Venus’ clouds as inferred from the phase curves acquired by IR1 and IR2 on board Akatsuki

Satoh, Takehiko; Ohtsuki, Shoko; Iwagami, N.; Ueno, Munetaka; Uemizu, Kazunori; Hashimoto, George L.; Sakanoi, Takeshi; Kasaba, Yasumasa; Nakamura, Ryosuke; Imamura, Takeshi; Nakamura, Masato; Fukuhara, Tetsuya; Yamazaki, Atsushi

doi:10.1016/j.icarus.2014.10.030

Cited by 14 publications

(17 citation statements)

References 22 publications

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“…The measurements at 0.90 and 1.01 μm will yield information about the surface material (Baines et al 2000;Hashimoto and Sugita 2003;Hashimoto et al 2008). IR2 utilizes atmospheric windows at wavelengths of 1.73, 2.26 and 2.32 μm (Satoh et al 2015). With these wavelengths, IR2 is most sensitive to thermal radiation originating from altitudes of 35-50 km.…”

Section: Methodsmentioning

confidence: 99%

“…1 View of AKATSUKI. The five photometric sensors employed as mission instruments included a 1-μm infrared camera (IR1), 2-μm infrared camera (IR2), ultraviolet imager (UVI), long-wave infrared camera (LIR), and lightning and airglow camera (LAC) reflected sunlight (Satoh et al 2015) and an astronomical H-band centered at 1.65 μm. The UVI is designed to measure ultraviolet radiation scattered from the cloud top altitudes in two bands centered at 283 and 365 nm .…”

Section: Methodsmentioning

confidence: 99%

“…Comparisons between the time series of the images at the two channels (283 and 365 nm) will also shed light on their relationship with the cloud top structure. The solar phase angle dependence of aerosol scattering and darkbright contrasts will be used to develop an aerosol model and determine the vertical distribution of UV absorbers, SO 2 , and the unknown UV absorber (Lee et al 2015;Petrova et al 2015;Satoh et al 2015). This aerosol model will be taken into account in albedo calculations, and the optical depth of the UV absorbers can be estimated in a similar manner to method used by Molaverdikhani et al (2012).…”

Section: First Images Of Venus By the Camerasmentioning

confidence: 99%

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AKATSUKI returns to Venus

et al. 2016

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AKATSUKI is the Japanese Venus Climate Orbiter that was designed to investigate the climate system of Venus. The orbiter was launched on May 21, 2010, and it reached Venus on December 7, 2010. Thrust was applied by the orbital maneuver engine in an attempt to put AKATSUKI into a westward equatorial orbit around Venus with a 30-h orbital period. However, this operation failed because of a malfunction in the propulsion system. After this failure, the spacecraft orbited the Sun for 5 years. On December 7, 2015, AKATSUKI once again approached Venus and the Venus orbit insertion was successful, whereby a westward equatorial orbit with apoapsis of ~440,000 km and orbital period of 14 days was initiated. Now that AKATSUKI's long journey to Venus has ended, it will provide scientific data on the Venusian climate system for two or more years. For the purpose of both decreasing the apoapsis altitude and avoiding a long eclipse during the orbit, a trim maneuver was performed at the first periapsis. The apoapsis altitude is now ~360,000 km with a periapsis altitude of 1000-8000 km, and the period is 10 days and 12 h. In this paper, we describe the details of the Venus orbit insertion-revenge 1 (VOI-R1) and the new orbit, the expected scientific information to be obtained at this orbit, and the Venus images captured by the onboard 1-µm infrared camera, ultraviolet imager, and long-wave infrared camera 2 h after the successful initiation of the VOI-R1.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: First Images Of Venus By the Camerasmentioning

confidence: 99%

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AKATSUKI returns to Venus

et al. 2016

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“…B Imaging of the Earth and the moon: October 26, 2010, at 2.02 μm (normal gain and 6.97-s integration). C Disk-integrated photometry of Venus: February-March 2011 at 2.02 μm (normal gain and 6.97-s integration) (Satoh et al 2015). To lessen excessive stresses between metal and glass at low temperatures, while tolerating the harshest environment of launch, "slitted" spacers in both radial and axial directions are used to hold and align the lenses Dataset A is a full-longitude scan of the ecliptic plane to study zodiacal light in the H-band.…”

Section: In-flight Calibrationmentioning

confidence: 99%

Development and in-flight calibration of IR2: 2-μm camera onboard Japan’s Venus orbiter, Akatsuki

et al. 2016

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IR2, a near-infrared camera in the 2-μm region onboard Akatsuki has been developed to primarily study the middleto-lower atmospheric dynamics of Venus as probed in the 1.74-and 2.3-μm "windows" of the CO 2 atmosphere on the night side. The spatial and temporal variability of CO below the clouds is also studied by differentiating 2.32-μm CO-band images from simultaneous 2.26-μm images. Images of the night-side disk in these wavelengths will enable us to determine the zonal and meridional winds near the cloud-base altitudes. IR2 also images at 2.02 μm, the center of a CO 2 absorption band. Such images can visualize the variation of the cloud-top altitudes as contrast features due to different absorption path lengths of the reflected sunlight. Tracking of the 2.02-μm features will also enable us to obtain wind information at the cloud-top level. Together with the other cameras and the radio science equipment on Akatsuki, IR2 will contribute to understanding of the production and maintenance mechanism of super-rotation in the Venusian atmosphere. During cruise, IR2 observed zodiacal light with a broad-band H filter (1.65 μm), imaged the Earth-moon remotely from a distance of ~30 million km, and determined Venus's phase curves at small phase angles. We have just started the early phase operation check of IR2 at Venus, as the orbit insertion in December 2015 was successful.

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“…Although LIR cannot directly observe this wave at lower altitudes, a simulation showed that a wave generated by an atmospheric perturbation caused by the surface topography could propagate to the cloud-top layer. Since 1-and 2-μm cameras (IR1 and IR2) observe an aspect of the lower atmosphere in nightside by detecting the wavelengths in the atmospheric windows of Venus (Iwagami et al 2011;Satoh et al 2015), comparison of images acquired by LIR with those acquired by IR1 and IR2 should reveal the propagation process of the stationary gravity wave in some detail.…”

Section: Introductionmentioning

confidence: 99%

Absolute calibration of brightness temperature of the Venus disk observed by the Longwave Infrared Camera onboard Akatsuki

Fukuhara

Taguchi

Imamura

et al. 2017

Earth Planets Space

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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.

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Venus’ clouds as inferred from the phase curves acquired by IR1 and IR2 on board Akatsuki

Cited by 14 publications

References 22 publications

AKATSUKI returns to Venus

AKATSUKI returns to Venus

Development and in-flight calibration of IR2: 2-μm camera onboard Japan’s Venus orbiter, Akatsuki

Absolute calibration of brightness temperature of the Venus disk observed by the Longwave Infrared Camera onboard Akatsuki

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