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

Tetsuya Fukuhara, Makoto Taguchi, Takeshi Imamura, Akane Hayashitani, Takeru Yamada, Masahiko Futaguchi, Toru Kouyama, Takao M. Sato, Mao Takamura, Naomoto Iwagami, Masato Nakamura, Makoto Suzuki, Munetaka Ueno, George L. Hashimoto, Mitsuteru Sato, Seiko Takagi, Atsushi Yamazaki, Manabu Yamada, Shin Ya Murakami, Yukio YamamotoKazunori Ogohara, Hiroki Ando, Ko Ichiro Sugiyama, Hiroki Kashimura, Shoko Ohtsuki, Nobuaki Ishii, Takumi Abe, Takehiko Satoh, Chikako Hirose, Naru Hirata

Research output: Contribution to journalArticle

10 Citations (Scopus)

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 languageEnglish
Article number141
JournalEarth, Planets and Space
Volume69
Issue number1
DOIs
Publication statusPublished - Dec 1 2017

Keywords

  • Akatsuki
  • Thermal infrared
  • Venus

ASJC Scopus subject areas

  • Geology
  • Space and Planetary Science

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    Fukuhara, T., Taguchi, M., Imamura, T., Hayashitani, A., Yamada, T., Futaguchi, M., Kouyama, T., Sato, T. M., Takamura, M., Iwagami, N., Nakamura, M., Suzuki, M., Ueno, M., Hashimoto, G. L., Sato, M., Takagi, S., Yamazaki, A., Yamada, M., Murakami, S. Y., ... Hirata, N. (2017). 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. Earth, Planets and Space, 69(1), [141]. https://doi.org/10.1186/s40623-017-0727-y