All Sky Imager (ASI)

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The PEARL All Sky Imager provides information on airglow and auroral emissions over the full sky above Eureka. The airglow emissions are the hydroxyl, sodium and atomic oxygen green line emissions. These emissions are centred around average heights of 87, 90, and 96 km, respectively. Smaller scale periodic spatial and temporal variations in the observed radiances are interpreted as signatures of buoyancy or gravity waves which occur naturally and are ubiquitous in the atmosphere. They are thought to be produced lower in the atmosphere and then propagate vertically to mesopause heights. Diagnosing their characteristics at these heights is of scientific importance as these waves are thought to drive a global pole-to-pole circulation in the atmosphere. The longer period, larger scale variations in the airglow are also of interest as they provide information on tidal and planetary wave perturbations to the atomic oxygen at mesopause heights and large scale transport of atomic oxygen. The imager also provides information on auroral features in part to ensure the airglow observations are being undertaken correctly and in part to study them in their own right. The imager also allows clouds to be identified and serves as a means of integrating the other airglow observations together by providing a global view of the variations overhead and discerning what parts of the sky the other instruments are observing.