Development Institution: University of California, Berkeley (UCB) and University of Calgary (UofC), Canada
ASI Leads: S. Mende, UCB; Eric Donovan, UofC
Purpose: Observe the optical aurora over Alaska and Canada to determine the timing and location of the auroral substorm onset in relation to the events in the magnetosphere.
The ground-based All-Sky Imager (ASI) array observes the aurora over the Northern American continent from Canada to Alaska in order to determine where and when the auroral substorm onset occurs. There are 20 cameras along with a ground-based magnetometer (GMAGs) and together they are known as the ground-based observatories (GBOs). The ASI will allow scientists to observe the aurora across a huge section of the auroral oval with one-kilometer resolution. The array have an image repetition rate of 3 seconds which combined with the large area coverage provides unprecedented time resolution. Not only is this a unique opportunity for auroral scientists, but for THEMIS the GBOs provide the precise timing of the auroral onset relative to the magnetospheric events and onset.
The ASIs take images and movies of the Northern Lights by looking up at the sky from horizon to horizon above each ASI location. This is accomplished by using a "fish-eye" lens. The cameras take images and movies in black and white, gathering all the visible light from the aurora that they can. In this way, they can record even very faint aurora that our eyes cannot see with a 1 second exposure. The cameras are located in a small housing with a dome on top. The electronics and small computers operating the instrument and recording the data are generally in an adjacent building or in a separate environmentally controlled box. In these boxes the electronics, computer, and camera are heated/cooled in order to keep the ASIs operational during the cold winters/hot summers.
These cameras, and the entire GBO data acquisition system, including its interface with the GMAGs were developed by the University of California, Berkeley specifically for the THEMIS mission. They are based on extensive optics design heritage for space and ground applications and remote geophysical observatory operations by UCB investigators over the past 20 years. The ASIs are unfiltered (white light) cameras using a combination of very efficient (F/095) fish eye optical system with a highly sensitive charge-coupled device camera. The fielding of the cameras in the Canadian sector, and the data retrieval and software for camera operation and for data analysis, is based on contributions from the Canadian colleagues at UofC. The THEMIS GBOs are the next generation of low-cost distributed arrays for ground-based space research.
The thermal control systems are modeled after camera systems that were made for Antarctica to run without any human help and without any local electrical power. Although these cameras are on the ground, they are in remote areas, which are hard to reach. Reliability and maintenance-free operation are key issues. For example, there are no roads to get to many of the GBO sites, located in rural Canada or Alaska and the weather, such as snowstorms, can lead to days of waiting to fly to the site.