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1-micron Camera (IR1)

NSSDCA ID: 2010-020D-02

Mission Name: Akatsuki

Description

The 1-micron camera (IR1) studies the surface and lower atmosphere of Venus at near-infrared wavelengths. On the dayside IR1 measures the 0.90-micron solar radiation scattered by clouds and quantifies the horizontal wind vectors by using a cloud-tracking technique. On the nightside IR1 uses three channels centered at 0.90, 0.97, and 1.01 micron to detect thermal emission mostly from the surface and a little from the lowermost atmosphere. The latter two channels are a differential absorption pair for measuring the surface H2O abundance with the 1.01 micron channel as a reference. IR1 also searches for active volcanism.

IR1 camera is composed of a baffle, lenses, filters, a detector, and electronics. The detector is a cryo-cooled, silicide CSD (charge sweeping device) / CCD with 1024 x 1024 pixels and pixel size of 17 x 17 micron. The camera has a focal length of 84.2 mm, an aperture ratio of f/8, a field of view of 12 x 12 deg, and a pixel resolution of 0.012 deg. IR1 has one very narrow bandpass filter centered at 0.90 micron with a 0.0091-micron bandwidth; three narrow bandpass filters at 0.90, 0.97, and 1.01 micron, and one diffuse filter at 0.75 micron. The standard exposure time is 7.8 s for the dayside images and 30.8 s for all nightside images. The onboard control electronics, common with IR1 and IR2, digitizes the pixel analog data to 14-bit unsigned integers, then performs dark current subtraction. An onboard application program uses a lossless image compression method called HIREW (Takada, et al. 2007) to reduce the image size for downlinking.

During Venus orbit, IR1 obtained images from April 2016 until 09 December 2016 when the driving electronics for both IR1 and IR2 failed. More than 600 dayside images and about 150 nightside images (limited due to light scattered from the bright dayside) were obtained. The 0.90-micron dayside images are of sufficient quality to retrieve the wind field in the cloud region and the quality of the nightside 1.01-micron images is sufficient for a search for active volcanism. The quality of the 0.97-micron images may be insufficient to achieve the expected spatial resolution for determining the near-surface H2O mixing ratio.

Alternate Names

  • Akatsuki/1micronCamera(IR1)
  • IRI
  • urn:jaxa:darts:context:instrument:vco.ir1

Facts in Brief

Mass: 2.3 kg
Power (avg): 2.6 W
Bit rate (avg): 16 kbps

Funding Agency

  • Japan Aerospace Exploration Agency (Japan)

Discipline

  • Planetary Science: Atmospheres

Additional Information

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

 

Personnel

NameRoleOriginal AffiliationE-mail

Selected References

  • Iwagami, N., et al., Science requirements and description of the 1 um camera onboard the Akatsuki Venus Orbiter, Earth Planets Space, 63, 487-492, doi:10.5047/eps.2011.03.007, June 2011.
  • Iwagami, N., et al., Initial products of Akatsuki 1-um camera, Earth Planets Space, 70, 6, doi:10.1186/s40623-017-0773-5, Jan. 2018.
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