ALIS, the Auroral Large Imaging System.

``One of the symptoms of an approaching nervous breakdown is the belief that one's work is terribly important.''

The first proposal for an Auroral Large Imaging System (ALIS), [Steen, 1989] suggested a net of 28 auroral imaging stations in northern Scandinavia spaced 100 km apart and with an average field-of-view ( $\mathit{FoV_{}}$ ) of $90^{\circ}$ (Figure 2.1).

Figure 2.1: The first proposed layout of ALIS with 28 stations in northern Scandinavia separated by about 100 km, each with a field-of-view of about $90^{\circ}$. The suggested station sites are marked with crosses. The four stations enclosed in a dotted line represent a suggested mini version of ALIS. The large circle illustrates the field-of-view of an all-sky camera in Kiruna at ionospheric altitudes. [After Steen, 1989]

It was anticipated that ALIS would be jointly funded and operated by the participating countries. In a later publication, [Steen et al., 1990], the Swedish part of ALIS (Swe-ALIS) was considered in more detail. Here the station baseline was reduced to 50 km for 14 stations within Sweden with an average field-of-view of $60^{\circ}$ (Figure 2.2).

Figure 2.2: A proposed layout for the Swedish part of ALIS (Swe-ALIS). This layout was partly followed when deciding the final sites for the ALIS stations as given in Figure 2.4 and Table 2.3. [after Steen et al., 1990]

In 1990 funding for the costs for an initial subset of Swe-ALIS was received. This ``mini-ALIS'' would consist of four to eight stations (corresponding to stations numbered 1-8 in Figure 2.2). As design and construction work commenced, it became practice to use the acronym ``ALIS'' instead of ``mini-ALIS'' or ``Swe-ALIS''. As the title suggests, this practice will be adhered to also in this thesis. However, it is useful to remember that the present work represents only a first small step towards the auroral large imaging system that was originally envisioned [Steen, 1989; Steen et al., 1990].

Design work on ALIS started in the fall of 1990. Construction work on the basic infrastructure started in 1991. The first camera became operational at the end of 1993 and the first auroral observations were carried out with it during early 1994. Later in 1995 ALIS consisted of 3 complete stations (and 3 stations without cameras), and participated for the first time in a scientific campaign [Aso et al., 1998a; Aso et al., 1998b]. During this campaign two additional intensified CCD-cameras were operated, giving a total of five observing sites. At this time most ALIS stations had no filter-wheels or camera positioning systems. In the following years, ALIS expanded to six fully-equipped stations. Table 2.1 shows the ALIS time-line.

Table 2.1: The ALIS time-line 1993-2001. `Stations' represent the number of stations on site. `Cameras' denotes the number of operational ALIS cameras, `Images' lists the total number of images recorded each year.

Year	1993	1994	1995	1996	1997	1998	1999	2000	2001
Stations	3	4	6	6	6	8	9	9	9
Cameras	1	1	4	5	5	6	6	6	6
Images	51	454	2374	3020	4034	15053	18905	19844	55878

This chapter focuses on the basic scientific and technical considerations affecting the design of the six-station ALIS, which was in full operation until April 2001.