THEMIS Ground-based All Sky Imager Keogram, Level-1

THEMIS Ground All Sky Imager Keograms for all observatories. Keograms are composed of thin images slices taken down the middle of all-sky images and graphed against time. Keograms allow for substorm analysis without the need for full sized raw images. The ASI stations each 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. 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.