The THEMIS All-Sky Imager Array

THEMIS (Time History of Events and Macroscale Interactions During Substorms) is a NASA MIDEX mission scheduled for launch in 2006. THEMIS will consist of five satellites on equatorial orbits with apogees at 10, 20, and 30 Re, relatively phased on those orbists so every four days the five satellites are in conjunction over central Canada. The primary scientific objective of the THEMIS mission is to elucidate the physical sequence of events leading up to substorm expansive phase onset. THEMIS has a significant ground-based observational component which includes a continent wide array of white light auroral All-Sky Imagers (ASIs), sixteen of which will be deployed in Canada. The ASIs will operate at a cadence of one image every five seconds, and will be useds to identify the location and timing of auroral substorm onset. Data from the ASIs will be available in real time and retrospectively from a web-based data archive. The first of these imagers was deployed in Athabasca in the summer of 2003 (see http://www.phys.ucalgary.ca/NORSTAR/themis/themis_main.html). We will deploy five more imagers in Canada in each of the next three years.