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.
Highlights
The Venus Climate Orbiter Akatsuki was successfully inserted into a Venus orbit in December 2015 after spending 5 years orbiting the sun under unintended environmental conditions
A thermal infrared image of Venus taken by Pioneer Venus orbiter (PVO) showed the limb darkening effect in which temperature distribution systematically decreases as a function of the zenith angle of the emission (Taylor 1980)
The effect depended on the vertical structure of the Venus atmosphere, the local time, and the emission angle at the time of observation
Summary
The Venus Climate Orbiter Akatsuki was successfully inserted into a Venus orbit in December 2015 after spending 5 years orbiting the sun under unintended environmental conditions. The data number for each pixel is converted to brightness temperature based on the reference data, which were derived from the blackbody images acquired during calibration tests at Institute of Space and Astronautical Science (ISAS) of JAXA, in a vacuum environment before launch (Fukuhara et al 2011). Background variation in the observed image Average temperatures of the Venus disk and deep space were retrieved from the brightness temperature of each LIR image derived from formula (3). Temperature stabilization of the power supply unit for LIR The brightness temperature distribution of deep space as a function of the baffle temperature is shown, where images were obtained from March to September 2016 with m = 32 and n = 32.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
