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Concluding remarks

``Cur invideamus posteritati nostris laboribus frui?
Majori laudi ducteur Seculo nostro observationes veras ad posteritatis memoriam transmisisse, quam falsas & facile refellendas hypotheses.
Utinam priora Secula rerum naturalium experientias potius, quam varias opiniones nobis reliquissent!''
This report has attempted to provide a thorough documentation of the ALIS-project. Naturally, the focus of this work has been on the design, operation and calibration of the instrument, as this has been the main occupation of this author for more than one decade. Apart from ALIS, which provides imaging spectroscopic absolute-measurements of column emission rates, there has been some work carried out related to colour imaging of aurora, as is briefly described in Appendix C.

Since April 2001, only occasional campaigns related to the study of HF pump-enhanced airglow have been carried out with 1-2 stations that were operated manually. As there has recently emerged increased interest in a more extensive operation of ALIS, an outline of the required actions, as well as some ideas for the future appear in Appendix D.

Chapter 6 provided a survey of the versatile scientific applications of a multi-station low-light imaging system such as ALIS. Although many results already have been obtained, scientific questions that have arisen from this work require further analysis of existing data-sets as well as new measurements.

At present, the scientific highlights from ALIS include the first unambiguous observations of HF-pump enhanced aurora [Brändström et al., 1999] and the first tomographic estimate of volume distribution of HF-pump enhanced airglow emissions [Gustavsson et al., 2001a]. The task of following up some of the new scientific questions raised by these observations would alone motivate the continued operation of ALIS for many years. The recent promising observations of Leonid meteor-trails (Section 6.6.2) might also prove to be a fruitful field of future studies with ALIS.

As a spin-off effect, the combined use of the ALIS detector together with an imaging spectrometer resulted in the first daytime ground-based optical image of the aurora which was acquired on 2 May 1999 [Rees et al., 2000].

It can therefore undoubtably be said that there exist strong multi-disciplinary scientific arguments for the continued operation of ALIS.

A reader interested in further information related to three-dimensional imaging of the aurora and airglow, geometrical calibration, etc., is recommended to study Gustavsson [2000], as these topics were only briefly touched upon in the present work. Further reading related to the processing of multi-station auroral image data is found in the work by Rydesäter [2001].

Simultaneous auroral imaging from space-borne optical instruments would be an effective complement to the ground-based images. Ideally a sounding rocket launched through an auroral structure, resulting in simultaneous measurements from both ground and space, would certainly provide new insights into the auroral altitude distribution and the possibility to further validate and enhance the 3D-reconstruction techniques.

Observations of the rich and interesting night-sky phenomena related to auroral and ionospheric space plasma physics as well as the environmentally important atmospheric physics is a long-term commitment involving many disciplines as well as ground-based and space-borne instruments of various types. The diversity of the scientific results summarised in this chapter provides an example of what can be achieved on a moderate budget.

In this field of science, long-term stability, not only in terms of continuous observations, but also in terms of budget and staffing, combined with long-term plans for technical maintenance and development is important.

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