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2-micron Camera (IR2)

NSSDCA ID: 2010-020D-03

Mission Name: Akatsuki


The 2-micron camera (IR2) studies the middle-to-lower atmospheric dynamics of Venus at near-infrared wavelengths. On the dayside IR2 measures sunlight reflected at 2.02 micron to determine the altitude of cloud tops. On the nightside IR2 observes contrast features at 1.735 and 2.26 micron which are the silhouette of spatially inhomogeneous scatterers and absorbers, back-illuminated by the glow of the hot, 300 - 500 K, lower atmosphere. Nightside observations at 2.32 micron map the distribution of CO below clouds. IR2 also observes zodiacal light at 1.65 micron.

IR2 camera is composed of a baffle, lenses, filters, a detector, and electronics. The detector is a cryo-cooled, platinum-silicide Schottky barrier CSD (charge sweeping device) / CCD with 1040 x 1040 pixels and a pixel size of 17 x 17 micron. The camera has a focal length of 84.2 mm, an aperture ratio of f/4, a field of view of 12 x 12 deg, a pixel resolution of 0.012 deg. IR1 has four narrow bandpass filter centered at 1.65, 1.735, 2.26, 2.32, and 2.02 micron and a broad-band H filter centered at 1.65 micron. The standard exposure durations are 122.83 s (at 1.65 micron); 6.97 s (at 1.735, 2.26, and 2.02 micron); and 18.97 (at 2.32 micron). The onboard control electronics, common with IR1 and IR2, digitizes the pixel analog data to 14-bit unsigned integers, then performs dark current subtraction for Venus observations. For zodiacal light observations, every dark and star-field image is 2 x 2-pixel-binned resulting in a 520 x 520-pixel frame.

During cruise, IR2 observed zodiacal light at 1.65 micron for about 24 hours beginning on 22 October 2023 06:08 UT. A plane tilted about 3 deg off the ecliptic was scanned from 37 deg W to 37 E of the Sun by turning the spacecraft every 5.5 deg around its Y axis. Zodiacal light signal may be difficult to detect in the first 19 images due to saturation from excessive dark current. On 26 October 2010, IR2 performed 2.02-micron imaging of the Earth-Moon system from a distance of about 30 million km.

After failing Venus orbit insertion in December 2010, Akatsuki was placed in a solar orbit with a perihelion distance of about 0.62 AU. In March 2011, when Venus appeared as a ""full-moon"" phase when viewed from the spacecraft, IR2 performed multi-color photometric observations to detect modulation of the light curves possibly caused by planetary-scale waves; and to characterize the phase curves of Venus from UV to IR at small phase angles.

During Venus orbit, IR2 obtained images from April 2016 until 9 December 2016 when the driving electronics for both IR2 and IR2 failed. IR2 acquired a total of 3091 images of Venus: 1420 dayside images at 2.02 micron; and 1671 night side images at 1.735, 2.26, and 2.32 micron.

Alternate Names

  • Akatsuki/2micronCamera(IR2)
  • IR2
  • urn:jaxa:darts:context:instrument:vco.ir2

Facts in Brief

Mass: 1.1 kg
Power (avg): 5 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

  • Satoh, T., et al., Development and in-flight calibration of IR2: 2-um camera onboard Japan's Venus orbiter, Akatsuki, Earth Planets Space, 68, 74, doi:10.1186/s40623-016-0451-z, June 2016.
  • Satoh, T., et al., Performance of Akatsuki/IR2 in Venus orbit: the first year, Earth Planets Space, 69, 154, doi:10.1186/s40623-017-0736-x, Nov. 2017.
  • Satoh, T., et al., In-flight observations performed by Akatsuki/IR2, Europlanet Sci. Congress Abstracts, 6, EPSC-DPS2011-965-1, EPSC-DPS Joint Meeting 2011, Nantes, France, Oct. 2011.
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