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Ultraviolet Imager (UVI)

NSSDCA ID: 2010-020D-01

Mission Name: Akatsuki


The Ultraviolet Imager (UVI) studies the spatial distributions of ultraviolet absorbers in the atmosphere of Venus and their relationships with the cloud structure and the wind field. UVI measures the ultraviolet solar radiation scattered at the altitude of the Venusian cloud tops at 283 nm for SO2 observations and 365 nm for the unknown absorber.

The UVI utilizes an ultraviolet-coated, back-illuminated, full-frame-transfer, silicide CCD with 1024 x 1024 pixels. The field of view is 12 x 12 deg with a spatial resolution of about 200 m at 1000 km and about 76 km at 60 Rv. Optics have an aperture size 39.89 mm and a focal length of 63.3 mm (F-number of 16). UVI has two narrow bandpass filters centered 283 nm and 365 nm. The readout signal of the CCD is 12 bits. The onboard Digital Electronics (DE) equipment converts the original 12 bits data to 16 bits, then performs data processing for the imaging sensors, such as median filtering, dark current subtraction, and desmearing. An onboard application program uses a lossless image compression method called HIREW (Takada, et al. 2007) to reduce the image size from 2 megabytes to several hundred kilobytes for downlinking.

During Venus orbit, UVI is activated by executing the observation programs on the DE equipment and is nominally performed every 2 hours. Higher observation frequencies are inhibited to maintain the thermal condition of the instrument. The exposure time of UVI can be selected by a single command from 0.004 s to 11 s with 24 steps. The chosen Venus image exposure time for 283 nm is 0.25 s before 5 June 2016 and/or 0.50 s after 6 June 2016, while the exposure time for 365 nm is 0.046 s from 7 December 2015.

Alternate Names

  • Akatsuki/UltravioletImager(UVI)
  • UVI
  • Ultra-Stable Oscillator
  • urn:jaxa:darts:context:instrument:vco.uvi

Facts in Brief

Mass: 4.1 kg
Power (avg): 19 W

Funding Agency

  • Japan Aerospace Exploration Agency (Japan)


  • Planetary Science: Atmospheres

Additional Information

Questions and comments about this experiment can be directed to: Dr. David R. Williams



NameRoleOriginal AffiliationE-mail

Selected References

  • Yamazaki, A., et al., Ultraviolet imager on Venus orbiter Akatsuki and its initial results, Earth Planets Space, 70, 23, doi:10.1186/s40623-017-0772-6, Feb. 2018.
  • Takada, J., et al., A fast progressive lossless image compression method for space and satellite images, 2007 IEEE International Geoscience and Remote Sensing Symposium, Barcelona, pp. 479-481, doi:10.1109/IGARSS.2007.4422835, July 2007.
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