THEMIS Ground-based All Sky Imager; ASI Thumbnails Data

THEMIS Ground All Sky Imager at 32 x 32 pixel resolution images of auroral oval. The ASI stations monitor a 170 degree field of view imaging the auroral oval at kilometer resolution. The ASI is comprised of a fisheye lens and CCD in a stainless steel enclosure topped with a transparent acrylic dome. The CCD has a resolution of 256 x 256 pixels. Exposure control ranges from 5 s to 1 ms although the typical data rate is one image every 3 seconds. Silicone heaters keep the instrument within the nominal temperature range. During daylight hours a sun shades deploy to protect the CCD.