VIIRS Day/Night Band (DNB) Stray Light Correction Approach February 7, 2013 Stephanie Weiss NGAS.
Stray Light Correction Algorithm for Multi-channel ...€¦ · Stray Light Correction Algorithm for...
Transcript of Stray Light Correction Algorithm for Multi-channel ...€¦ · Stray Light Correction Algorithm for...
Stray Light Correction Algorithm for Multi-channel Spectrographs
Steve Brown, Yuqin Zong, Ping Shaw, Keith Lykke, Carol Johnson NIST
Stephanie J. Flora, Michael E. Feinholz, Mark A. Yarbrough
Moss Landing Marine Laboratories
Dennis K. Clark Marine Optical Consulting
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Multi-channel Spectrographs
Typical Layout
• In a conventional single-channel spectrograph, the entrance slit is imaged on the detector plane
• In a multi-channel spectrograph, the entrance slit is divided into channels for inputs from different targets
– Simplest way to do this is to use optical fibers – often simply epoxied onto the entrance slit
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Entrance slit
Optical fibers
Detector Array
Spectral
Spat
ial
Motivation for the work arises from survey of fields with applications using Multiple-input (or multi-channel) Spectrographs
— Medical imaging
— High throughput screening
— Machine vision
—Multi-channel process monitoring
— Remote sensing
—Astronomy
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Intermediate step between 1-d SLC algorithm and full point spread response correction algorithm
Ocean Color Multi-channel Spectrograph built by Resonon for Moss Landing
14-channel spectrograph Image on the CCD from an 14-channel spectrograph
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Detector
Spectrograph
Fiber Input
Characterization/Performance Issues
Output from a standard fiber shows an extended halo that may cause scattered light within the spectrograph
Grating scatter
Ghost image
Spurious reflection peaks
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Impacts Along-track (spectral) and Cross-track (spatial) performance
Reflection Peak
Wavelength (nm)
Rel
ativ
e R
esp
on
se (
a.u
.)
Astronomy Example: Baryon Oscillation Spectroscopic Survey (BOSS)
Movie Provided by Claire Cramer, NIST
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images, tunable laser excitation
• BOSS has 1000 fiber inputs >
“Big Boss” – 5000 inputs
• 2.5 m telescope at Apache
Point Observatory, New Mexico
• Used to study large-scale
structure of the universe Wav
elen
gth
Individual fibers
Algorithm for Single Input System: Review
IB SLmeasS S S
S r L dmeas
S r L d r L dmeas ib oob
555 556 557 558 559 560 561 562 563 564
0.0
0.2
0.4
0.6
0.8
1.0
Norm
aliz
ed R
esponse
Wavelength [nm]Wavelength [nm]
Rel
ativ
e R
esp
on
se (
a.u
.)
Wavelength (nm)
In-Band Out-of-Band
SStray Light: Development of the SDF Matrix
The SDF matrix, Dn×n
Spectrum Line Spread Function (LSF)
Stray-light distribution function (SDF)
1,1 1,2 1, 1,n 1 1,n
2,1 2, 2 2, 2, n-1 2, n
i,1 , 2 , , n-1 , n
n-1,1 n-1, 2 n-1, n-1, n-1 n-1, n
n,1 n, 2 n, n, n-1 n, n
. . . .
. . . .
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. . . . . . . . .
. . . .
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. . . . . . . . .
. . . .
. . . .
J
J
i i J i i
J
J
d d d d d
d d d d d
d d d d d
d d d d d
d d d d d
D
Colum 400
Relative scattering from pixel j into all other pixels in the array
Relative scattering from all other pixels in the array into pixel i
Zero’s along the diagonal
The Stray Light Distribution (SDF) matrix, D
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1,1 1,2 1, 1,n 1 1,n
2,1 2, 2 2, 2, n-1 2, n
i,1 , 2 , , n-1 , n
n-1,1 n-1, 2 n-1, n-1, n-1 n-1, n
n,1 n, 2 n, n, n-1 n, n
. . . .
. . . .
. . . . . . . . .
. . . . . . . . .
. . . .
. . . . . . . . .
. . . . . . . . .
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. . . .
J
J
i i J i i
J
J
d d d d d
d d d d d
d d d d d
d d d d d
d d d d d
D
A little Matrix Algebra …
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Stray-light correction matrix.
IB
1
1
meas IB
meas IB
measIB
measIB
S S D S
S I D S
S I D S
C I D
S C S
SL IBD SS
“Truth”
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Two Example Results of Stray-light Correction
A Green LED A Green Optical Filter
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
Rela
tive S
ign
al
-1.0E-04
0.0E+00
1.0E-04
2.0E-04
3.0E-04
4.0E-04
5.0E-04
6.0E-04
7.0E-04
8.0E-04
9.0E-04
200 300 400 500 600 700 800 900
Wavelength (nm)
Rela
tive S
ign
al
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
Rela
tive S
ign
al
-1.0E-04
0.0E+00
1.0E-04
2.0E-04
3.0E-04
4.0E-04
5.0E-04
6.0E-04
7.0E-04
8.0E-04
9.0E-04
200 300 400 500 600 700 800 900
Wavelength (nm)
Rela
tive S
ign
al
1 count
1 count
log log
linear
linear
Magnitude of Stray Light: Broadband v. Narrowband calibrations
6.5E+08
7.0E+08
7.5E+08
8.0E+08
8.5E+08
9.0E+08
730 735 740 745 750
Wavelength [nm]
Ab
so
lute
Sp
ec
tra
l R
es
po
ns
ivit
y
Lamp-ISS Uncorrected for stray light
Lamp-ISS Stray light corrected
SIRCUS
ib iii drR
555 556 557 558 559 560 561 562 563 564
0.0
0.2
0.4
0.6
0.8
1.0
Norm
aliz
ed R
esponse
Wavelength [nm]Wavelength [nm]
Ab
solu
te R
esp
on
sivi
ty (
a.u
.)
~10 %
Extension of the Algorithm to a Multiple Channel Spectrograph
• Take each of the input channels and create one long nx1 matrix, where n=# of channels multiplied by the number of elements in the array (dispersion direction)
• Example:
– For a system with 4 inputs, 1024 elements in the along track direction, the array is a 4096 x 1 array
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describes the cross-track scattering from track I into track j
Consider a 4-channel system 1
11 12 13 142
21 22 23 24
33431 32 33
41 42 43 44 4
SIB
D D D D
SD D D D IBD SIB
D D D D SIB
D D D DS
IB
,Di i
,Di j
D matrix now comprised of sub-arrays
describes the along-track scattering
SL IBD SS
As with the 1-d case,
Only D and S now have different meanings.
Multiple Input Spectrograph System • ISA (Jobin Yvon) f/2 spectrograph with reflective concave holographic
grating; 25 mm slit
• Andor 1024x256 cooled CCD array, 25 mm pixels
• Breadboard system had 4 1 mm fibers separated by ~500 mm
Lens, aperture, & shutter
CCD &
spectrograph
Fiber bundle
Input fibers
Shutter drive circuit
Lens, aperture, & shutter
CCD &
spectrograph
Fiber bundle
Input fibers
Shutter drive circuit
Spectralon sphere
Input fibers
Spectralon sphere
Input fibers
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4-Channel Input into Spectrograph
All 4 channels illuminated with LED Image expanded to 1 % full scale
Cross-track coupling
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Xenon source, Only Track 2 Illuminated
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Pixel
Sign
al(A
DU
/pix
el/s
eco
nd
) Along-track
Cross-track
0
2000
4000
6000A
ndo
r L
ite
(A
DU
/pix
/se
c)
965 901 837 774 711 648 586 524 463 401 340Wavelength (nm)
0 100 200 300 400 500 600 700 800 900 10000
5
10
15
20
Pixel
An
do
r L
ite
(A
DU
/pix
/se
c) 0.15%
0.15%
0.06%
Track1
Track2
Track3
Track4
Ratio of Track x to Track 2
0 200 400 600 800 10000
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0.05R
atio T
rack X
/ T
rack 2
Pixel
T1 / T2
T3 / T2
T4 / T2
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Stray light characterization using tunable lasers
Laser characterization data (subset of full data set)
Second order diffraction
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400 500 600 700 800 900
10-4
10-3
10-2
Wavelength (nm)
An
do
r T
rack
1 L
ase
r D
ata
(n
orm
alize
d t
o m
axi
mu
m)
Stray Light Distribution Function Matrix
Along-track Sub-Matrix D22 Cross-track Sub-Matrix D43
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(normalized by the in-band area)
Second order diffraction peak Not zero along the diagonal
4-channel D-matrix
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Smeas: Track 2 only Illuminated
22 Array Element
Sign
al (
AD
U/p
ixel
/sec
) (L
oga
rith
mic
sca
le)
0 4000
D S
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1
11 12 13 142
21 22 23 24
33431 32 33
41 42 43 44 4
SIB
D D D D
SD D D D IBD SIB
D D D D SIB
D D D DS
IB
Validation: Single track Illuminated
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Wavelength [nm]
Log
Sign
al [
a. u
.]
Validation (Logarithmic Scale) Full = all tracks illuminated; Single = single track illuminated
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400 600 800
100
Tra
ck
1
Full
Single
Cor(F)
Cor(S)
400 600 800
100
Tra
ck
2
400 600 800
100
Wavelenght (nm)
Tra
ck
3
400 600 800
100
Wavelenght (nm)
Tra
ck
4
Wavelength [nm] Wavelength [nm]
Xe source Xe source, PER filter
Xe source, BG-39 filter Xe source, BG-28 filter
Validation (Linear Scale)
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400 600 800
0
10
20
30
40
50
Tra
ck
1
Full
Single
Cor(F)
Cor(S)
400 600 800
0
10
20
30
40
50
Tra
ck
2
400 600 800
0
10
20
30
40
50
Wavelenght (nm)
Tra
ck
3
400 600 800
0
10
20
30
40
50
Wavelenght (nm)
Tra
ck
4
Wavelength [nm] Wavelength [nm]
Xe source Xe source, PER filter
Xe source, BG-39 filter Xe source, BG-28 filter
Residual signal near 800 nm originates from incomplete characterization
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400 500 600 700 800 900
10-4
10-3
10-2
Wavelength (nm)
An
do
r T
rack
1 L
ase
r D
ata
(n
orm
alize
d t
o m
axi
mu
m)
400 600 800
0
10
20
30
40
50
Tra
ck
1
Full
Single
Cor(F)
Cor(S)
400 600 800
0
10
20
30
40
50
Tra
ck
2
400 600 800
0
10
20
30
40
50
Wavelenght (nm)
Tra
ck
3
400 600 800
0
10
20
30
40
50
Wavelenght (nm)
Tra
ck
4
400 500 600 700 800 900
Wavelength [nm]
Wavelength [nm]
Wavelength [nm]
Magnitude of the correction
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400 500 600 700 8000.9
0.92
0.94
0.96
0.98
1T
rack
1Ratio of cor/uncor (Full)
450 500 550 600 650 7000.9
0.92
0.94
0.96
0.98
1
Tra
ck
2
450 500 550 600 650 7000.9
0.92
0.94
0.96
0.98
1
Wavelenght (nm)
Tra
ck
3
400 450 500 550 600 6500.9
0.92
0.94
0.96
0.98
1
Wavelenght (nm)
Tra
ck
4
Future Direction: Finite Point Spread Response correction
• Limit as the width of a channel decreases to one pixel and the # of channels increases to # of elements
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Proposed point spread response correction for MODIS
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Random granules analyzed
Analysis of a time series of imagery (same site, different cloud cover) 1. Ground truth site (MOBY Site) 2. A site where the radiometric properties of the ocean are known and constant Southern Ocean?
Y-axis Logarithmic scale For these granules, most measured
elements are close to clouds!
Future Direction
• MODIS
31 Gerhard Meister and Charles R. McClain, Appl. Opt. 49, 6276-6285 (2010)
(Band 11 centered at 531 nm)
Thank you for your attention.
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