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The Digital All-Sky Imager (DASI) consists of a low-light-level television camera fitted with an all-sky lens (180 degree field of view) and a narrow band interference filter at 557.7 nm. The main purpose is to study the relationship between the aurora and ionospheric electric field patterns as observed by the STARE and EISCAT radars. Collaborative studies with other experiments such as HEATING and IRIS are also undertaken. The instrument began recordings in 1993. The lens and filter can be changed. Current options include a 45 and 90 degree field of view lens and 630 nm filter.

DASI Image

A 486-PC controls the experiment which runs entirely automatically. The computer determines the safe night-time recording intervals using sun and moon position prediction algorithms. The lens shutter and camera gain are also controlled by the computer. Video images are averaged digitally in time (typically 10 seconds) using real-time frame grabber and image processing hardware. The image is then transformed into a geographic grid of 67.6-72.6 North in steps of 0.1 degrees and 13.5-26.0 East in steps of 0.25 degrees at an altitude of 100 km. The resulting digital image is then saved to a high capacity magneto-optical disk for later analysis. Simultaneous video recordings may also be performed. Operational parameters such as the integration time and the transform grid are user defined.

Cloud detection is performed by a separate imager, SCASI.


 M. J. Kosch

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