The Hayabusa Spacecraft Asteroid Multi-band Imaging Camera (AMICA)

Abstract

The Hayabusa Spacecraft Asteroid Multiband Imaging Camera (AMICA) has acquired more than 1400 multispectral and high-resolution images of its target asteroid, 25143 Itokawa, since late August 2005. In this paper, we summarize the design and performance of AMICA. In addition, we describe the calibration methods, assumptions, and models, based on measurements.Major calibration steps include corrections for linearity and modeling and subtraction of bias, dark current, read-out smear, and pixel-to-pixel responsivity variations. AMICA v-band data were calibrated to radiance using in-flight stellar observations. The other band data were calibrated to reflectance by comparing them to ground-based observations to avoid the uncertainty of the solar irradiation in those bands. We found that the AMICA signal was linear with respect to the input signal to an accuracy of << 1% when the signal level was < 3800 DN.We verified that the absolute radiance calibration of the AMICA v-band (0.55 µm) was accurate to 4% or less, the accuracy of the disk-integrated spectra with respect to the AMICA v-band was about 1%, and the pixel-to-pixel responsivity (flatfield) variation was 3% or less. ! The uncertainty in background zero-level was 5 DN. From wide-band observations of star clusters, we found that the AMICA optics have an effective focal length of 120.80 ± 0.03 mm, yielding a field-of-view (FOV) of 5.83° x 5.69°. The resulting geometric distortion model was accurate to

Updated inflight calibration of Hayabusa2's optical navigation camera (ONC) for scientific observations during the cruise phase

“…However, during the touchdown sequences the spatial coverage of the field-of-view (FOV) changes rapidly over the short time duration of these operations, and appropriate 0-sec exposures with the same spatial coverage as the proper exposure image cannot be acquired. In this operational case, the read-out smear removal process will be conducted after the images have been downlinked using the method described by Ishiguro et al (2010):…”

Distribution of boulders and the gravity potential on asteroid Itokawa

“…From the distance and the information about the AMICA camera provided by Ishiguro et al (2010) (pixel size: 12 lm; focal distance: 0.1208 m), it is possible to compute the image scale ðscale ¼ distance à pixel size=focal distanceÞ. The surface area is then calculated as the area in pixels times the square of the image scale.…”

Disk-Resolved Spectra of (25143) Itokawa with Hayabusa/AMICA observations

“…The major steps in calibration include corrections for linearity, modeling and subtraction of bias, dark current, read-out smear, pixel-to-pixel responsivity variations, and flux calibration. It was reported that AMICA images are contaminated by light scattered inside the optics in the longer wavelength (Ishiguro et al 2010). Unlike telescopic observations carried out in dark places, off-axis light from the Sun or target bodies may be an inherent problem with space exploration data.…”