1 PHYSICS Progress on characterization of a dualband IR imaging spectrometer Brian Beecken, Cory Lindh, and Randall Johnson Physics Department, Bethel University, St. Paul, MN Paul LeVan Air Force Research Lab, Kirtland AFB 18 March 2008 Orlando, Florida SPIE Conference 6940 Infrared Technology and Applications XXXIV
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1 PHYSICS Progress on characterization of a dualband IR imaging spectrometer Brian Beecken, Cory Lindh, and Randall Johnson Physics Department, Bethel.
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1
PHYSICS
Progress on characterization of a dualband IR imaging spectrometer
Brian Beecken, Cory Lindh, and Randall JohnsonPhysics Department, Bethel University, St. Paul, MN
Paul LeVanAir Force Research Lab, Kirtland AFB
18 March 2008Orlando, Florida
SPIE Conference 6940Infrared Technology and Applications XXXIV
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PHYSICS Overview
• The Goal: Hyperspectral IR Imaging from a space-based sensor
• Why? - More Info with
• Our Method:
– Using a dualband FPA gives improvements over traditional 2 channel approach
– Precise wavelength calibration
– Demonstrated recovery of BB spectral content
• One Application:
– When scanning for targets, only a few pixels may be available for each target. Can you still determine what it is?
– Our instrument is a resource that can be used to test a method of determining T of “small targets” in large FOV
Shorter waveband material absorbs shorter wavelength photons, transmitting longer wavelength photons to the (deeper) longer waveband
“Simultaneous”operation•both photocurrents integrated during the same frame time with overlapping integration times•alternative is switched with shared duty cycle, t1 + t2 < 100%
•Two Point Gain and Offset Calibration at 498 K and 373 K•Data shown is average down each full column of the array•Intermediate BB spectrums recovered•Efficacy of recovered spectrum is limited by a compromised bias voltage
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PHYSICS BB Calibration at MWIR only
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PHYSICS Calibration with 2nd and 3rd Order!
3rd order 2nd order
Columns 331 to 433•Small MCT response in 2nd order•Poor grating efficiency in 3rd order•Competition between these two effects•May be able to “tease out” proper calibration
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PHYSICS
Tsol
404.405
398.186
392.031
Tsolve 393.561
0 5 10 15 200
5 10 9
1 10 8
1.510 8
2 10 8
Wavelength, microns
lam
da*S
-lam
bda,
W/c
m2
Longer band fixed @ 12 μm
Variation of shorter bands
Uncertainties decrease at shorter wavelengths, but still some increase in dilution by reflected solar
5 & 12 μm seem to provide good tradeoff in this case
Shorter waveband, microns (SNR)
Derived temperature +/- uncertainty
(Kelvin)
12 (50) ∞
11 (53) 394 +76 / -53
9 (56) 394 +17 / -15
7 (47) 395 +8 / -8
5 (23) 398 +6 / -6
3 (6) 470 +12 / -13
Derived space object temperatures: 50% visible reflection 50% infrared emissivity 394 K equilibrium
Modeling Determination of Space Object Temperatures
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PHYSICS
Two Wavebands to determineBB Temperature
423 K
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PHYSICS Recovered BB Spectrum
Actual 423 KRecovered 407-424 K
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PHYSICS
Greater Separation of the Two Wavebandsused to determine BB Temperature
423 K
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PHYSICS Better Results
Actual 423 KRecovered 422-427K
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PHYSICS Using Dualband Capability
•Two Point Gain and Offset Calibration at 498 K and 373 K•Data shown is average down each column of the array, but only 5 pixels•Intermediate BB spectrums recovered, but look poor due to limited average•Quality of recovered spectrum is also limited by a compromised bias voltage
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PHYSICS
Two widely separated wavebandsto determine BB Temperature
423 K
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PHYSICS
Results compromised bynoisy LWIR band
Actual 423 KRecovered 397-449 K
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PHYSICS
Two more widely separated wavebandsto determine BB Temperature
423 K
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PHYSICS Good results despite noisy LWIR
Actual 423 KRecovered 413-423 K
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PHYSICS Summary
• Novel Dualband IR Imaging Spectrometer
– Several advantages for space-based applications
– Precisely wavelength calibrated over two octaves
– Successfully recovered BB spectrum between offset and gain calibration temperatures
• Demonstration of Determination of Space Object T’s– Use only two very narrow wavebands