted from the at least one reference source is not
additional reference has a temperature and a spectrum
imaged by the third detector array .

different from the known temperature and the known spec

Embodiment 73

trum of the at least one reference source .

40 The system of any of Embodiments 60 - 72 , wherein the
Embodiment 64
third detector array has a field of view greater than a field of
The system of any of Embodiments 60 -63, wherein the view of the at least two detector arrays.
temperature of the additional thermal reference is less than
Embodiment 74
the known temperature .
45

The system of any of Embodiments 60 -73 , wherein the at
Embodiment 65
least one reference is imaged by the third detector array .
The system of any of Embodiments 60 -64 , wherein the
Embodiment 75
temperature of the additional thermal reference is greater sothan the known temperature .
The system of any of Embodiments 60 -74 , further com
prising a third reflecting element disposed outside the field
Embodiment 66
of view of the at least two detector arrays and configured to
The system of any of Embodiments 60 -65 , wherein the at 55 image the at least one reference onto the third detector array .
least one reference is displaced away from a conjugate
Embodiment 76
image plane of the at least two detector arrays such that theimage of the at least one reference captured by the at least
The system of any of Embodiments 60 - 75 , further com
two detector arrays is defocused .
prising a first and a second temperature - controlled element
60 removably positioned to block IR radiation incident on the
Embodiment 67
optical system from reaching the optical FPA unit.
The system of any of Embodiments 60 -66 , wherein the at
Embodiment 77
least one reference is positioned at a conjugate image planeof the at least two detector arrays such that the image of the 65 The system of any of Embodiments 60 -76 , wherein theat least one reference captured by the at least two detector optical system includes components associated with threearrays is focused .

optical channels.

US 10 ,444 ,070 B2
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11
Embodiment 78

The system of any of Embodiments 60 - 77 wherein the
optical channels.
Embodiment 79
The system of any of Embodiments 60- 78 , wherein the
optical system includes components associated with six 10
optical channels .
Embodiment 80
The system of any of Embodiments 60- 79 , wherein the 15
optical system includes components associated with eight
optical channels.
Embodiment 81
optical system includes components associated with four

The system of any of Embodiments 60 -80 , wherein the20

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
positioned to transfer IR radiation incident on the

optical system towards the optical FPA unit , the optical
FPA unit comprising at least two detector arrays dis
posed at a distance from two corresponding focusing
lenses ;a first temperature -controlled reference imaged by the atleast two detector arrays ;a second temperature -controlled reference imaged by theat least two detector arrays ; anda data -processing unit configured 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 first and second
references ; anddynamically calibrate the at least two detector arrays toaddress a difference in a temperature estimate of the

optical system includes components associated with ten

optical channels.

first and second references between the two detector

arrays .

Embodiment 82
25
Embodiment 90
The system of any of Embodiments 60 -81, wherein the
The system of Embodiment 89, wherein the first reference
optical system includes components associated with twelve
is maintained at a first temperature .
optical channels.
30
Embodiment 91
Embodiment 83

The system of any of Embodiments 89 - 90 , wherein the

The system of any of Embodiments 60 -82, wherein thesecond reference is maintained at a second temperature .

optical system includes components associated with sixteen

optical channels.

35

Embodiment 84

Embodiment 92

The system of any of Embodiments 89 -91, wherein the

The system of any of Embodiments 60 -83 , wherein the first temperature is greater than the second temperature .
optical system includes components associated with twenty .
Embodiment 93
four optical channels .
40

The system of any of Embodiments 89-92 , wherein thefirst temperature is less than the second temperature .

Embodiment 85

The system of any of Embodiments 60 -84 , wherein eachof the at least two detector arrays is configured to image the 43

same portion of the at least one reference so as to consis
tently provide a common reference temperature .

Embodiment 94

The system of any of Embodiments 89 -93, wherein thefirst and the second references are displaced away from a

Embodiment 86

conjugate image plane of the at least two detector arrays
50 such that the image of the first and the second references

The system of any of Embodiments 60 -85 , wherein thedata -processing unit comprises processing electronics .

captured by the at least two detector arrays is defocused .

Embodiment 87
The system of any of Embodiments 60 - 86 , wherein thedata - processing unit comprises a processor.

Embodiment 95

55

The system of any of Embodiments 89 -94 , wherein thefirst and the second references are positioned at a conjugate

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

Embodiment 88

The system of any of Embodiments 60 -87 , wherein thedata- processing unit comprises one or more processors.
Embodiment 89

An infrared (IR ) imaging system , the imaging systemcomprising:60

at least two detector arrays is focused .

Embodiment 96

The system of any of Embodiments 89- 95 , further com
prising:
65 a first reflecting element configured to direct radiationfrom the first reference toward the at least two detector
arrays; andUS 10 ,444 ,070 B2
13
a second reflecting element configured to direct radiationfrom the second reference toward the at least two

14
removably positioned to block IR radiation incident on the
optical system from reaching the optical FPA unit.

detector arrays.

Embodiment 97

Embodiment 106
The system of any of Embodiments 89 - 105 , wherein the

The system of any of Embodiments 89 - 96 . wherein thefirst reflecting element is disposed outside a field of view of

optical system includes components associated with three
optical channels .

the at least two detector arrays .

Embodiment 107
Embodiment 98
The system of any of Embodiments 89-106 , wherein the
opticalsystem includes components associated with four
The system of any of Embodiments 89 - 97 , wherein the optical channels.
second reflecting element is disposed outside a field of view 15
10of the at least two detector arrays .

Embodiment 99

Embodiment 108

The system of any of Embodiments 89- 107, wherein the
optical system includes components associated with five

The system of any of Embodiments 89- 98 , further com - - optical channels.

prising a third detector array disposed between the at least

two detector arrays .

Embodiment 109

The system of any of Embodiments 89-108 , wherein the
25 opticalsystem includes components associated with six
The system of any of Embodiments 89 -99 , wherein the optical channels.
data -processing unit is configured to :Embodiment 110
acquire a plurality of frames using the third detector array ;30 Theand
The system of anany of Embodiments 89 - 109, wherein the
dynamically calibrate the third detector array to address a optical system includes components associated with sevendifference in the temperature estimate of the first and optical channels .
second references between the third detector array andthe two detector arrays .
Embodiment 111
35

Embodiment 100

The system of any of Embodiments 89 -110 , wherein thehe opticalop channels.
The system of any of Embodiments 89 -100 , wherein thefirst and second references are not imaged by the third 40
Embodiment 112
detector array.
The system of any of Embodiments 89- 111, wherein the
Embodiment 101

optical system includes components associated with eight

Embodiment 102

optical system includes components associated with ten
optical channels.
The system of any of Embodiments 89 -101, wherein the 45
Embodiment 113
third detector array has a field of view greater than a field ofview of the at least two detector arrays.

The system of any of Embodiments 89- 112 , wherein the
Embodiment 103
50 optical channels .
The system of any of Embodiments 89- 102 , wherein r first
Embodiment 114
and second references are imaged by the third detector array.
The system of any of Embodiments 89- 113 ,wherein each
55 of the at least two detector arrays is configured to image the
Embodiment 104
same portion of the first reference source so as to consis
tently provide a common first reference temperature and
The system of any of Embodiments 89 - 103, further com whereineach of the at least two detector arrays is configured
prising a third reflecting element disposed outside the fieldof view of the at least two detector arrays and configured to to image the same portion of the second reference source so

optical system includes components associated with twelve

image the first and second references onto the third detector 60 as to consistently provide a common second reference
temperature .
array.

Embodiment 115
65 The system of any of Embodiments 89 - 114 , further com
The system of any of Embodiments 89 - 104 , further com - prising a temperature controller configured to control theprising a first and a second temperature -controlled element temperature of the first or second reference .
Embodiment 105

US 10 , 444 ,070 B2

15

16

Embodiment 116
The system of any of Embodiments 89 - 115 , further com

the calibration surface of the cameras in the plurality ofcameras agree with each other.

Embodiment 125
The system of Embodiment 124 ,wherein the one ormore
parameters is associated with a gain of the cameras in the
Embodiment 117
plurality of cameras.
The system of any of Embodiments 89- 116 , wherein the
Embodiment 126
one or more sensors are configured to communicate
unicate the 10
measured temperature of the first or the second reference to
The system of any of Embodiments 124 -125 , wherein thea temperature controller.
one or more parameters is associated with a gain offset of theprising one or more sensors configured to measure a tem
perature of the first or the second reference .

Embodiment 118

15

cameras in the plurality of cameras .

Embodiment 127

The system of any of Embodiments 89 - 117 , wherein theone or more sensors are configured to communicate the

The system of any of Embodiments 124 - 126 , wherein themeasured temperature of the first or the second reference tocalibration surface is displaced away from a conjugate
image plane of the plurality of cameras such that an image

the data -processing unit.

of the surface is defocused .

Embodiment 119

Embodiment 128

The system of any of Embodiments 89 - 118 , wherein thefirst or the second reference is associated with a heater.

The system of any of Embodiments 124 - 127 , wherein thecalibration surface is positioned at a conjugate image planeof the plurality of cameras such that an image of the surface
Embodiment 120
is focused .
The system of any of Embodiments 89 -119 , wherein the 30

first or the second reference is associated with a cooler.

Embodiment 129

Embodiment 121

The system of any of Embodiments 124 - 128 , further
comprising at least one reflecting element configured to

The system of any of Embodiments 89 - 120 wherein the 35 image the surface onto the plurality of cameras.

data -processing unit comprises processing electronics.

Embodiment 130
The system of any of Embodiments 124 -129, further

Embodiment 122
The system of any of Embodiments 89 - 121, wherein thedata - processing unit comprises a processor.
Embodiment 123

40 comprising a first and a second temperature -controlled ele
ment removably positioned to block IR radiation incident on

the optical system from reaching the plurality of cameras .

The system of any of Embodiments 89 -122 , wherein the

The system of any of Embodiments 124 - 130 , wherein thedata - processing unit comprises one or more processors .
Embodiment 124

Embodiment 131

45

optical system includes components associated with three
optical channels.
50

Embodiment 132
An infrared ( IR ) imaging system , the imaging system
The system of any of Embodiments 124 -131, wherein thecomprising:
optical system includes components associated with fouran optical system including components associated with4 55 optical channels.
at least two optical channels , said at least two optical 55
channels being spectrally different from one another ,Embodiment 133
each of the at least two optical channels positioned totransfer IR radiation incident on the optical system
The system of any of Embodiments 124 -132 , wherein the
towards a plurality of cameras ;60
opticalsystem includes components associated with six
at least one calibration surface with unknown temperature ou optical channels.

and imaged by each of the at least two detectors ; anda data -processing unit configured to :Embodiment 134

adjust one or more parameters of the cameras in the

optical system includes components associated with eightacquire a plurality of image frames with the plurality ofcameras including the imaged surface ; and65
plurality of cameras such that a temperature estimate of

The system of any of Embodiments 124- 133, wherein the

optical channels.

US 10 ,444 ,070 B2
17

18
Embodiment 145

Embodiment 135
The system of any of Embodiments 124 -134 , wherein the
optical system includes components associated with ten
optical channels.
Embodiment 136

The system of any of Embodiments 141 - 144, wherein anumber of optical filters is two.

Embodiment 146

The system of any of Embodiments 141 - 145, wherein a
The system of any of Embodiments 124 - 135 , wherein the number of optical filters is three .
optical system includes components associated with twelve 10
Embodiment 147
optical channels.
The system of any of Embodiments 141 -146 , wherein a
Embodiment 137
number of optical filters is four.

The system of any of Embodiments 124 -136 , wherein the 15

data -processing unit comprises processing electronics .

Embodiment 148

Embodiment 138

The system of any of Embodiments 141- 147 , wherein theplurality of optical filters comprise at least one long passliments 124 - 137., wherein ththe 20 (LP ) filter.
The system of any of Embodiments

data -processing unit comprises a processor .
Embodiment 139

Embodiment 149

The system of any of Embodiments 141- 148, wherein the
25 plurality of optical filters comprise multiple long pass (LP)The system of any of Embodiments 124 - 138 , wherein the - > filters

data -processing unit comprises one or more processors .
Embodiment 140

Embodiment 150

The system ofany of Embodiments 141 - 149 , wherein the

The system of any of Embodiments 124 - 139, wherein the » plurality of optical filters comprise at least one short passcalibration surface comprises a sidewall of a housing of theersystem .

Embodiment 141

35

Embodiment 151
The system of any of Embodiments 141 - 150, wherein the

An infrared ( IR ) imaging system , the imaging system
plurality of optical filters comprise multiple short pass (SP )filters.
at least four spatially and spectrally different opticalchannels configured to receive IR radiation from a
Embodiment 152
common object , each of the at least four spatially and 40

comprising:

spectrally different optical channels comprising at least

The system of any of Embodiments 141 - 151, wherein the

one imaging lens configured to image the object on aplurality of optical filters comprise at least one band pass

Focal Plane Array (FPA ) unit ; and(BP ) filter.

processing electronics in communication with the FPA 45
unit,

wherein said infrared system is configured to :acquire multispectral optical data from the at least four
different optical channels ; andEmbodiment 153
The system of any of Embodiments 141- 152 , wherein theplurality of optical filters comprise at one short pass (SP )process the multispectral optical data to detect one or 50 filter and one long pass (LP ) filter.
more target species present in the object.
Embodiment 154
Embodiment 142
The system of any of Embodiments 141- 153 , wherein the
The system of Embodiment 141, further comprising FPA unit comprises a plurality of FPAS.
twelve optical channels .
Embodiment 155
Embodiment 143
The system of any of Embodiments 141 -154 , further
The system of any of Embodiments 141- 142, configured comprising first and second temperature-controlled elements
to simultaneously acquiremultispectral optical data from the 60 removably positioned to block IR radiation incident on theimaging system from reaching the FPA unit.
at least four different optical channels.
Embodiment 144
Embodiment 156
The system of any of Embodiments 141- 143, further 65 The system of any of Embodiments 141- 155 , further
comprising a plurality of optical filters associated with the comprising a field reference configured for dynamicallycalibrating a plurality of the FPAs in the FPA unit.
optical channels.

US 10 ,444 ,070 B2

20

19
Embodiment 157

Embodiment 167

The system of any of Embodiments 141- 166 , further
The system of any of Embodiments 141 -156 , wherein thecomprising five optical channels.
of an image generated by a plurality of the FPAs in the FPA 5

field reference is configured to obscure a peripheral region

Embodiment 168
The system of any of Embodiments 141- 167 , further
comprising six optical channels.

unit.

Embodiment 158

The system of any of Embodiments 141- 157, configured 10
to compare spectral data in at least one of the four optical
Embodiment 169
channels acquired at a first instant of time with spectral datain the at least one of the four optical channels acquired at a
The system of any of Embodiments 141- 168, further
second instant of time to generate a temporal difference is comprising seven optical channels .
image .
Embodiment 170
Embodiment 159

The system of any of Embodiments 141- 169, further

The system of any of Embodiments 141-158, configured 20 comprising eight optical channels.
to use a difference between the multispectral optical dataacquired by the two optical channels to correct parallax
Embodiment 171
induced imaging errors .

The system of any of Embodiments 141- 170 , further
Embodiment 160
25 comprising nine optical channels .
The system of any of Embodiments 141- 159, configured
Embodiment 172

to use a difference between the multispectral optical data
T . ..
The
system of any of Embodiments 141- 171 , further
between the system and the object.
30 comprising ten optical channels .
Embodiment 161
Embodiment 173
acquired by the two optical channels to estimate a distance

The system of any of Embodiments 141- 160 , configured

to estimate a size of the object based on the estimated
The system of any of Embodiments 141- 172, further
distance and an optical magnification factor of the two » comprising eleven optical channels .

optical channels .

Embodiment 174

Embodiment 162

The system of any of Embodiments 141 - 173 , wherein a

The system of any of Embodiments 141- 161, configured tº number of optical filters is five .

to compare spectral data in one of the at least four opticalchannels with spectral data in another one of the at least four
Embodiment 175
optical channels to generate a spectral difference image .
45 The system of any of Embodiments 141- 174 , wherein a
Embodiment 163
number of optical filters is six .

The system of any of Embodiments 141 -162 , further

comprising a visible light imaging sensor.

Embodiment 176

50 The system of any of Embodiments 141- 175 , wherein a
Embodiment 164
number of optical filters is seven .
The system of any of Embodiments 141 - 163 , configured
to use the visible light imaging sensor to compensate for
Embodiment 177

motion - induced imaging errors .

55 The system of any of Embodiments 141 - 176 , wherein a
Embodiment 165
number of optical filters is eight.
The system of any of Embodiments 141- 164, configured
Embodiment 178
to process the multispectral optical data by cross - correlating
multispectral optical data from at least one of the optical 60 The system of any of Embodiments 141- 177 , wherein achannels with a reference spectrum .

number of optical filters is nine .

Embodiment 166

Embodiment 179

The system of any of Embodiments 141 - 165, configured 65

The
ofof any
141- 178 , wherein ausing spectral number
The systemsystemanfiltersof Embodimentsof opticalis ten .

to process the multispectral optical data using spectral
unmixing

US 10 ,444 ,070 B2

21

22

portion of the thermal reference so as to consistently provide

Embodiment 180

a common reference temperature .

The system of any of Embodiments 141- 179, wherein anumber of optical filters is eleven .

Embodiment 193

Embodiment 181

The system of any of Embodiments 141 - 192, wherein atemperature of the same portion of the thermal reference is

The system of any of Embodiments 141 - 180 , wherein aunknown .

number of optical filters is twelve.

10
Embodiment 182
The system of any of Embodiments 141- 181 , wherein theprocessing electronics comprises one or more processors .
Embodiment 183

15

Embodiment 194

The system of any of Embodiments 141 - 193 , configured

to acquire the multispectral optical data at a frame rate
between about 5 Hz to about 200 Hz.
Embodiment 195

The system of any of Embodiments 141 - 182 , further
comprising a thermal reference configured to be imaged
The system of any of Embodiments 141 - 194 ,wherein one
onto the FPA unit such that a plurality of frames of the or more
the at least four optical channels is configured toacquired multispectral optical data has an image of the 20 collect IRofradiation
to provide spectral data corresponding tothermal reference source .
a discrete spectral band located in the wavelength range
between about 7.9 um and about 8 .4 um .
Embodiment 184
The system of any of Embodiments 141- 183 , wherein the 25

thermal reference has a known temperature .

Embodiment 196

The system of any of Embodiments 141- 195 , whereineach optical channel is configured to transfer spectrally

Embodiment 185

distinct, two - dimensional image data of the common object
The system of any of Embodiments 141-184 , wherein the 20 to one or more imaging sensors .
thermal reference is a temperature - controlled reference

Embodiment 196

source .

The system of any of Embodiments 1 - 24 , wherein the one
Embodiment 186
or more sensors are configured to communicate the mea
The system of any of Embodiments 141 - 185 , wherein the » sured temperature of the at least one reference source to atemperature - controlled reference source includes a heater.
temperature controller.
Embodiment 197
Embodiment 187

The system of any of Embodiments 141- 186 , wherein the 40

temperature - controlled reference source includes a cooler .

The system of any of Embodiments 1- 24 , wherein the one

or more sensors are configured to communicate the mea

sured temperature of the at least one reference source to thedata -processing unit .
Embodiment 188
Embodiment 198
The system of any of Embodiments 141 - 187 , further 43
comprising a mirror configured to image the thermal refer
The system of any of Embodiments 26 -42 , wherein theence onto the FPA unit .
one or more sensors are configured to communicate mea
Embodiment 189

The system of any of Embodiments 141- 188, wherein atemperature of the thermal reference is unknown.
Embodiment 190

sured temperature of the first or the second reference to a

50 temperature controller.
Embodiment 199

The system of any of Embodiments 26 -42 , wherein the

55 one or more sensors are configured communicate the mea

The system of any of Embodiments 141- 189, wherein thesured temperature of the first or the second reference to thedata -processing unit.
Embodiment 200

thermal reference is a surface.

Embodiment 191

The system of any of Embodiments 141 -190 ,wherein thesurface comprises a wall of a housing of the system .
Embodiment 192

The system of any of Embodiments 141- 191, whereindifferent optical channels receive IR radiation from the same60

An infrared (IR ) imaging system for imaging a target

species in an object, the imaging system comprising :an optical system comprising an optical focal plane array(FPA ) unit and defining a plurality of spatially and65

spectrally different optical channels to transfer IR
radiation towards the optical FPA unit , each opticalchannel positioned to transfer a portion of the IR

US 10 ,444 ,070 B2
25

26

tangible, non -transitory computer -readable storage medium

tangible , non -transitory computer- readable storage medium

to use the temporal reference image to generate a temporalto process data received from the visible light imaging

difference image.

sensor to compensate for motion - induced imaging errors .

Embodiment 219
The system of any of Embodiments 200 -218 , wherein theprocessor is configured to execute instructions stored in a

Embodiment 229

The system of any of Embodiments 200-228 , wherein theprocessor
is configured to execute instructions stored in atangible , non - transitory computer-readable storage medium
tangible, non- transitory computer-readable storage medium
to process the acquired optical data to estimate a volumeof 1010 tto construct, in the single occurrence of data acquisition, ame 01
a gas cloud .
multispectral data cube of the object, the multispectral data

cube comprising a number of spectrally different images ofEmbodiment 220
the object, each spectrally different image comprising IR
imagedata transferred to the optical FPA unit by a corre
The system of any of Embodiments 200-219 , wherein IR 15 sponding
optical channel.
radiation measured at a pixel comprises a spectrum com
prising a sum of component spectra , and wherein the pro
Embodiment 230
cessor is configured to execute instructions stored in atangible , non -transitory computer -readable storage medium

The system of any of Embodiments 200 -229 , wherein theto unmix the spectrum .
20 portion of the IR radiation corresponds to a region of
wavelengths of the spectrum of wavelengths , the region of
Embodiment 221
wavelengths at least partially overlapping another region of
wavelengths
transferred by another optical channel.
The system of any of Embodiments 200 -220 , wherein the
optical FPA unit includes a bolometer configured to operate 25
Embodiment 231
without being cooled .
An infrared ( IR ) imaging system , the imaging system
Embodiment 222
comprising:of spatially and spectrally different optical
The system of any of Embodiments 200 -221, further 30a a plurality
channels, at least some of the plurality of opticalcomprising a field reference for dynamically adjusting datachannels configured to receive IR radiation from a
output from the optical FPA unit.
common object, each of the plurality of spatially andspectrally different optical channels comprising at least
Embodiment 223
one imaging lens configured to image the object on a
Focal Plane Array ( FPA ) unit ; andThe system of any of Embodiments 200 - 222 , wherein theprocessing electronics in communication with the FPA
field reference comprises an array of field stops .
unit,
wherein said infrared system is configured to :Embodiment 224
acquire multispectral optical data from the plurality ofdifferent optical channels ; andThe system of any of Embodiments 200 -223 , wherein the 40 process
the multispectral optical data to detect one or
field reference comprises a uniform temperature across its
more target species present in the object, andsurface .

wherein the system is further configured to compare
spectral data in at least one of the plurality of optical

Embodiment 225
45
channels acquired at a first instant of timewith spectral
The system of any of Embodiments 200 -224 , wherein thedata in at least one of the plurality of optical channels
acquired at a second instant of time to generate afield reference is adapted to obscure or block a peripheral
temporal difference image .
portion of the IR radiation propagating from the object
towards the optical FPA unit.
50
Embodiment 232
Embodiment 226
An infrared ( IR ) imaging system , the imaging system
The system of any of Embodiments 200 -225 , further comprising:a plurality of spatially and spectrally different opticalcomprising a visible light imaging sensor.
55
channels, at least some of the plurality of opticalchannels configured to receive IR radiation from a
Embodiment 227
common object, each of the plurality of spatially and
The system of any of Embodiments 200 -226 , wherein the
spectrally different optical channels comprising at least
processor is configured to execute instructions stored in a
one imaging lens configured to image the object on atangible , non -transitory computer- readable storage medium 60
to process data received from an imaging sensor to com

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

Embodiment 228

wherein said infrared system is configured to :acquire multispectral optical data from the plurality ofpensate for motion - induced imaging errors .

The system of any of Embodiments 200 - 227, wherein theprocessor is configured to execute instructions stored in a

unit,

65

different optical channels ; andprocess the multispectral optical data to detect one ormore target species present in the object , andUS 10,444 ,070 B2
28

21

wherein the system is configured to use a difference
between the multispectral optical data acquired by two
optical channels to correct parallax -induced imaging

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

errors .

unit,

Embodiment 232

wherein said infrared system is configured to :acquire multispectral optical data from the plurality of
The system of Embodiment 231, wherein spectral chardifferent optical channels ; andacteristics of the two optical channels are identical.
processthe multispectral optical data to detect one or10
more target species present in the object , andEmbodiment 233
wherein the system is configured to compensate formotion - induced imaging errors .
An infrared ( IR ) imaging system , the imaging systemcomprising:
Embodiment 237
a plurality of spatially and spectrally different optical 15
channels, at least some of the plurality of optical
An infrared ( IR ) imaging system , the imaging systemchannels configured to receive IR radiation from a comprising:common object, each of the plurality of spatially anda plurality of spatially and spectrally different, at least
spectrally different optical channels comprising at least 2020
some of the plurality of optical channels configured to
one imaging lens configured to image the object on areceive IR radiation from a common object, each of the
Focal Plane Array (FPA ) unit; andplurality of spatially and spectrally different opticalprocessing electronics in communication with the FPA
channels comprising at least one imaging lens config
unit,
ured to image the object on a Focal Plane Array (FPA )wherein said infrared system is configured to :acquire multispectral optical data from the plurality of25

different optical channels; andprocess the multispectral optical data to detect one ormore target species present in the object, andwherein the system is configured to use a difference 30
between the multispectral optical data acquired by two
optical channels to estimate a distance between thesystem and the object.
35
Embodiment 234

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; andprocess the multispectral optical data to detect one ormore target species present in the object by crosscorrelating multispectral optical data from at least oneof the optical channels with a reference spectrum .
Embodiment 238
The system of Embodiment 233, wherein spectral characteristics of the two optical channels are identical.
An infrared ( IR ) imaging system , the imaging system
40
comprising:
Embodiment 235
a plurality of spatially and spectrally different optical, atleast some of the plurality of optical channels config
An infrared (IR ) imaging system , the imaging systemured to receive IR radiation from a common object,comprising :each of the plurality of spatially and spectrally different
a plurality of spatially and spectrally different optical, at
optical channels comprising at least one imaging lens
least some of the plurality of optical channels config - 45
configured to image the object on a Focal Plane Array
ured to receive IR radiation from a common object,(FPA ) unit; andeach of the plurality of spatially and spectrally different
optical channels comprising at least one imaging lensprocessing electronics in communication with the FPA
configured to image the object on a Focal Plane Arrayunit,
50 wherein said infrared system is configured to :(FPA ) unit;
acquire multispectral optical data from the plurality ofa visible light imaging sensor ; andprocessing electronics in communication with the FPA
different optical channels; andprocess the multispectral optical data to detect one orunit,
more target species present in the object by using
wherein said infrared system is configured to :acquire multispectral optical data from the plurality of 55
spectral unmixing .
different optical channels ; andEmbodiment 239
process the multispectral optical data to detect one ormore target species present in the object .
An infrared (IR ) imaging system , the imaging system
60 comprising:
Embodiment 236
an optical system including an optical focal plane array(FPA ) unit, the optical system includes components
An infrared (IR ) imaging system , the imaging systemcomprising:associated with at least two optical channels, said at
a plurality of spatially and spectrally different optical, atleast two optical channels being spatially and spectrally
least some of the plurality of optical channels config - 65
ured to receive IR radiation from a common object ,each ofthe plurality of spatially and spectrally different

different from one another, each of the at least two

optical channels positioned to transfer IR radiation

incident on the optical system towards the optical FPA

US 10 ,444 ,070 B2
29

30

unit, the optical FPA unit comprising at least two
FIG . 6B depicts theoretical plots of transmission characdetector arrays disposed at a distance from two corre - teristics of a spectrally multiplexed notch -pass filter combi
sponding focusing lenses;
nation used in an embodiment of the system .
at least one thermal reference having a known tempera FIG . 6C shows theoretical plots of transmission charac
ture , wherein one of the at least two detector arrays is 5 teristics of spectrally multiplexed long-pass filter combina
configured to image the at least one reference ; andtion used in an embodiment of the system .
a data -processing unit , said data -processing unit config ured to :FIG . 6D shows theoretical plots of transmission characteristics of spectrally multiplexed short -pass filter combina

tion used in an embodiment of the system .
acquire a plurality of frames with one of the at least two
age 10 FIG . 7 is a set of video -frames illustrating operability ofdetector arrays having regions in the plurality of image
an embodiment of the system used for gas detection .
frames that correspond to the image of the reference ;and

FIGS . 8A and 8B are plots (on axes of wavelength indynamically calibrate another of the at least two detector

microns versus the object temperature in Celsius represent

Embodiment 240

different embodiments of an imaging system comprising an
arrangement of reference sources and mirrors that can be
20 used for dynamic calibration .

effective optical intensity of the object ) illustratingarray to match a temperature estimate of another of the 15 ing
resultsof dynamic calibration of an embodiment of theat least two detector array with the temperature esti
system .
mate of one of the at least two detector array.
FIGS. 9A and 9B illustrate a cross - sectional view of

The system of any of Embodiments 1-59 , wherein theplurality of cameras are configured to acquire multispectral
image data from an object continuously for a duration oftime.

Embodiment 241

FIGS. 10A - 10C illustrate a plan view of different embodi
ments of an imaging system comprising an arrangement ofreference sources and mirrors that can be used for dynamic
calibration.
25
Like reference numbers and designations in the various

drawings indicate like elements .

The system of any of Embodiments 1 -59 , comprising at
DETAILED DESCRIPTION
least two spectrally and spatially distinct optical channels
configured to transfer two- dimensional image data of an 30 The following description is directed to certain imple
mentations for the purposes of describing the innovative
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 the nary skill in the art will readily recognize that the teachings
accompanying drawings and the description below . Other herein can be applied in a multitude of different ways. The
features, aspects , and advantages will become apparent from 35 described implementations may be implemented in any
the description , the drawings and the claims. Note that thedevice , apparatus, or system that can be configured torelative dimensions of the following figures may not be

drawn to scale .

operate as an imaging system such as in an infra -red imaging

system . The methods and systems described herein can be

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG . 1 shows an embodiment of an imaging system

devices used in oil and gas exploration , refining, and transincluding a common front objective lens that has a pupil

spectroscopy, multispectral and hyperspectral imaging

portation , agriculture , remote sensing , defense and home

divided spectrally and re - imaged with a plurality of lenses land security , surveillance , astronomy, environmental moni
45 toring, etc . The methods and systems described herein haveonto an infrared FPA .

FIG . 2 shows an embodimentwith a divided front objec tive lens and an array of infrared sensing FPAs.
FIG . 3A represents an embodiment employing an array of

applications in a variety of fields including but not limited toagriculture , biology, physics , chemistry , defense and homeland 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 50 tions depicted solely in the Figures, but instead have wide

optical components corresponding to the embodiment of
FIG . 3A .
FIG . 4 is a diagram of the embodiment employing anarray of field references ( e.g ., field stops that can be used asordinary skill in the art.

applicability as will be readily apparent to one having
Various embodiments disclosed herein describe a divided
aperture infrared spectral imaging (DAISI) system that isreferences for calibration ) and an array of respectively 55 structured and adapted to provide identification of target
corresponding relay lenses .
chemical contents of the imaged scene. The system is based
FIG . 5A is a diagram of a 4 -by -3 pupil array comprising on spectrally -resolved imaging and can provide such iden
circular optical filters ( and IR blocking material between the tification with a single-shot (also referred to as a snapshot)
optical filters ) used to spectrally divide an optical wavefront comprising a plurality of images having different wave
60 length compositions that are obtained generally simultane
imaged with an embodiment of the system .
FIG . 5B is a diagram of a 4 -by -3 pupil array comprising ously . Without any loss of generality , snapshot refers to arectangular optical filters (and IR blocking material between system in which most of the data elements that are collected
the optical filters ) used to spectrally divide an optical are continuously viewing the light emitted from the scene. In
wavefront imaged with an embodiment of the system .

contrast in scanning systems, at any given time only a

FIG . 6A depicts theoretical plots of transmission charac - 65 minority of data elements are continuously viewing a scene,teristics of a combination of band - pass filters used with anfollowed by a different set of data elements , and so on , until
the full dataset is collected . Relatively fast operation can beembodiment of the system .

US 10 ,444,070 B2
31
achieved in a snapshot system because it does not need touse spectral or spatial scanning for the acquisition of infra

32
Some embodiments described herein can also be less sus
ceptible to motion artifacts in comparison with spatiallyred ( IR ) spectral signatures of the target chemical contents.

and /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 .

optical channels having different wavelength profiles can betial 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

plane arrays or FPAs) associated with a plurality of different 5

FIG . 1 provides a diagram schematically illustrating spa

sponding to different wavelength ranges, in various embodi- 10 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

Similarly, in certain embodiments multiple snap shots may
be obtained and a portion of these can be selected andFPA or an array of FPAs. Each detector in the detector array
136 can be disposed at the focus of each of the lenses in theembodiments , these multiple snapshots can be averaged .

embodiments , the detector array 136 can include a single

possibly averaged . Also , in contrast to commonly used IR 15 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

below 300 Kelvin . As another example , in various imple
include detectors configured to be cooled to a temperature

wavelength range, mid infra - red wavelength range , or long
infra -red wavelength range ,). In various embodiments, theplurality of photo -sensitive devices can include CCD or

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 20 between 1 um and 20 um ( for example , in near infra -red
mentations, the imaging systems disclosed herein do not

below 273 Kelvin . As yet another example , in various

CMOS sensors, bolometers, microbolometers or other

implementations, the imaging systems disclosed herein do 25 detectors that are sensitive to infra - red radiation .
not include detectors configured to be cooled to a tempera An aperture of the system 100 associated with the front

ture below 250 Kelvin . As another example , in various

objective lens system 124 is spatially and spectrally divided

implementations, the imaging systems disclosed herein doby the combination of the array of optical filters 130 and the

not include detectors configured to be cooled to a tempera array of reimaging lenses 128 . In various embodiments, the30 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 atages over existing IR spectral imaging systems, most if not spectrally divided pupil that is disposed forward of theall of which may require FPAs that are highly sensitive andoptical detector array 136 . The spatial and spectral division
cooled in order to compensate , during the optical detection , of the aperture into distinct aperture portions forms a plu
for the reduction of the photon flux caused by spectrum - 35 rality of optical channels 120 along which light propagates .
scanning operation . The highly sensitive and cooled FPA
In various embodiments , the array 128 of re -imaging lenses
systems are expensive and require a great deal of mainte - 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 withof optical channels 120 can be spatially and/or spectrally
out spatial and/or spectral scanning, the instrument can 40 distinct. The plurality of optical channels 120 can be formed

receive photons from a plurality of points ( e . g., every point )of the object substantially simultaneously , during the single
reading. Accordingly , the embodiments of imaging systemin the object space and/ or image space . In one implemen
tation , the distinct channels 120 may include optical channels that are separated angularly in space . The array ofdescribed herein can collect a substantially greater amountspectral filters 130 may additionally include a filter -holding

order ofmagnitude more photons) at any given moment inmaterials such as ceramic , metal, or plastic ). Light from theof optical power from the imaged scene ( for example , an 45 aperture mask ( comprising, for example , IR light-blocking

time 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 50 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
cations. For example , in various implementations, the imag -implementations, the detector array 136 can include at leasting systems disclosed herein do not include detectors con one FPA . In various embodiments , each of the re - imaging
figured to be cooled to a temperature below 300 Kelvin . As 55 lenses 128a can be spatially aligned with a respectively
another example , in various implementations , the imaging
corresponding spectral region . In the illustrated implemensystems disclosed herein do not include detectors configured
tation , each filter element from the array of spectral filters
to be cooled to a temperature below 273 Kelvin . As yet

130 corresponds to a different spectral region . Each reanother example , in various implementations , the imaging

imaging lens 128a and the corresponding filter element ofsystems disclosed herein do not include detectors configured 60 the array of spectral filter 130 can coincide with ( or form ) a

to be cooled to a temperature below 250 Kelvin . As anotherportion of the divided aperture and therefore with respec

of operation during day and night, and are less expensive .

optical channels 120 travels along the optical path of eachexample , in various implementations , the imaging systems tively - corresponding spatial channel 120 . Accordingly , indisclosed herein do not include detectors configured to be various embodiment an imaging lens 128a and a corre
cooled to a temperature below 200 Kelvin . Imaging systems sponding spectral filter can be disposed in the optical path ofincluding uncooled detectors can be capable of operating in 65 one of the plurality of optical channels 120. Radiation fromextremeweather conditions, require less power, are capable
the object 110 propagating through each of the plurality ofUS 10 ,444 ,070 B2
33
re -imaging lens 128a and the corresponding filter element of
the array of spectral filter 130 and is incident on the detector( e.g ., sub - image ) of the object 110 . The image formed by thearray (e.g ., FPA component) 136 to form a single image

34
pendicular to optical axis of the lens 124 , thus the function

a lity of the system 100 is not necessarily compromised when
the objective lens 124 is not included . Generally , however,the field apertures corresponding to different optical chandetector array 136 generally includes a plurality of sub - 5 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 andspectral information of the object 110 . The different spatial
information results from some parallax because of theaging lens 128a and/ or filters in the divided aperture 130 incertain implementations . In one implementation , the field
apertures corresponding to different optical channels can bedifferent spatial locations of the smaller apertures of the 10 located in different planes and the different planes can bedivided aperture . In various embodiments, adjacent sub images can be characterized by close or substantially equal

optical conjugates of one another. Similarly , while all of thefilter elements in the array of spectral filters 130 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(not shown ). The processor 150 can be programmed to 15 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 the another. However, in other embodiments, the different filter
object 110 within the spectral region defined by the combielements can be disposed in non - conjugate planes .
nation of the filter elements in the array of spectral filters 20 In contrast to the embodiment 100 , the front objective lens

130 . Additionally , in various embodiments , the processor orprocessing electronics 150 may be programmed to deter -124 need not be a single optical element, but instead can
include a plurality of lenses 224 as shown in an embodimentmine the unique absorption characteristic of the object 110 .

200 of the DAISI imaging system in FIG . 2 . These lenses

Also , the processor/processing electronics 150 can , alterna -224 are configured to divide an incoming optical wavefront

tively or in addition , map the overall image data cube into 25 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

within the field of view associated with the object 110 .

wavefront emitted by the object that is directed toward theDAISI system . The plurality of front objective lenses 224

Various implementations of the embodiment 100 can
divide the wavefront spatially into non - overlapping sections .
include an optional moveable temperature -controlled refer - 30 FIG . 2 shows three objective lenses 224 in a front opticalence source 160 including, for example , a shutter system
portion of the optical system contributing to the spatial

comprising one or more reference shutters maintained at
different temperatures. The reference source 160 can include
a heater, a cooler or a temperature - controlled element con

division of the aperture of the system in this example. The
as a two -dimensional ( 2D ) array of lenses. FIG . 2 presents

plurality of objective lenses 224 , however, can be configured

figured to maintain the reference source 160 at a desired 35 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 isdetail 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 40 includes a field reference 204 at the front end of the system .

the object 110 to the detector array ( e. g ., FPA component )136 along at least one of the channels 120 . The removable

The field reference 204 can be used to truncate the field ofview . 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 45 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 .

Each pair of lenses in the array 224 and the array 128

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

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- 50 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 theof parallax . As the distance between the imaging system 200
whole system . In this specific case, the aperture stop sub (portion 202 ) and the object 110 increases, the overlapping
stantially spatially coincides with and/ or is about the same region 230 between the FOVs of the individual lenses 224

size or slightly larger, as the plurality of smaller limiting 55 increases while the amount of parallax 228 remains approxi

apertures corresponding to different optical channels 120 . As
a result , the positions for spectral filters of the different

optical channels 120 coincide with the position of theaperture stop of the whole system , which in this example ismately the same, thereby reducing its effect on the system
200 . When the ratio of the parallax -to -object -distance issubstantially equal to the pixel-size - to -system - focal- length
ratio then the parallax effect may be considered to beshown as a surface between the lens system 124 and the 60 negligible and , for practical purposes, no longer distinguisharray 128 of the reimaging lenses 128a . In various imple
able . While the lenses 224 are shown to be disposed submentations, the lens system 124 can be an objective lens stantially in the same plane , optionally different objective
124 .However, the objective lens 124 is optional and various lenses in the array of front objective lenses 224 can beembodiments of the system 100 need not include the objec - disposed in more than one plane . For example , some of thetive lens 124 . In various embodiments, the objective lens 65 individual lenses 224 can be displaced with respect to some124 can slightly shifts the images obtained by the different

other individual lenses 224 along the axis 226 (not shown )detectors in the array 136 spatially along a direction per-and/ or have different focal lengths as compared to someUS 10 ,444 ,070 B2
35
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

36

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

lenses integrated or molded in association with a monolithic 5 (lenses 324a , 128a ; detector elements 336 ) is used behind
substrate . Such an arrangement can reduce the costs andthe temperature controlled reference target 160 . The fieldcomplexity otherwise accompanying the optical adjustment reference aperture 338 can be adapted to obscure and /orof individual lenses within the system . An individual lens
224 can optionally include a lens with varying magnifica -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 10 the field reference 338 obscures and / or blocks the border or

Alvarez plates can be used in at least a portion of the front
objective lens system . Without any loss of generality, theperipheral portion (s ) of the images of the object 110 formedon the FPA elements located along the perimeter 346 of theAlvarez plates can produce a change in focal length when

detector system . Generally , two elements of the FPA unittranslated orthogonally with respect to the optical beam
will produce substantially equal values of digital counts
In further reference to FIG . 1 , the detector array 136 ( e . g ., 15 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
can be configured as a single imaging array ( e. g., FPA ) 136 .

This single array may be adapted to acquire more than one

any of these input parameters ( for example , scene to beobserved , spectral content of light from the scene, or opticalelements delivering light from the scene to the two detector

image ( formed by more than one optical channel 120) 20 elements ) differ, the counts associated with the elements ofsimultaneously . Alternatively, the detector array 136 may
include a FPA unit . In various implementations, the FPA unit

can include a plurality of optical FPAs. At least one of these

the FPA unit will differ as well. Accordingly , and as an
example , in a case when the two FPAs of the FPA unit 336(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 , 25 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.

FPAS 236 are provided corresponding to the three objective 30

FIG . 4 illustrates schematically a portion of anotherlenses 224 . In one implementation of the system , the FPA

embodiment of an imaging system 400 that contains an array

unit can include an array of microbolometers . The use ofmultiple microbolometers advantageously allows for an

424 of front objective lenses 424a . The array 424 of lenses
424a adapted to receive light from the object 110 and relay

inexpensive way to increase the total number of detection

the received light to the array 128 of re -imaging lenses 128a

data cube in a single acquisition event (i. e . one snapshot). In
various embodiments , an array of microbolometers more

and through an array 440 of the relay lenses . The spectral
characteristics of the field references /field stops 438a can beelements ( i.e . pixels ) for recording of the three -dimensional 35 through an array 438 of field references (or field stops ) 438a ,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 40 the object 110 , by respectively corresponding front objective
lenses 424a. When refractive characteristics of all of theexist when using a single microbolometer.
FIG . 3A illustrates schematically an embodiment 300 of

front objective lenses 424a are substantially the same, all of

the imaging system in which the number of the front

the field references 438a are disposed in the same plane. A

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 45 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 acquicessed by the processor 150 . The array 440 of relay lenses
sition of the IR light transmitted from the object 110 through 50 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 havepast the calibration apparatus that includes two temperaturea uniform temperature across its surface and be character

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

ized by a predetermined spectral curve of radiation emanat- module 456 . In various embodiments , the detector module
ing therefrom . In various implementations , the field refer - 55 456 can include a microbolometer array or some other IR
ence 338 can be used as a calibration target to assist in
FPA .
calibrating or maintaining calibration of the FPA . Accord The embodiment 400 has several operational advantages .
ingly , in various implementations , the field reference 338 is.
It is configured to provide a spectrally known object within
used for dynamically adjusting the data output from eachevery image ( e .g ., sub - image ) and for every snapshot acqui

FPA 336 after acquisition of light from the object 110 . This 60 sition which can be calibrated against. Such spectral cer
dynamic calibration process helps provide that output of thetainty can be advantageous when using an array of IR FPAS
different ( e. g., most, or each of the ) FPA 336 represents like microbolometers, the detection characteristics of whichcorrect acquired data , with respect to the other FPAs 336 for can change from one imaging frame to the next due to , inpart, changes in the scene being imaged as well as theanalysis , as discussed below in more detail.
FIG . 3B illustrates the plan view perpendicular to the axis 65 thermal effects caused by neighboring FPAs. In various
226 of an embodiment 300 of the imaging system illustrated
in FIG . 3A . For the embodiment shown in FIG . 3B , theembodiments , the field reference array 438 of the embodi
ment 400 — can be disposed within the Rayleigh range

US 10 ,444 ,070 B2
37(approximately corresponding to the depth of focus ) asso

ciated with the front objective lenses 424 , thereby removing
unusable blurred pixels due to having the field reference

38
depicted in FIG . 6B . Filters of FIG . 6C can be referred to aslong -wavelength pass, LP filters . An LP filter generally
attenuates shorter wavelengths and transmits (passes ) longer
wavelengths (e . g., over the active range of the target IR

outside of this range. Additionally , the embodiment 400 ofof the spectrum ). In various embodiments, short
FIG . 4 can be more compact than , for example, the con - 5 portion
wavelength - pass filters , SP, may also be used . An SP filter
figuration 300 of FIG . 3A . In the system shown in FIG . 3A ,for example , the field reference 338 may be separated fromthe lens array 324 by a distance greater than several (forexample , five ) focal lengths to minimize/reduce blur con -generally attenuates longer wavelengths and transmits(passes) shorter wavelengths ( e.g ., over the active range ofthe target IR portion of the spectrum ). At least in part due tothe snap -shot/non - scanning mode of operation , embodi

tributed by the field reference to an image formed at a 10 ments of the imaging system described herein can use lessdetector plane.

In various embodiments , the multi -optical FPA unit of the
IR imaging system can additionally include an FPA config

ured to operate in a visible portion of the spectrum . In

sensitive microbolometers without compromising the SNR .
The use of microbolometers , as detector-noise -limited
devices, in turn not only benefits from the use of spectrally

multiplexed filters , but also does not require cooling of thereference to FIG . 1. for example , an image of the scene of 15 imaging system during normal operation .
Referring again to FIGS. 6A , 6B , 6C , and 6D , each of theinterest formed by such visible - light FPA may be used as afilters(Ob . . . 3d ) transmits light in a substantially wider
background to form a composite image by overlapping an IR
region of the electromagnetic spectrum as compared to thoseimage with the visible -light image . The IR image may beof the filters ( 0a . . . 3a ). Accordingly , when the spectrally
overlapped virtually , with the use of a processor and spe

multiplexed set of filters (Ob . . . 0d ) is used with ancifically -designed computer program product enabling suchch 2020 mu

data processing, or actually , by a viewer. The IR image may embodiment of the imaging system , the overall amount oflight received by the FPAs ( for example , 236 , 336 ) is larger
be created based on the image data acquired by the indi
than would be received when using the bandpass filters
vidual FPAs 136 . The so - formed composite image facilitates( Oa . . . 4a ). This “ added ” transmission of light defined by thethe identification of the precise spatial location of the target
species, the spectral signatures of which the system is able 25 use of the spectrally -multiplexed LP (or SP ) filters facilitates
an increase of the signal on the FPAs above the level of theto detect/recognize .
detector noise . Additionally , by using , in an embodiment of
Optical Filters.

imaging system , filters having spectral bandwidths
The optical filters , used with an embodiment of the thegreater than those of band - pass filters , the uncooled FPAs ofsystem , that define spectrally - distinct IR image (e .g ., sub
the embodiment of the imaging system experience lessimage ) of the object can employ absorption filters , interferer.- 3030 heatingtheincident thereon from the imaged
ence filters, and Fabry -Perot etalon based filters , to name scene andfromfromradiation
radiation emanating from the FPA in ques
just a few . When interference filters are used , the image
tion itself. This reduced heating is due to a reduction in theacquisition through an individual imaging channel defined back- reflected thermal emission ( s ) coming from the FPA
by an individual re - imaging lens ( such as a lens 128a of35
andreflecting off of the filter from the non -band - pass
FIGS. 1, 2 , 3, and 4 ) may be carried out in a single spectral 35 regions. As the transmission region of the multiplexed LP
bandwidth or multiple spectral bandwidths . Referring again
(
or
SP
)
filters is wider, such parasitic effects are reduced
to the embodiments 100 , 200, 300, 400 of FIGS . 1 through thereby improving
the overall performance of the FPA unit .
4 , and in further reference to FIG . 3B , examples of a 4 -by - 3
In one implementation , the LP and SP filters can bearray of spectral filters 130 is shown in FIGS. 5A and 5B .
Individual filters 1 through 12 are juxtaposed with a sup - 40 combined , in a spectrally -multiplexed fashion , in order toincrease or maximize the spectral extent of the transmission
filter -array plane that is oriented , in operation , substantially region of the filter system of the embodiment.

wn )) toto define
definerea
porting opto -mechanical element (not shown

The advantage of using spectrally multiplexed filters isperpendicularly to the general optical axis 226 of the imag appreciatedbased on the following derivation , in which a
ing system . In various implementations, the individual filters
Apprecomponents
45
systemofMis examined (although it is understood
1 through 12 need not be discrete optical components. 45 thatsys in practicefiltersanembodimentof the invention can employ
Instead , the individual filters 1 through 12 can comprise one any number of filters ). As an illustrative, the caseormore coatings that are applied to one or more surfaces of of M = 7 is considered . Analysis presentedexample
below
tothe reimaging lenses (such as a lens 128a of FIGS . 1, 2 , 3 , one spatial location in each of the images (e . g ., subrelates- images )and 4 ) or the surfaces of one or more detectors .

The optical filtering configuration of various embodi - 50 formed by the differing imaging channels (e . g ., different

ments
disclosed herein may advantageously use a bandpass
filter defining a specified spectral band. Any of the filters Oa

optical channels 120 ) in the system . A similar analysis canspectrally -multiplexed filters can comprise a plurality oflong pass filters , a plurality long pass filters , a plurality ofofband pass filters and any combinations thereof. An example

be represented by:be performed for each point at an image ( e. g ., sub - image ),through 3a the transmission curves of which are shown inand thus the analysis can be appropriately extended as
FIG . 6A may , for example , be used. The filters may be required .
placed in front of the optical FPA (or generally, between the 55 The unknown amount of light within each of the M
optical FPA and the object). In particular, and in further spectral channels ( corresponding to these M filters ) is
reference to FIGS. 1, 23 , and 4 , when optical detector arrays
denoted with f , f , fz, . . . fy , and readings from corre
136 , 236 , 336 , 456 include microbolometers , the predomisponding detector elements receiving light transmitted bynant contribution to noise associated with image acquisition each filter is denoted as 81, 82, 83 . . . SM , while measurement
is due to detector noise . To compensate and/ or reduce the errors are represented by ni , n2, nz, . . . nm . Then , thenoise , various embodiments disclosed herein utilize spec 60 readings
at the seven FPA pixels each of which is opticallytrally -multiplexed filters . In various implementations, thefiltered by a corresponding band - pass filter of FIG . 6A canof the spectral transmission characteristics of spectrally - 65
multiplexed filters Ob through 3d for use with various

embodiments of imaging systems disclosed herein is

81 = fi +n1,
82 = 42 +12,

US 10 , 444 ,070 B2
40
83 = f3 +93,
84- 44+ 14,

fa = 1/ (- 81 - 82- 83+ g4 + 85 + 86 + 87),

85 = 15 + 15,

fo= 1/4(- 81 + 82 + g3+ g4 + 85 - 86- 87),bs = 1/ ( + 81- 82+g3 + 84- 85 + 86 - 87),

86 =f6 +16 ,f_= 14 (+81+ 82- 83+84-85- 86+ 87),
Thesef; are unbiased estimates when the n ; are zero mean
87= fz+na,
stochastic
variables, so that < f; - f > = 0 . The measurement
These readings (pixelmeasurements ) g; are estimates of variance corresponding
to the ith measurement is given by
the spectral intensities f;. The estimates g; are not equal to the 10 theequation
below:
corresponding f; values because of the measurement errors
ni. However, if the measurement noise distribution has zero
< :-1:12 > =1/160 %mean , then the ensemble mean of each individualmeasure
From
above equation , it is observed that by employing
ment can be considered to be equal to the true value , i.e |. 15 spectrallythe-multiplexed
system the signal-to -noise< g:> = f;. Here, the angle brackets indicate the operation of

calculating the ensemble mean of a stochastic variable . The
variance of the measurement can , therefore , be represented
as :ratio (SNR ) of a measurement is improved by a factorof V16 /7 = 1.51.
For N channels, the SNR improvement achieved with aspectrally -multiplexed system can be expressed as (N + 1)/
20 ( 2VN ). For example , an embodiment employing 12 spectral
In embodiments utilizing spectrally -multiplexed filters, inchannels ( N = 12 ) is characterized by a SNR improvement,
comparison with the embodiments utilizing band -pass fil - over a non -spectrally -multiplexed system , comprising aof up to 1. 88 .
ters, the amountofradiant energy transmitted by each of the factor
Two additional examples of related spectrally -multi
spectrally -multiplexed LP or SP filters towards a given
detector element can exceed that transmitted through a 25 plexed filter arrangements Oc through 3c and Od through 3d<(8:-F:)2> = <n ;2> = ospectralband of a band -pass filter. In this case , the intensities
of light corresponding to the independentspectralbands canthat can be used in various embodiments of the imaging

systems described herein are shown in FIGS. 6C and 6D ,respectively. The spectrally -multiplexed filters shown inbe reconstructed by computational means. Such embodi
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 30 systems employing uncooled FPAs ( such as microbolom
eters). FIG . 6C illustrates a set of spectrally -multiplexed
includes a Hadamard matrix requiring " negative ” filters that
may not be necessarily appropriate for the optical embodi- long -wavelength pass (LP ) filters used in the system . An LP

filter generally attenuates shorter wavelengths and transmits(passes ) longer wavelengths (e .g ., over the active range ofthat is multiple of four minus one) or a row - doubled Had - 35 the target IR portion of the spectrum ). A single spectral
channel having a transmission characteristic corresponding
amard matrix (requiring a number of filters to be equal to andifference between the spectral transmission curves ofinteger multiple of eight) can be used in various embodi toat theleast two of these LP filters can be used to procurements. Here , possible numbers of filters using an S -matrix
setup are 3 , 7 , 11, etc and , if a row -doubled Hadamard imaging data for the data cube using an embodiment of thements disclosed herein . An S -matrix approach (which is

restricted to having a number of filters equal to an integer

matrix setup is used , then the possible number of filters is 8 . 40 system described herein . In various implementations, thespectral filters disposed with respect to the different FPAS
16 , 24 , etc . For example , the goal of the measurement may
measurements g ; as follows:

can have different spectral characteristics . In various imple
mentations, the spectral filters may be disposed in front of

81 = f1 + 0 + f3 + 0 + f3 + 0 + f7 + 11,

45 configured to receive unfiltered light . For example , in somebe to measure seven spectral band f, intensities using seven

82= 0+ f2 +f3 +0 + 0 + f6 + f7 +12
83 = fi + f2 +0 +0 + f3 + 0 + f7 + nz
84 +0 + 0 + 0 + f4 + fs +f7+ f3 +N4

85 = f1+ 0 + f3+ f4+ O + f6+0 +ng

only some of the FPAs while the remaining FPAs may be

implementations, only 9 of the 12 detectors in the 4x3 arrayof detectors described above may be associated with aspectral filter while the other 3 detectors may be configured

to received unfiltered light. Such a system may be config
50 ured to acquire spectral data in 10 different spectral channels

in a single data acquisition event.

The use of microbolometers , as detector- noise -limited

devices , in turn not only can benefit from the use of

860+42 + 3 + 4 + 5+ 0 + 0 + 16
spectrally multiplexed filters , but also does not require
55 cooling of the imaging system during normal operation . In
87= fi +f2+ 0 +f4+ 0 + 0 + fz+ n7
contrast to imaging systems that include highly sensitive
Optical transmission characteristics of the filters
FPA units with reduced noise characteristics , the embodi
described above are depicted in FIG . 6B . Here , a direct ments of imaging systems described herein can employ lessestimate of the f; is no longer provided through a relationshipsensitive microbolometers without compromising the SNR .

similar to < g :> = f;. Instead , if a “hat” notation is used to 60 This result is at least in part due to the snap - shot/nondenote an estimate of a given value , then a linear combina
tion of the measurements can be used such as, for example ,fi =14 (+ 81- 82 + 83 - 84+ 85 - 86 + 87),

f2= 14 (- 81 + g2+ 83- 84 - 85 + 86 +87),

Fx = 14(+81+82-83-84+85+86-87),

scanning mode of operation .
As discussed above , an embodimentmay optionally, andin addition to a temperature -controlled reference unit (forexample temperature controlled shutters such as shutters

65 160 ; 160a , 160b , 460a , 460b ), employ a field referencecomponent ( e .g ., field reference aperture 338 in FIG . 3A ), or

an array of field reference components (e .g ., filed referenceUS 10 ,444 ,070 B2
41
apertures 438 in FIG . 4 ), to enable dynamic calibration .

Such dynamic calibration can be used for spectral acquisition of one or more or every data cube. Such dynamic

42

Here , goffset is the pixel offset value (in units of counts ),and y is the pixel gain value (in units of counts per radianceunit ). The solutions of these two equations with respect tocalibration can also be used for a spectrally -neutral camera
the two unknowns goffset and y can be obtained if the values
to - camera combination to enable dynamic compensation of 5 of g , and g2 and the radiance values L? and L2 are available .
parallax artifacts . The use of the temperature- controlled

These values can , for example , be either measured by areference unit ( for example , temperature -controlled shutter

reference instrument or calculated from the known tempera

system 160 ) and field -reference component(s ) facilitates
maintenance of proper calibration of each of the FPAS

tures T , and T , together with the known spectral response of
the optical system and FPA . For any subsequent measure
10 ment, one can then invert the equation (s ) above in order toindividually and the entire FPA unit as a whole .

In particular, and in further reference to FIGS. 1, 2 , 3 , and

4 , the temperature -controlled unit generally employs a sys
tem having first and second temperature zones maintained at
first and second different temperatures . For example, shutter

estimate the radiance value of the object from the detector

measurement, and this can be done for each pixel in each
FPA within the system .
As already discussed , and in reference to FIGS. 1 throughsystem of each of the embodiments 100 , 200 , 300 and 400 15 4 , the field -reference apertures may be disposed in an object

can employ not one but at least two temperature- controlled

shutters that are substantially parallel to one another andtransverse to the general optical axis 226 of the embodiment(s ) 100 , 200 , 300 , 400 . Two shutters at two different

space or image space of the optical system , and dimensioned

to block a particular portion of the IR radiation received

from the object. In various implementations, the fieldreference aperture , the opening of which can be substantiallytemperatures may be employed to provide more information 20 similar in shape to the boundary of the filter array (forfor calibration ; for example , the absolute value of theexample , and in reference to a filter array of FIGS. 3B ,difference between FPAs at one temperature as well as the 5B4e.g ., rectangular ). The field - reference aperture can bechange in that difference with temperature change can beplaced in front of the objective lens ( 124 , 224 , 324 , 424 ) at
recorded . Referring , for example , to FIG . 4 , in which sucha distance that is at least several times in one implemen
multi-shutter structure is shown, the use of multiple shutters 25 tation — at least five times ) larger than the focal length of theenables the user to create a known reference temperature lens such that the field - reference aperture is placed closer todifference perceived by the FPAs 456 . This reference tem - the object. Placing the field -reference aperture closer to theperature difference is provided by the IR radiation emitted

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

individual FPAs pixels can be adjusted but also the gain

generally , can facilitate , effectuates and /or enable dynamic

system having first and second temperature zones may

and temporally - stable object within every scene to referenceby the shutter (s ) 160a , 160b when these shutters are posi- ment 400 of FIG . 4 , the field -reference aperture can betioned to block the radiation from the object 110 . As a result, 30 placed within the depth of focus of an image conjugate plane
not only the offset values corresponding to each of theformed by the front objective lens 424 . The field reference ,values of these FPAs. In an alternative embodiment, thecompensation in the system by providing a spectrally known

include a single or multi -portion piece . This single or 35 and stabilize the output from the different FPAs in the array .
Because each FPA ' s offset value is generally adjusted
piece may be mechanically -movable across the optical axis from each frame to the next frame by the hardware, comwith the use of appropriate guides and having a first portion
paring the outputs of one FPA with another can have an error
at a first temperature and a second portion at a second that is not compensated for by the static calibration param

multi -portion piece may comprise for example a plate . This

Indeed , the process of calibration of an embodiment of the

40 eters goffer and y established , for example , by the movable
shutters 160 . In order to ensure that FPAs operate in radio

performing measurements of radiation emanating, indepen dently , from at least two temperature - controlled shutters ofof each detector array to view a reference source (such as thefield reference 338 in FIG . 3A , for example ) over a plurality

temperature .

imaging system starts with estimating gain and offset by

metric agreement over time, it is advantageous for a portion

known and different radiances . The gain and offset can vary 45 of frames obtained over time. If the reference source specfrom detector pixel to detector pixel. Specifically , first thetrum is known a priori (such as a blackbody source at a

response of the detector unit 456 to radiation emanating

known temperature ), one can measure the response of eachfrom one shutter is carried out. For example , the first shutter
160a blocks the FOV of the detectors 456 and the tempera -FPA to the reference source in order to estimate changes tothe pixel offset value . However, the temperature of theture T , is measured directly and independently with therm - 50 reference source need not be known. In such implementa
istors . Following such initialmeasurement, the first shutter
tions, dynamic calibration of the different detectors can be
160a is removed from the optical path of light traversing the performed by monitoring the change in the gain and theembodiment and another second shutter ( for example , 160b ) offset for the various detectors from the time the movable
is inserted in its place across the optical axis 226 to prevent shutters used for static calibration are removed . An example
the propagation of light through the system . The temperature 55 calculation of the dynamic offset proceeds as follows.
of the second shutter 160b can be different than the firstAmong the FPA elements in an array of FPAs in an
shutter ( T2 + T ) . The temperature of the second shutter 160b

embodiment of the imaging system , one FPA can be selected

is also independently measured with thermistors placed in

to be the “ reference FPA " . The field reference temperature

contact with this shutter, and the detector response to radia

measured by all the other FPAs can be adjusted to agree withtion emanating from the shutter 160b is also recorded . 60 the field reference temperature measured by the reference as
Denoting operational response of FPA pixels ( expressed in
discussed below . The image obtained by each FPA includes
digitalnumbers, or “ counts” ) as g; to a source of radiance Lig a set of pixels obscured by the field reference 338 . Using thethe readings corresponding to the measurements of the two

shutters can be expressed as:
81 = YL (T1) + goffset
g2 = yL2( T2) + goffset

previously obtained calibration parameters goffset and y (thepixel offset and gain ), the effective blackbody temperature T ;65 of the field reference as measured by each FPA is estimatedusing the equation below :T;=mean {(g +Agi+ offsed/Y}=mean {(8 -8offse)/Y}+ AT;

US 10 ,444,070 B2
43

Using the equation above , the mean value over all pixels

that are obscured by the field reference is obtained . In the44

as well as by post -processing of the acquired imaging ,parallax is scene- induced and is not so easily correctable . In

above equation Ag; is the difference in offset value of the addition , the spectral differencing method is vulnerable tocurrent frame from Agoffset obtained during the calibration radiance calibration errors. Specifically, if one FPA registers
step . For the reference FPA , Agi can be simply set to zero . 5 radiance of light from a given feature of the object as that

Then , using the temperature differences measured by eachhaving a temperature of 40° C ., for example , while the datafrom another FPA represents the temperature of the same
objectfeature as being 39° C ., then such feature of the object
Ti - Tref=mean {(g + Agi+ & offset(Y} +AT;-mean {(g -Softwill
beenhanced or highlighted in the difference imageset)/y} =AT;
10 ( formed at least in part based on the images provided byOnce AT; for each FPA is measured , its value can be

FPA , one obtains

subtracted from each image in order to force operational

these two FPAs) due to such radiance -calibration error.

methodology of calibration with respect to radiance value
can also be implemented .
Examples of Methodology of Measurements.
Prior to optical data acquisition using an embodiment ofat another time. Such reference image , which is subtracted
from other later obtained images, may be referred to as atemporal reference image . This solution can be applied to

One solution to some of such problems is to compare(e.
g ., subtract ) images from the same FPA obtained at
the calibration procedure has been discussed above in ref
erence to calibration of temperature , a procedurally similar 15 different instances in time. For example , images can be

agreement between such FPA and the reference FPA . While

compared to or subtracted from a reference image obtained

the IR imaging system as described herein , one or more, 20 spectral difference images as well . For example , the image

most, or potentially all the FPAs of the system can becalibrated . For example, greater than 50 % , 60 % , 70 % , 80 %or 90 % or the FPAs 336 can be initially calibrated . As shownin FIG . 3 , these FPAS 336 may form separate images of thedata resulting from spectral difference images can be nor
malized by the data corresponding to a temporal reference
image. For instance , the temporal reference images can be
subtracted from the spectral difference image to obtain theobject using light delivered in a corresponding optical 25 temporal difference image . This process is referred to , forchannel thatmay include the combination of the correspond the purposes of this disclosure , as a temporal differencing

ing front objective and re - imaging lenses 324 , 128 . The

calibration procedure can allow formation of individual

algorithm or method and the resultant image from subtract
ing the temporal reference image from another image ( such

images in equivalent units ( so that, for example , the reading
as the spectral difference image ) is referred to as the temfrom the FPA pixels can be re -calculated in units of tem - 30 poral difference image . In some embodiments where spec

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

tral differencing is employed , a temporal reference image

process can also allow the FPAs (e . g ., each of the FPAS) tobe spatially co -registered with one another so that a given

may be formed , for example , by creating a spectral differ
ence image from the two or more images registered by the

pixel of a particular FPA can be optically re -mapped throughtwo or more FPAs at a single instance in time. This spectral

the optical system to the same location at the object as the 35 difference image is then used as a temporal reference image.

corresponding pixel of another FPA .

To achieve at least some of these goals, a spectral differ
encing method may be employed . The method involves

forming a difference image from various combinations of

The temporal reference image can then be subtracted fromother later obtained images to provide normalization that canbe useful in subtracting out or removing various errors ordeleterious effects. For example , the result of the algorithm

the images from different channels . In particular, the images 40 is not affected by a prior knowledge of whether the object orused to form difference images can be registered by two or scene contains a target species (such as gas of interest),
more different FPAs in spectrally distinct channels having because the algorithm can highlight changes in the scenedifferent spectral filters with different spectral characteris
tics. Images from different channels having differentspectral

characteristics. Thus, a spectral difference image can be

Comparing ( e .g ., subtracting ) these images, can therefore

time and can be subtracted from the temporal reference

the filter element of the array of spectral filters 130 corre -difference image is thus a normalized difference image . The

sponding to a particular FPA 336 transmits light from thedifference between the two images (the temporal difference

calculated from multiple spectral channels as discussed

characteristics will provide different spectral information . 45 above based on a snap - shot image acquisition at any lateryield valuable spectral based information . For example , if

image to form a temporal difference image. This temporal

object 110 including a cloud of gas , for example , with a 50 image ) can highlight the target species ( gas) within thecertain spectrum that contains the gas absorption peak or agas emission peak while another filter element of the arraynormalized difference image , since this species was notpresent in the temporal reference frame. In various embodi

of spectral filters 130 corresponding to another FPA 336

ments , more than two FPAs can be used both for registering

does not transmit such spectrum , then the difference between
the temporal reference image and a later -acquired difference
the images formed by the two FPAs at issue will highlight 55 image to obtain a better SNR figure of merit . For example ,the presence of gas in the difference image .
if two FPAs are associated with spectral filters having the
A shortcoming of the spectral differencing method is that same spectral characteristic, then the images obtained by thecontributions of some auxiliary features associated withimaging (not just the target species such as gas itself ) can

two FPAs can be combined after they have been registered
to get a better SNR figure .

also be highlighted in and contribute to the difference image . 60 While the temporal differencing method can be used toSuch contributing effects include , to name just a few , parreduce or eliminate some of the shortcomings of the spectral
allax -induced imaging of edges of the object, influence of differencing, it can introduce unwanted problems of its own.

magnification differences between the two or more optical

For example , temporal differencing of imaging data is lessfor by increasing the accuracy of the instrument constructionof interest (such as particular gas , for example ) is highchannels , and differences in rotational positioning and orisensitive to calibration and parallax induced errors than theentation between the FPAs. While magnification - related 65 spectral differencing of imaging data . However , any change
errors and FPA - rotation - caused errors can be compensatedin the imaged scene that is not related to the target speciesUS 10 ,444 ,070 B2
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46

lighted in a temporally - differenced image . Thus such change
in the imaged scene may be erroneously perceived as aalso be useful. Greater than 2 , for example , 3 or 4 , or more
FPAs can be used to establish parallax for parallax correc

location of the target species triggering , therefore , an errortion . In certain embodiments two central FPAs and one

in detection of target species . For example , if the tempera
corner FPA are used for parallax correction . These FPA may ,ture of the background against which the gas is being 5 in certain embodiments , have substantially similar or thedetected changes (due to natural cooling down as the day same spectral characteristics, for example , have filters hav
progresses, or increases due to a person or animal or anothering similar or the same transmission spectrum or have no
object passing through the FOV of the IR imaging system ), filter at all.
then such temperature change produces a signal difference
Another capability of the embodiments described herein
as compared to the measurement taken earlier in time. 10 is the ability to perform the volumetric estimation of a gas

Accordingly , the cause of the scenic temperature change (thecooling object, the person walking , etc . ) may appear as thecloud . This can be accomplished by using ( instead ofcompensating 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
two or more similar spectral response images (e . g ., two oramong the individual FPAs of a multi-FPA IR imaging 15 more channels or FPAs) can be used to estimate a distancesystem with the use of methods that turn on spectral or between the imaging system and the gas cloud or between
temporal differencing can cause additional problems 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 - between two images is related to the distance , z , between thecaused errors that are not readily correctable and / or com - 20 cloud or object 110 and the imaging system according to thepensatable . Accordingly , there is a need to compensate forequation ZF - sz '/d . Here , s , is the separation between two

image data acquisition and processing errors caused bymotion of elements within the scene being imaged . Various

similar spectral response images , and z ' is the distance to theimage plane from the back lens. The value for z ' is typicallyembodiments of data processing algorithmsdescribed herein

approximately equal to the focal length f of the lens of theaddress and fulfill the need to compensate for such motion - 25 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 more each image pixel on the gas cloud , Ax', corresponds to apredetermined FPAs, another difference image can be usedphysical size in object space Ax = Ax '/m . To estimate thethat is formed from the images of at least two different FPAs 30 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 cloudby comparing the images from two different FPAswhere thecan be assumed . For example , the cloud image can beposition between the FPAs is known. The parallax can berotated about a central axis running through the cloud image

calculated from the known relative position difference . Dif-

to create a three dimensional volume estimate of the gas

ferences between the images from these two FPAs can be 35 cloud size . It is worth noting that in the embodiments

attributed to parallax , especially, if the FPA have the samedescribed herein only a single imaging system is required forspectral characteristics , for example have the same spectral

such volume estimation . Indeed , due to the fact that thefilter or both have no spectral filters. Parallax error correc
tion , however, can stillbe obtained from two FPAs that haveinformation about the angle at which the gas cloud is seenby the system is decoded in the parallax effect, the image

different spectral characteristics or spectral filters , especially 40 data includes the information about the imaged scene

if the different spectral characteristics , e . g ., the transmission

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

viewed by the system in association with at least two angles .

When the temporal differencing algorithm is used forprocessing the acquired imaging data , a change in the scenethat is not caused by the target species can inadvertently be

example , when the spectral differencing of the image data is 45 highlighted in the resulting image . In various embodiments ,performed with the use of the difference between the images

compensation for this error makes use of the temporalcollected by the outermosttwo cameras in the array ( such as ,differencing between two FPAs that are substantially equallyfor example , the FPAs corresponding to filters 2 and 3 of thearray of filters of FIG . 5A ), a difference image referred to as

spectrally sensitive to the target species . In this case , thetemporal difference image will highlight those pixels thea " difference image 2 - 3 " is formed . In this case , the alter - 50 intensity of which have changed in time (and not in wave

native “ difference image 1 - 4 ” is additionally formed fromthe image data acquired by, for example , the alternative
FPAs corresponding to filters 1 and 4 of FIG . 5A . Assuming

length ). Therefore , subtracting the data corresponding tothese pixels on both FPAs, which are substantially equally
spectrally sensitive to the target species , to form the result

or ensuring that both of these two alternative FPAs haveing image, excludes the contribution of the target species toapproximately the same spectral sensitivity to the target 55 the resulting image . The differentiation between (i) changes

species , the alternative “ difference image 1 - 4 ” will highlightin the scene due to the presence of target species and ( ii )pixels corresponding to parallax - induced features in theimage. Accordingly, based on positive determination that thechanges in the scene caused by changes in the background
not associated with the target species is, therefore , possible .

samepixels are highlighted in the spectral “ difference image

In some embodiments , these two channels having the same2 - 3 ” used for target species detection , a conclusion can be 60 or substantially similar spectral response so as be substan

made that the image features corresponding to these pixels
are likely to be induced by parallax and not the presence of

tially equally spectrally sensitive to the target species may
comprise FPAs that operate using visible light. It should also

target species in the imaged scene. It should be noted that be noted that, the data acquired with a visible light FPA
compensation of parallax can also be performed using(when present as part of the otherwise IR imaging system )images created by individual re- imaging lenses, 128a , when 65 can also be used to facilitate such differentiation and com
using a single FPA or multiple FPA ' s as discussed above . pensation of the motion -caused imaging errors . Visible
FPAs spaced apart from each other in different directions can cameras generally have much lower noise figure than IR

US 10 ,444 ,070 B2
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48

cameras (at least during daytime). Consequently , the tem -value of correlation coefficient), the presence or absence ofporal difference image obtained with the use of image datamethane in the gas cloud can be detected .

from the visible light FPA can be quite accurate . The visible
FPA can be used to compensate for motion in the system as

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 to 5 optical channels and 12 corresponding microbolometermotion 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 the video
corresponds to images of a standard labo
visible region of the spectra . This has the added benefit of ratory sequence
scene
and
measurements are perproviding an additional level of false alarm suppression 10 formed with the usetheofcalibrationareferencesource including two
without reducing the sensitivity of the system since many shutters, as discussed above, one at room
temperature andtargets such as gas clouds cannot be observed in the visible
one
5º
C
.
above
room
temperature
.
The
use
of 12 FPAS
spectral region . In various implementations, an IR camera allows increased chance of simultaneous detectionand estican be used to compensate for motion artifacts .
mation of the concentrations of about 8 or 9 gases present at
Another method for detection of the gases is to use a 15 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 is requirements 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 - 20 ture difference (or NETD ) is preferred and is analogous toment spectrum . The component spectra are generally takenfrom a predetermined spectral library ( for example , fromthe SNR commonly used in visible spectrum instruments .
The array ofmicrobolometer FPAs 336 is characterized tosometimes one can use the scene to estimate these as wellmeasurement was carried out by summing four consecutive

data collection that has been empirically assembled ), though

perform at NETDs72 mK at an f-number of 1.2 . Each

( often called " endmember determination ” ). In various 25 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
cloud in the scene and/ or to estimate the concentration of thefore , the FPA NETD should be about 36 mK .
It is worth noting that the use of optically - filtered FPAs invarious gases in the gas cloud, an absorption / emission 30 various embodiments of the system described herein can

spectrum of the various gases of interest can be obtained byprovide a system with higher number ofpixels. For example ,comparing the measured brightness with an estimate of theembodiments including a single large format microbolom

expected brightness . The spectral unmixing methodology

eter FPA array can provide a system with large number of

can also benefit from temporal, parallax , and motion com
pixels . Various embodiments of the systems describedpensation techniques .
35 herein can also offer a high optical throughput for a sub
In various embodiments , a method of identifying thestantially low number of optical channels. For example , thepresence of a target species in the object includes obtaining systems described herein can provide a high optical throughthe radiance spectrum ( or the absorption spectrum ) from the put for a number of optical channels between 4 and 50 . By
object in a spectral region indicative of the presence of the having a lower number of optical channels ( e.g ., between 4target species and calculating a correlation (e.g ., a correla - 40 and 50 optical channels ), the systems described herein havetion coefficient ) by correlating the obtained radiance spec trum ( or the absorption spectrum ) with a reference spectrum

wider spectral bins which allows the signals acquired withineach spectral bin to have a greater integrated intensity .

for the target species. The presence or absence of the target

An advantage of the embodiments described herein over

species can be determined based on an amountof correlation

various scanning based hyperspectral systems that are conpresence of the target species in the object can be confirmed

detection ) is that, the entire spectrum can be resolved in aif the amount of correlation or the value of correlation
coefficient is greater than a threshold . In various implemen -snapshotmode (for example, during one image frame acquisition by the FPA array). This feature enables the embodi( e . g ., a value of correlation coefficient) . For example , the 45 figured for target species detection ( for example , gas cloud

tations, the radiance spectrum (or the absorption spectrum )ments of the imaging systems described herein to takecan be obtained by obtaining a spectral difference image 50 advantage of the compensation algorithms such as the

between a filtered optical channel and /or another filtered
optical channel/ unfiltered optical channel or any combina tions thereof.
For example , an embodiment of the system configured toparallax and motion compensation algorithms mentioned
above. Indeed , as the imaging data required to implement
these algorithms are collected simultaneously with the tar
get -species related data , the compensation algorithms aredetect the presence of methane in a gas cloud comprises 55 carried out with respect to target -species related data and not

optical components such that one or more of the plurality of
optical channels is configured to collect IR radiation toprovide spectral data corresponding to a discrete spectralwith respect to data acquired at another time interval. This
rapid data collection thus improves the accuracy of the datacompensation process . In addition , the frame rate of data

band located in the wavelength range between about 7 .9 um

acquisition is much higher. For example , embodiments ofabsorption spectrum of methane in the wavelength range
between about 7 . 9 um and 8 . 4 um . In various implementa

from about 5 Hz to about 60 Hz or 200 Hz. Thus, the user
is able to recognize in the images the wisps and swirls

and about 8 . 4 um corresponding to an absorption peak of 60 the imaging system described herein can operate at video
methane . The multispectral data obtained in the one or more
rates from about 5 Hz and higher. For example , various
optical channels can be correlated with a predetermined
embodiments described herein can operate at frame rates
tions, the predetermined absorption spectrum of methane 65 typical of gas mixing without blurring out of these dynamic

can be saved in a database or a reference library accessibleby the system . Based on an amount of correlation (e.g ., aimage features and other artifacts caused by the change ofscene (whether spatial or spectral) during the lengthy mea

US 10 ,444 ,070 B2
49
50
surements . In contradistinction , scanning based imaging tive and applicable to objects kept at different temperature .
systems involve image data acquisition over a period of time Accordingly, the algorithm is substantially temperature
exceeding a single -snap -shot time and can , therefore, blur independent.
the target gas features in the image and inevitably reduce the Dynamic Calibration Elements and References
otherwise achievable sensitivity of the detection . This result 5 FIGS. 9A and 9B illustrates schematically different imple
is in contrast to embodiments of the imaging system mentations 900 and 905 respectively of the imaging systemdescribed herein that are capable of detecting the localized that include a variety of temperature calibration elements tofacilitate dynamic calibration of the FPAs. The temperature
concentrations of gas without it being smeared out with the calibration
can include mirrors 975a, 975b (repareas of thinner gas concentrations . In addition , the higher 10 resented aselements
M14
,
M94
, etc.) as well as reference sources
frame rate also enables a much faster response rate to a leak 972a and 972b . The implementation
can be similarlyof gas (when detecting such leak is the goal) . For example, configured as the embodiment 300 and900
include one ormore
an alarm can trigger within fractions of a second rather than front objective lens, a divided aperture , one or more spectral
several seconds.
filters, an array of imaging lenses 928a and an imaging
To demonstrate the operation and gas detection capability
ability 1515 element 936 . In various implementations , the imaging eleof the imaging systems described herein , a prototype was ment 936 ( e.g., camera block ) can include an array ofconstructed in accordance with the embodiment 300 of FIG . cameras. In various implementations , the array of cameras
3A and used to detect a hydrocarbon gas cloud of propylene can comprise an optical FPA unit . The optical FPA unit can
at a distance of approximately 10 feet. FIG . 7 illustrates comprise a single FPA , an array of FPAs. In various imple
video frames 1 through 12 representing gas - cloud -detection 20 mentations, the array of cameras can include one or more
output 710 ( seen as a streak of light) in a sequence from t= 1
detector arrays represented as detector array 1 , detector array
to t= 12 . The images 1 through 12 are selected frames taken 5 , detector array 9 in FIGS. 9A and 9B . In various embodi

from a video -data sequence captured at a video -rate of 15
frames /sec . The detected propylene gas is shown as a streakments , the FOV of each of the detector arrays 1, 5, 9 can bedivided into a central region and a peripheral region . Withof light 710 (highlighted in red ) near the center of each 25 out any loss of generality , the central region of the FOV ofimage. The first image is taken just prior to the gas emerging
from the nozzle of a gas - contained , while the last image

each of the detector arrays 1 , 5 , 9 can include the region
where the FOV of all the detector arrays 1 , 5 , 9 overlap . In
the embodiment illustrated in FIG . 9A , some temperature
calibration elements , namely, reference sources 972a andrepresents the system output shortly after the nozzle has
onstrate 3030 972b are placed at a distance from the detector arrays 1, 5 ,The same prototype of the system can also demonstrate
9 , for example , and mirrors to image them onto the detector
the dynamic calibration improvement described above by arrays
placed at the location of the scene reference
imaging the scene surrounding the system (the laboratory ) apertureare( ethen
.
g
.
,
338
of FIG . 3A ).
with known temperature differences. The result of imple
In
FIG
.
9A
,
the
temperature -calibration elements 975a
menting the dynamic correction procedure is shown in1 35 and 975b comprise mirrorsthat reflect radiation from thebeen turned off .

FIGS. 8A , 8B , where the curves labeled " obj” ( or “ A ” )represent temperature estimates of an identified region in thescene. The abscissa in each of the plots of FIGS. 8A , 8B

reference sources 972a and 972b (represented as ref A and

expected that when all detector elements receive radiant datatations , the FOV of the detector array 5 could be greater thanref B ). The mirrors 975a and 975b can be disposed awayfrom the central FOV of the detector arrays 1, 5 , 9 such thatindicates the number of a FPA , while the ordinate corre
the central FOV is not blocked or obscured by the image ofsponds to temperature (in degrees C .). Accordingly , it is 40 the reference source 972a and 972b . In various implemen
that, when interpreted as the object' s temperature , indicatesthe FOV of the detector arrays 1 and 9 . In such implementhat the object's temperature perceived by all detector ele -tations , the mirrors 975a and 975b can be disposed away

ments is the same, any given curve would be a substantiallyfrom the central FOV of the detector array 5 at a location
flat line. Data corresponding to each of the multiple " obj” 45 such that the reference source 972a and 972b is imaged bycurves are taken from a stream of video frames separated
the detector array 5 . The mirrors 975a and 975b mayfrom one another by about 0 . 5 seconds ( for a total of 50
comprise imaging optical elements having optical power
frames ). The recorded " obj” curves shown in FIG . 8A
that image the reference sources 972a and 972b onto theindicate that the detector elements disagree about thedetector arrays 1 and 9 . In this example, the reference

object’s temperature , and that difference in object’ s tem - 50 sources 972a and 972b can be disposed in the same plane asperature perceived by different detector elements is as highthe re - imaging lenses 928a , however, the reference sources

as about 2 .5° C . In addition , all of the temperature estimates

972a and 972b can be disposed in a different plane or inare steadily drifting in time, from frame to frame. The curves different locations . For example, the reference sources 972alabeled “ ref” (or “ C ” ) correspond to the detectors ' estimatesand 972b can be disposed in a plane that is conjugate to theof the temperature of the aperture 338 of the embodiment 55 plane in which the detector array 1, detector array 5 , and300 of FIG . 3A . The results of detection of radiation carrieddetector array 9 are disposed such that a focused image ofout after each detector pixel has been subjected to the the reference sources 972a and 972b is formed by the
dynamic calibration procedure described above are detector arrays. In some implementations, the reference
expressed with the curved labeled “ obj corr” (or “ B ” ) . Now ,sources 972a and 972b can be disposed in a plane that isthe difference in estimated temperature of the object among 60 spaced apart from the conjugate plane such that a defocused

the detector elements is reduced to about 0 .5° C . ( thereby
improving the original reading at least by a factor of 5 ) .
FIG . 8B represents the results of similar measurements
corresponding to a different location in the scene ( a location

image of the reference sources 972a and 972b is formed byence sources 972a and 972b need not be disposed in thethe detector arrays . In various implementations, the refersame plane .

which is at a temperature about 9° C . above the estimated 65

As discussed above, in some embodiments , the reference

temperature of the aperture 338 of FIG . 3A ). As shown, thesources 972a and 972b are imaged onto the detector array 1

correction algorithm discussed above is operable and effec -and detector array 9 , without much blur such that theUS 10 ,444 ,070 B2
51
reference sources 972a and 972b are focused . In contrast, inother embodiments , the image of the formed of reference

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

52
in a conjugate planes of the detector arrays 1 and 9 . Although
the lenses 928a are described as providing blurred or defo

cused images, in various embodiments , reference sources orarray 9 are blurred such that the reference sources 972a andsurfaces are imaged on the detectors arrays 1 , 5 , 9 without
972b are defocused , and thereby provide some averaging , 5 such blur and defocus and instead are focused images .
smoothing, and/ or low pass filtering . The reference sources
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 attachedfocused images .

thereto or in thermal communication therewith . For
The temperature of the reference sources 972b , 972a can
example , the reference source 972a and 972b may comprises 10 be different. For example , the reference source 972a can beheaters and coolers respectively or may comprise a surface
at a temperature TA, and the reference source 972b can be atwith a temperature sensor and a heater and sensor respec - a temperature TR lower than the temperature Tg. A heater cantively in direct thermal communication therewith to control be provided under the temperature -controlled element 972a
the temperature of the reference surface . In various imple
to maintain it at a temperature T4, and a cooler can bementations, the reference sources 972a and 972b can include 15 provided underneath the temperature - controlled elementa temperature controller configured to maintain the reference972b to maintain it at a temperature To . 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 theinstead of two references sources 972a and 972b maintained
temperature of the reference sources 972a and 972b and 20 at different temperatures . It is understood that the single

communicate the measured temperature to the temperaturereference source need not be thermally controlled . For

controller. In some implementations, the one or more sen sors can communicate the measured temperature to theexample , in various implementations, a plurality of detectors
in the detector array can be configured to image a samedata - processing unit. In various implementations, the refer -surface of at least one calibration element whose thermal

ence sources 972a and 972b may comprise a surface of 25 and spectral properties are unknown. In such implementa

unknown temperature . For example , the reference sources
may comprise a wall of a housing comprising the imaging
system . In some implementations, the reference sources

tions, one of the plurality of detectors can be configured asa reference detector and the temperature of the surface of theat least one calibration element imaged by the plurality of

972a and 972b comprising a surface need not be associateddetectors can be estimated using the radiance spectrumwith sensors , temperature controllers . However , in other 30 obtained by the reference detector. The remaining plurality

implementations , the reference sources 972a and 972b com -of detectors can be calibrated such that their temperature

prising a surface can be associated with sensors , temperature
controllers .

and / or spectral measurements agree with the reference
detector. For example , detector arrays 1 and 9 can be

In FIG . 9B , the temperature - calibration elements com

calibrated to agree with each other. As another example ,prise temperature -controlled elements 972a and 972b ( e . g ., 35 detector arrays 1 , 5 and 9 can be calibrated to agree witha thermally controlled emitter, a heating strip , a heater or acooler ) disposed a distance from the detector arrays 1, 5 , 9 .
In various embodiments , the temperature -controlled ele ments 972a and 972b can be disposed away from the central

each other.
The reference sources 972a and 972b can be coated witha material to make it behave substantially as a blackbody(for which the emission spectrum is known for any given

FOV of the detector arrays 1, 5, 9 such that the central FOV 40 temperature ). If a temperature sensor is used at the location
is not blocked or obscured by the image of the reference of each reference source, then the temperature can besource 972a and 972b . The radiation emitted from thetracked at these locations. As a result, the regions in thereference sources 972a and 972b is also imaged by theimage of each camera ( e . g ., on the detector arrays 1 and 9 )detector array 936 along with the radiation incident from thein which the object has such known temperature (and ,object . Depending on the position of the reference sources 45 therefore , spectrum ) can be defined . A calibration procedure

972a and 972b the image obtained by the detector array of

can thus be used so that most of the cameras (if not every

the reference sources can be blurred (or defocused ) or sharp( or focused ). The images 980a , 9806, 9800 , 9800 , 980e andcamera ) so operated agrees, operationally, with most or
every other camera , for objects at the temperatures repre

980f of the temperature - controlled elements 972a and 9726

sented by those two sources. Calibrating infrared cameras

can be used as a reference to dynamically calibrate the one 50 using sources at two different temperatures is known as aor more cameras in the array of cameras .

" two -point" calibration , and assumes that the measured

detector arrays 1 , 5 and 9 are configured to view (or image )both the reference sources 972a and 972b . Accordingly,

irradiance . Since this calibration can be performed duringmultiple , more , or even every frame of a sequence , it is

In the implementations depicted in FIGS. 9A and 9b , thesignal at a given pixel is linearly related to the incident

multiple frames ( e . g ., every or substantially every frame ) 55 referred to as a " dynamic calibration ” .

within a sequence of images contains one or more regions in

the image in which the object image has known thermal andspectral properties . This allows multiple ( e .g ., most or each )cameras within the array of cameras to be calibrated to agree

An example of the dynamic calibration procedure is asfollows. If there is a temperature sensor on the reference
sources or reference surface , then the temperature measurem ents obtained by these temperature sensors can be used towith other ( e . g ., most or every other ) camera imaging the 60 determine their expected emission spectra . These tempera

same reference source (s ) or surface (s ). For example , detec - ture measurements are labeled as T [ R ], TR [ R ], and T [ R ]tor arrays 1 and 9 can be calibrated to agree with each other.
for the “ reference temperatures” of sources /surfaces A , B ,As another example , detector arrays 1, 5 and 9 can be
and C . These temperature measurements can be used as
calibrated to agree with each other. In various embodiments,
scalar correction factors to apply to the entire image of athe lenses 928a provide blurred ( or defocused ) images of the 65 given camera , forcing it to agree with the reference tem
reference sources 972a , 972b on the detector arrays 1 and 9
peratures. Correcting the temperature estimate of a given

because the location of the reference sources are not exactly

pixel from T to T' can use formulae analogous to thoseUS 10 ,444 ,070 B2

53

54

discussed below in reference to FIGS. 10A , 10B , 10C . If no

direct temperature sensor is used , then one of the cameras

This design is an enhancement to the systems 300 and 400

shown in FIGS. 3A and 4A . In the system 1000 shown in

can be used instead . This camera can be referred to as the
FIG . 10A , an array of two or more imaging elements ( curved" reference camera ” . In this case , the same formulae as those mirrors , for example ) is installed at a distance from theprovided below can be used , but with TIR ) and TR 5 FPAs, for example, in the plane of the reference aperture 160

representing the temperatures of the reference sources/ surshown in FIG . 3A . These elements (mirror or imaging

In the configuration illustrated in FIG . 9B , the reference

sources 972a and 972b are placed such that the images of theof cameras in the array can image both the reference sources

sources on the detector arrays are blurred . The configuration

A and B instead of imaging one of the two reference source

A and B . Accordingly , most or all of the outer ring of

this configuration , the array of reference apertures, similar todifferent cameras or imaging different portions of the refer) are used to image one or more temperature
faces A and B as estimated by the reference camera. By elements
reference sources A and B onto the detector
applying the dynamic calibration correction formulae , all of controlledelementsoftwo or more of the cameras . The primary
the other cameras are forced to match the temperature 10 difference between
embodiment 1000 and embodiment 300
estimates of the reference camera .
or 400 is that now a plurality ormost or all of the outer ringillustrated in FIG . 9A is similar to the system 400 illustrated 15 cameras image an identical reference source or an identicalin FIG . 4 where the reference sources are placed at an set of reference sources (e .g ., both the reference sources Aintermediate image plane (e.g ., a conjugate image plane ). In and B ) rather than using different reference sources forreference apertures 438a in FIG . 4 , will have an accompa -ence sources as shown in FIGS. 3A and 4A . Thus, thisnying array of reference sources or reference surfaces such 20 approach 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

additional thermal sensors estimating each reference source .

array such as FPAs 1 , 5 , 9 . With this approach , the reference
source or surface images are at a conjugate image plane and

The imaging elements in the system 1000 ( shown as
mirrors in FIGS. 10A and 10B ) image one or more conthus are not appreciably blurred , so that their images can be 25 trolled -temperature reference sources or a surface of amade to block a smaller portion of each camera ' s field ofview .

A " static" calibration (a procedure in which the scene islargely blocked with a reference source such as the moving

calibration element (shown as A and B in FIGS. 10A and
10B ) into the blocked region of the cameras ' fields of view .
FIG . 10B shows an example in which mirror Mo , images
reference source /surface A onto camera 0 , and mirror MOR

shutters 960 in FIGS . 9A and 9B , so that imaging of a 30 images reference source/ surface B onto camera 0 , andunknown scene cannot be performed in parallel with calilikewise for cameras 1 , 2 , and 3 . This way, each of thebration ) allows a plurality of the cameras ( for example , mostmirrors is used to image a reference source / surface onto a

or each camera ) to accurately estimate the temperature of aplurality of elements ( for example , most or each element in

detector array of a camera , so that many, most, or every
frame within a sequence of images contains one or more

the scene ) immediately after the calibration is complete . It 35 regions in the image in which the object image has known

cannot, however, prevent the cameras ' estimates from drift-

thermal and spectral properties . This approach allowsmost

ing away from one another during the process of imaging anof the camera , if not each camera , within the array of

unknown scene . The dynamic calibration can be used tocameras to be calibrated to agree with most or every other

FIG . 10A illustrates schematically a related embodiment1000 of the imaging system , in which one or more mirrors

other. As yet another example , cameras 0 , 1 , 2 , 3, 7 , 11, 10 ,
9 , 8 , 4 , 5 and 6 can be calibrated to agree with each other.

reduce or prevent this drift, so that all cameras imaging acamera imaging the same reference source or sources . For
scene can be forced to agree on the temperature estimate of 40 example , cameras 0 , 1 , 2 , 3 , 7 , 11, 10 , 9 , 8 and 4 can be
the reference sources /surfaces , and adjust this correction
calibrated to agree with each other. As another example ,during every frame.
cameras 0 , 1, 2 and 3 can be calibrated to agree with each

Mo , . . .M14 and More . . .M
are placed within the fields 45 Accordingly , in various implementations , two , three , four,of view of one or more cameras 0 , . . . , 11 , partially blocking
five, six , seven , eight, nine, ten , eleven or twelve cameras
the field of view . The cameras 0 , . . . , 11 are arranged to form
can be calibrated to agree with each other. In certain
an outer ring of cameras including cameras 0 , 1 , 2 , 3 , 7 , 11 ,embodiments , however, not all the cameras are calibrated to
10 , 9 , 8 and 4 surrounding the central cameras 5 and 6 . In
agree with each other. For example , one, two, or morevarious implementations , the FOV of the central cameras 5 50 cameras may not be calibrated to agree with each other while

and 6 can be less than or equal to the FOV of the outer ringof cameras 0 , 1 , 2 , 3 , 7 , 11, 10 , 9 , 8 and 4 . In suchothers may be calibrated to agree with each other. In various
embodiments , these mirrors may be configured to image theimplementations, the one or more mirrors Mo 4 , . . . M

reference sources /surfaces A and B onto different respectiveand

MOR , . . . Mug can be placed outside the central FOV of the pixels a given FPA . Without any loss of generality , FIGS.
cameras 5 and 6 and is placed in a peripheral FOV of the 55 10A and 10B represent a top view of the embodiment shown
cameras outer ring of cameras 0 , 1 , 2 , 3 , 7 , 11 , 10, 9 , 8 andin FIG . 9A .
4 which does not overlap with the central FOV of the
FIG . 10C illustrates schematically a related embodimentcameras 5 and 6 such that the reference sources A and B are
1050 of the imaging system , in which one or more reference
not imaged by the cameras 5 and 6 . In various implemen sources Roa, . . . , RU14 and RoB , . . . RUB are disposed
tations, the FOV of the central cameras 5 and 6 can be 60 around the array of detectors 0 , . . . , 11 . In various

greater than the FOV of the outer ring of cameras 0 , 1, 2 , 3 ,implementations , the one or more reference sources

7 , 11 , 10 , 9 , 8 and 4 . In such implementations , the one or RA, . . . R114 and ROB, . . . , Rug can be a single reference
more mirrors Mp4 , . . . M114 and MoB, . . .M e can besource that is images by the detectors 0 , . . . , 11 . In various
placed in a peripheral FOV of the cameras 5 and 6 which
implementations, central detector arrays 5 and 6 can have adoes overlap with the central FOV of the outer ring of 65 FOV that is equal to or lesser than the FOV of the outer ringcameras 0 , 1 , 2 , 3 , 7 , 11 , 10 , 9 , 8 and 4 such that the reference

sources A and B are imaged by the cameras 5 and 6 .

of the detectors 0 , 1 , 2 , 3 , 7 , 11, 10 , 9 , 8 and 4 . In such

implementations, the reference sources Roa · . . , R114 canUS 10 , 444,070 B2
55
be disposed away from the central FOV of the detector

56

References throughout this specification to “ one embodi

arrays 5 and 6 such that the radiation from the reference
sources Roa, . . . , RU14 is imaged only by the outer ring ofdetectors 0 , 1 , 2 , 3 , 7 , 11 , 10 , 9 , 8 and 4 . In various

ment," " an embodiment," " a related embodiment,” or simi
lar language mean that a particular feature , structure , orcharacteristic described in connection with the referred to

FOV that is greater than the FOV of the outer ring of thepresent invention . Thus , appearances of the phrases “ in one

detectors 0, 1, 2, 3, 7, 11 , 10 ,R 9, 8 and 4 R. In such
implebe. . canmentations, the reference sources

embodimentthis," "specificationin an embodiment,” andsimilarlanguagethroughout
may, but
do notnecessarily, allimplementations, central detector arrays 5 and 6 can have a 5 " embodiment” is included in at least one embodiment of thedisposed in the peripheral FOV of the detector arrays 5 and refer to the same embodiment. It is to be understood that no
6 such that the radiation from the reference sources 10 portion of disclosure, taken on its own and in possible
ROA, . . . , Ru14 is imaged only by the outer ring of detectors connection with a figure , is intended to provide a complete

0 , 1 , 2 , 3, 7 , 11, 10 , 9 , 8 and 4 . The radiation from the description of all features of the invention .
In the drawings like numbers are used to represent theouter ring of detectors 0 , 1, 2, 3 , 7 , 11, 10 , 9 , 8 and 4 as well same or similar elements wherever possible . The depicted
as central cameras 5 and 6 . Without any loss of generality, 15 structural elements are generally not to scale , and certain
FIG . 10C represents a top view of the embodiment shown in components are enlarged relative to the other components
for purposes of emphasis and understanding. It is to be
FIG . 9B .
reference sources ROA , . . . , Ru14 is therefore imaged by the

In various implementations, one can use a heater under-

understood that no single drawing is intended to support aneath , adjacent to , or in thermal communication with refercomplete description of all features of the invention. In othera cooler underneath , adjacent to , or in thermal communica
tion with reference source B to give it a lower temperaturesome, and generally not all, features of the invention . A
given drawing and an associated portion of the disclosure
containing a description referencing such drawing do not,ence source /surface A to give it a higher temperature Ty, and 20 words, a given drawing is generally descriptive of only

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 asingle reference source A instead of two references sources 25 features that can be presented is this view , for purposes of
A and B maintained at different temperatures. As discussed
simplifying the given drawing and discussion , and to directabove, the embodiments illustrated in FIGS . 10A , 10B and the discussion to particular elements that are featured in thisdrawing . A skilled artisan will recognize that the invention
10C can be configured to image a same surface of acalibration element. In such implementations, the tempera may possibly be practiced without one or more of theture of the surface of the calibration element need not be 30 specific features , elements , components, structures, details ,known. Many, most or each reference source/surface can beor characteristics, or with the use of other methods, com

there are known regions in the image of these cameras inwhich the object has a known temperature (and therefore
spectrum ). Then one can perform a calibration procedure .
This procedure can provide thatmany, most or every camera

may be implied unless the context of the description requires
otherwise. In other instances, well known structures, details ,coated with a material to make it behave approximately as
ponents , materials , and so forth . Therefore , although aa blackbody , for which the emission spectrum is known for particular detail of an embodiment of the invention may not
any given temperature . If many, most, or each camera in the be necessarily shown in each and every drawing describing
array of cameras images both of references A and B , so that 35 such embodiment, the presence of this detail in the drawing

materials, or operations may be not shown in a given

drawing or described in detail to avoid obscuring aspects ofso operated agrees with various, most, or every other cam - 40 an embodiment of the invention that are being discussed .
era , for objects at the temperatures represented by those two
Furthermore , the described single features , structures, orsources. For example , two, three , four, five, six , seven , eight,
characteristics of the invention may be combined in any
nine , ten , eleven or twelve cameras can be calibrated tosuitable manner in one or more further embodiments .

The features recited in claims appended to this disclosureagree with each other. In certain embodiments, however, not
all the cameras are calibrated to agree with each other. For 45 are intended to be assessed in light of the disclosure as a

example , one, two , or more cameras may not be calibrated
whole, including features disclosed in prior art to whichto agree with each other while others may be calibrated to reference is made.
Atleast some elements of a device of the invention can be
agree with each other. As discussed above , calibration of
infrared cameras using sources at two different temperatures controlled — and at least some steps of a method of theis known as a " two - point” calibration , and assumes that the 50 invention can be effectuated , in operation — with a programmeasured signal at a given pixel is linearly related to theincident irradiance .
The dynamic calibration is used to obtain a corrected

temperature T ' from the initial temperature T estimated at

mable processor governed by instructions stored in a
(RAM ), read -only memory (ROM ), flash memory or any

memory . The memory may be random access memory

other memory , or combination thereof, suitable for storingeach pixel in a camera using the following formulae:

55 control software or other instructions and data . Those skilled

T”[x,y,c]=(7[x,y,c]- TA[R ])G [c]+ TA[R ]where is TA [R ] is a dynamic offset correction factor, and ,may be delivered to a processor in many forms, including ,TA [R ]G [41c ] = 1TBTB[[Rc]] –- TA[c ] '

in the art should also readily appreciate that instructions orprograms defining the functions of the present invention

but not limited to , information permanently stored on non
60 writable storage media ( e . g . read - only memory devices

within a computer, such as ROM , or devices readable by acomputer I/ O attachment, such as CD - ROM or DVD disks ),information alterably stored on writable storage media (e.g .
floppy disks , removable flash memory and hard drives ) oris a dynamic gain correction factor. The term c discussed 65 information conveyed to a computer through communica
above is a camera index that identifies the camera whosetion media , including wired or wireless computer networks .
In addition , while the invention may be embodied in soft
data is being corrected .

57

US 10 ,444, 070 B2

ware , the functions necessary to implement the invention

58
Certain features that are described in this specification in

may optionally or alternatively be embodied in part or in
the context of separate implementations also can be imple
whole using firmware and /or hardware components, such as mented in combination in a single implementation . Con
combinatorial logic , Application Specific Integrated Circuits
versely , various features that are described in the context of(ASICs), Field - Programmable Gate Arrays ( FPGAs) or 5 a single implementation also can be implemented in multiple
other hardware or some combination of hardware, software implementations separately or in any suitable subcombina

tion . Moreover, although features may be described above asin certain combinations and even initially claimed as
While examples of embodiments of the system and acting
acti
such
,
one
ormore features from a claimed combination canmethod of the invention have been discussed in reference to
in
10
in
some
cases
be excised from the combination , and thethe gas -cloud detection , monitoring , and quantification (in - 1 claimed combination
may be directed to a subcombination
and / or firmware components .

cluding but not limited to greenhouse gases such as Carbon
Dioxide , Carbon Monoxide, Nitrogen Oxide as well asor variation of a subcombination .

hydrocarbon gases such as Methane , Ethane, Propane , n -Bu
What is claimed is :tane, 150 -Butane, n -Pentane, 180 -Pentane, neo -Pentane, 15 1. An infrared ( IR ) imaging system , the imaging system
Hydrogen Sulfide, Sulfur Hexafluoride , Ammonia , Benzene , comprising:p - and m - Xylene , Vinyl chloride , Toluene , Propylene oxide ,an optical system including an optical focal plane array
Propylene , Methanol, Hydrazine , Ethanol, 1, 2 -dichloroeth(FPA ) unit , the optical system comprising components
ane , 1, 1- dichloroethane, Dichlorobenzene, Chlorobenzene ,associated with at least two optical channels spatiallyto name just a few ), embodiments of the invention can be 20
and spectrally different from one another , each of the atleast two optical channels positioned to transfer IR
readily adapted for other chemical detection applications .
For example , detection of liquid and solid chemical spills ,radiation from an object incident on the optical system
biological weapons, tracking targets based on their chemical
towards the optical FPA unit, the optical FPA unit
composition , identification of satellites and space debris,comprising at least two detectors disposed at a distance

ophthalmological imaging , microscopy and cellular imag - 25from two corresponding focusing lenses ; anding , endoscopy ,mold detection , fire and flame detection , andpesticide detection are within the scope of the invention .

a data -processing unit configured to obtain a spectral

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

difference image by comparing images obtained by theat least two detectors , said infrared imaging system
configured to identify a target species based on said

is intended to cover: a , b , c , a -b , a -c , b -c , and a -b - c .

2 . The imaging system of claim 1 , wherein the imaging

single members. As an example, " at least one of: a , b , or c" 30

spectral difference image .

If implemented in software , the functions may be stored

system is further configured to identify target species basedon or transmitted over as one or more instructions or code on

on a comparison of a first spectral difference image and aa computer-readable medium . The steps of a method orsecond spectral difference image , said second spectral dif

cessor -executable software module which may reside on atime from the first spectral difference image .

algorithm disclosed herein may be implemented in a pro - 35 ference image acquired by the at least two detectors at a latercomputer - readable medium . Computer-readable media

3 . The imaging system of claim 1 , wherein the FPA unit

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

does not require cooling during normal operation .
4 . The imaging system of claim 1, wherein the IR radia

EEPROM , CD -ROM or other optical disk storage, magnetic

6 . The imaging system of claim 1, wherein the compo

a computer program from one place to another. A storage 40 tion comprises wavelengths between about 1 micron andmedia may be any available media that may be accessed byabout 20 microns .
a computer. By way of example , and not limitation , such
5 . The imaging system of claim 1 , wherein the object
computer- readable media may include RAM , ROM ,comprises a gas cloud .
disk storage or other magnetic storage devices , or any other 45 nents associated with the at least two optical channels
medium that may be used to store desired program code incomprise at least two spectral filters , each filter positioned in
the form of instructions or data structures and that may be

a respective one of said at least two optical channels .

accessed by a computer. Also , any connection can be prop erly termed a computer -readable medium . Disk and disc , as

7 . The imaging system of claim 6 , wherein the at least two
spectral filters comprise at least one long pass (LP ) filter .

used herein , includes compact disc (CD ), laser disc, optical 50

8 . The imaging system of claim 6 , wherein the at least twodisc , digital versatile disc (DVD ), floppy disk , and blu -rayspectral filters comprise at least one short pass (SP ) filter.

discs reproduce data optically with lasers. Combinations ofmovable temperature reference at a known temperaturedisc where disks usually reproduce data magnetically , while
the above also may be included within the scope of com

9. The imaging system of claim 1 , further comprising a
configured to be inserted into an optical path from the object

puter-readable media . Additionally, the operations of a 55 to the FPA unit along at least one of the two optical channels

method or algorithm may reside as one or any combination

to block IR radiation and configured to be removed from theor set of codes and instructions on a machine readable

optical path .

medium and computer-readable medium , which may beincorporated into a computer program product.

10 . The system of claim 9 , wherein the data -processing

unit is configured to calibrate the FPA unit based on the
Variousmodifications to the implementations described in 60 known temperature .

this disclosure may be readily apparent to those skilled in the

11 . The imaging system of claim 9 , wherein the movable

art, and the generic principles defined herein may be applied

temperature reference comprises a first shutter at a firstto other implementations without departing from the spirit ortemperature and a second shutter at a second temperature .

scope of this disclosure . Thus , the claims are not intended to
12 . The imaging system of claim 9 , wherein the movablebe limited to the implementations shown herein , but are to 65 temperature reference comprises a system having a firstbe accorded the widest scope consistent with this disclosure,portion at a first temperature and a second portion at asecond temperature .
the principles and the novel features disclosed herein .

US 10 ,444 ,070 B2
59
13 . The imaging system of claim 1 , wherein at least oneof the two detectors comprises a microbolometer .
14 . The imaging system of claim 1 , wherein the dataprocessing unit is configured to obtain the spectral difference

image by subtracting images obtained by the at least two 5
detectors , said images obtained by the at least two detectors
having different spectral characteristics .

15 . The imaging system of claim 14 , wherein the dataprocessing unit is configured to compare the obtained spec10
tral difference image with a reference image .
16 . The imaging system of claim 15 , wherein the reference image is obtained at a time interval prior to a timeinterval when the spectral difference image is obtained .

60