3. TV Observations and Problems Using Them

[9]  The most widespread television data of auroral observations are obtained by all-sky cameras. The TV image in VHS standard consists of 230-240 vertical lines. Therefore the spatial resolution in the center of the image at the height of the aurora, about 100 km, is at best about 1.5 km. The resolution along a line is usually no better. A little bit better spatial resolution can be obtained using a camera with narrower field of sight, however in such cases only a small sector of the sky is recorded.

[10]  For processing, the TV signal is digitized using various types of equipment with varying characteristics. However, it is clear that to take complete advantage of the standard VHS resolution it is necessary to digitize the TV image with a resolution not worse then 256 256. The number of gray scale gradations also depends on the equipment being used, and is usually no more than 256, i.e., up to 8 bits per point. Unfortunately, for television data, there is no exact binding on the auroral intensity. Therefore it is impossible to consider these gray scales as absolute or even as relative intensities of luminosity.