Abstract
The Venus Climate Orbiter Akatsuki arrived at Venus in December 2015, and the Longwave Infrared Camera (LIR) onboard the spacecraft started making observations. LIR has acquired more than 8000 images during the first two Venusian years since orbit insertion without any serious faults. However, brightness temperature derived from LIR images contained an unexpected bias that related not to natural phenomena but to a thermal condition of the instrument. The bias could be partially eliminated by keeping the power supply unit for LIR always active, while the residual bias was simply correlated with the baffle temperature. Therefore, deep-space images were acquired at different baffle temperatures on orbit, and a reference table for eliminating the bias from images was prepared. In the corrected images, the brightness temperature was ~ 230 K at the center of the Venus disk, where the effect of limb darkening is negligible. The result is independent of the baffle temperature and consistent with the results of previous studies. Later, a laboratory experiment with the proto model of LIR showed that when the germanium (Ge) lens was heated, its actual temperature was slightly higher than the temperature measured by a thermal sensor attached to the lens holder. The experiment confirmed that transitory baffle heating accounted for the background bias found in the brightness temperature observed by LIR.[Figure not available: see fulltext.]
| Original language | English |
|---|---|
| Article number | 141 |
| Journal | Earth, Planets and Space |
| Volume | 69 |
| Issue number | 1 |
| DOIs | |
| Publication status | Published - Dec 1 2017 |
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Keywords
- Akatsuki
- Thermal infrared
- Venus
ASJC Scopus subject areas
- Geology
- Space and Planetary Science
Cite this
Absolute calibration of brightness temperature of the Venus disk observed by the Longwave Infrared Camera onboard Akatsuki Akatsuki at Venus : The First Year of Scientific Operation Masato Nakamura, Dmitri Titov, Kevin McGouldrick, Pierre Drossart, Jean-Loup Bertaux and Huixin Liu 7. Planetary science. / Fukuhara, Tetsuya; Taguchi, Makoto; Imamura, Takeshi; Hayashitani, Akane; Yamada, Takeru; Futaguchi, Masahiko; Kouyama, Toru; Sato, Takao M.; Takamura, Mao; Iwagami, Naomoto; Nakamura, Masato; Suzuki, Makoto; Ueno, Munetaka; Hashimoto, Joji; Sato, Mitsuteru; Takagi, Seiko; Yamazaki, Atsushi; Yamada, Manabu; Murakami, Shin Ya; Yamamoto, Yukio; Ogohara, Kazunori; Ando, Hiroki; Sugiyama, Ko Ichiro; Kashimura, Hiroki; Ohtsuki, Shoko; Ishii, Nobuaki; Abe, Takumi; Satoh, Takehiko; Hirose, Chikako; Hirata, Naru.
In: Earth, Planets and Space, Vol. 69, No. 1, 141, 01.12.2017.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Absolute calibration of brightness temperature of the Venus disk observed by the Longwave Infrared Camera onboard Akatsuki Akatsuki at Venus
T2 - The First Year of Scientific Operation Masato Nakamura, Dmitri Titov, Kevin McGouldrick, Pierre Drossart, Jean-Loup Bertaux and Huixin Liu 7. Planetary science
AU - Fukuhara, Tetsuya
AU - Taguchi, Makoto
AU - Imamura, Takeshi
AU - Hayashitani, Akane
AU - Yamada, Takeru
AU - Futaguchi, Masahiko
AU - Kouyama, Toru
AU - Sato, Takao M.
AU - Takamura, Mao
AU - Iwagami, Naomoto
AU - Nakamura, Masato
AU - Suzuki, Makoto
AU - Ueno, Munetaka
AU - Hashimoto, Joji
AU - Sato, Mitsuteru
AU - Takagi, Seiko
AU - Yamazaki, Atsushi
AU - Yamada, Manabu
AU - Murakami, Shin Ya
AU - Yamamoto, Yukio
AU - Ogohara, Kazunori
AU - Ando, Hiroki
AU - Sugiyama, Ko Ichiro
AU - Kashimura, Hiroki
AU - Ohtsuki, Shoko
AU - Ishii, Nobuaki
AU - Abe, Takumi
AU - Satoh, Takehiko
AU - Hirose, Chikako
AU - Hirata, Naru
PY - 2017/12/1
Y1 - 2017/12/1
N2 - The Venus Climate Orbiter Akatsuki arrived at Venus in December 2015, and the Longwave Infrared Camera (LIR) onboard the spacecraft started making observations. LIR has acquired more than 8000 images during the first two Venusian years since orbit insertion without any serious faults. However, brightness temperature derived from LIR images contained an unexpected bias that related not to natural phenomena but to a thermal condition of the instrument. The bias could be partially eliminated by keeping the power supply unit for LIR always active, while the residual bias was simply correlated with the baffle temperature. Therefore, deep-space images were acquired at different baffle temperatures on orbit, and a reference table for eliminating the bias from images was prepared. In the corrected images, the brightness temperature was ~ 230 K at the center of the Venus disk, where the effect of limb darkening is negligible. The result is independent of the baffle temperature and consistent with the results of previous studies. Later, a laboratory experiment with the proto model of LIR showed that when the germanium (Ge) lens was heated, its actual temperature was slightly higher than the temperature measured by a thermal sensor attached to the lens holder. The experiment confirmed that transitory baffle heating accounted for the background bias found in the brightness temperature observed by LIR.[Figure not available: see fulltext.]
AB - The Venus Climate Orbiter Akatsuki arrived at Venus in December 2015, and the Longwave Infrared Camera (LIR) onboard the spacecraft started making observations. LIR has acquired more than 8000 images during the first two Venusian years since orbit insertion without any serious faults. However, brightness temperature derived from LIR images contained an unexpected bias that related not to natural phenomena but to a thermal condition of the instrument. The bias could be partially eliminated by keeping the power supply unit for LIR always active, while the residual bias was simply correlated with the baffle temperature. Therefore, deep-space images were acquired at different baffle temperatures on orbit, and a reference table for eliminating the bias from images was prepared. In the corrected images, the brightness temperature was ~ 230 K at the center of the Venus disk, where the effect of limb darkening is negligible. The result is independent of the baffle temperature and consistent with the results of previous studies. Later, a laboratory experiment with the proto model of LIR showed that when the germanium (Ge) lens was heated, its actual temperature was slightly higher than the temperature measured by a thermal sensor attached to the lens holder. The experiment confirmed that transitory baffle heating accounted for the background bias found in the brightness temperature observed by LIR.[Figure not available: see fulltext.]
KW - Akatsuki
KW - Thermal infrared
KW - Venus
UR - http://www.scopus.com/inward/record.url?scp=85030993784&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85030993784&partnerID=8YFLogxK
U2 - 10.1186/s40623-017-0727-y
DO - 10.1186/s40623-017-0727-y
M3 - Article
AN - SCOPUS:85030993784
VL - 69
JO - Earth, Planets and Space
JF - Earth, Planets and Space
SN - 1880-5981
IS - 1
M1 - 141
ER -