第126回 地球電磁気・地球惑星圏学会 総会・講演会(2009年)
○Y. Obuchi(Genesia Co.), T. Sakanoi(Tohoku Univ.), M. Kagitani(Tohoku Univ.), N. Takeyama(Genesia Co.), A. Enokuchi(Genesia Co.), and S. Okano(Tohoku Univ.)
We have developed a camera using an innovative occulting mask for the observation of
planets. When we observe faint emission close to a bright source like a planet, stray
light due to scattering in the telescope deteriorates the S/N ratio of the faint object.
In order to prevent such an effect, a dense filter is usually placed in order to occult
a bright source. When we make observation of the Io plasma torus (IPT), we use a filter
to occult the Io disk. However, the Io disk still disturbs observation of IPT, especially
in a region close to Io, since Io moves relative to Jupiter during observation. Therefore,
a mask that can be variable in its position and also in its shape in the FOV is strongly
required.
In order to realize this requirement, we have developed a camera using an occulting mask
that employed a DMD (Digital Micromirror Device). A DMD is a device which can select the
light incident on it dynamically by flipping tiny mirrors (Flipping angle is +/- 12 degrees
relative to the array surface). The size of each mirror is 13um x 13um, and they are
arranged in an array of 1024 x 768. Each tiny mirror element can be independently
controlled by a computer. Based on preliminary experiments, unwanted light could be
reduced to 10-3 - 10-4 relative to a bright object, and we expect this to be sufficient
for observation of IPT. Diffracted light from the DMD surface and scattered light from
the edge of each mirror of the DMD are obstructed by a physical stop on an exit pupil of
a camera.
By using such an innovative DMD mask, we will be able to observe not only IPT mentioned
above, but also the inner planets, like Mercury. In addition, various observations are
expected when a camera system using a DMD mask is onboard space vehicles.
The optical performance of the product will be presented.
