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zenith camera
A zenith camera is an astrogeodetic telescope used today primarily for the local surveys of Earth's gravity field. Zenith cameras are designed as transportable field instruments for the direct observation of the plumb line (astronomical coordinates) and vertical deflections.
== Instrument ==
A zenith camera combines an optical lens (about 10–20 cm aperture) with a digital image sensor (CCD) in order to image stars near the zenith. Electronic levels (tilt sensors) serve as a means to point the lens towards zenith.
Zenith cameras are generally mounted on a turnable platform to allow star images to be taken in two camera directions (two-face-measurement). Because zenith cameras are usually designed as non-tracking and non-scanning instruments, exposure times are kept short, at the order of few 0.1 s, yielding rather circular star images. Exposure epochs are mostly recorded by means of the timing-capability of GPS-receivers (time-tagging).
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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