ABSTRACT
To investigate the dynamics of auroras and faint upper atmospheric emissions, a new type of imaging instrument was developed. The instrument is a wide field of view, narrow-spectral-band imaging system using an intensified S.E.C. TV camera in a time exposure mode. Pictures were taken at very low light levels of a few photons per exposure per resolution element. These pictures are displayed in the form of a pseudocolor presentation in which the color represents spectral ratios of two of the observed auroral spectral emission features. The spectral ratios play an important part in the interpretation of auroral particle dynamics. A digital picture processing facility is also part of the system which enables the digital manppulation of the pictures at standard TV rates. As an example, hydrogen auroras can be displayed having been corrected for nonspectral background by subtracting a picture obtained by a suitable background filter. The instrumentation was calibrated in the laboratory and was used in several field xperiments. Elaborate exposure sequences were developed to extend the dynamic range and to cover the large range of auroral brightnesses in a fairly linear manner.
ABSTRACT
The design considerations that are necessary to optimize the performance of a tilting-filter photometer are presented. Such a photometer is described, and some typical measurements of aurora and airglow illustrate the application of this technique to low light level spectrophotometry. The digital approach used with photomultipliers at these low light levels is also discussed. Comparison of the tilting-filter photometer with other spectral scanning instruments reveals a superiority for many applications. A final section discusses possible space applications.
