Compact thermal imager: a flight demonstration of infrared technology for Earth observations

D. E. Jennings; D. E. Jennings; M. D. Jhabvala; C. J. Tucker; A. W. Lunsford; A. W. Lunsford; A. T. La; T. P. Flatley; T. P. Flatley; K. K. Choi; D. L. Wu; D. C. Morton; T. R. Holmes; Y. Fitts; P. G. Cappelaere; A. N. Cillis; K. A. Turck; T. Hewagama

doi:10.1364/AO.450442

Applied Optics
Vol. 61,
Issue 14,
pp. 4215-4225
(2022)
•https://doi.org/10.1364/AO.450442

Compact thermal imager: a flight demonstration of infrared technology for Earth observations

D. E. Jennings, M. D. Jhabvala, C. J. Tucker, A. W. Lunsford, A. T. La, T. P. Flatley, K. K. Choi, D. L. Wu, D. C. Morton, T. R. Holmes, Y. Fitts, P. G. Cappelaere, A. N. Cillis, K. A. Turck, and T. Hewagama

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D. E. Jennings, M. D. Jhabvala, C. J. Tucker, A. W. Lunsford, A. T. La, T. P. Flatley, K. K. Choi, D. L. Wu, D. C. Morton, T. R. Holmes, Y. Fitts, P. G. Cappelaere, A. N. Cillis, K. A. Turck, and T. Hewagama, "Compact thermal imager: a flight demonstration of infrared technology for Earth observations," Appl. Opt. 61, 4215-4225 (2022)

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- Optical Devices, Sensors, and Detectors
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About this Article
History
- Original Manuscript: December 3, 2021
- Revised Manuscript: April 10, 2022
- Manuscript Accepted: April 11, 2022
- Published: May 10, 2022

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Abstract

During 2019, an infrared camera, the compact thermal imager (CTI), recorded 15 million images of the Earth from the International Space Station. CTI is based on strained-layer superlattice (SLS) detector technology. The camera covered the spectral range from 3 to 11 µm in two spectral channels, 3.3–5.4 and 7.8–10.7 µm. Individual image frames were ${{26}} \times {{21}}\;{\rm{km}}^2$ projected on the ground, with 82 m pixel resolution. A frame time of 2.54 s created continuous image swaths with a 13% along-track image overlap. Upper limits determined on the ground and in flight for the electronic offset, read noise, and dark current demonstrated the stability of the SLS detector and camera over many months. Temperature calibration was established using a combination of preflight and in-flight measurements. A narrowband approximation of temperature as a function of photon counts produced an analytic relationship covering a temperature range of 0°–400°C. Examples of CTI images illustrate temperature retrievals over sea ice, urban and agricultural areas, desert, and wildfires.

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SLS Array Format	$320 \times 256 P i x e l s$	Telescope Focal Length	150 mm
Pixel size	30 µm	Telescope lens diameter	45 mm
Array temperature	$< 83 K$	ISS altitude	410 km
Dark current	$1 0^{8} - 1 0^{9} e^{-} / s$	Orbital speed	7.7 km/s
Read noise	$\sim 800 e^{-}$	Pixel ground IFOV	82 m
ROIC well capacity	$1.8 \times 1 0^{7} e^{-}$	Array ground FOV	$26 \times 21 {k m}^{2}$
Bias, band 1/band 2	$- 0.8 / + 0 . 8 V$	Band 1, band 2 along-track offset	9.1 km
Band 1 coverage	2.2–5.6 µm	Frame time (each band)	2.54 s
Band 2 coverage	2.2–10.7 µm	Band 1, band 2 timing offset	1.27 s
Shortwave channel	3.3–5.4 µm	Data rate	1.03 Mbits/s
Longwave channel	7.8–10.7 µm	Telescope temperature	20°C
Integration time, band 1	0.010 s	Cooler power (at 28 V)	7 W
Integration time, band 2	0.0018 s	Mass	4.1 kg

Parameter	Band 1	Band 2
Integration time	10 ms	1.8 ms
Target (25°C)	4410 counts^a	12550 counts^a
Deep space^b	25,500	18,500
stability over 0.28 yrs^c	90	130
Instrument emission	390	1190
Dark current counts	4360	15,510
Dark current	$1.1 \times 1 0^{8} e^{-} / s$	$2.1 \times 1 0^{9} e^{-} / s$
Electronic offset	20,800	1800
Stability over 1.8 yrs^c	50	170
Read noise	4.25	3.97
Read noise charge	$827 e^{-}$	$771 e^{-}$
Stability over 1.8 yrs^c	0.11	0.01

Parameter	Band 1	Band 2	Units
$A$	3346	1776	Kelvin
$B$	$2.350 \times 1 0^{8}$	$2.537 \times 1 0^{6}$	A/D counts
$N_{0}$	1265	5960	A/D counts

SLS Array Format	$320 \times 256 P i x e l s$	Telescope Focal Length	150 mm
Pixel size	30 µm	Telescope lens diameter	45 mm
Array temperature	$< 83 K$	ISS altitude	410 km
Dark current	$1 0^{8} - 1 0^{9} e^{-} / s$	Orbital speed	7.7 km/s
Read noise	$\sim 800 e^{-}$	Pixel ground IFOV	82 m
ROIC well capacity	$1.8 \times 1 0^{7} e^{-}$	Array ground FOV	$26 \times 21 {k m}^{2}$
Bias, band 1/band 2	$- 0.8 / + 0 . 8 V$	Band 1, band 2 along-track offset	9.1 km
Band 1 coverage	2.2–5.6 µm	Frame time (each band)	2.54 s
Band 2 coverage	2.2–10.7 µm	Band 1, band 2 timing offset	1.27 s
Shortwave channel	3.3–5.4 µm	Data rate	1.03 Mbits/s
Longwave channel	7.8–10.7 µm	Telescope temperature	20°C
Integration time, band 1	0.010 s	Cooler power (at 28 V)	7 W
Integration time, band 2	0.0018 s	Mass	4.1 kg

Parameter	Band 1	Band 2
Integration time	10 ms	1.8 ms
Target (25°C)	4410 counts^a	12550 counts^a
Deep space^b	25,500	18,500
stability over 0.28 yrs^c	90	130
Instrument emission	390	1190
Dark current counts	4360	15,510
Dark current	$1.1 \times 1 0^{8} e^{-} / s$	$2.1 \times 1 0^{9} e^{-} / s$
Electronic offset	20,800	1800
Stability over 1.8 yrs^c	50	170
Read noise	4.25	3.97
Read noise charge	$827 e^{-}$	$771 e^{-}$
Stability over 1.8 yrs^c	0.11	0.01

Abstract

Data availability

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Figures (11)

Tables (3)

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Applied Optics